Head and Neck Flashcards
Foreign Body Rhinitis
- Imaging diagnosis of nasal foreign body rhinitis often depends on whether the foreign object can be directly visualized.
- When the object is not seen, as is often the case with plant awns or small wood fragments, diagnostic features include focal turbinate destruction, hyperplasia of the remaining overlying nasal mucosa, and regional accumulation of fluid or mucoid exudates.
- Foreign body rhinitis is usually unilateral except when multiple foreign bodies are present, which can occur with plant awn inhalation.
- The severity of the secondary imaging findings can be related to the chronicity of the disorder as well as the inertness of the foreign material.
- In most patients, imaging abnormalities are limited to the nasal cavity or nasopharynx and do not usually involve the paranasal sinuses
Non-specific rhinitis
Nonspecific rhinitis is a general term that includes:
- Inflammatory nasal disorders from viral, bacterial, parasitic, or allergic causes.
- Rhinitis may also occur as an extension of severe periodontal disease.
Radiographic findings:
- May be normal
Cross‐ sectional imaging findings:
- May range from minimal to marked
- Exudative fluid is present bilaterally within the interstices of the nasal cavity, and fluid is generally present within the frontal and maxillary sinuses and the sphenoid recesses.
- Fluid can be distinguished from underlying hyperplastic mucosa on MRI and on contrast‐enhanced CT.
- Mucosa is typically prominent and enhances intensely and uniformly.
- The underlying nasal turbinate pattern is often unaffected, but turbinate atrophy, particularly the delicate bone of more peripheral turbinate regions, can occur with chronic or severe disease.
- Dense bone of the nasal septum and nasal cavity margins is rarely affected, although productive reactivity of the maxillary and frontal bones can be seen with chronic disease.
- Up to a third of cats with nasal disorders of any type and many dogs with nasal disease also have secondary bulla effusion associated with auditory tube occlusion.
- Nasal polyps are periodically encountered in associa- tion with chronic inflammatory disease. Nasal polyps occasionally ossify and can be mistaken for intranasal neoplasia, such as osteosarcoma
Mycotic Rhinitis
Aspergillosis:
Canine:
- Most common organism responsible for canine mycotic rhinitis, but other less common organisms include Cryptococcus, Rhinosporidium, and Blastomyces.
- Cryptococcus is the most common causative agent in cats with mycotic rhinitis, but aspergillosis has also been reported.
- In earlier phases of canine nasal aspergillosis, cross‐sectional imaging characteristics often include a unilateral increase in nasal mucosal volume, presumably due to mucosal inflammation, hyperplasia, and associated exudates.
- With progressive disease, there is marked turbinate destruction and atrophy with resulting cavitation in the affected nasal cavity, which may be most evident in the rostral to mid nasal cavity.
- The nasal cavity may have a rim of soft‐tissue thickening, peripherally consisting of fungal plaque and thickened mucosa.
- A soft‐tissue mass component may be present in the caudal nasal cavity or frontal sinus. These fungal masses have characteristic features that include a nonuniform gas and fluid pattern.
- Frontal sinus epithelial lining thickening is routinely present, and affected frontal sinuses may contain fluid.
- Affected maxillary, frontal, and vomer bones may become thickened with irregular margins due to reactivity.
- In some affected dogs, bone lysis also occurs.
- Erosion or overt destruction of the ethmoid bone (cribriform plate) resulting in communication with the cranial vault may also occur. This latter feature is important to evaluate since ethmoid destruction may affect therapeutic options and has been associated with a marked worsening of prognosis for successful treatment. In our experience, this parameter can be evaluated using either CT or MRI
- Although the majority of patients have unilateral disease, some animals have bilateral imaging findings.
Cats:
- Feline aspergillosis is uncommon but occurs frequently enough that it must be included in a differential of feline nasal disease
- Imaging features include bilateral involvement, moderate to marked nasal turbinate destruction, and a greater degree of fluid and mucosal hyperplastic replacement compared to dogs. Maxillary and/or frontal bone remodeling and bone destruction can be seen.
- Contrast-enhanced images accentuate the difference between noncontrast‐enhancing nasal exudates and adjacent contrast‐enhancing nasal mucosa.
- Frontal sinus involvement is also seen, but sinus contents appear more fluid and fungal masses are not as prevalent.
- A common finding is the presence of a mass lesion in the nasopharynx, which on endoscopic exam is found to be granulomatous reactive tissue.
Cryptococcus:
Feline nasal cryptococcosis appears to occur in two forms:
- The first is that of localized rhinitis
- The second is that of nasal extension of more aggressive regional or systemic fungal disease.
- In cats with localized cryptococcal rhinitis, the disease is bilateral and nondestructive.
- Turbinates do not appear disrupted; however, the normally air‐filled interstices between the turbinates appear fluid filled.
- In the more aggressive form, fungal granulomas can produce space‐occupying masses that can erode adjacent bone and may extend caudally through the cribriform plate
Oronasal Fistula (Canine)
6mo M Australian Shepherd with an oronasal fistula resulting from a bite injury at 1 week of age. Two attempts had been made to close the fistula.
There is a large defect in the left palatine bone and maxilla seen on the transverse and 3D images (b: arrows). Multiple maxillary teeth are absent, and there is mild turbinate loss in the left nasal passage secondary to inflammation
Nasopharyngeal Stenosis (Canine)
1y F Italian Greyhound with chronic nasal discharge.
There is focal occlusion of the nasopharyngeal lumen near the level of the pterygoid processes and 1 cm caudal to the caudal margin of the hard palate (b,d: arrow). The pharyngeal lumen rostral and caudal to this focal lesion appears normal (a,c: arrow). The soft tissues associated with the occlusive lesion mildly contrast enhance (b).
Nasopharyngeal stenosis was confirmed rhinoscopically, and biopsy revealed moderate chronic active neutrophilic, eosinophilic, and lymphoplasmacytic pharyngitis and rhinitis.
Cryptococcosis (Feline)
15y M Domestic Shorthair with stertor, sneezing, and progressive open‐mouth breathing.
The left and right nasal passages are completely opacified with soft tissue material, but bony turbinates are largely preserved (a: arrows). The left and right maxillary recesses, the nasopharynx (c: open arrow), and the left frontal (d: black open arrow) and sphenopalatine (d: asterisk) sinuses are also completely opacified with soft‐tissue or fluid attenuating material. The dorsal wall of the nasopharynx appears irregular and thickened (d: black arrow), and the nasopharyngeal lumen is narrowed.
Rhinoscopy revealed polypoid pharyngeal mucosal inflammation (e), and Cryptococcus neoformans was cultured from the tissue.
Nasal Lymphoma (Canine)
3y MC Rhodesian Ridgeback with a 3‐month history of nasal discharge and stertor.
There is a predominantly right‐sided nasal mass that extends beyond midline to fill the ventral part of the left nasal cavity rostral to the maxillary sinuses. The mass extends caudally to the nasopharynx (d: asterisk). Nearly complete osteolysis of the right nasal ectoturbinates is evident (a,b), and there is destruction of the palatine portion of the maxilla and the palatine bone (a,b: arrow). Vomer bone destruction is also present where the mass extends across midline (a,b: arrowhead).
Retrograde rhinoscopy revealed a nasopharyngeal mass (e).
Canine lymphosarcoma
Nasal Transitional Cell Carcinoma (Canine)
7y MC Golden Retriever cross with a 2‐month history of right‐sided epistaxis.
A large soft‐ tissue mass fills the right nasal cavity and extends across midline (a). The right ectoturbinates are obliterated by the mass, and there is right maxillary and nasal septum destruction (a). Regional destruction of the right side of the cribriform plate is seen (b), and the right frontal sinus is filled with fluid‐attenuating material. The nasal mass enhances heterogeneously and extends through the breach in the right maxillary bone (c: arrow). There is prominent meningeal enhancement adjacent to the right cribriform osteolytic region (d: large arrow) as well as an associated mild midline shift of the interolfactory longitudinal fissure (d: small arrow). Material within the right frontal sinus does not contrast enhance, confirming fluid and exudate entrapment from sinus obstruction.
Nasal biopsy revealed transitional cell carcinoma.
Nasal Carcinoma (Canine)
12y FS Australian Shepherd with progressive stertor.
Transverse images (a–c) are at the same anatomic level at the rostral extent of the cribriform plate. Representative dorsal plane images (d–e) are ordered from dorsal to ventral. A large mass of mixed‐signal intensity fills the right nasal cavity, obliterating the right ecto‐ and endoturbinates. Cribriform bone margins are ill‐defined or absent and indicative of destruction (b,e–g: arrow). There is right olfactory and frontal lobe T2 hyperintensity associated with the breach of the cribriform plate and intracranial extension of the contrast‐enhancing mass (h: arrows). Right frontal obstructive sinusitis is also present (a–c,g).
Nasal Carcinoma (Canine)
Normal Ear Anatomy
The ear is divided into external, middle, and internal components.
- The external ear includes the:
- Pinna
- External ear canal
- External acoustic meatus.
- The middle ear includes the:
- Tympanic membrane
- Osseous bulla
- Auditory ossicles.
- The inner ear located within the temporal bone, includes the:
- Semicir cular canals
- Vestibule
- Cochlea
CT findings:
- The normal canine ear on CT examination with thin collimation and bone algorithm.
- The vestibular aqueduct (AV) contains an extension of the membranous labyrinth and connects with the meninges of the brain.
- The cochlea is visible as a small, circular structure (C).
- The incus (I) and malleolus (M) are visible in the dorsal portion of the ear.
- The air‐filled space of the ear is divided into the tympanic cavity (TC) and tympanic bulla (TB) by the tympanic septum (not shown).
MRI findings:
- MR images of the normal canine ear. A trans- verse T1 image is shown on the left, T2 on the right.
- The cochlea is visible as a hyperintense structure on the T2 image (b: arrowhead).
Otitis Externa
Uncomplicated otitis externa is characterized by inflammation of the external ear canal. Hyperplastic thickening of the canal lining occurs as a response to chronic inflammation, causing ceruminous and aqueous exudates to fill the canal lumen.
Ceruminous and aqueos exudates:
- Exudates are generally hypoattenuating to adjacent canal epithelium on CT images.
- Exudates are typically hyperintense on MR T2 images and of variable intensity on T1 images depending on the cellular and macromolecular content of the exu dative fluid.
Hyperplasia:
- Canal lining hyperplasia is strongly contrast enhancing on CT and MR images because of the high vascular density of the inflamed canal wall
Case findings:
1y MC Maltese with a history of chronic otitis externa. The external ear canals are occluded because of stenosis and exudates (a). Contrast‐enhanced images show marked enhancement and redundancy of the external ear canal walls (b,c). Gas and fluid within the canal lumen can be distinguished from adjacent enhancing epithelium (b). Biopsy revealed severe diffuse chronic lymphoplasmacytic otitis externa with epithelial hyperplasia and ceruminous and sebaceous gland hyperplasia.
Inflammatory polyps
Inflammatory polyps may arise from the external ear canal epithelium in association with otitis externa. Polyps are typically vascular, resulting in moderate enhancement and increased conspicuity on contrast‐enhanced CT and MR images.
Polyps may also arise from the epithelial lining of the tympanic membrane or within the auditory canal extending into the nasopharynx and most commonly occur in the cat.
- Polyps may not be readily distinguished from surrounding fluid on unenhanced CT and MR images but are easily detected on contrast‐ enhanced images.
- Neoplastic masses may also occasionally arise within or adjacent to the tympanic bulla and should be distinguished from inflammatory polyps.
Case findings:
1y MC Domestic Shorthair with history of right‐sided ear infections. Fluid/soft‐tissue opacity within the right external ear canal and tympanic bulla is indicative of otitis externa and otitis media (a). On a contrast‐enhanced image, a well‐delineated contrast‐enhancing mass is seen within the horizontal part of the right external ear canal and the bulla (b: arrow). The mass is distinguished from nonenhancing fluid in the bulla. An excisional biopsy revealed inflammatory polyp and suppurative otitis externa.
Otitis Media
Bulla effusion may be the only abnormal imaging feature in early otitis media, although the disorder is often present concurrent with otitis externa and may involve the petrosal part of the temporal bone, depending on chronicity and severity. Exudative effusion appears soft‐tissue attenuating on CT images, hyperintense on T2 images, and of intermediate intensity on T1 images. The bulla lining typically becomes thickened and irregular and markedly contrast enhances on both CT and MR images. With increasing chronicity, the bulla wall may become thickened and irregularly margined as a result of reactive osteitis, and the bulla cavity volume may increase, presumably because of the effect of hydrostatic pressure from the effusion.
- On CT images, one must use caution in assessing the thickness of the osseous bulla wall because replacement of air by fluid within the bulla cavity may artifactually increase apparent thickness.
- Thickening and/or expansion of the osseous bulla may also be present without other abnormal imaging findings in patients with previous otitis media that has resolved.
Case findings:
10y M Golden Retriever with uncomplicated otitis media. The tympanic bulla contains material of mixed intensity on both the unen- hanced T1 image and the T2 image (a,b). The majority of the contents contrast enhance in the periphery of the bulla, indicating a pro- nounced thickening of the bulla lining (c). The nonenhancing regions represent entrapped fluid. The wall of the bulla is nonuniform in thickness and is irregularly margined because of reactive bulla osteitis (c). External ear canal stenosis, canal wall thickening, and marked contrast enhancement are indicative of concurrent otitis externa.
Otitis Media with Thickened Tympanic Bulla (Canine)
Otitis Media with Thickened Tympanic Bulla (Canine)
5y FS Labrador Retriever with a history of chronic bilateral otitis externa. Both external ear canals and tympanic bullae are filled with fluid‐attenuating material. The left tympanic bulla cavity has expanded. There is a marked irregular proliferative bony response involving both bulla walls. The proliferative response is consistent with reactive osteitis associated with chronic otitis media.
Otitis Interna
Osteitis of the petrous temporal bone is commonly associated with chronic otitis media, and progression to otitis interna is suggested by the presence of cranial nerve VII and VIII deficits. Infection may progress through the internal acoustic meatus or by direct extension through osteolysis of the petrous temporal bone. Some combination of osteosclerosis and osteolysis of the petrous temporal bone may be seen, and meningeal and cranial nerve VII/VIII enhancement is often present on contrast‐enhanced images.
Cholesteatoma
Cholesteatoma
Aural cholesteatomas are epidermoid cysts that form expansile masses of keratin debris and keratinized squamous epithelium. They may be congenital or acquired; however, in dogs cholesteatomas appear to be acquired and are likely initiated by underlying otitis media. Cholesteatomas are most often unilateral, but bilateral lesions can occur.
Imaging findings include a combination of:
- Bulla expansion
- Reactive osteoproliferation
- Bulla osteolysis
- A soft‐tissue mass is present centrally in the region of the tympanic bulla, which usually contrast enhances heterogeneously or peripherally.
- In some patients, osteolysis of the petrous and squamous parts of the temporal bone may occur, with resulting intracranial extension of disease. In these cases, neurologic signs associated with cranial nerves VII and VIII may be evident, and regional meningeal contrast enhancement is sometimes present.
- Sclerosis and osteoproliferation of the temporomandibular joint and paracondylar process can be seen.
Case findings:
15y FS Miniature Poodle with a 6‐month history of right‐sided otitis externa. Marked expansion and osseous remodeling of the right tympanic bulla is seen. Soft‐tissue attenuating material fills the bulla and the horizontal ear canal. Bulla contents and soft tissues adjacent to the bulla wall are mildly contrast enhancing. Histologic features of biopsy material were consistent with cholesteatoma.
Otolithiasis
Otolithiasis of the middle ear has been described in dogs with active or previous otitis media. Authors ascribed the otoliths to mineralization of necrotic debris in the osseous bulla, but otoliths sometimes appear to arise directly from the internal bulla margins and may well represent a proliferative osseous response.
On CT images:
- Otoliths appear within the tympanic bulla as solitary or multiple mineral densities of variable shape and size
- Concurrent otitis media may also be seen.
Case findings:
9y MC Australian Shepherd with chronic nasal discharge. The left tympanic bulla is fluid filled and contains multiple discrete mineral opacities. Biopsy acquired during bulla osteotomy yielded a histologic diagnosis of chronic otitis media with inspissated and mineralized debris.
Ceruminous Adenocarcinomas
- Ceruminous adenocarcinomas are often well advanced by the time of imaging evaluation, and the specific site of origin may not be easily determined.
- These tumors are aggressive and highly invasive, typically obliterating the external ear canal and often extending to the middle and inner ear.
- Adenocarcinomas are also highly destructive, resulting in osteolysis of the osseous bulla and erosion of the petrous and squamous parts of the temporal bone. These tumors are highly but heterogeneously contrast enhancing on both CT and MR images.
- Depending on the size of the mass, adjacent structures, such as the pharynx, larynx, mandibular salivary gland, and temporal musculature, may be involved.
- Intracranial extension can occur with advanced disease, resulting in intracranial mass effect and meningeal contrast enhancement.
- The scan volume should always include the mandibular and medial retropharyngeal lymph nodes since reactive lymphade nopathy and regional metastasis are common.
- ddx: SCC
Case findings:
11y FS Lhasa Apso with a previously diagnosed right‐sided ceruminous gland adenocarcinoma that was partially excised as part of an external ear canal ablation 1 year prior to the CT scan. Complete osteolysis of the tympanic bulla and partial osteolysis of the petrous temporal bone are evident on the unenhanced CT image (a). A large soft‐tissue mass is present adjacent to the skull base, causing laryngeal displacement to the left of midline. Mass margins are ill defined, and normal fascial planes are obscured. The mass enhances on the contrast‐enhanced image (b). Margins are moderately well defined, but there is intracranial extension of the mass through the petrous temporal bone defect.
CT
Otitis Media and Interna—Cranial Nerve VIII Involvement (Canine)
6y MC Cocker Spaniel with chronic ear infections. Bilateral ear canal ablations were performed 2 years previously, and the dog has recently developed right‐sided peripheral vestibular signs. On sequential unenhanced images, the right tympanic bulla is filled with fluid‐attenuating material, and there is partial osteolysis of the bulla wall laterally. The right internal acoustic meatus (b: arrowhead) and a portion of the cochlea (b: arrow) are seen. On contrast‐enhanced images, there is enhancement of tissues surrounding the tympanic bulla consistent with a clinically confirmed abscess. There is also focal intracranial contrast enhancement in the location of the cochlear branch of the vestibuloc- ochlear nerve (c,d: arrow), suggesting extension of disease through the internal acoustic meatus.
MRI
Chronic otitis externa/media
13y West Highland White Terrier with a history of chronic otitis externa/media. A left‐sided external ear canal ablation and bulla osteotomy were performed 18 months previously. The dog currently has peripheral vestibular signs.
Images a–d are all at the same level. Image e is slightly more caudal. The residual bulla cavity is fluid and tissue filled. There is increased signal intensity of the left petrous temporal bone on all image sequences. There is also focal T2 hyperintensity of the left vestibulocochlear nerve (b: arrowhead), which is seen as increased signal intensity on the FLAIR sequence (c: arrowhead), suggesting cranial nerve VIII neuritis. Focal meningeal and petrosal contrast enhancement are present (d: arrow), indicative of meningitis. Enlargement of the left vestibulocochlear nerve is also seen on contrast‐ enhanced images (e: arrowhead).
CT
Squamous Cell Carcinoma
Squamous Cell Carcinoma (Canine)
12y FS Golden Retriever with a mass associated with the right ear. A large, irregularly margined mass arises from the right middle ear (a). The external ear canal is not evident, and osteolysis of portions of the tympanic, petrosal, and squamous parts of the temporal bone is seen. The mass moderately and heterogeneously contrast enhances, and the bulk of the mass appears to be contained by the residual bulla and grossly distended external ear canal (b: arrowheads). There is also intracranial extension of the mass through a fenestration in the temporal bone (b: arrow). Ill‐defined contrast enhancement is also present in peritumoral tissues. Biopsy of the mass revealed aural squamous cell carcinoma.
CT
Cartilage Mineralization (Canine)
6y M German Shepherd Dog with longstanding history of bilateral otitis externa. Pronounced mineralization of the horizontal and vertical external ear canal walls is evident (a,b). External ear canals are occluded because of stenosis and exudates (a,b). Fluid‐attenuating material is also present within the left tympanic bulla, indicative of concurrent otitis media (a). Biopsy of the canal wall revealed chronic neutrophilic otitis externa with osseous metaplasia.
CT
Otitis Media with Otolith (Canine)
9y MC Australian Shepherd with chronic nasal discharge. The left tympanic bulla is fluid filled and contains multiple discrete mineral opacities. Biopsy acquired during bulla osteotomy yielded a histologic diagnosis of chronic otitis media with inspissated and mineralized debris.
Temporomandibular joint
- Anatomy
- Developmental Problems
- Degenerative Disorder
The normal temporomandibular joint (TMJ) includes the articular surfaces of the condyloid process of the mandible and the mandibular fossa of the temporal bone, between which lies a cartilaginous articular disc. These structures are surrounded by a joint capsule and supported by a lateral ligament and adjacent muscles of mastication. High‐resolution imaging protocols are necessary to visualize these structures. Osseous structures are well visualized on CT images, although the intrinsic soft tissues of the joint are not clearly delineated. On MR images, the condyloid process and region of the mandibular fossa appear T1 and T2 hyperintense centrally, as a result of medullary fat, with a well to poorly defined signal void peripherally defining the subchondral bone margins. The articular disc is sometimes visible and has T1 iso‐ to hyperinten- sity and variable T2 intensity compared to muscle.
Development disorders:
- Sunchondral cysts
- Temporomandibular joints
- Craniomandibular osteopathy
- Trauma
- Inflammatory disorders - septis and osteomyelitis
- Neoplasia - osteomas, sarcomans, carinomas
Degenerative disorders:
- Osteoarthritis
- Ankylosis
Subchondral bone cysts
Are occasionally seen in the condyloid process and are often clinically silent.
- Some cysts appear to be closed
- While others may communicate with the joint space at the caudal aspect of the process.
On CT images, cysts appear as spherical defects with well‐ demarcated dense bone margins.
On MR images, cysts are typically T2 hyperintense and T1 hypointense centrally with a well‐defined signal void peripher- ally because of the dense bone margin.
Case findings:
3y M Rottweiler. A CT scan of the head was performed as part of a diagnostic evaluation for chronic otitis. A well‐delineated circular subchondral bone cyst is seen in the left mandibular condylar process (a). Contents are fluid‐dense and surrounded by a thin rim of compact bone. The left condyle (b) is unremarkable and included in this figure in the same orientation for comparison. The cyst was clinically silent and identified as an incidental finding on this study.
Temporomandibular Dysplasia
Temporomandibular dysplasia has been reported in several canine breeds, including Dachshunds, Cocker Spaniels, Cavalier King Charles Spaniels, and Irish Setters. The disorder is clinically characterized by:
- Temporomandibular joint laxity, resulting in subluxation or luxation,
- Inability to close the mouth.
CT imaging features include:
- Flattening of the condyloid process and mandibular fossa
- Hypoplasia of the retroarticular process.
- Although overt luxation is uncommon, the joint frequently appears incongruent or subluxated.
As with other forms of dysplasia, the phenotypic expression of this disorder is variable, and imaging findings may be subtle in some patients.
Case findings:
3y MC Lhasa Apso presented to the emergency service with temporomandibular luxation. The representative transverse images (a,b) are ordered from caudal to rostral. The left condyloid process is luxated rostrodorsally (b,d,e: arrow), and the right condyloid process is subluxated (a,c). The condyloid processes are misshapen, and the mandibular fossae are flattened with hypoplastic retroarticular processes (c: arrowheads).
Craniomadibular Osteopathy
Craniomandibular osteopathy is an autosomal recessive developmental disease primarily affecting young West Highland White and other Terriers but also reported in a number of other breeds.
Clinical signs include:
- Swelling of the jaw due to bilaterally symmetrical new bone production, which can involve the mandibular body, ramus, and articular parts of the mandible.
- With severe manifestations, proliferative new bone encases the temporomandibular joints and extends to the temporal regions of the calvarium.
Although radiographic evaluation usually suffices for diagnosis of the disorder, CT imaging may be useful to more accurately characterize the extent of temporomandibular joint involvement.
CT imaging features include:
- Symmetrically distributed uniformly dense proliferative medullary and external woven bone formation involving the mandible and possibly the temporomandibular joints.
Case findings:
- 1y MC Golden Retriever with a history of mandibular swelling and pain. The representative transverse images (a–c) are ordered from rostral to caudal. There is marked, irregular, periosteal productive response that is symmetrically affecting the caudal mandible and temporomandibular joints. This productive response has extended to the temporomandibular joints (a: black arrows) and involves the temporal bones (b–d: arrows).
Inflammatory arthritis and osteomyelitis
of the TMJ
Septic arthritis and osteomyelitis of the temporomandibular joint are occasionally encountered as a result of extension of otitis externa/media or a direct penetrating injury and may include articular cartilage and subchondral bone destruction, joint distension, and surrounding cellulitis.
Case findings:
8y FS Rhodesian Ridgeback with regional cellulitis associated with otitis media/interna. T2 hyperintensity is seen adjacent to the medial margin of the right temporomandibular joint, the right lateral pterygoid muscle, and the dorsal aspect of the pharynx (a: arrows). The same region contrast enhances (b: large arrows), and additional meningeal enhancement is evident (b: small arrows). There is periarticular contrast enhancement involving the right temporoman- dibular joint, with associated intraarticular enhancement, and a diminished subchondral signal void (c: arrow). The left temporomandibular joint is normal by comparison (d).
TMJ Neoplasia
Although uncommon, neoplasia involving the temporomandibular joint may arise from intrinsic structures of the joint or from encroachment from adjacent neoplasms.
- Benign bone tumors, such as osteomas that arise from the mandible or temporal bone, may impinge on the temporomandibular joint and will typically appear as a dense, well‐delineated mass on CT and as a low or no signal intensity mass on all MR sequences.
- CT features of sarcomas and carcinomas in this region may include osteolysis and soft‐tissue mass with nonuniform contrast enhancement.
- MR features are similar and may also include replacement of T1 and T2 hyperintense medullary fat with lower intensity tumor
Case findings:
6y M Golden Retriever with recent onset of oral pain. A large, aggressive bone‐destructive mass is centered on the caudal aspect of the left side of the mandible. Osteolysis of the left mandibular ramus (a: arrows) and condyloid process (b: arrow) is evident. Bone destruction extends to and includes the subchondral bone of the process, implying an intraarticular component to the mass. On comparable contrast‐enhanced images, the mass has a complex, lobular appearance (c,d). Aspiration biopsy revealed the mass to be a fibrosarcoma.
TMJ Osteoarthrosis
Although commonly performed in people because of the high incidence of debilitating degenerative temporomandibular joint disorders, there are few reports on the use of high‐resolution CT and MR imaging for diagnosis of this disorder in veterinary medicine. Although articular cartilage and the articular disc should be well visualized by MR using appropriate coils and pulse sequences, MR features of degenerative temporomandibular joint disease have not been fully described in dogs and cats.
CT imaging features include:
- Narrowing of the joint space (best seen on sagittal plane reformatted images)
- Condyloid process remodeling
- Subchondral bone sclerosis
- Periarticular new bone formation
Similarly, MR imaging findings may include joint space narrowing and subchondral bone and periarticular new bone signal void.
Case findings:
6y MC Miniature Schnauzer with a history of difficulty opening its mouth. Tests to assess for the presence of immune‐mediated joint disease were negative. In the sagittal image, rostral is oriented to the left and caudal is to the right. Marked narrowing of the temporomandibular joint space is evident on both the transverse and sagittal images (a,b), implying a loss of articular cartilage and meniscal degeneration. Imaging findings are consistent with temporomandibular osteoarthrosis.
TMJ Ankylosis
Occasionally, periarticular productive remodeling may be exuberant enough to restrict temporomandibular joint range of motion. This can be due either to primary temporomandibular degenerative joint disease or an adjacent proliferative response of the temporal bone associated with chronic otitis. True ankylosis is defined as bone fusion or synostosis. Most patients with reduced range of motion, in fact, have extracapsular or fibrous ankylosis.
CT imaging findings:
- Osteoarthrosis features in addition to more pronounced periarticular new bone formation.
Comparable MR features would be expected in the form of ill‐defined and nonuniform periarticular signal void on all sequences.
CT
Mandibular Condylar Dysplasia (Canine)
10mo MC Bassett Hound with a history of pain when opening the mouth and periodic episodes of inability to close the mouth. The sagittal reformatted image is oriented rostral to the left and caudal to the right. The left manibular condyle is misshapen (a,b: asterisk), and there is evidence of subluxation of the temporomandibular joint (a–c: arrow). The sagittal image reveals abnormal flattening of the articulating surfaces and striking hypoplasia of the retroarticular process resulting in ventral subluxation (b: arrowhead). Temporomandibular joint findings were bilaterally symmetrical in this dog.
CT
Inflammatory Mandibular Mass with Temporomandibular Subluxation (Feline)
12y FS Domestic Shorthair with iatrogenic open wound in the oropharyngeal region following a traumatic pill administration. Clinical signs included malocclusion, oral pain, and inability to close the mouth. The cat had a previous enucleation that is unrelated to the current presenting complaint. The transverse images are comparable unenhanced and contrast‐enhanced images. The two images reformatted in the sagittal plane are oriented in the same direction for easier comparison. In both images, rostral is to the left and caudal is to the right. A heterogenously contrast‐enhancing mass is evident surrounding the body of the mandible on the left (b: arrowhead). The left temporo-mandibular joint is subluxated as a result of extraarticular encroachment by the mass (c: arrow). The right temporomandibular joint is normal by comparison (d). Biopsy of the oro-pharyngeal region confirmed the presence of suppurative abscess and cellulitis.
CT
Condylar Fossa Fracture (Canine)
1y German Shepherd Dog hit by a car 24 hours previously. The representative transverse images are ordered from rostral to caudal. A transverse fracture is seen in the rostral part of the right zygomatic bone near its articulation with the maxilla (a: arrow). A second, mildly displaced comminuted articular fracture is present near the origin of the zygomatic process of the right temporal bone (b–d: arrow). Another fracture line is evident coursing parallel to the subchondral bone margin of the fossa (b: arrowheads).
MR
Temporomandibular Septic Arthritis (Canine)
8y FS Rhodesian Ridgeback with regional cellulitis associated with otitis media/interna. T2 hyperintensity is seen adjacent to the medial margin of the right temporomandibular joint, the right lateral pterygoid muscle, and the dorsal aspect of the pharynx (a: arrows). The same region contrast enhances (b: large arrows), and additional meningeal enhancement is evident (b: small arrows). There is periarticular contrast enhancement involving the right temporomandibular joint, with associated intraarticular enhancement, and a diminished subchondral signal void (c: arrow). The left temporomandibular joint is normal by comparison (d).
MR
Temporal Bone Chondrosarcoma (Canine)
8y FS German Shepherd Dog with neurologic signs relating to left cerebral and thalamic disease. A large, locally invasive complex mass arises from the temporal bone, with components extending intracranially and into the adjacent temporal musculature. Left temporal bone medullary signal intensity is reduced on unenhanced T1 images (a: arrow) as a result of marrow displacement by the mass, and cortical margins are attenuated. Multiple high intensity foci suggest the mass is multicameral and cystic (b). The mass is nonuniformly contrast enhancing (c,d). Biopsy revealed a highly anaplastic chondrosarcoma.
MR
Temporomandibular Sarcoma (Canine)
8y MC Rottweiler with progressive right temporal and masseter muscle atrophy and pain upon opening the mouth. A poorly margined lobular mass arises in the region of the right mandibular process, resulting in mandibular cortical bone destruction and diminished marrow signal intensity on the unenhanced T1 image (b: arrows). The mass is moderately and uniformly contrast enhancing (c–e). Replacement of the normal right condyloid process architecture by the mass with extension into the right temporomandibular joint space is best seen on the right sagittal image (c: arrow). The left temporomandibular joint is normal by comparison (f). Right temporal and masseter muscle atrophy is seen associated with increased T2 and T1 signal intensity (a,d: asterisk), consistent with dysfunction of the mandibular branch of the right trigeminal nerve. Aspiration biopsy of abnormal spindle cells was consistent with sarcoma.
Skull
- Developmental disorders
- Inflammatory disorders
- Neoplasia
Developmental disorders of the skull:
- Occipitoatlantoaxial malfomrations
- Atlantooccipital overlappin
- Benign calvarial hyperostosis
- Trauma
Inflammatory disorders:
- Masticatory muslce myositis
- Abscess
- Osteomyelitis
Neoplasia:
- Ostoemas
- Osteosarcomas
- Multilobular osteochondrosarcomas
- Meningioma
- Pituatary adenoma
Occipitoatlantoaxial Malformations
Congenital occipitoatlantoaxial malformations are rare in dogs; however, hypermotility or stenosis can cause severe neurologic compromise secondary to compression of the spinal cord. The occipital bone, foramen magnum, atlas, and ligamentous structures make up this region. The spectrum of abnormalities includes:
- Hypoplasia of the occipital condyles
- Fusion of the atlas to the occiput
- Multiple separate centers of ossification
- Malformation of the dens
- The abnormally fused cranial segments may result in atlantoaxial instability or subluxation causing spinal cord compression.
CT and MR imaging allow 3D visualization of the malformation itself as well as the effects on the spinal cord. Dogs should be positioned with care if instability is suspected.
Atlantoccipital Overlapping
Atlantooccipital overlapping is rostral malposition of the atlas and axis resulting in compression of the cerebellum and kinking of the medulla oblongata. Since it is seen with other congenital anomalies, such as Chiari‐like malformation and dens hypoplasia resulting in atlantoaxial instability, it may be a consequence of other anomalies; however, it can also be seen as a sole abnormality.
Syringomyelia, seen as a continuous or intermittent T2 hyperintense fluid collection in the spinal cord parenchyma, is associated with the chronic compression. Fibrous bands dorsal to the atlantoaxial or atlantooccipital junctions can also be seen with many of these disorders and contribute to the spinal cord compression.
Benign Calvarial Hyperostosis
Benign calvarial hyperostosis has been described in young Bull Mastiffs as a diffuse thickening of the bones of the calvarium, with some similarities to craniomandibular osteopathy.
On MR images of one patient, the frontal bones were markedly thickened with hypointense T1 and T2 signal due to loss of normal marrow signal and T2 hyperintensity of the surrounding tissues. T2* GRE images accentuated the signal from bone and provided good image quality for evaluating hyperostosis. Contrast‐enhanced T1 images with fat saturation were recommended to reveal tissue enhancement.
CT imaging also demonstrates the increased bone attenuation in this syndrome (Figure 1.4.2).
Traumatic Skull Fractures
Common regions of trauma to the calvarium include:
- Sphenoid and pterygoid bones
- Frontal bone
- Temporal bone
Fractures of the temporomandibular joint and maxilla/mandible are discussed in Chapters 1.3 and 1.9.
- Gas may enter the calvarium as a result of open trauma to the skull and is identified as signal void on MR images and hypoattenuating regions on CT images.
- Associated hemorrhage may be seen in the dural tissues or brain
- 3D reformations of CT images of the skull may be helpful in depicting the spatial location of fragments. However, small fractures are often best seen in the two‐dimensional images.
Masticatory Muscle Myositis
Masticatory myositis is an autoimmune inflammatory condition of the masseter, temporal, and pterygoid muscles in which autoantibodies are directed against myosin.
- Affected dogs have pain opening the mouth and atrophy of the muscles of mastication. The atrophy can be seen on both CT and MR images. The affected muscles are hypoattenuating on CT on unenhanced images and have diffuse or peripheral enhancement on contrast-enhanced images.
- Regions of myositis appear hyperintense on MR T2 sequences and, similar to CT, are contrast enhancing.
- Nonenhancing regions represent areas of necrosis
Case findings:
1.5y MC Rottweiler with rapidly progressive inability to open mouth. Representative CT images were acquired immediately following contrast medium administration. There is moderate, diffuse contrast enhancement of the left masseter and temporal muscles (a,b: arrows). Pterygoid muscles appear relatively unaffected (a,b: arrowhead). Muscle biopsy revealed diffuse, chronic, lymphoplasmacytic myositis with muscle atrophy and fibrosis.
Abscess
Abscesses can occur in the musculature of the head secondary to penetrating wounds from the skin, oral cavity, and pharynx or secondary to otitis media. Areas of abscessation appear hypoattenuating on CT and hyper-intense on T2 MR images. On both modalities, contrast enhancement tends to be peripheral.
A contrast‐enhancing tract may help to localize any foreign material or to trace the origin of the wound.
Case findings:
9y FS Chow with pain when opening mouth. A focal draining lesion was seen in the caudal oral cavity. The contrast‐enhanced image shows a poorly delineated cavitary lesion within the left temporal muscle, consistent with an intramuscular abscess (b: arrow). Peripheral contrast enhancement extends to the medial surface of the coronoid process of the left mandible and to the external surface of the left parietal bone, but overt bone reactivity is not appreciated. Fascial and muscle contrast enhancement is also evident ventrally (b: arrowheads), indicative of more diffusely distributed cellulitis. Biopsy revealed chronic suppurative cellulitis.
Osteomas
Osteomas are benign tumors of unknown etiology, comprised of compact or cancellous bone, that occasionally occur in the skull.
- Periosteal osteomas arise from the surface of the bone
- Endosteal osteomas develop in the center of the bone
These tumors have been reported in cats and dogs in the region of the skull. These may appear on CT images as:
- Primarily compact peripheral types, with uniform, hyperattenuating centers and smooth margins
- Central cancellous types, with slightly lower attenuation and more irregular margins with invasion into adjacent bone
These masses may affect the skull, oral cavity, or orbit.
Case findings:
2y MC Golden Retriever with cranial mass. There is a smooth, dense production of bone centered on the parietal bone and expanding both intracranially and extracranially. The mass is hyperattenuating and uniform on CT images (a).
On MR images, the mass effect is evident with compression of the brain and lateral ventricle next to the mass (b,c), as well as displacement of the falx cerebri to the right (d). There is T2 hyperintensity of the white matter next to the mass, (b) indicating edema.
Osteosarcoma
Osteosarcoma occurs most commonly in the maxilla and mandible in the axial skeleton and also occurs in the bones of the calvarium
Chondrosarcoma occurs in the flat bones of the skull, most commonly in the nasal cavity.
Imaging characteristics of primary bone tumors
- are similar on CT and MR images
- expansile irregular new bone production
- cortical lysis
- associated soft‐tissue masses with heterogeneous contrast enhancement
Other primary bone tumors, such as fibrosarcoma, hemangiosarcoma, as well as metastatic neoplasia, are infrequently encountered.
Case findings:
4y F Bull Mastiff with a 2‐month history of a right facial mass. Representative images are unenhanced (a,b) and contrast enhanced (c,d) at comparable anatomic levels. Images are ordered from rostral to caudal. A variably attenuating expansile mass appears to arise from within the right zygomatic bone (a,b) and is heterogeneously contrast enhancing (c,d: arrowhead). Cortical remnants of the zygomatic bone are still evident (b: arrowheads). The mass fills the orbital space, displacing the right globe dorsally (c: arrow). Biopsy revealed osteosarcoma with minimal osteoid, which reflects the predominantly destructive appearance of the mass on CT.
Multilobular osteochondrosarcoma
Multilobular osteochondrosarcoma occurs in the flat bones of the skull of dogs and occasionally in cats. It is comprised of multiple lobules of bone or cartilage separated by fibrous septae, which give it a characteristic stippled appearance on CT images. These tumors tend to be round and well circumscribed to irregular in shape. They often expand into the calvarium or orbit, causing a significant mass effect.
- Brain edema can be seen as T2 hyperintensity
- Obstructive hydrocephalus may result
On CT images, the masses are mildly contrast enhancing.
MR imaging characteristics of these masses include T1 and T2 hypointensity with regions of hyperintensity. Contrast enhancement is heterogeneous to uniform.
Case findings:
12y FS Dachshund Terrier cross with large craniofacial mass. Two representative images at the level of rostral extent (a) and middle (b) of the frontal sinus are included here. A partially and diffusely mineralized mass arises from the right frontal bone and extends around the right zygomatic arch. The mineralized component of the mass has a coarse, granular appearance characteristic of multilobular osteochondrosarcoma. The mass is osteodestructive (a,b: arrow) and displaces normal soft‐tissue structures (b: arrowhead, right globe) but has virtually no soft‐tissue component beyond the osseous margins. The 3D rendering reveals the full surface extent of the mass (c). Excisional biopsy confirmed multilobular osteochondrosarcoma.
Meninigioma
Rarely, intracranial tumors, such as meningioma, can expand outside the calvarium.
- Meningioma in cats can also cause hyperostosis of the adjacent calvarium
- Hyperostosis with bone lysis has been reported in the dog.
Tumors of the soft tissues surrounding the head, such as adenocarcinoma or squamous cell carcinoma, can also involve the bones of the skull.
What is the typical HO of lipoma/liposarcoma?
Lipomas or liposarcomas have a characteristic fat attenuation (–100 HU) within the musculature or soft tissues
Case findings:
8y FS Doberman Pinscher with a left‐sided facial mass. Representative CT images are ordered from rostral to caudal. A well‐defined fat‐attenuating mass is present within the left masseter muscle. The striated pattern within the mass is due to adipose infiltration between muscle fasciculi A subchondral bone cyst is noted in the left condyloid process incidentally. Biopsy confirmed infiltrative lipoma.
Pituatary adrenomas
Cats with pituitary adenomas may develop acromegaly secondary to secretion of growth hormone and insulin‐like growth factor. They tend to develop increased frontal bone thickness and excess soft tissue in the nasal cavity, sinuses, and pharynx, which can be seen on CT images.
CT
Occipitoatlantoaxial Dysplasia
Occipitoatlantoaxial Dysplasia (Canine)
8mo MC Yorkshire Terrier with atlantoaxial instability. An imaging diagnosis of occipital dysplasia was made as a component of a more complex anomaly of the atlantoaxial–occipital region. The transverse image is of the caudal aspect of the occipital bone at the level of the foramen magnum. The foramen magnum is larger than normal and elongated in the dorsal–ventral axis (a,b: two‐headed arrow). The rostral margin of the dorsal arch of the atlas extends into the dorsal part of the foramen resulting in atlantooccipital overlapping (a,b: arrowhead). The occipital condyles (c: arrows) are hypoplastic but appear to articulate well with the articular fovea of the atlas (c: arrow- heads). Marked rotational subluxation of the atlantoaxial joint is evident, and the odontoid process of the axis is hypoplastic (b).
Benign Calvarial Hyperostosis
Benign Calvarial Hyperostosis (Canine)
1y M Bernese Mountain Dog with prominent midline cranial mass. An irregular but well‐defined osseous mass arises from the dorsal calvarium. The proliferative mass is dense and highly organized and has no appreciable overlying soft‐tissue component. Bone biopsy revealed essentially normal bone tissue with considerable woven bone embedded in dense fibrous tissue overlying lamellar bone. This entity has previously been described in young Bull Mastiffs.
Trauma
5y MC Domestic Shorthair that sustained trauma of unknown cause within the past 48 hours. This cat sustained a number of skull fractures commonly associated with high‐impact trauma. Representative images are ordered from rostral to caudal. Injuries include:
- fracture–luxation involving the nasal and maxillary bones (a: arrow)
- mandibular symphyseal separation (b: arrow)
- fractures of the perpendicular processes of the palatine bones (c: arrows)
- separation of the palatine symphysis (c: arrowhead)
- fractures of the pterygoid bones (d: arrows)
- caudal luxation of the right condyloid process (e: arrowhead)
- fracture through the zygomatic process of the left temporal bone (e: arrow).
MR
Masticatory Muscle Myositis
Masticatory Myositis (Canine)
9mo Miniature Pinscher with recent onset of left temporal muscle atrophy. The unenhanced T1 and T2 images are at the same anatomic level. The contrast‐enhanced T1 image is more caudal. Marked atrophy of the left temporal muscle and moderate atrophy of the left masseter muscle are evident on all sequences. There is a pronounced increase in signal intensity of affected temporal (a: large arrows), masseter (a: small arrow), and pterygoid (a: arrowheads) muscles on the T2 image that corresponds to regions of mild hyperintensity present on the T1 image (b). The same regions markedly contrast enhance (c). Serum creatinine kinase was significantly elevated and an antibody test confirmed the diagnosis of masticatory myositis.
MR
Masticatorty Muscle Myositis
Masticatory Myositis (Canine)
8y FS Golden Retriever with a 2‐week history of weight loss, stridor, cranial nerve deficits, and temporal muscle atrophy. Bilaterally symmetrical temporal muscle atrophy is evident on all sequences. There is marked, diffuse, and symmetrical hyperintensity of temporal (c: large arrows), masseter (c: small arrows), and pterygoid (c: arrowheads) muscles on the T2 and STIR images corresponding to regional enhancement on the contrastenhanced T1 image (b). A similar diffuse T2 hyperintensity and contrast enhancement pattern of the laryngeal tissues is evident (b: arrow). Necropsy revealed severe, bilateral, chronic, and diffuse lymphoplasmacytic myositis with myonecrosis and myodegeneration. This dog also had laryngeal cellulitis.
CT
Chondrosarcoma
Chondrosarcoma (Canine)
8y MC Golden Retriever with a progressively enlarging rostral cranial mass. Representative CT images are ordered from rostral to caudal. Osteolysis and unorganized osteoproliferation of the caudal aspect of the right maxilla (a: arrow) and both frontal bones (b,c) is seen. The right frontal sinus is also filled with soft‐tissue attenuating material that subsequently nonuniformly contrast enhances. There is also evidence of osteolysis of the internal margin of the right frontal bone (c: arrowhead). Slight meningeal enhancement at this site was noted on the contrast‐enhanced images, but there was no evidence of further tumor extension. Biopsy revealed chondrosarcoma.
CT & MR
Mandibular Osteosarcoma
Multilobular Osteochondrosarcoma (Canine)
7y FS Golden Retriever with a recent history of progressive incoordination. Neurologic examination localized neurologic deficits to the brainstem. A spherical mass arises from the occipital bone, causing extensive occipital osteolysis, and extends both intracranially and extracranially. The mass is hypointense on the unenhanced T1 image (b), has heterogeneous intensity and perilesional edema on the T2 image (a), and intensely and nonuniformly contrast enhances (c,d,g). The intracranial component of the mass is predominantly within the caudal fossa, causing rostral cerebellar displacement (d: large arrow), cerebellar and brainstem compression (d: small arrows), and obstructive hydrocephalus (d,g). The rostrodorsal aspect of the mass also encroaches on the caudal aspect of the rostral fossa, compressing the occipital lobes (d,g: arrowheads). Occipital osteolysis is also appreciated on the CT images (e). The coarse, granular, and diffuse mineralization (e,f) is characteristic of multilobular osteochondrosarcoma. Excisional biopsy confirmed the diagnosis of multilobular osteochondrosarcoma.
Adenocarcinoma
Adenocarcinoma (Feline)
17y FS Domestic Shorthair with a 2‐month history of pain on opening its mouth. Representative images include unenhanced and contrast‐enhanced images at the level of the zygomatic process (a,b) of the frontal bone and a contrast‐enhanced image near the level of the temporomandibular joint (c). A pronounced productive periosteal response is seen involving both the medial and lateral cortical surfaces of the left mandible. Contrast‐enhanced images reveal a poorly defined, heterogeneously enhancing mass extending the length of the left mandible and extending into the left orbit. A biopsy of the mass was interpreted as adenocarcinoma of possible salivary origin.
CT
Aggressive Epithelial Neoplasia (Canine)
11y Dalmatian with recent onset right‐sided exophthalmia. A poorly defined right orbital mass is seen associated with aggressive osteolysis of the right frontal (a: arrowheads) and palatine (a: arrow) bones. The mass extends into the right frontal sinus and the rostral cranial vault and is in intimate contact with the contrast‐enhancing meninges of the right olfactory bulb and frontal lobe (b,c: arrows). Fine‐needle aspiration biopsy yielded a diagnosis of malignant epithelial neoplasia of possible basal cell origin.
CT & MR
Squamous Cell Carcinoma
Squamous Cell Carcinoma (Canine)
11y MC Shetland Sheepdog with left‐sided epistaxis. There is a highly invasive and poorly defined soft‐tissue mass centered on the left retropharyngeal region, causing profound osteolysis of the basisphenoid bone (a: large arrow) and obliterating the left pterygoid muscles (b: arrow). Periosteal reaction and sclerosis of the zygomatic process of the left temporal bone is also seen (a,c: arrowhead), and the left digastricus and masseter muscles are atrophied (c: arrows). Mass margins extend intracranially, and pronounced meningeal enhancement is evident ventrally and adjacent to the left temporal lobe (d: arrows). The oval foramina remain intact (a: small arrows), but the mandibular branch of the left trigeminal nerve cannot be delineated within the mass (d). The location and aggressive imaging features of this lesion are characteristic of squamous cell carcinoma. Biopsy of the mass confirmed squamous cell carcinoma.
Normal Orbit
- Images b–e are ordered from rostral to caudal. The orbit is represented by the shaded circle (a) and is mainly comprised of the frontal bone and zygomatic arch.
- The extraocular muscles (b: white arrowhead) are surrounded by fat.
- The zygomatic salivary gland is strongly contrast enhancing in the ventrolateral orbit.
- The pterygoid muscle (b: asterisk) lies medial to the gland.
- The orbital ligament (c: double‐ended arrow) joins the zygomatic process of the frontal bone (a: #) to the zygomatic arch. Focal mineralization is common (c: small arrowhead).
- The lacrimal gland is ventral to the orbital ligament (b: thin white arrow) and is contrast enhancing.
- The ramus of the mandible is medial to the zygomatic arch.
- The optic nerve (d: black arrowhead) is hypoattenuating and travels toward the optic canal.
- The optic chiasm (f: open arrow) is visible within the calvarium.
- F (frontal sinus), M (mandible), S (zygomatic salivary gland), Z (zygomatic arch).
The Nasolacrimal System
This CT study was acquired following instillation of iodinated contrast medium through the lacrimal punctum. Representative images are ordered from caudal to rostral, mimicking the order in which contrast medium flows through the duct. The normal nasolacrimal duct originates from the lacrimal sac, enters the lacrimal canal through the lacrimal bone (a: arrow), and continues rostrally within the maxillary bone (b,c: arrow). The duct exits the maxillary bone and continues to course rostrally (d,e: arrow), terminating in the nasal cavity (f: arrow). Contrast medium in the ventral aspect of the nasal cavity has exited the duct and is distributed in the dependent interstices of the turbinates (b–f: arrowhead).
Nasolacrimal Cyst
CT & MR
3y MC Golden Retriever with right‐sided epiphora of 2‐month duration. Images b–f are at approximately the same anatomic level near the proximal extent of the lacrimal canal. Similarly, images a and g–i are at the same anatomic level in the dorsal plane.
- A large expansile mass arises from the region of the lacrimal bone, causing resorptive deformation of the adjacent lacrimal, maxillary, and frontal bones (a,b,e,h: arrows).
- The mass also extends medially into the nasal cavity and causes deformation of the dorsal aspect of the maxillary sinus (c: arrow).
- Centrally, the mass is fluid attenuating on CT and is T2 hyperintense and T1 hypointense.
- A sedimentary layer is also appreciated on the transverse T2 image (d: arrow), further documenting a cystic character.
- The thin cystic wall minimally contrast enhances on both CT and MR studies (c,f,i).
- The normal appearance of the caudal extent of the contralateral lacrimal canal (b: large arrowhead) and the infraorbital canal (b: small arrowhead) is seen on the left.
- Excisional biopsy confirmed this to be a ductular cyst that arose near the proximal origin of the nasolacrimal duct.
Trauma
2y MC Domestic Shorthair with acute head trauma of unknown cause. There is a moderately displaced fracture of the right ventromedial orbit (a–c: arrow). The fracture line is in the region of the convergence of the maxillary, lacrimal, and zygomatic bones. The cat also sustained a displaced fracture of the hard palate and separations of the incisive and mandibular symphyses (c: arrowheads).
Chronic Trauma
16mo M Chihuahua bitten in the face 1 year prior. The representative transverse images a–c are ordered from rostral to caudal. Images e and f are contrast‐enhanced images comparable to b and c, respectively. There is marked deformation of the right maxilla and frontal bone (a,b: arrowheads) and multiple fenestrations within the right maxilla and left frontal bone (b,c: arrows), causing both orbits to be misshapen. The 3D rendering (d) shows the extent of trauma and remodeling of the dorsal margin of the right orbit. Right‐sided phthisis bulbi (e: arrow) and an intracranial cyst (f: asterisk) resulting from the previous trauma are also evident.
Retrobulbar Cellulitis
11y FS Pointer with 24‐hour history of left‐sided exophthalmos. Images a–c depict the same anatomy. Image d is slightly more ventral.
- There is a mild diffuse increase in extraocular musculature and adipose volume in the left retrobulbar space (a: arrow).
- There is also a loss of definition of muscle, scleral, conjunctival, and intraocular margins seen on all sequences.
- Diffuse retrobulbar and conjunctival enhancement is evident on the left (c,d).
Conjunctival biopsy revealed neutrophilic and plasmocytic conjunctivitis. Clinical signs rapidly resolved with systemic and topical antibiotic therapy.
Extraocular Myositis
1y MC Labrador Retriever with bilateral blepharospasm and reduced response to retropulsion. Images d–e are at the level of the globe and images g–i are further caudal within the retrobulbar space.
- There is an increase in volume and loss of definition of the extraocular muscles (a–c,g–i). This is associated with an increase in extraocular muscle signal intensity on T2 images (b,h).
- There is diffuse contrast enhancement of the extraaxial muscles (c,i) and ocular adnexa (f), bilaterally.
- Focal meningeal enhancement is also present in the frontal lobar region bilaterally (c: arrowheads) and may represent an extension of the inflammatory response through the optic canal or orbital fissure.
Extraocular muscle biopsy revealed chronic lymphohistiocytic myositis and myocyte atrophy, which is consistent with the microscopic description reported for extraocular myositis. Conjunctival biopsy revealed marked subacute fibrinosuppurative conjunctivitis.
Retrobulbar Abscess
10y MC Newfoundland with acute onset left‐sided conjunctival hyperemia. Representative dorsal plane images all depict the same anatomy. These images are ventral to the globes and depict the ventral aspect of the orbits.
- A fusiform abscess that has T1 hypointensity and T2 hyperintensity (a–d: arrows) is evident centrally.
- The core does not contrast enhance, but the periphery intensely enhances (c,d).
- Distribution of contrast enhancement is best seen on the fat‐suppressed contrast‐enhanced T1 image (d).
- The left zygomatic salivary gland is also mildly enlarged and contrast enhances more than the contralateral gland as a result of secondary sialadenitis (a,d: arrowhead).
Aspiration cytology revealed marked septic suppurative inflam- mation with a mixed bacterial population.
Pterygoid Abscess (Canine)
3y M Golden Retriever with right‐sided buphthalmos and pain opening the mouth.
- There is an irregularly shaped, hypoattenuating region in the right pterygoid muscle (a,c).
- The pterygoid muscle is located medial to the hyperattenuating zygomatic salivary gland on the transverse images (a) and on ultrasound (b).
- The region of inflammation is hypoechoic and irregular on ultrasound images (b).
- There is additional soft‐tissue opacity in the left nasal cavity indicating rhinitis.
- No migrating foreign bodies were observed, but this remains a primary differential as a cause of the abscess.
Zygomatic Sialoadenitis (Canine)
8y MC German Shepherd cross with resistance to retropulsion of the right eye. Images a–c and d–g depict the same anatomy in dorsal and transverse planes, respectively.
- A well‐demarcated lobular mass is seen in the ventral aspect of the right retrobulbar space (a–g).
- The mass is highly contrast enhancing and has a complex internal architecture consistent with salivary glandular tissue (b,f,g).
- Images c and g show the value of fat suppression for increasing conspicuity of contrast‐enhancing lesions in the retrobulbar space.
Aspiration biopsy of the mass revealed salivary tissue and chronic granulomatous inflammation.
Retrobulbar Lymphoma (Feline)
Mature cat of unknown age with left‐sided exophthalmos. Representative transverse images are ordered from rostral to caudal.
- A large uniformly attenuating mass (a,b: asterisk) within the left retrobulbar space causes marked displacement of the globe.
- The mass has eroded through the perpendicular (a,b: arrowhead) and horizontal laminae of the palatine bone (a: large arrow) and fills the nasopharynx and the left sphenoidal sinus.
- The mass has also eroded through endoturbinates and the left ventral part of the cribriform plate (b: small arrow).
- Both frontal sinuses are fluid filled (b) as a result of obstructive sinusitis from the intranasal component of the mass (not seen).
Aspiration biopsy confirmed lymphoma.
Orbital Melanoma (Canine)
13y FS Golden Retriever with right‐sided exophthalmos. Representative transverse CT images (a–c) are ordered from rostral to caudal. The gross pathology image e is approximately comparable to CT image a.
- A well‐delineated sessile soft‐tissue mass is seen within the medial aspect of the right orbit (a–d: asterisk), causing compression and lateral displacement of the adjacent globe (a: arrowhead).
- The mass is only minimally contrast enhancing.
Tissue biopsy revealed melanotic melanoma. A highly pigmented mass is seen in the dorsomedial aspect of the right orbit on the gross pathology image (e: arrow).
Metastatic Orbital Carcinoma (Feline)
17y FS Domestic Shorthair with swelling of the left side of the head and diminished retropulsion of the left eye. A right middle lung lobe mass was seen on thoracic radiographs. Representative transverse CT images are through the caudal aspect of the retrobulbar spaces and are ordered from rostral to caudal.
- An ill‐defined, peripherally contrast‐enhancing mass is present within the caudal extent of the left retrobulbar space (b).
- Contrast enhancement also extends to surrounding musculature and fascial planes (a).
- A large well‐defined mass is present in the ventral part of the right middle lung lobe (c: asterisk).
Tissue biopsies from necropsy revealed a primary bronchogenic carcinoma of the right middle lung lobe and an aggressive, highly invasive metastatic mass of the left retrobulbar space.
Orbital Fibrosarcoma (Canine)
7y FS Retriever cross with right‐sided exophthalmos and intracranial neurologic signs. Representative unenhanced (a–c) and comparable contrast‐enhanced (d–f) images are ordered from rostral to caudal.
- An ill‐defined partially mineralized soft‐tissue mass is present in the right retrobulbar space (a–c: arrows), causing dorsal and rostral displacement of the right globe (d: arrowhead).
- There is osteolysis and medial displacement of the right frontal bone, perpendicular lamina of the right palatine bone, and ethmoturbinates (a,b: arrowheads).
- The mass extends into the olfactory and frontal regions of the cranial vault (d–f: asterisk).
- The expansile intracranial component of the mass also results in attenuation and lateral displacement of the left frontal and palatine bones (c,f: arrowheads).
- The mass has a heterogeneous contrast‐enhancement pattern in the retrobulbar space (d,e) and a peripheral enhancement pattern intracranially (f: asterisk).
Histologic diagnosis following necropsy was highly anaplastic sarcoma consistent with fibrosarcoma. The intracranial component was centrally necrotic, consistent with the pattern of contrast enhancement seen on CT images.
Orbital Rhabdomyosarcoma (Canine)
3y MC Tibetan Terrier with a 2‐week history of left‐sided exophthalmos. Representative dorsal plane images are at (a–c) and ventral to (d–f) the level of the eyes.
- There is a large irregularly shaped mass within the retrobulbar space (a–c,g,h: asterisk), which is isointense to gray matter on both T1 and T2 images.
- The mass invades the left temporal muscle (a–c: arrow) and appears to cause osteolysis of the left zygomatic bone (d,h: arrowheads).
- The mass is nonuniformly contrast enhancing.
Histologic diagnosis following necropsy was rhabdomyosarcoma.
Orbital Meningioma (Canine)
7y MC Cavalier King Charles Spaniel with a 4‐month history of progressive right‐sided exophthalmos. The first three images (a–c) depict the same anatomy and are at the level of the caudal aspect of the retrobulbar spaces.
- There is a well‐defined mass in the caudal aspect of the right retrobulbar space that is hyperintense to gray matter on both T1 and T2 images (a,b: arrow).
- The mass is moderately and uniformly contrast enhancing (c,d: arrowhead).
- The caudal extent of the mass is adjacent to the region of the orbital fissure and optic canal (d–e,f: arrow). These structures are not clearly seen on the images, but the arrows indicate their approximate location.
Upon surgical exploration, the mass was found to arise from the ophthalmic branch of the right trigeminal nerve (cranial nerve V) as it exited the orbital fissure. Excisional biopsy revealed meningioma. Although a specific preoperative diagnosis could not be made from MR images, the caudal and central location of the mass within the retrobulbar space and the uniform contrast‐enhancement pattern is suggestive of a neoplasm arising from one of the nerves arising from the orbital fissure or optic canal.
Feline Restrictive Orbital Myofibroblastic Sarcoma (Feline)
16y FS Siamese with bilateral conjunctival and episcleral hyperemia, corneal ulcerations, and reduced extraocular muscle function. Images a–d are at the same anatomic level. Image e is somewhat more ventral and highlights the caudoventral recesses of the orbits.
- There is pronounced thickening of the sclera and episcleral tissues, which is best seen on the contrast‐enhanced images (d–f: arrows).
- Periorbital edema is also evident on the STIR image (c: arrows).
- There is a loss of thickening of the extraocular muscles and loss of muscle margin definition associated with retrobulbar contrast enhancement (e: arrowheads).
Biopsy confirmed a diagnosis of restrictive orbital myofibroblastic sarcoma involving both orbits. Thomasy et al (2013).16 Reproduced with permission from Wiley.
Normal Globe (Canine)
- The lens is hyperattenuating (a: asterisk) and maintains its position through circumferential attachment to the ciliary body (b: white arrowhead).
- The anterior chamber (a: black arrowhead) and vitreous chamber (a: open arrow) are fluid attenuating.
- The sclera is hyperattenuating and surrounds the posterior portion of the eye (a: white arrow).
Normal Globe (Feline)
- The lens is visible as a hypointense structure with a hyperintense capsule (b: asterisk).
- The ciliary body supports the lens (c: arrowhead) and is contrast enhancing (d).
- The anterior (b: small white arrow), posterior (d: <), and vitreous chambers (b: open arrow) are hypointense on T1 and hyperintense on T2 images.
- The cornea (d: arrowhead) is visible anteriorly.
- The enhancing retina (b: large solid white arrow) is present posterior to the vitreous.
Trauma with Proptosis (Canine)
3y FS Brittany Spaniel with acute head trauma of unknown cause. Transverse images are ordered from rostral to caudal. The globe is located cranial and lateral to the orbit (a).
- There is soft‐tissue swelling within the orbit (b: asterisk), likely due to hemorrhage and edema.
- The optic nerve appears enlarged and surrounded by hypoattenuating tissue as it crosses this region (b: arrow).
Anterior Uveitis (Canine)
1y M Labrador Retriever with progressive swelling and cloudiness of the right eye. Glaucoma and uveitis were diagnosed following a complete ophthalmic examination.
- There is increased signal intensity of the right anterior chamber on T1 images (a: arrow) compared to the normal eye. There is a similar but more subtle increase in vitreous attenuation in the same eye.
- On contrast‐enhanced images, there is marked enhancement of the fluid in the anterior chamber (c).
The eye was enucleated after a corneal rupture, and plant material was found within the lens capsule.
Scleritis/Episcleritis (Canine)
9y F Border Collie mix that was presented for eye infection.
- There is thickening of the tissues surrounding the eye as well as the sclera itself, best seen on contrast‐enhanced images (c,f: arrow).
- The sclera is contrast enhancing and thickened compared to the normal eye (b,c,f).
Intraocular Melanoma (Canine)
11y M Golden Retriever with red‐eye of 3-week duration. This was a melanotic melanoma of the anterior uvea, explaining the pronounced T1 hyperintensity on the unenhanced image. The diagnosis was confirmed histologically following enucleation.
Intraocular Melanoma (Canine)
11y MC German Shepherd Dog with aspergillosis and an incidentally discovered ocular mass.
- The mass (a: arrows) is visible as a lobular, soft‐tissue attenuating structure caudal to the lens.
- There is interruption of the frontal bone and absent nasal turbinates (c: asterisk) due to previous rhinosinusitis.
Vitreous humor aspirate revealed melanotic melanoma.
Intraocular Lymphoma (Feline)
12y MC Domestic Longhair who is FIV positive, with blindness and decreased mentation.
- There is nuclear sclerosis of the right lens (a).
- Retinal detachment is present (d: arrow) with thickening of the retinal tissue on contrast‐enhanced images (c: arrow). The material posterior to the retina is T2 hyperintense and T1 hypointense (a,b: arrowhead).
- The anterior chamber is filled with contrast‐enhancing material (f: asterisk).
- The optic nerve is enlarged and contrast enhancing, extending through the orbital fissure to a hyperintense, contrast‐enhancing mass within the brain (g: open arrows).
Lymphoma was diagnosed after enucleation of the eye.
Intraocular Hemorrhage, Retinal Separation and Panuveitis (Canine)
11y MC Border Collie with a history of ocular hemorrhage.
- There is increased intensity within the vitreous chamber of the left globe on T1 (a) and T2 (b) weighted sequences.
- The retina is poorly defined and appears detached.
- There is a clearly demarcated line (a: arrow) separating two different fluid signals in the vitreous chamber. Neither component nulls on the FLAIR image (c), and the lesion does not enhance on contrast‐enhanced images (d).
- The normal right globe (e) can be compared with the abnormal globe (f) on sagittal images.
A hemangiosarcoma metastasis was found in the iris on histopathology and was the source of intraocular hemorrhage, which was confirmed on postmortem examination. The partitioning was thought to be due to separation of serum and cellular components.
Bullous Retinal Detachment (Feline)
8y MC Domestic Shorthair with hypertension, acute onset blindness, and obtundation. The CT study was performed on an emergent basis to evaluate for intracranial causes of obtundation.
- There is a broad‐based, hyperattenuating structure (arrow) on the ventral aspect of the globe.
- The most caudal aspect of the structure is in the region of the optic disc.
- The hyperattenuation indicates hemorrhage or proteinaceous fluid.
- Nuclear sclerosis was also present.
Imaging findings were confirmed by full ophthalmic examination.
Retinal Detachment (Feline) MR
18y MC Domestic Shorthair with progressive central nervous system disease, diabetes mellitus, and chronic renal failure.
- There is bilateral retinal detachment with a classic “V” shape centered at the optic disc.
- The material posterior to the retina is hyperintense on T2 images (a) and slightly hyperintense on T1 images (b) and represents retroretinal exudate.
Bullous serous retinal detachment, confirmed by complete ophthalmic examination, was thought to be secondary to systemic hypertension.
Hypermature Cataract (Canine)
11y Poodle/Maltese cross. A cataract had been developing in the right eye for the previous 4 years.
- In the bone window (a) and soft‐tissue window (b), mineral attenuating regions are visible in the peripheral and central regions of the right lens.
The cataract was brunescent and resulted in loss of vision.
Luxated Lens, Hypermature Cataract, Retinal Detachment (Canine)
- The left lens is in a normal position caudal to the iris (a: white arrow).
- The right lens is misshapen and reduced in size as a result of a hypermature cataract (b,c: asterisk) and has been displaced caudal to the iris (b: >) into the vitreous (b–e).
- The sclera is slightly irregular in the right eye (e: black arrow), and the right globe is larger than the left (d,e).
- There is a thin hypointense linear structure (b: arrowheads) medial to the luxated lens that represents the detached retina.
These findings, confirmed on postmortem examination, were attributed to glaucoma and to systemic hypertension.
Normal Parotid and Mandibular Salivary Glands (Canine)
Representative images were acquired immediately following contrast medium administration and are ordered from rostral to caudal.
- The normal mandibular salivary glands are characteristically oval in shape and smoothly margined (a–d: arrows).
- The normal parotid salivary glands are more elongated and have lobular margins (a–c: arrowheads).
- Both glands are highly and uniformly contrast enhancing.
- The major sublingual salivary gland is a small triangular structure fused to the cranial margin of the mandibular salivary gland (d: open arrow).
Normal Parotid and Mandibular Salivary Glands (Canine)
The normal mandibular salivary glands are characteristically oval in shape and smoothly margined (a–c: arrows). The normal parotid salivary glands are more elongated and have a mildly heterogeneous appearance (a–c: arrowheads). Although the glands have similar hyperintensity to muscle on unenhanced T1 images, the mandibular salivary glands are hyperintense compared to the parotid glands on T2 images. Both glands are intensely and uniformly contrast enhancing (c).
Normal Zygomatic Salivary Gland (Canine)
Normal zygomatic salivary glands moderately contrast enhance (large arrows). The nonuniformity of enhancement is consistent with the glandular architecture. The medial pterygoid muscle is located adjacent and medial to the zygomatic salivary gland at this level (small arrows).
Normal Zygomatic Salivary Gland (Canine)
Zygomatic salivary glands (a–d: arrows) are extremely variable in both size and shape. Glands are hyperintense to adjacent musculature on both T1 and T2 images (a,b) and are moderately and uniformly enhancing on contrast‐enhanced T1 images (c,d).
Zygomatic Sialadenitis (Canine)
2y MC Australian Shepherd with left‐sided exophthalmos.
- A multicameral cystic mass arises from the left zygomatic salivary gland (a–c: arrow), causing dorsal displacement of the left globe.
- The right zygomatic salivary gland is normal in appearance.
Aspiration cytology of the mass revealed neutrophilic inflammation consistent with zygomatic sialoadenitis.
Zygomatic Sialadenitis (Canine)
9y FS Cocker Spaniel with left‐sided exophthalmos.
- The left zygomatic salivary gland (a–f: large arrow) is markedly enlarged and is T1 hypointense and T2 hyperintense to the contralateral gland (a–c: small arrow).
- The contrast‐enhanced images reveal that the glandular architecture is retained, including the arborizing ductal pattern, suggesting diffuse inflammation rather than neoplasia.
Clinical signs resolved with antibiotic and anti‐inflammatory therapy.
Mandibular Salivary Gland Abscess (Canine)
12y MC Rottweiler with a ventral cervical mass. Representative contrast‐enhanced images are ordered from rostral to caudal.
- There is a large predominantly fluid attenuating cavitary mass contiguous with the lateral margin of the right mandibular salivary gland (a: asterisk).
- The lateral contour of the gland is altered, and the fluid center extends into the glandular parenchyma (a).
- The mass is thick walled, peripherally enhancing, and poorly margined.
- The center consists predominantly of fluid but also includes a small volume of fragmented gas (b).
A mixed bacterial population was cultured from a fluid aspirate.
Mandibular Salivary Adenocarcinoma (Feline)
8y FS Siamese with a ventral cervical mass. Representative images are at the level of the mandibular salivary glands.
- There is a large, spherical, low‐attenuation mandibular salivary mass in the right ventral cervical region (a,b: large arrow).
- The mass contrast enhances nonuniformly centrally and has a thin but prominent peripheral rim of enhancement (b).
- The normal left mandibular salivary gland is also evident (a,b: small arrow).
Biopsy confirmed mandibular salivary adenocarcinoma.
Mandibular Sialocele (Canine)
10y MC Afghan Hound. The CT study was performed as part of a diagnostic evaluation of suspected pituitary‐dependent Cushing’s syndrome.
- An oval fluid‐dense mass (a: asterisk) is located medial to the left digastricus muscle (a: arrow).
- The attenuation of the fluid was 0 HU and was similar on unenhanced and contrast‐enhanced images.
The clinical diagnosis was sialocele arising from the mandibular salivary gland (not seen in this image).
Sialocele with Sialoliths (Canine)
CT
10y MC Maltese with a fluctuant ventral cervical mass. The CT image is at a level just rostral to the mandibular salivary gland.
- An ill‐defined and diffusely hypoattenuating mass (arrow) is present adjacent to the right external ear canal and tympanic bulla.
- Multiple focal mineral opacities are distributed within the mass.
- Smaller numbers are seen on the left side.
The mass was thought to represent a sialocele containing multiple sialoliths.
Normal Mandibular Lymph Nodes (Canine)
- Mandibular lymph node aggregates are seen ventrally (a: arrows).
- Normal mandibular nodes are variable in both size and number.
- Normal lymph nodes are highly and uniformly contrast enhancing (b).
- The facial vein (b: arrows) courses next to the lymph nodes and should be distinguished from them by viewing serial contiguous images (not shown).
Normal Mandibular Lymph Nodes (Canine)
MRI
- Mandibular lymph node aggregates are seen ventrally, appearing isointense to muscle on T1 images (a: arrows) and hyperintense on T2 images (b: arrows).
- Normal mandibular lymph nodes are variable in both size and number.
- Normal lymph nodes are highly and uniformly contrast enhancing (c).
- The facial vein (b: arrowheads) courses next to the lymph nodes and can be distinguished from the lymph nodes on MR by the flow void artifact.
Normal Medial Retropharyngeal Lymph Nodes (Canine)
- On transverse images (a), the medial medial retropharyngeal lymph nodes (a: arrow) appear as oval, isoattenuating structures medial to the mandibular salivary gland (a: M) and lateral to the carotid artery.
- A hypoattenuating linear structure representing fat in the hilus is visible in the rostral portion of the lymph node (a: open arrow).
- Sagittal and dorsal plane images (b,c) show the elongated, oval shape of the lymph node (b,c: arrows).
- Strong, mildly heterogeneous contrast enhancement is visible on all images.
Pyogranulomatous Lymphadenopathy & Lymph Node Abscess (Canine)
7y MC Weimaraner with recent‐onset difficulty swallowing and pain on manipulation of the head and neck. Representative contrast‐ enhanced CT images are at the level of the mandibular (a) and retropharyngeal (b) lymph nodes.
- Mandibular lymph nodes are enlarged and have extensive nodal and ill‐defined perinodal contrast enhancement (a: arrows).
- Similar findings are seen associated with the medial retropharyngeal lymph nodes (b: arrows).
- In addition, the left medial retropharyngeal lymph node is greatly enlarged and contains a fluid component ventrally consistent with frank abscessation.
Aspiration cytology from the medial retropharyngeal lymph node confirmed suppurative inflammation and necrosis.
Regional Lymph Node Metastasis
8y MC Labrador Retriever with previously excised right tonsillar squamous‐cell carcinoma. Representative CT images are at the level of the medial retropharyngeal lymph nodes and are ordered from rostral to caudal.
- The left medial retropharyngeal lymph node (a: arrow) is normal in size, shape, and contrast enhancement. The central linear filling defect represents the normal fat‐filled lymph node hilus.
- The right medial retropharyngeal lymph node is markedly enlarged and has irregular margins (b: arrow). Multiple parenchymal contrast filling defects are characteristic of lymph node metastatic deposits
Aspiration cytology of the right medial retropharyngeal node confirmed metastatic squamous cell carcinoma.
Lymphoma (Canine)
9y M Fox Terrier. CT was performed for lymphoma staging. Representative unenhanced (a,b) and contrast‐enhanced (c,d) images are at the level of the mandibular (a,c: arrows) and medial retropharyngeal (b,d: arrows) lymph nodes.
- The lymph nodes are markedly enlarged but retain an oval shape and smooth contours.
- Contrast enhancement is characteristically uniform with a slightly foamy appearance.
- The right parotid lymph node, often not easily recognized on CT in normal dogs, is prominent in this patient (a,c: arrowheads).
Mandibular lymph node biopsy documented T‐cell lymphoma.
Normal Tooth Anatomy (Canine)
- The central lucent pulp cavity (small black arrow) is surrounded by a dense cementum layer (large black arrow).
- The thin lucent layer of the periodontal ligament (small white arrow) is in turn surrounded by the dense lamina dura of the alveolus (large white arrow).
- The outer layers of the crown (black arrowhead) are composed of dense enamel and dentin.
Pulp > cementum > dense enamel and dentin > periodontal ligament > lamina of the alveolus
Periapical Abscess (Canine)
11y FS Australian Cattle Dog. The CT scan was performed for an unrelated disorder. Representative sequential images acquired at the level of the fourth maxillary premolar are shown and ordered from rostral to caudal.
- There is focal destruction of periapical alveolar bone of the rostral (a: arrows) and caudal (b: arrow) roots, and of the left maxillary fourth premolar.
Imaging findings are characteristic of periapical abscess.
Abscess and Rhinitis (Feline)
CT
- The left maxillary canine tooth is fractured at the tip (a: arrow), and the pulp chamber is widened compared to the right side (a: arrowhead).
- The adjacent nasal cavity is filled with soft‐tissue opacity material (b: open arrow).
- The alveolus is lytic and open to the adjacent nasal cavity (c: arrow).
Radicular Cyst (Canine)
10y MC Labrador Retriever with a facial mass. The right maxillary fourth premolar was previously removed on suspicion of tooth root abscess. Unenhanced (a,b) and comparable contrastenhanced transverse images (c,d) are ordered from rostral to caudal.
- On bone windowed images, a cystic expansile lesion is present in the right maxilla (b: solid arrow), extending from the third premolar to the right mandibular first molar tooth roots (b: open arrow) and into the orbit.
- There is peripheral enhancement of the lesion on contrast enhanced images (c: arrows), and fluid‐attenuating material is present centrally.
- The circular‐shaped mandibular lysis can be seen on the 3D image (e).
- The fourth maxillary premolar is absent.
Exisional biopsy confirmed the mass to be a radicular cyst.
Squamous Cell Carcinoma (Canine)
8y FS Border Collie with possible infected tooth.
- There is marked osteolysis and irregular bone production surrounding the caudal left mandible (a,b: open arrows).
- Multiple teeth are absent.
- There is a large soft‐tissue mass associated with the osseous lesion, which is intensely, heterogeneously contrast enhancing (d: arrows).
- The 3D image shows the extent of the osseous component of mandibular lesion (e).
Biopsy confirmed squamous cell carcinoma.
Melanotic Melanoma (Canine)
10y MC Labrador Retriever with difficulty eating.
- There is a mass in the region of the soft palate and tonsils that is multilobular in shape (b: arrows).
- On contrast‐enhanced images, the mass is peripherally and heterogeneously enhancing (e: arrows).
- The left mandibular lymph node is enlarged with a central, hypoattenuating, nonenhancing region (c,f: open arrow) and peripheral contrast enhancement.
Primary melanotic melanoma with regional lymph node metastasis was confirmed by excisional biopsy.
Maxillary Fibrosarcoma (Canine)
11y Standard Poodle with enlarging left maxillary mass. Representative CT images are at the level of the maxillary canine teeth.
- There is a left‐sided soft‐tissue mass with an intranasal component, the latter of which has resulted in adjacent ectoturbinate destruction (a: asterisk).
- The left maxillary canine tooth is missing, and osteolysis of the alveolus and lateral maxillary cortex is evident (a: arrows).
- The mass moderately and heterogeneously contrast enhances (b).
Biopsy revealed fibrosarcoma.
Maxillary Osteosarcoma (Canine)
12y MC Miniature Schnauzer with left‐sided facial swelling and an infraorbital draining tract.
- There is a mixed productive and destructive mass originating from the left maxilla (a: arrows).
- The mass extends into the nasal cavity, obliterating the ventral nasal turbinates.
- The mass is mildly enhancing on contrast‐enhanced images.
Biopsy confirmed osteosarcoma.
Hyoid Trauma (Canine)
5y FS Jack Russell Terrier with a 3‐month history of coughing, gagging, and nasal discharge. Images a and b are the same image with and without annotation. These are 5 mm collimated transverse images that include the basihyoid bone (b: arrowhead), caudal ends of the ceratohyoid bones (b: small arrows), portions of the epihyoid bones (b: large arrows), and the distal end of the left stylohyoid bone (b: black arrow). The caudal end of the angular process of the right mandible is also seen (b: black arrowhead). The right epihyoid bone is displaced laterally, indicative of trauma.
Hematoma (Canine)
MR
8y MC Golden Retriever. Previous endoscopy (1 week prior) with laryngeal biopsy resulted in a hematoma.
- A large, well‐circumscribed mass that is hypointense to muscle on T1 sequences and hyperintense to muscle on T2, PD, and FLAIR sequences is present in the right cranioventral cervical region adjacent to the larynx (a: arrows).
- There is a thin, peripheral rim of enhancement on contrast‐enhanced images (d: arrowhead).
- The mass partially suppresses on the FLAIR image (e).
Nasopharyngeal Polyp (Feline)
4y FS Domestic Shorthair with upper respira- tory noise and open‐mouth breathing.
- There is soft‐tissue attenuating material filling the nasopharynx and choana on transverse images (a,b: arrows).
- The mass is well circumscribed and peripherally contrast enhancing (c: arrowhead).
- The left tympanic bulla is filled with a combination of mineral and soft‐ tissue attenuating material (d: open arrow).
Retropharyngeal Cellulitis (Canine)
4y FS Pit Bull Terrier with progressive dyspnea. Representative contrast-enhanced images are at the cranial cervical level and are ordered from cranial to caudal.
- A contrast‐enhancing perilaryngeal and retropharyngeal mass (a–d: arrow) is evident, bounded by the longus capitus muscles dorsally (a–c: asterisks).
- The medial retropharyngeal lymph nodes (a,b: arrowheads) are moderately enlarged and have a nonuniform contrast‐enhancement pattern.
Biopsy of retropharyngeal tissue confirmed chronic neutrophilic and plasmacytic cellulitis with extensive fibrosis.
Laryngeal Rhabdomyosarcoma (Canine)
11y MC English Setter with a left‐sided laryngeal mass. Images a and b are at the level of the larynx. Images c and d are at the level of the mandibular and medial retropharyngeal lymph nodes, respectively.
- There is a centrally hypoattenuating left laryngeal mass (a,b: arrow) that peripherally contrast enhances and causes rotational displacement of the cranial border thyroid cartilage (b: arrowhead).
- Ipsilateral mandibular (c: arrows) and medial retropharyngeal (d: arrow) lymph nodes appear normal.
Biopsy revealed granular cell rhabdomyosarcoma. The dog was alive, and there was no evidence of mass recurrence 4 years following mass excision and permanent tracheostomy.
Neuroendocrine Tumor (Canine)
14y FS Golden Retriever cross with a right ventral cervical mass. Images d–f are at the level of the larynx.
- An irregularly margined, ovoid mass is seen adjacent to the larynx in the region of the right retropharyngeal lymph node.
- The mass has a solid but heterogeneous center (a–f) and markedly contrast enhances (c,f).
- The right carotid artery is displaced laterally (d: arrow) compared to the left carotid artery (d: open arrow).
- Both thyroid lobes were identified and appeared normal (not shown).
Biopsy revealed the mass to be a neuroendocrine tumor of indeterminate origin.
Neuroendocrine Tumor (Feline)
10y FS Siamese with intermittent dyspnea of 1‐month duration.
- A large, predominantly right‐sided contrast‐enhancing mass (a,b: asterisk) arises from the right laryngeal wall, displacing and partially occluding the intralaryngeal ostium and caudal nasopharynx (a: arrow).
Aspiration cytology revealed this mass to be a malignant neuroendocrine tumor.
Nasopharyngeal Undifferentiated Round Cell Tumor (Canine)
2y MC Labrador Retriever with progressive dyspnea.
- A well‐defined, uniformly contrast‐enhancing mass arises from the dorsal nasopharyngeal wall and nearly completely obstructs the nasopharyngeal lumen (a,b: arrow).
Endoscopically acquired biopsy (c) revealed the mass to be a primitive undifferentiated round‐cell tumor.
Thyroid Adenoma (Feline)
7y Himalayan with recent history of dysphagia and anorexia.
- An ovoid hypoattenuating mass is present in the left ventral cervical region on ultrasound examination (a). On CT images, the mass has attenuation less than adjacent soft tissues but significantly more than fat (b: arrow).
- The mass contrast enhances nonuniformly and margins are well defined (c: large arrow).
- The left common carotid artery is displaced dorsally (c: small arrowhead), and the left jugular vein is displaced laterally (c: large arrowhead).
- The right thyroid gland appears normal (c: small arrow).
Excisional biopsy confirmed a diagnosis of thyroid adenoma.
Thyroid Carcinoma (Canine)
12y FS Labrador Retriever with previously diagnosed pulmonary and cervical masses.
- The mass is mildly hypoattenuating on an unenhanced CT image (b: arrow).
- The left thyroid lobe appears normal in size and is hyperattenuating (b: arrowhead).
- The mass moderately contrast enhances but less so than surrounding normal thyroid tissue (c: arrow) and the contralateral thyroid lobe.
- On dorsal plane maximum‐intensity projections (MIP) of contrast‐enhanced imaging data, a thick‐slab MIP reveals the course of the two common carotid arteries dorsal to the thyroid lobes (d: arrowheads). A thinner‐ slab MIP excluding the carotid arteries reveals the thyroid lobes (e: arrows) and the specific location of the mass within the right lobe (e: arrowhead).
Excisional biopsy revealed solid and follicular thyroid carcinoma with vascular and capsular invasion.
Thyroid Carcinoma and Thyroid Adenoma (Canine)
12y FS Australian Shepherd with a right‐sided ventral cervical mass. Ultrasound examination revealed a large, solid vascular mass in the region of the right thyroid lobe (a). A smaller hypoechoic mass was seen within the body of the left thyroid lobe (b). Unenhanced and contrast‐enhanced transverse CT images (c–f) are paired and ordered from cranial to caudal.
- A large right‐sided, uniformly contrast‐enhancing mass is present (c–f: large arrow). The mass margin is poorly defined ventrally, and there appears to be extracapsular extension of the mass and diffuse enhancement of adjacent tissues (e,f: arrowhead).
- A normal‐appearing left thyroid lobe is seen on the more cranial CT image (c,e: small arrow). On the more caudal image, the left thyroid lobe is larger and has lower attenuation characteristics than expected, suggesting the presence of a second smaller left thyroid mass (d,f: small arrow).
Imaging findings were corroborated at the time of surgical excision (i,j: arrows). Excisional biopsy revealed right‐ sided thyroid carcinoma with extracapsular inva- sion and left‐sided thyroid adenoma.
Invasive Thyroid Carcinoma (Canine)
10y MC Labrador cross with a 3‐month history of dysphagia and ventral cervical mass. Representative CT images are paired unenhanced (a–c) and contrast‐enhanced (d–f) images ordered from cranial to caudal.
- An extensive soft‐tissue mass with heterogeneous attenuation is seen in the right cervical region, extending from the hyoid apparatus rostrally to the mid‐cervical region caudally.
- The mass displaces the larynx to the left, crosses midline, and extends into the dorsal and left lateral laryngeal and retropharyngeal regions.
- The mass is highly and heterogeneously contrast enhancing.
- The mass displaces the larynx to the left, invades the laryngeal soft tissues (e: small arrow), and incorporates the carotid artery and internal jugular vein on the right (e: black arrow). There are filling defects and distension of these vessels caudally (f: arrowheads) and of the right facial vein (d: arrowhead), indicating tumor invasion and the presence of tumor thrombus.
- The left retropharyngeal lymph nodes are enlarged and have a heterogeneous pattern of enhancement (e: arrowhead), suggesting contralateral regional lymph node metastasis.
Postmortem examination confirmed a diagnosis of thyroid carcinoma involving both thyroid lobes with extensive infiltration into the adjacent soft tissues and metastasis to regional lymph nodes and lung. The mass extended into and expanded the oropharyngeal wall with marked compression of the pharynx and laryngeal opening.
Malignant Carotid Body Tumor (Canine)
9y FS Boston terrier with a cervical mass. Carotid body tumors (Chemodectoma) are similar in location to thyroid masses.
- However, the normal, high‐attenuating thyroid lobes are easily identified adjacent to the tracheal wall on the unenhanced image in this patient (a: arrows).
- The carotid body tumor is highly vascular and intensely contrast enhancing.
- In comparison to thyroid tumors where the carotid artery is usually displaced laterally, the carotid artery is contained within the mass (b: open arrow).
Regional lymph node metastasis (not shown) was also confirmed from surgical excisional biopsy.
