Vertebral Column & Spinal Cord

Question 1

Vertebral Malformations

Answer 1

Malformations of the vertebrae are common, and although some are clinically significant, many are seen as incidental findings on imaging studies. Malformations can be categorized as simple or complex, and a recent review of spinal anomalies proposed specific classifica­tion of anomalous vertebrae based on a similar scheme used in people.

• Those anomalies that occur during the early embryonic period include centrum median cleft (butterfly vertebrae), true hemivertebrae, mediolateral wedged vertebrae, and transitional vertebrae.
• Anomalies that develop during the later fetal period include block vertebrae, articular process hypoplasia, and centrum hypoplasia or aplasia (dorsoventral wedged vertebrae).
• Vertebral anomalies can be further classified as arising from defects in formation (e.g. wedged, hemi‐, and butterfly vertebrae) versus incomplete or absent segmen­tation (e.g. block vertebrae).

German Shepherd Dogs are overrepresented for developing transitional vertebrae at the lumbosacral junction. Certain screw‐tailed breeds, such as Bulldogs, French Bulldogs, Pugs, and Boston Terriers, are highly predisposed to complex vertebral anomalies, particularly in the midthoracic region.

Vertebral anomalies can result in a combination of scoliosis, kyphosis, lordosis, or rotational spinal abnormalities; can cause spinal canal stenosis; and may predispose to spinal injury from what might otherwise be clinically insignificant trauma. In animals with vertebral canal stenosis, spinal cord diameter is often focally decreased as a result of chronic compression atrophy, even in patients without overt neurologic deficits.

An uncommon vertebral anomaly, caudal articular facet hypoplasia or aplasia in the thoracolumbar vertebral column, has been reported with spinal cord compression due to contralateral facet and ligamentum flavum hypertrophy.

The CT appearance of vertebral anomalies will vary depending on the specific malformation, but common findings include alteration in vertebral shape, reduced attenuation when mineralization is incomplete, and ver­tebral column curvature abnormalities. Vertebral canal stenosis suggests spinal cord impingement or compres­sion, which can be documented using CT myelography. Lumbosacral transitional vertebrae can predispose to cauda equina syndrome, and asymmetrical transitional vertebra at this level can result in pelvic rotation leading to coxofemoral malar­ticulation.

MR features are similar to those seen with CT, and spinal cord pathology is often more clearly detected.

Question 2

Atlantoaxial instability

Answer 2

Atlantoaxial instability

Atlantoaxial instability can be caused by malformation of either or both of the first two cervical vertebrae, with dorsal subluxation of the axis in relation to the atlas causing spinal cord compression. Malformations can include:

• Fusion of adjacent vertebrae
• Grossly abnormal vertebral shape
• Hypoplastic, aplastic, or misshaped dens
• The latter feature is associated with abnormalities of ligaments of the dens, which in turn exacerbate insta­bility.

Caution should be used when imaging patients with suspected craniocervical junction malformations since abnormalities are often unstable.

CT imaging features of atlantoaxial malformations include the abnormalities described above as well as separation of the cranial part of the spinous process of the atlas from the dorsal arch of the atlas with mild cervical flexion. Abnormalities of the dens can some­ times be more clearly seen on sagittal or dorsal plane reformatted images. Dorsal subluxation of the axis in relation to the atlas also results in decreased vertebral canal diameter.

MR features of atlantoaxial malformations include those described for CT imaging. Spinal cord compres­sion can also be seen as a narrowing of the hyperintense subarachnoid column on T2 images and narrowed spinal cord diameter due to dorsal–ventral cord compression. The MR appearance of the ligamentous structures of the normal canine occip­itoatlantoaxial region has been described in a cadaveric study, but they can be challenging to accurately identify in small patients.

Question 3

Chiari-like Malformation

Answer 3

Although imaging features of Chiari‐like malformation are detailed in Chapter 2.3, a striking imaging feature of the disorder worth mentioning here is the often pronounced saccular syringohydromyelia that can result from altered cerebrospinal fluid dynamics and is best seen on T2 images as a hyperintense dilatation of the central canal.

Question 4

Cervical spondylomyelopathy

Answer 4

Cervical spondylomyelopathy

Canine cervical spondylomyelopathy (CSM) is challeng­ ing to concisely summarize because the etiology is unclear, the underlying pathology is variable, and the clinical presentation varies with breed and age of the patient. Genetic, congenital, body conformational, and nutritional etiologies have all been postulated, and the disorder may stem from a combination of these factors. CSM usually occurs in large‐ to giant‐breed dogs between 2 and 8 years of age, and Doberman Pinschers are overrepresented. Although the disorder appears to occur more often in males, there is no confirmed sex predilection.

Clinical signs include cervical pain and spinal cord compressive myelopathy that is neuroanatom­ically localized to the cervical region. Cord compression is due to some combination of three distinct mechanisms:

• Compression can occur from intervertebral disk protru­sion, which tends to occur most frequently between C5 and C7. This manifestation of the disorder occurs in older large‐breed dogs and is common in Doberman Pinschers.
• Osseous stenotic compression is due to inherent vertebral canal stenosis and from proliferative new bone formation occurring on the lamina, pedicles, and articular facet margins of affected vertebrae. This manifestation occurs in younger large‐ and giant‐breed dogs and often involves many of the cervical vertebrae.
• Intermittent or dynamic compression can also occur with change in cervical spine position, usually in extension.

CT imaging features can include:

• Angulation of the endplate subchondral bone margin, associated with vertebral bodies having a rhomboidal rather than rectangular shape as viewed on sagittal images.
• Dogs with a component of intervertebral disk disease will have imaging signs referable to intervertebral disk protrusion.
• In dogs with osseous stenotic manifes­ tations, bone‐attenuating proliferative changes are seen involving the lamina, pedicles, and articular facets, result­ ing in decreased vertebral canal diameter, which is most pronounced in the lateromedial direction.
• This results in a change of canal cross‐sectional shape from round to rectangular or triangular and causes predominantly lat­eral or dorsolateral spinal cord compression and atrophy, which can be documented using CT myelography.
• In those dogs with a dynamic component to spinal cord compression, traction studies can be used to document reduction.

Anatomical features of CSM on MR images are similar to those in CT.

• Dense new bone will appear T1 and T2 hypointense.
• Spinal cord compression is usually clearly defined by attenuation of the subarachnoid column and cord flattening, seen best on T2 images.
• The affected region of the spinal cord may be reduced in diameter from atrophy, and change in signal intensity sometimes occurs as a result of central canal dilation, edema, or gliosis

Question 5

Osteochondrosis

Answer 5

Osteochondrosis

Osteochondrosis involving the lumbosacral junction has been reported in dogs, and articular facet subchon­dral bone fragmentation is occasionally seen either in isolation or as a sequela to other disorders, such as cervical spondylomyelopathy. For lumbosacral osteochondrosis, male dogs and Boxer, Rottweiler, and German Shepherd Dog breeds are overrepresented. Clinical signs are those of cauda equina neuropathy, and mean age at presentation is 6.3 years. Approximately 90% of lesions involve the craniodorsal margin of the body of the sacrum, while the remainder involve the caudodorsal margin of the body of the last lumbar vertebra.

On CT images, lumbosacral osteochondrosis lesions appear as one or more separate, bone‐attenuating bodies associated with an underlying defect within the sub­chondral bone of the parent vertebra. Osteochondrosis lesions may be isolated or associated with other develop­ mental or degenerative processes of the lumbosacral junction.

In a report of MR features of lumbosacral osteochon­ drosis in seven dogs, affected endplates were predomi­nantly T1 spin‐echo hypointense, T1 gradient‐echo hyperintense, variably T2 hyperintense, and contrast enhanced. Concurrent intervertebral disk disease was present in five of seven dogs.

Question 6

Intradural arachnoid diverticula

Answer 6

Intradural arachnoid diverticula

Intradural arachnoid diverticula, sometimes termed arachnoid or subarachnoid cysts, are focal, subdural, and usually dorsally located dilatations containing cerebrospinal fluid and most often confluent with the subarachnoid space. The etiology of intradural arach­noid diverticula is not known, but when seen in young animals they are thought to be developmental. A broader discussion of the various forms of arachnoid diverticula, both developmental and acquired, is included in Chapter 3.5.

• In young dogs, presumed developmental arachnoid diverticula commonly occur in the C2–C4 region in large breeds and in the thora­columbar region in all breeds.
• Male dogs and Pug, French Bulldog, and Rottweiler breeds are overrepre­ sented.
• Imaging features of intradural arachnoid diverticula are described in Chapter 3.5

Question 7

Spinal neural tube defects (spinal dysraphism)

Answer 7

Spinal neural tube defects (spinal dysraphism)

Neural tube defects result from abnormal closure or failure of closure of the developing neural tube.

• Closure errors in the rostral part of the tube lead to cranial defects
• While those that occur caudally lead to vertebral column and spinal cord anomalies

Folate deficiency is one well‐established cause of the disorder in people, and a hereditary link has been identified in neural tube defects described in Weimaraner dogs.

Terminology and classification of the various spinal neural tube defects are both inconsistent and confusing, and we choose to use a simplified scheme for this discussion.

• Errors of ectoderm, mesoderm, and neuro­ ectoderm development and differentiation, primarily associated with incomplete dorsal migration and closure, result in a grouping of related disorders under the overarching term spina bifida, which often involves the caudal lumbar and sacral region.
• Spina bifida can be further subclassified as spina bifida occulta or spina bifida cystica.
  
  • Spina bifida occulta is limited to incomplete dorsal closure of affected vertebra and is periodically seen on imaging studies as an incidental finding.
  • Spina bifida cystica includes dorsal meningeal defects leading to meningocele alone or the most clinically significant form that includes defective meningeal and cord development resulting in myelomeningocele.
• Spina bifida can further be characterized as closed or open to the external environment.
• Sacrocaudal dysgenesis of the Manx cat is a complex spinal neural tube defect that includes developmental abnormalities of the sacral and caudal vertebrae and associated spinal cord segments, which can include meningomyelocele and can be closed or open.
• Other manifestations of abnormal neural tube development, such as spinal duplication, are rare.

Question 8

Spina Bifida

Answer 8

Spina bifida occulta

• The specific CT or MR imaging feature of spina bifida occulta is incomplete closure of the dorsal arch and spinous process of one or more vertebrae.
• The meninges and spinal cord should appear unaffected.

Spina bifida cystica

• MR imaging features of meningocele include T1 hypoin­tense, STIR and T2 hyperintense dorsal dilation of the subarachnoid space in the region of the lumbosacral junction. The terminal spinal cord and associated spinal nerves remain within the vertebral canal. Meningocele is also present in patients with myelomeningocele, but the terminal spinal cord or the associated spinal nerves are displaced dorsally into the meningocele. If the lesion is open, sagittal or transverse STIR or T2 images can be used to document a communicating tract as a linear hyperintensity

Question 9

Spinal Dermoid Sinus

Answer 9

Dermoid sinus is an uncommon disorder that also results from neural tube closure errors. Failure of normal cell separation and differentiation into developing spine and skin leads to a dorsal sinus that histologically contains skin elements, such as hair follicles and sebaceous glands. The sinus can have a closed end at its most internal extent or connect to the meninges or spinal cord via a closed or patent tract. A grading scheme has been proposed, ranging from I to IV depending on the internal extent and character of the sinus, with increasing grade reflecting a more invasive lesion. Of the few reported cases, most are at the level of the cervical or cranial thoracic vertebral column. Dermoid sinuses have been reported in dogs and cats, and Rhodesian Ridgebacks are predisposed.

CT imaging features may be unremarkable other than a possible skin surface defect. Conventional radiographic sinusography has been used to determine the internal margin of the sinus and assess its association to the underlying vertebral column, meninges, and spinal cord, and CT would likely be of similar value. Reported MR imag­ing features include superficial mass with mixed T1 inten­sity, mild T2 hyperintensity, and STIR hyperintensity. In some instances, a sinus tract was not seen, and the depth of the lesion was underestimated. In one other patient, a T2 hyperintense tract was clearly identified coursing from the superficial mass to the dura matter.

Question 10

Answer 10

Atlantoaxial Instability (Canine)

5mo MC Yorkshire Terrier with acute onset cer­vical pain of 1‐week duration. Image a is the same as image b without annotations.

• Dorsal subluxation of the axis (b: large arrows) is pre­sent in relation to the atlas (b: arrowheads), causing marked narrowing of the vertebral canal in the dorsal–ventral axis (b: asterisk).
• The angulation of the vertebral column at the atlantoaxial joint, the gap between the caudal margin of the dorsal arch of the atlas, and the cranial margin of the spinous process of the axis (b: two‐headed arrow) are further evidence of atlantoaxial instability.
• The dens is also absent (b: small arrow).
• The abnormal relation­ship of the atlas and axis is also clearly seen on 3D renderings (c,d).
• Aplasia of the dens is best seen from the dorsal view (d: arrow).

Question 11

Answer 11

Chiari‐like Malformation with Syringohydromyelia (Canine)

1.5y F Chihuahua with recent‐onset paroxysmal episodes.

• The caudal cranial vault is small as a result of occipital hypoplasia (a: arrowhead), and moderate generalized hydrocephalus is evident (a).
• Marked saccular syringohydromyelia is present throughout the cervical and cranial thoracic spinal cord (b: arrows).
• There is also T2 hyperintensity within cord parenchyma, which is likely due to edema (b: arrowhead).

A diagnosis of Chiari‐like malformation with syringohydromyelia was made based on clinical and imaging findings.

Question 12

Answer 12

Cervical Spondylomyelopathy (Canine)

3y MC Mastiff with hypermetria in all limbs. CT myelographic images a, b, and c are at the approximate level of the C2–3, C3–4, and C4–5 intervertebral disk spaces, respectively.

• Hyperattenuating new bone of the lamina (a–c: arrow) and articular facets (a–c: arrowheads) at all three levels results in reduction of vertebral canal cross‐sectional area and change in shape, with greatest narrowing occurring in the horizontal axis.
• Remodeled articular facet margins impinge on the spinal cord to the greatest extent at C4–5, although a thin subarachnoid contrast column is retained (c).
• Additional sites with similar abnormalities were present more caudally (not shown).

Question 13

Answer 13

Cervical Spondylomyelopathy (Canine)

3y MC Labrador Retriever with myelopathy neuroanatomically localized to C1–5. The CT myelographic image is at the level of C4–5.

• Hyperattenuating new bone of the lamina (black arrow) and articular facets (arrowheads) results in reduction of vertebral canal cross‐sectional area and change in shape, with greatest narrowing occurring in the horizontal axis.
• The spinal cord is grossly distorted by bilateral compression from hypertrophied articular facets.
• There is also a separate osseous fragment associated with the distal margin of the right caudal aspect of the fourth cervical articular facet (white arrow), consistent with osteochondrosis.

Question 14

Answer 14

Sacral Osteochondrosis (Canine)

4y FS Miniature Schnauzer with a diagnosis of portosystemic shunt and no neurologic abnormalities. A CT examination was performed for surgical planning.

• Multiple small but highly attenuating osseous fragments are seen within the vertebral canal at the level of the lumbosacral junction (a,b: arrow).
• There is an underlying defect of the craniodorsal margin of the first sacral body, manifest as an angular flattening of the bone (a: large arrowhead).
• The lumbosacral intervertebral disk space is widened, and a soft‐tissue mass containing the fragmented bone protrudes into the vertebral canal, indicative of intervertebral disk herniation (a: small arrowhead) and possible dorsal longitudinal ligament hypertrophy.

Question 15

Answer 15

Intradural Arachnoid Diverticulum (Canine)

10mo FS Boxer cross with myelopathy neuroanatomically localized to C1–5.

• Conventional and CT myelographic images show an elongated teardrop‐shaped dilation of the dorsal subarachnoid space at the level of the second cervical vertebra (a–c: arrow), resulting in pronounced spinal cord compression (a–c: arrowhead).
• Contrast enhancement within this focal dilation is evidence that it communicates with the rest of the subarachnoid space.

A large cyst‐like structure was surgically removed following durotomy and was histologically confirmed to be an arachnoid diverticulum.

Question 16

Answer 16

Myelomeningocele (Canine)

6mo M English Bulldog with urinary and fecal incontinence since birth.

• The spinous process and pedicle margins of the caudal‐most lumbar vertebra are missing, consistent with spina bifida (a,b).
• There is dorsal deviation of the dural sac (c,d: arrow), which contains neural elements (c,e,f: white arrowhead), defining this as a myelomeningocele.
• A thin stalk (e: black arrowhead) extends from the dorsum of the myelomeningocele to the skin surface, which is dimpled.
• The hyperintensity in image c defining the volume of the meningocele does not extend dorsally within the stalk, and clinically this was determined to be a closed meningomyelocele.

Question 17

Vascular Cord Trauma

Contusion/hemorrhage

Answer 17

Contusion/hemorrhage

Spinal cord trauma is usually but not always accompanied by overt vertebral column trauma. Neurologic deficits range from clinically silent to complete spinal cord transection. In addition to the primary spinal cord injury that results directly from trauma, secondary injury occurs from vascular damage, local cytotoxic biochemical responses to injury, and inflammatory response, the combination of which can lead to progres­ sive disease. Postmortem examination of spinal cords of dogs and cats that sustained traumatic injury revealed thoracolumbar necrosis that correlated with the degree of static compression from vertebral column injury. Cervical cord injury often included central hemorrhagic necrosis that was more consistent with transient impact trauma than static cord compression.

MR features of spinal cord contusion include:

• Focal to regional increased T2 intensity with mild to no enhance­ment following contrast administration (Figure 3.2.18).
• T2* sequences reveal parenchymal susceptibility effects when there is a hemorrhagic component.
• Syringohy­dromyelia is often a late sequela to spinal cord trauma and appears as a focal to regional and central to eccentric T2 hyperintensity.

Question 18

Vascular disorders of Spinal Cord

Fibrocartilagenous Embolism

Answer 18

Fibrocartilagenous embolism

Early reports indicated that fibrocartilaginous embo­lism (FCE) occurs primarily in middle‐aged to older, large‐ and giant‐breed dogs; however, a more recent review in which diagnosis was based on clinical signs and MR imaging findings suggests that small and medium‐sized dogs are also commonly affected. The disorder has also been reported in cats. The clinical presentation is often a peracute onset of symmetrical or asymmetrical motor dysfunction immediately following exercise or minor trauma, with lower motor neuron signs also present in some patients. Initial clinical signs can include transient pain and can be progressive for the first 2 hours but are often nonprogressive thereafter. The cervicothoracic (C5–T2) and lumbosacral (L3–S3) regions appear to be predisposed. Pathology in histologically confirmed patients includes spinal cord infarction and hemorrhage with cartilaginous emboli in meningeal or spinal vessels. In some patients, extensive myelomalacia may also be present, but pathology is likely to be more severe in those patients that were euth­anized and confirmed as having FCE. A poorer prognosis is seen in patients with involvement of the intumescences, symmetrical neurological signs, and decreased deep pain sensation. A recent review of dogs with ischemic myelopathy found that a combination of lesion length greater than twice a vertebral length and cross‐sectional involvement of greater than 67% had a positive correlation with an unsuccessful outcome. Recovery rates for FCE are unclear since patients who do respond are not definitively diagnosed. However, a majority of patients with stable disease seem to partially or fully recover neurologic function.

CT imaging features can be limited to a noncompres­sive focal increase in spinal cord diameter, indicative of an intrinsic lesion.

MR features include focal T1 iso‐ to hypointensity and T2 hyperintensity within the affected spinal cord segments. Lesions prefer­entially affect gray matter and can be either symmetrical or asymmetrical. Spinal cord diameter can also appear locally enlarged but without compression. Intervertebral disk T2 signal intensity at the level of the spinal cord lesion is often less than that of adjacent disks

Question 19

Answer 19

Occipitoatlantal Luxation (Canine)

1y FS Keeshond cross with acute cervical injury after being struck by an automobile earlier in the day. A CT examination was performed with the dog on a backboard in lateral recumbency. Images a–c were acquired at the level of the occipitoatlantal joint and are ordered from cranial to caudal.

• The right occipital condyle (a–d: arrow) is axially subluxated in relation to the cranial articular fovea of C1 (a–c: asterisk).
• The left occipital condyle is ventrally luxated (c,d: arrowhead).

Closed reduction of the luxation was successfully performed using fluoroscopic guidance.

Question 20

Answer 20

Cervical Vertebral Subluxation with Articular Facet Fracture (Canine)

5y F Terrier cross bitten in the cervical region by a larger dog earlier in the day. Currently has neurologic deficits neuroanatomically localized to C6–T2.

• Survey radiographs reveal dorsal subluxation of C7 relative to C6 and narrowing of the C6–7 intervertebral disk space (a: arrowhead).
• Similar findings are also seen on sagittal and 3D reformatted CT images (b,f: arrowhead). In addition, there is a highly comminuted and displaced fracture of the right cranial articular process of C7 (c–e: arrow).
• The left articular process is normal by comparison (f: arrow). On MR images, the C6–7 intervertebral disk space is reduced in width and T2 signal intensity (i: arrow), and extruded disk material is present in the right ventral vertebral canal (g,h: arrowhead).
• There is evidence of spinal cord compression (g–i) and spinal cord T2 hyperintensity at the level of C6–7 (h,i), indicative of an intrinsic component to the injury.

Disk material was removed from the canal, and the subluxation was reduced and stabilized surgically.

Question 21

Answer 21

L3 Lamina Depression Fracture (Feline)

8y FS Domestic Shorthair bitten by a dog 2 days previously. Currently has a nonambulatory T3–L3 myelopathy.

• On CT images, a depression fracture arising from the cranial margin of the L3 lamina (a,b: arrowhead) impinges on the dorsal margin of the spinal cord.
• A ventral oblique 3D rendering with the vertebral bodies removed further illustrates the displacement of the fracture fragment into the canal (c: arrowhead).
• The fracture fragment is T2 hypointense on MR images (d,e: arrowhead) and impinges on the spinal cord, causing deformation and compression.
• There is also marked increase in spinal cord T2 signal intensity at this level due to intrinsic edema and hemorrhage.
• The T2 signal intensity of the L3–4 intervertebral disk is also reduced, suggesting possible traumatic intervertebral disk extrusion.

Spinal cord compression was relieved with a hemilaminectomy, and the L3–4 vertebral column was stabilized, resulting in gradual return of neurologic function.

Question 22

Answer 22

Spinal Cord Contusion (Canine)

4y MC Border Collie stepped on by a bull 1 day previously, resulting in injuries to the lumbar spine and abdomen. Current neurologic deficits are referable to an L3–L5 myelopathy. Spinal radiographs were unremarkable.

• There is moderate diffuse spinal cord T2 hyperin- tensity centered at the level of L3 and L4 (a,d: arrowheads) indicative of an intrinsic lesion.
• The spinal cord mildly and diffusely enhances following contrast administration (c,f: arrowheads).
• A T2* sequence reveals pinpoint susceptibility artifacts within the spinal cord indicative of multifocal hemorrhage (g: arrow).

Question 23

Answer 23

Hematomyelia (Canine)

12y FS Pit Bull Terrier with acute‐onset tetraparesis. The owners have administered aspirin twice weekly for chronic osteoarthrosis.

• There is T2 hyperintensity of the spinal cord parenchyma and focal central canal dilation centered on C5 (b,e: arrow).
• Cord diameter is enlarged at this level, indicative of intrinsic pathology, but there is no evidence of compression.
• The internal venous plexus also appears dilated (a,b: arrowheads).
• T2* sequences document hemorrhage within the effected spinal cord segment, as evidenced by prominent susceptibility effect (c,f: arrowhead).

Postmortem examination confirmed hematomyelia, myelomalacia, and subdural hemorrhage. An underlying cause was not determined, and chronic aspirin administration was thought to have induced a spontaneous hemorrhage. The two vertically oriented curvilinear lines superimposed on the spinal cord in image e are artifacts caused by an out‐of‐field microchip.

Question 24

Answer 24

Fibrocartilaginous Embolism (Canine)

4y FS Yorkshire Terrier with peracute onset of tetraparesis shortly after returning from a walk with the owner.

• A myelographic examination reveals a pronounced increase in spinal cord diameter centered on C6 (a: arrowheads).
• CT myelography further documents a caudal cervical intrinsic lesion (b–d: arrowheads).
• Although there is normally an increase in diameter of the cervical intumescence, the magnitude of the diameter change is abnormal and causes annular attenuation of the subarachnoid contrast column (d: arrowhead).
• A transverse cranial thoracic image acquired caudal to the spinal cord lesion shows a more normal spinal cord diameter and prominent contrast‐enhanced subarachnoid space (e).

Postmortem examination confirmed regional myelomalacia caused by multiple fibrocartilaginous emboli. The degree of spinal cord diameter enlargement in this patient is somewhat unusual and would be less likely to occur in patients with recoverable disease.

Question 25

Answer 25

Fibrocartilaginous Embolism (Canine)

4y FS Irish Wolfhound with acute‐onset pelvic limb paraparesis with no known initiating cause.

• There is diffuse T2 hyperintensity in the caudal spinal cord consistent with an intrinsic lesion (a–c: arrow).
• There is mild, diffuse cord enhancement following contrast administration (e,f: arrow).
• The central T2 hyperintensity and contrast enhancement suggests predominantly gray matter involvement (b,f: arrow).

Neurologic deficits persisted for 14 days with no evidence of improvement. Postmortem examination revealed severe bilateral myelomalacia with hemorrhage from spinal segment L6 caudally. Multiple fibrocartilaginous emboli were present in both the meningeal and spinal vessels.

Question 26

Answer 26

Fibrocartilagenous Embolism (Canine)

8y MC Labrador Retriever with acute‐onset neurologic deficits anatomically localized to C6–T2.

• There is focal T2 hyperintensity and T1 hypointensity of the spinal cord at the level of C5–6 (a,b,d,e: arrow) with no evidence of enhancement following contrast administration (c,f).
• The intensity changes are centrally distributed, and spinal cord diameter is focally increased, indicative of an intrinsic lesion.
• A T2* sequence shows no evidence of hemorrhage within the affected cord parenchyma (g).

The owners elected to euthanize the dog, and postmortem examination revealed locally extensive, primarily gray matter, myelomalacia, hemorrhage, and neuronal necrosis in the C5–C7 spinal cord segments (h). Multiple fibrocartilaginous emboli were evident in meningeal and spinal vessels. It is unclear why the T2* sequence failed to show the intraparenchymal sites of hemorrhage. One possibility is that because of the peracute nature of the disorder, MR imaging was performed early enough after the initial insult that hemoglobin degradation products were not yet present in adequate concentration to yield a susceptibility effect.

Question 27

Steroid responsive meningitis–arteritis

(SRMA)

Answer 27

Steroid responsive meningitis–arteritis (SRMA) is a systemic immune‐mediated disorder that includes inflammatory responses of the leptomeninges and associated blood vessels, which has been reported in young Bernese Mountain Dogs, Beagles, Nova Scotia Duck Tolling Retrievers, Corgis, Boxers, and other breeds.

The disorder involves the spinal cord primarily and, to a lesser extent, the brain. Although MR features of meningeal thickening and contrast enhancement have been reported, our experience is that imaging studies in dogs with SRMA are often unremarkable.

Question 28

Bacterial (suppurative) discospondylitis

Answer 28

In a large retrospective study involving over 500 canine patients diagnosed with discospondylitis, 2/3 were male, older dogs were more likely to be affected, and Great Danes were overrepresented.8\ Staphylococcus, Brucella, Streptococcus, and Escherichia species are most frequently isolated, although many others have been reported. Dogs with bacterial discospondylitis most often have an underlying infection of the urinary tract, skin, or other organ system, which leads to bacteremia and embolic seeding of vulnerable disks.

Conventional radiographic examination is an excellent test for diagnosis and monitoring of discospondylitis. CT and MRI are most often employed when neurologic deficits are present or the patient has other clinical signs not explained by radiographic findings or other diagnostic tests.

Imaging features vary widely and depend on the stage of the disease. CT features of early active disease can include vertebral endplate osteolysis and intervertebral joint space widening. In later phases of active disease, more pronounced endplate destruction is seen, which is associated with underlying bone sclerosis, reactive new bone formation, and collapse of the disk space. If there is significant proliferative soft‐tissue inflammatory response or intervertebral joint subluxation, spinal cord compression can occur with resultant neurologic signs. In the convalescent or reparative phase, complete collapse of the joint may occur with bridging reactive new bone. Soft tissues within the disk space, medullary bone, and surrounding soft tissues moderately to markedly contrast enhance during the active phases of disease, reflecting the presence of discitis, osteomyelitis, and cellulitis.

MR features of bacterial discospondylitis are similar and include mixed T2 intensity within the disk space and T1 hypointensity and T2 and STIR hyperintensity within affected vertebral bodies and adjacent soft tissues during the early active phase of disease. The disk, medullary bone, and adjacent soft tissues intensely contrast enhance during the active phases of disease. MR may be less sensitive than CT for monitoring bone destruction and production in the active and reparative phases, respectively.

Question 29

Spondylitis

Answer 29

In some geographic areas, inhaled plant awns can migrate through airways and lung parenchyma and exit caudally into the cranial sublumbar region, following the path of the attachment of the pars lumbalis of the diaphragm to the ventral margins of the third and fourth lumbar vertebrae. Pyogranulomatous myositis and frank abscess adjacent to the vertebrae lead to spondylitis.

Imaging features of spondylitis include:

• Periosteal new bone formation of the ventral and lateral margins of affected vertebral bodies.
• Underlying bone sclerosis may also be present depending on the duration and severity of infection, resulting in hyperattenuation on CT images and hypointensity on T1 and T2 MR images.
• Cellulitis or abscess is present with active disease, which will appear as a hypoattenuating sublumbar mass on CT images and a T1 hypointense, T2 hyperintense mass on MR images.
• Marked, heterogeneous soft‐tissue contrast enhancement occurs on images of both modalities

Question 30

Spinal epidural empyema

Answer 30

Infections within the spinal epidural space are uncommon and can occur by direct extension of discospondylitis or other local infection or through hematogenous dissemination. Signs include fever and progressive myelopathy, which may have a compressive component.

CT findings can be equivocal but include signs of discospondylitis as described above. Subarachnoid and epidural space contrast enhancement can be incomplete or nonuniform on CT myelographic images, and there may be evidence of focal, multifocal, or diffuse spinal cord compression.

MR features include mixed or increased T2 intensity within the epidural space, as well as T2 hyperintensity within the spinal cord at the site of infection. Moderate diffuse or peripheral enhancement is seen following contrast administration with both modalities

Question 31

Answer 31

Presumptive Spinal Granulomatous Meningoencephalomyelitis (Canine)

4y FS Chinese Crested Dog with a 3‐day history of difficulty walking, most pronounced in the thoracic limbs, and neuroanatomic localization to C1–T2.

• There is a T2 hypointense, T1 isointense focus in the dorsal spinal cord at the level of caudal C2 (a–d: arrow).
• Two smaller intrinsic foci with similar intensity are seen at the level of the C2–3 intervertebral disk space (a,c: arrowhead).
• There is diffuse T2 hyperintensity in the cranial cervical spinal cord due to surrounding edema (a).
• A discrete, uniformly enhancing mass is seen following contrast administration (e,f: arrow), and faint enhancement of the two smaller lesions is also evident (e: arrowhead).

Diagnosis was made from results of cerebrospinal fluid analysis consistent with granulomatous meningoencephalomyelitis, absence of infectious agents, and response to immunosuppressive doses of steroids.

Question 32

Answer 32

Spinal Granulomatous Meningoencephalomyelitis (Canine)

4y FS Jack Russell Terrier with recent onset of nystagmus and circling.

• There is diffuse moderate T2 hyperintensity of the brainstem and cranial cervical spinal cord associated with parenchymal swelling (a).
• There is mild nonuniform enhancement within the brainstem following contrast administration, and three ill‐defined contrast‐enhancing intrinsic lesions are seen in the dorsal cervical spinal cord (c: arrowheads).

Postmortem examination revealed angiocentric inflammatory lesions consistent with granulomatous meningoen­cephalitis. Multifocal suppurative inflammation with necrosis was also noted.

Question 34

Answer 34

Suppurative Discospondylitis (Canine)

5y FS Greyhound with back pain that developed a few weeks following treatment of an inflammatory pulmonary disorder.

• Vertebral radiographs reveal vertebral endplate osteolysis, surrounding bone sclerosis, and narrowing of the L3–4 intervertebral disk space (a,b: arrow).
• These findings are also evident on CT images, and the degree of endplate destruction is more apparent (d,e: arrow).
• There is a loss of the normally fat‐attenuating ventral epidural space (c: arrow), and there is regional enhancement adjacent to the vertebral column (f: arrowhead) and within the ventral epidural space (f: arrow) following contrast administration, indicative of local extension of the inflammatory response.

Fine‐needle aspiration cytology revealed suppurative inflammation. Microbial culture failed to yield a causative agent, although the dog had been on antibiotics prior to sampling.

Question 35

Answer 35

Suppurative Discospondylitis (Canine)

1.5y MC Boxer with hunched back and stiff pelvic limb gait but minimal neurologic deficits. The radiographic image shows vertebral endplate osteolysis, surrounding bone sclerosis, and mild disk space narrowing of the L2–3 intervertebral disk space (a: arrowhead).

• On MR images, the L2–3 disk space is ill defined with heterogeneous T2 and T1 hyperintensity (b,c,e,f: arrowhead).
• There is also mild T2 hyperintensity and T1 hypointensity of adjacent bone in the vertebral bodies (b,c: arrows).
• The affected intervertebral disk (d,g: large arrowhead), adjacent bone (d: arrows), and surrounding soft tissues (g: small arrowhead) intensely contrast enhance.

Fine‐needle aspiration cytology of the lesion revealed suppurative inflammation, and Staphylococcus intermedius was cultured.

Question 36

Answer 36

Suppurative Spondylitis (Canine)

3y F Labrador Retriever with 2‐week history of listlessness, weight loss, and lumbar pain.

• There is ill‐defined new bone formation on the ventral aspect of the L1 and L2 vertebral bodies on a survey radiographic examination (a: arrowheads).
• The right sublumbar musculature (quadratus lumborum and psoas minor) is focally enlarged at the level of the first lumbar vertebra (b: arrow), which proves to be a peripherally enhancing sublumbar abscess following contrast administration (c: arrow).
• A spiculated periosteal productive response is present on the ventral margin of the first lumbar vertebral body (b: arrowhead).
• An additional tract is seen extending toward the right lateral paraspinal region (c: arrowhead).

A migrating “foxtail” plant awn was removed at the time of surgical exploration. Actinomyces, Pasteurella, and multiple anaerobic species were cultured from the abscess site.

Question 37

Answer 37

Spinal Epidural Empyema (Canine)

8y FS Irish Wolfhound with 2‐week history of progressive reluctance to stand and signs referable to lumbar or pelvic pain. Images a–c were acquired at the level of the caudal end of the seventh lumbar vertebra.

• There is mixed T1 and T2 intensity of fat within the vertebral canal, intervertebral foramina, and perivertebral regions (a,b: arrowheads).
• There is marked heterogenous enhancement of these areas following contrast administration (c,d: arrowheads), consistent with epidural empyema and surrounding cellulitis.
• Epidural space enhancement is most pronounced in the L7 to sacral region of the vertebral column and is best appreciated on image d.
• Tissues adjacent to the medial iliac lymph nodes also enhance, indicating regional lymphadenopathy (d: arrow).
• Necrotic fat and collections of purulent material were found at the time of L6–S1 dorsal laminectomy.

Biopsy of epidural fat revealed acute fibrinosuppurative steatitis with Gram‐positive cocci. There was no growth on microbial cultures, but the dog had been on antibiotics.

Question 38

Juxtavertebral neoplasia

Answer 38

Malignant soft‐tissue neoplasms that arise adjacent to the vertebral column can invade vertebrae and the verte­ bral canal. Such neoplasms are often mesenchymal in origin and include:

• Hemangiosarcoma
• Fibrosarcoma
• Myxosarcoma
• Liposarcoma
• Synovial tumor

Question 39

Malignant Primary Bone Tumors of the

Vertebral Column

Answer 39

Primary bone tumors arising from the vertebral column include:

• Osteosarcoma
• Chondrosarcoma
• Fibrosar­coma

and typically have aggressive imaging features. Those tumors with significant osteoid production will appear predominantly osteoproductive or have osteoproductive/osteolytic components, while others may have a predominantly osteolytic appearance.

Tumors arise from a single vertebra, but reactivity or invasion of adjacent vertebrae may occur. Extension into the vertebral canal can cause spinal cord compression, and pathologic frac­ture can occur because of loss of structural integrity of the vertebral body.

CT features of primary bone tumors include heterogeneous osteolysis of affected bone with periosteal and endosteal reactive bone formation. Amorphous tumor new bone may also be present in osteoblastic tumors.

MR features include altered anatomic margins and T1 and T2 hypointensity in regions of reactive and tumor new bone formation. When the tumor mass includes a significant vascular soft‐tissue component, that region will have variable T1 and T2 intensity and can heteroge­neously contrast enhance

Question 41

Plasma Cell Tumor

Answer 41

Plasma cell neoplasms arise from malignant proliferation of B‐lymphocytes, and they may occur as:

• Solitary plasma­cytomas
• Multiple myeloma

Multiple myeloma typically affects bone, including vertebrae, ribs, pelvis, skull, and proximal or distal aspects of long bones, while plasmacy­tomas may occur in the skin, mucosa, gastrointestinal tract, and bone. Plasmacytomas of the vertebral column generally arise from a single vertebra but can involve adjacent segments. Multiple myeloma is multifocal and polyostotic and is usually widely distributed within both axial and appendicular bone.

CT and MR are superior to survey radiography for determining the presence and size of vertebral plasma cell tumors.

CT features of plasmacytoma include osteolysis, often associated with preservation of at least part of the cortical margin, and pathologic fractures are common. Tumor mass can also breach the cortical margin and encroach on the vertebral canal, causing extradural spinal cord compression. Plasmacytomas are soft‐tissue attenuating and mildly to markedly enhance following intravenous contrast administration on CT images. CT myelography can be used to assess presence and location of spinal cord compression.

On MR images, plasmacytomas are almost purely osteolytic, T1 iso‐ to hyperintense and T2 hyperintense compared to epaxial musculature, and variably but uniformly enhance follow­ ing intravenous contrast administration. Three‐dimensional gradient‐echo sequences can be used to more accurately assess bone destruction.

CT and MR features of multiple myeloma include multiple poorly margined to well‐demarcated foci of osteolysis, which are often most abundant in the verte­ bral column

Question 42

Lymphoma

Answer 42

Lymphoma associated with the vertebral column and spinal cord can be extradural, intradural–extramedullary, or intramedullary (intrinsic), although the latter is reported to be less common. Lymphoma is the most common spinal neoplasm in cats and is often a compo­nent of multicentric disease.

On CT images, extradural lymphoma masses are soft‐tissue attenuating and minimally to mildly contrast enhancing following intravenous contrast administration. CT myelography can be used to document spinal cord compression and to determine the compartment of origin, with extrinsic masses producing eccentric spinal cord displacement and compression and intrinsic lesions producing a focal increase in cord diameter and annular attenuation of the subarachnoid contrast column.

MR features include T1 hypo‐ to isointensity, T2 hyperintensity, and moderate homogeneous enhancement. Diffuse meningeal enhancement has also been reported. The compartment of origin can sometimes be determined, particularly by evaluat­ing the distribution of T2 hyperintense cerebrospinal fluid in relation to the tumor, although large masses may be more difficult to localize.

Question 43

Intradural-Extramedullary Spinal Cord

Neoplasia

Answer 43

Intradural–extramedullary neoplasia

Features of intracranial nervous system neoplasm have been described in Chapters 2.8 and 2.10 and spinal neoplasms of the same cell type often have similar imaging characteristics.

The most common intra­ dural–extramedullary neoplasms include:

• Meningi­oma
• Peripheral nerve sheath tumor
• Nephroblastoma
• Cerebrospinal fluid disseminated metastasis
• Round cell tumors, such as lymphoma and histiocytic sarcoma.

Question 44

Spinal Cord Meningioma

Answer 44

Meningioma is the most common central nervous system neoplasm of the spinal cord in dogs. Median age at onset of clinical signs is 9 years, and Golden Retrievers and Boxers appear to be overrepresented. Most canine spinal meningiomas are World Health Organization (WHO) grade I or II, with a small minority being more biologically aggressive grade III. Nearly 70% are located in the cervical region, about 25% are lumbar, and the remainder are thoracic or multifocal. Although less common, spinal meningioma has also been reported in the cat.

On CT images, spinal meningiomas are soft‐tissue attenuating space‐occupying masses within the vertebral canal that variably displace and compress the spinal cord, depending on tumor size in relation to the vertebral canal diameter. Meningiomas uniformly enhance following intravenous contrast administration and appear as a contrast‐filling defect within the subarachnoid space on CT myelography.

On MR images, menin­ giomas are mildly to moderately T1 hyperintense, mildly to markedly T2 hyperintense, and uniformly and intensely contrast enhancing. A dural tail sign may be present in some instances but is not consistent. Intradural–extramedullary localization is supported by peripheral T2/STIR hyperintensity due to subarachnoid space distension, comparable to the “golf tee” sign described for conventional myelography.

Using either imaging modality, localizing a meningioma to the intradural–extramedullary compart­ ment may not be possible when the tumor mass is large.

Question 45

Peripheral nerve sheath tumor

(PNST)

Answer 45

The term peripheral nerve sheath tumor (PNST) includes neoplasms that originate from:

• Schwann cells
• Fibroblasts
• Perineural cells

Because the terminology for this group of tumors has been inconsistent, we choose to use the all‐encompassing term PNST. Age of onset in dogs is reported to be bimodal, peaking at 2–3 years and 7–9 years, with no apparent breed predilection.

Question 46

Spinal Cord Nephroblastoma

Answer 46

Spinal cord nephroblastoma (SCN) is an uncommon neo­plasm of young dogs (6 months to 4 years) that arises from transformed embryological renal tissue that is entrapped within the spinal dura matter during development.

German Shepherd Dogs may be overrepresented, although total numbers reported to date are small. Most SCNs are located within the T9–L3 region of the vertebral column and are unencapsulated and intradural–extramedullary, although invasion into spinal cord parenchyma occurs, which has been correlated with a poorer prognosis.

CT and MR imaging features are similar to those described for other intradural–extramedullary masses. An SCN appears as a soft‐tissue attenuating mass on unenhanced CT images and as a contrast‐filling defect on CT myelog­raphy. Spinal cord nephroblastomas are T1 iso‐ to mildly hyperintense, T2 hyperintense, and homogeneously enhance following intravenous contrast administration

Question 48

Intramedullary Spinal Cord

Neoplasia

Answer 48

In a report of 53 dogs with intramedullary spinal cord neoplasia, approximately 2/3 of the tumors were of neuroepithelial origin. The remainder were metastatic neoplasms, the most common of which were:

• Hemangio­ sarcoma
• Transitional cell carcinoma

In this study, ependymoma was the most common neuroepithelial tumor, followed by astrocytoma. Dogs with primary neoplasms were significantly younger than dogs with metastatic disease (5.9 years vs. 10.8 years), and primary neoplasms were distributed in the cervical, caudal thoracic, and lumbar regions, while metastasis occurred predomi­nantly in the mid to caudal lumbar region.

A common feature of all intramedullary neoplasms is the presence of an intraparenchymal mass that causes an increase in spinal cord diameter and annular narrowing of the surrounding subarachnoid space. This appears as circumferential attenuation of the subarachnoid space on CT myelographic or T2 and STIR MR images

Question 50

Answer 50

Paravertebral Myxosarcoma (Canine)

13y FS Boston Terrier with a left‐sided lumbar mass that was determined to be a myxosarcoma by tissue biopsy. The mass has rapidly increased in size recently, and the dog now has pelvic limb paralysis.

• There is a large encapsulated soft‐tissue attenuating mass adjacent to the third lumbar vertebra (a: asterisk).
• Tissue within the vertebral canal is also uniformly soft‐tissue attenuating without evidence of epidural fat (a: arrowhead).
• The paravertebral mass heterogeneously enhances following intravenous contrast administration (b: asterisk), and there is an approximately 10 HU incremental increase in attenuation within the vertebral canal at this level (b: arrowhead), which does not occur at locations distant to the mass.
• An enhanced CT image cranial to the mass shows clearly defined spinal cord surrounded by lower‐attenuating epidural fat (c: arrowhead).

Postmortem examination confirmed infiltrative left paralumbar myxosarcoma with invasion of the spinal canal.

Question 51

Answer 51

Synovial Cell Sarcoma (Canine)

10y FS Rottweiler with neurologic deficits localized to C1–5.

• There is a large multilobular mass adjacent to the fourth cervical vertebra, which is T1 isointense and T2 hyperintense compared to adjacent muscle (a,b: white arrow).
• The mass has caused osteolysis of the left transverse process and invades the vertebral canal (a,b: large arrowhead) and transverse foramen (a,b: small arrowhead).
• There is marked displacement and compression of the cervical spinal cord (a,b: black arrow).
• The mass intensely but nonuniformly enhances fol­lowing intravenous contrast administration (c: white arrow).

Microscopic examination of tissue obtained from postmortem examination revealed this to be a poorly differentiated malignancy consistent with synovial cell sarcoma.

Question 52

Answer 52

Paravertebral Liposarcoma (Canine)

14y FS Bearded Collie with a 3‐week history of progressive pelvic limb ataxia and paresis.

• There is an irregularly margined T1 and T2 hyperintense mass dorsal to the caudal thoracic vertebral column (a–d: black arrow) that has caused osteolysis of the vertebral lamina and pedicles (b,d: black arrowhead).
• The mass also extends into the vertebral canal producing spinal cord compression (b,d: white arrow).
• The mass is hypointense on a fat‐suppressed contrast‐enhanced sequence and has minimal peripheral enhancement (e: white arrow).
• On CT images, the mass is predominantly fat attenuating (f: white arrow), and the osteolysis and spinal cord compression are again apparent (f: white arrowhead).

Imaging features are consistent with invasive liposarcoma, which was confirmed on postmortem examination.

Question 53

Answer 53

Osteochondroma (Canine)

10mo FS Dachshund with recent onset of paraparesis neuroanatomically localized to T3–L3.

• There is a well‐defined, bone‐attenuating mass arising from the caudal lamina of T6 that appears contiguous with more normal adjacent bone of the basilar part of the T6 spinous process (a–c: arrow).
• Encroachment into the vertebral canal implies spinal cord compression (a–c: arrowhead), although the cord is not clearly delineated.
• The mass also has T2 (d,e: arrow) and T1 (not shown) intensity similar to adjacent normal bone, and spinal cord compression is documented (d,e: arrowhead).

Surgical excision biopsy revealed the mass to be a solitary osteochondroma (f).

Question 54

Answer 54

Metastatic Hemangiosarcoma (Canine)

8y FS Labrador Retriever with progressive neuropathy of 2 weeks’ duration. A splenic hemangiosarcoma was identified on an abdominal ultrasound examination included as part of the initial diagnostic evaluation. Images d–f and h are at the level of the second thoracic vertebra.

• A large, irregularly shaped osteodestructive and expansile mass arises from the left side of the second thoracic vertebra and rib head (a,b,d,e: arrow).
• The mass has heterogeneous T1 and T2 hyperintensity compared to adjacent paraspinal muscle and intensely and nonuniformly enhances following intravenous contrast administration (c,f,g: arrow).
• Axially, it extends into the vertebral canal, causing right‐sided spinal cord displacement and compression (g: arrowhead).
• The lateral displacement of the cord without apparent distension of the subarachnoid space suggests an extramedullary localization (a: arrowheads).

The complex intensity pattern seen in all sequences suggests a hemorrhagic component, which was documented on subsequent gross examination (h). Both the splenic mass and the thoracic vertebral mass were histologically confirmed to be hemangiosarcoma.

Question 55

Answer 55

Extradural Lymphoma (Canine)

9y FS Labrador cross with a 2‐week history of acute‐onset left pelvic limb lameness. Images d and e are representative transverse images at the level of the fifth thoracic vertebra.

• Multiple extradural T2 isointense, mildly T1 hyperintense masses are widely distributed within the vertebral canal (a,b,d: arrowheads) and uniformly enhance following intravenous contrast administration (e: arrowhead).

Postmortem examination revealed the extradural masses to be B‐cell lymphoma (c,f: arrowheads) with widely disseminated multiple organ involvement.

Question 56

Answer 56

Extradural Nephroblastoma Metastasis (Canine)

2y F Great Dane with history of surgically excised cranial lumbar nephroblastoma 4 months previously. Representative transverse images a–c are through the caudal thoracic region.

• There are multiple T1 isointense, T2 hyperintense, ovoid extradural masses (a,b,d,f: arrows) that uniformly enhance following intravenous contrast administration (c: arrow).
• Masses are distributed widely throughout the thoracolumbar vertebral canal and correlate closely with the appearance seen on postmortem examination (e: arrows).

Masses were confirmed to be extradural nephroblastoma metastases presumably resulting from residual disease or surgical seeding.

Question 57

Answer 57

Meningioma (Canine)

12y MC Shih Tzu with progressive neuropathy anatomically localized to C1–C5.

• A representa­ tive CT myelographic image (a) at the level of the fifth cervical vertebra shows mild left‐sided displacement of the spinal cord and a split contrast column on the right, indicative of an intradural–extramedullary mass.
• The mass homogeneously enhances following intrave­nous contrast administration (b).

Postmortem examination confirmed a crescent‐shaped right‐ sided meningioma extending from C4–C6.

Question 58

Answer 58

Meningioma (Canine)

9y FS Boxer with progressive ataxia neuroanatomically localized to C1–C5. Representative transverse images (d–f) are at the level of the caudal end of the first cervical vertebra. Image h is a magnification of image g.

• There is a large T1 and T2 hyperintense, uniformly contrast‐enhancing oval mass within the vertebral canal at the level of C1–C2 (a–g: arrow) that results in profound spinal cord com­pression (d–g: arrowhead).
• A dural tail extends caudally from the mass, indicating meningeal involvement (h: arrow).
• The imaging appearance of the mass mirrors that seen on gross postmortem examination, which establishes its meningeal origin (i: arrowheads).

The mass was confirmed to be a grade I transitional meningioma.

Question 59

Answer 59

Peripheral Nerve Sheath Tumor (Canine)

8y FS Siberian Husky cross with slowly progressive pelvic limb gait abnormality. Representative transverse images (d–f) are through the fourth lumbar vertebra.

• There is a right‐sided T2 hyperintense, T1 isointense, uniformly contrast‐enhancing mass within the vertebral canal at the level of L4 (a–g: arrow) that results in marked spinal cord compression (d–f: arrowhead).
• Elevation of the cord (a: arrowhead) and what appears to be focal widening of the subarachnoid space adjacent to the mass (c: arrowhead) suggest it is intradural–extramedullary in location.
• This is confirmed on conventional myelographic examination, which shows a contrast filling defect (h: large arrowhead) and a “golf tee” sign (h: small arrowhead).

Biopsy of the mass confirmed a diagnosis of periph­ eral nerve sheath tumor.

Question 60

Answer 60

Presumptive Peripheral Nerve Sheath Tumor (Canine)

9y FS Border Collie with neck pain and myelopathy neuroanatomically localized to C1–C5. Representative transverse images d–f are at the level of the C1–2 articulation. Images h and i are immediately cranial and caudal, respectively, to images d–f.

• There is a large, lobular, mildly T2 hyperintense, T1 isointense mass within the right dorsal vertebral canal at the level of the C1–2 articulation that intensely enhances following intravenous contrast administration (a–h: arrow).
• The mass has an intradural–extramedullary component, evident from the focal widening of the subarachnoid space adjacent to its caudal margin (a,b: arrowhead), and has a narrow extradural stalk that courses through the right intervertebral foramen (g,h: arrowheads) before expanding into a larger, lobular juxtavertebral mass (g,i: asterisk).
• Marked spinal cord compression is evident, associated with central T2 hyperintensity immediately caudal to the mass (a).

A diagnosis of peripheral nerve sheath tumor of the right second spinal nerve was based on imaging features.

Question 61

Answer 61

Nephroblastoma (Canine)

7mo M West Highland White Terrier with a 2‐week history of pelvic limb weakness. Representative transverse images (d–f) are at the level of the first lumbar vertebra.

• MR images show a well‐demarcated T2 hyperintense, T1 isointense, uniformly enhancing ovoid mass within the cranial lumbar vertebral canal (a–f: arrow).
• The spinal cord is markedly compressed, but the persistence of epidural fat circumferentially (d,e: arrowhead) and flaring of the right cerebrospinal fluid column cranially and caudally (g: arrowheads) confirm the mass is intradural–extramedullary.

The age of the patient combined with imaging features and the location of the mass make ectopic nephroblastoma the likely diagnosis, which was confirmed on postmortem examination.

Question 63

Intervertebral disk disease

Answer 63

Intervertebral disk degeneration

The normal intervertebral disk is comprised of four major components:

• The nucleus pulposus
• The annulus fibrosis
• A transition zone
• The cartilaginous end­ plates

The nucleus pulposus is located eccentrically in the disk and has a high mucoprotein and water con­tent.

The annulus fibrosis surrounds the nucleus and is composed of multilayered fibrocartilage.

The transition zone is located between the mucoid nucleus and the fibrous annulus and appears to be wider and less distinct in chondrodystrophoid breeds.

Cartilag­inous endplates form the cranial and caudal margins of the disk with fibrous connections to the annulus and the adjacent bony endplates of the vertebrae.

Vascular supply to the intervertebral disk is minimal and limited to outer layers of the annu­lus.

In addition, the dorsal longitudinal ligament courses over the ventral surface of the spinal canal, and intercapital ligaments cross the intervertebral disks from T2–T10.

Deterioration of the extracellular matrix of the intervertebral disk leads to degeneration. As a disk degenerates, the nucleus pulposus and, to a lesser extent, the remainder of the disk dehydrate, causing narrowing of the disk. Nonphysiologic loading of the disk can also lead to annular tears and cartilaginous endplate fissures. Structural changes to the disk lead to herniation or extrusion.

Disk degenerative changes differ between chondrodystrophoid and nonchondrodystrophoid breeds. The nucleus pulposus of chondrodystrophoid breeds undergoes chondroid metaplasia, resulting in a loss of water and hydroelasticity. This process occurs along the entire vertebral column, with dystrophic mineralization a common sequela. Disks of nonchondrodystrophoid breeds tend to undergo fibrous metaplasia, charac­terized by fibrous collagenization of the nucleus pulpo­sus in concert with annulus fibrosis degeneration.

Degenerative changes in chondrodystrophoid breeds occur at an earlier age (3–7 years) and in the cervical and thoracolumbar spine, while nonchondrodystrophic degeneration occurs later (6–8 years) and preferentially affects the caudal cervical region and the lumbosacral junction, although thoracolumbar disease also occurs.

Intervertebral disk extrusion and protrusion

Intervertebral disk lesions are classified as type I or type II using a system first introduced by Hansen.

Hansen’s type I disk extrusion occurs when degenerated nucleus pulposus herniates through all layers of a ruptured annulus fibrosis. Type I disease occurs predominately in chondrodystrophic breeds but is also seen in larger nonchondrodystrophic breeds. Due to the altered physical characteristics of the chondroid metaplastic nucleus pulposus, type I disk extrusion tends to be acute and explosive. Because of the eccentric position of the nucleus within the disk, herniation occurs dorsally into the vertebral canal or dorsolaterally into the interverte­bral foramina.

Hansen’s type II disk protrusion occurs when fibroid degenerated disk material migrates dorsally or dorsolat­erally because of partial tearing or rupture of the annu­lus. Because the nucleus pulposus is still contained within the remaining annulus fibrosus, disk material is not extruded, and the dorsal longitudinal ligament remains intact. Hansen’s type II disk protrusion results from fibrous degeneration and is most common in nonchondrodystrophoid breeds.

Extrusion of apparently normal disk material can also occur as a result of physical activity or overt trauma. These are sometimes referred to as high‐velocity extrusions because of the force of extrusion and the predominately liquid composition of normal nucleus pulposus. A description of traumatic intervertebral disk disease can be found in Chapter 3.2 Acute spontaneous extrusion of hydrated disk material seemingly unrelated to activity or trauma can also occasionally occur. In one canine study, a variety of nonchondrodystrophic and chondrodystrophic breeds were represented with a median age of 9 years at the time of diagnosis. Clinical signs include acute onset tetraparesis or tetraplegia, and the mid to caudal cervical intervertebral disks are most commonly affected.

Question 65

Imaging features of Hansen’s type I disk extrusion

Answer 65

There are several studies that have compared the accuracy of unenhanced CT, contrast‐enhanced CT, MRI, and conventional myelography for detection of Hansen’s type I disk herniation.

Unenhanced CT has been reported to be 89–100% accurate for lesion localization, and CT myelography is slightly bet­ ter. CT has been shown to be better than conven­tional myelography for detecting disk herniation in large dogs, but myelography was found to be better in dogs weighing less than 5 kg. Authors of one report found similar detection accuracy for CT myelography and contrast‐enhanced CT following intravenous contrast administration.

MRI is thought to be the most accurate imaging method, but the degree of improvement compared to CT myelography is minor.

CT features of type I disk extrusion include:

• Presence of hyperattenuating disk material in the epidural space, with the density depending on the degree of mineralization.
• Disk material can migrate horizontally along the floor of the vertebral canal and circumferentially around the spinal cord.
• Material can also be dorsolaterally extruded into the intervertebral foramina.
• Depending on the volume and distribution of extruded disk material, the spinal cord is displaced and compressed.
• Subarachnoid contrast columns are attenuated at the site of compression on CT myelogra­phy.
• Diffuse alterations with mixed attenuation in the epidural space can be seen in acute disease associated with hemorrhage, and edema can cause an increase in cord diameter.
• The affected intervertebral disk space is often narrowed, and residual mineralized in situ disk material is sometimes present.

Similar features are seen on MR images, with:

• Disk material appearing T1 and T2 hypointense.
• Attenuation of the T2 hyperintense cerebrospinal fluid layer occurs at the site of cord compression, and T2 hyperintensity of cord parenchyma may also be seen as a result of edema.
• When present, hemorrhage appears as variable, mixed T1 and T2 intensity
• Other uninvolved disks will appear T2 hypointense because of disk dehydration.

Question 66

Imaging features of Hansen’s type II disk protrusion

Answer 66

CT may be less accurate for detecting type II disk protrusions according to one report.

CT features include:

• Variable decrease in intervertebral disk space width
• A mildly hyperattenuating mass arising from the dorsal aspect of the affected disk and extending into the ventral or ventrolateral vertebral canal.
• The bulg­ing annulus cannot be distinguished from the overly­ing dorsal longitudinal ligament.
• The spinal cord is displaced, and its shape is often distorted by impinge­ment of the disk even when overt compression is absent.
• Contrast columns are attenuated at the site of impingement or compression on CT myelographic images.

MR features of type II disk protrusions are similar to those seen on CT images.

• Protruding disk material is T1 and T2 hypointense and appears contiguous with in situ disk material and the overlying longitudinal ligament.
• The spinal cord can be displaced, distorted, and compressed, and the T2 hyperintense cerebrospinal fluid columns are attenuated at the site of protrusion.
• It is common to see multiple sites of involvement with varying degrees of disk protrusion, and in these patients it can be useful to use a single‐shot turbo spin‐echo sequence as a “rich man’s myelogram” to localize the clinically relevant site
• In patients with chronic disease, the spinal cord can be focally atrophic, with syringohydromyelia and T2 parenchymal intensity suggesting gliosis.
• Uninvolved disks are often T2 hypoin­tense because of dehydration.

Question 68

Imaging features of hydrated nucleus pulposus extrusion

Answer 68

MR imaging features include:

• Narrowing of the interver­ tebral disk
• T2 hyperintensity of extruded disk material that is difficult to distinguish from epidural fat
• A characteristic “seagull sign” on T2 transverse images representing the dorsal margin of the extruded mate­ rial.
• Extrusion results in spinal cord compression, and many dogs have intrinsic T2 hyperintensity at the site of compression

Question 69

Cauda equina and lumbosacral disorders

Answer 69

Static and dynamic lumbosacral abnormalities that cause cauda equina syndrome include:

• Intervertebral disk protrusion
• Lumbosacral subluxation
• Vertebral canal stenosis
• Proliferation of soft tissues within or adjacent to the vertebral canal
• Spondylotic new bone encroachment on the intervertebral foramina

Large‐breed male dogs are most commonly affected, and German Shepherd Dogs are highly overrepre­ sented. The lumbosacral angle of inclination, decreased lumbosacral joint mobility, articular process joint angle, and the presence of transitional vertebrae and sacral endplate osteochondrosis have all been postu­lated as inciting anatomical factors. Dogs with cauda equina syndrome are more likely to have a more sagit­tally oriented articular facet angle, a greater difference in caudal lumbar and sacral spine angle, and asymmetry of the facet articulations.

The caudal lumbar and sacral vertebral canal transverse areas, normalized to vertebral body sagittal diameter or transverse vertebral body area, have also been shown to be significantly smaller in dogs with cauda equina syndrome as compared to clinically normal dogs.

CT examinations acquired in hindlimb flexion and extension have been used to assess dynamic changes in vertebral canal diameter and intervertebral foraminal area in dogs with lumbosacral disease. The L7–S1 intervertebral foraminal area is significantly smaller on extended limb images, suggesting that positional imaging studies may be useful for diagnosis of dynamic foraminal nerve entrapment.

Imaging features of the lumbosacral region of dogs with cauda equina syndrome are highly variable. Although there seems to be excellent agreement between CT and MR for detection of intervertebral disk protrusion or extrusion, dural sac position, quantity of epidural fat, and spinal nerve root swelling, the correlation of these features with surgical findings is only moderate.

CT examinations should include thinly collimated transverse images through the caudal lumbar and sacral region acquired at an angle perpendicular to the verte­ bral canal.

CT features associated with cauda equina syndrome include:

• Lumbar spine (LS) subluxation
• Intervertebral disk degeneration and extrusion
• Spondy­losis
• Reduction of vertebral canal transverse area (pri­ marily due to reduced canal height) at the level of the LS junction, and loss of distinction of nerve roots at the LS junction due to diminished epidural fat
• Extruded intervertebral disk material can migrate into the caudal lumbar and LS intervertebral foramina causing nerve root compression and resulting lateralized clinical signs
• Extruded disk material is hyperattenuating and displaces the relatively low attenuating epidural fat in the vertebral canal and intervertebral foramina

MR imaging features are similar to those seen with CT.

• Nerve roots of the cauda equina are T1 and T2 hypoin­tense relative to surrounding epidural fat and are therefore well visualized on both sequences in the normal dog
• Vertebral canal and intervertebral foraminal T1 and T2 intensity is reduced when epidural fat is displaced because of intervertebral disk extrusion/protrusion, stenosis, or subluxation
• In addition to standard sequences, a 3D vol­ume acquisition (e.g. T1 + C SPGR) of the lumbosacral junction provides thinly collimated images that can pro­vide more in‐plane anatomical detail and be reformatted in other planes.
• Neuritis is sometimes detected because of enlargement and increased contrast enhancement compared to the contralateral spinal nerve.
• A dorsal plane, STIR, or fat‐suppressed contrast‐enhanced T1 sequence generally provides an excellent symmetrical view of the caudal lumbar spinal cord, the cauda equina, and associ­ated spinal nerves when performed with thin collimation (≤ 2 mm)

Question 70

Normal Intervertebral Disks (Canine)

Answer 70

The gross appearance of the dorsal annulus fibrosis (a,b: small arrowhead), the nucleus pulposus (a,b: arrow), and ventral annulus fibrosis (a,b: large arrowhead). Compare the appearance of the intervertebral disk in image b to the appearance on T1 (c: T1) and T2 (c: T2) images acquired in the same anatomic plane.

Question 71

Answer 71

Mineralized Type I Extrusion (Canine)

5y MC Dachshund found acutely paretic earlier in the day with neuroanatomic locali­ zation to T3–L3. Images a and b include the T11–12 and T12–13 intervertebral disk spaces. Images c and d are through the T11– 12 and T12–13 disks, respectively.

• CT images were acquired as part of a CT myelogram.
• An in situ mineralized nucleus pulposus is present at the T11–12 intervertebral disk space (a–c: small arrowhead).
• Mineralized disk material from the T12–13 intervertebral disk space has herniated into the ventral subdural space of the vertebral canal, causing focal spinal cord compression with attenuation of the contrast columns (b,d: arrow).
• The T12–13 disk space is narrow and contains residual mineralized disk material (a,b,d: large arrowhead).

A hemilaminectomy performed at T12–13 confirmed mineralized disk material within the extradural space. Adjacent disks were fenestrated.

Question 72

Answer 72

Type I Disk Extrusion with Hemorrhage (Canine)

2y FS Corgi with acute‐onset paraplegia neuroanatomically localized to T3–L3. Image a is centered on the T12–13 intervertebral disk space (a: 12,13). Images b and c are at the cranial end and midbody of T13, respectively. Image d is at the level of the midthoracic vertebral column. Images were acquired as part of a CT myelogram.

• There is moderately attenuating material in the caudal thoracic and cranial lumbar extradural space (a–c: arrowheads) producing right‐sided spinal cord displacement and compression.
• The sub­arachnoid contrast column is circumferentially attenuated at this level (a–c).
• The spinal cord and contrast column appear normal more cranially (d).

A double hemilaminectomy was performed at T11–T13, and disk material that had extruded from the T12–13 disk space and dispersed from T11 to L1 was removed from the extradural space. There was also extensive hemorrhage and regional spinal cord swelling. Neurologic status declined postoperatively, and postmortem examination revealed severe regional myelomalacia and extra­ dural/subdural hemorrhage.

Question 73

Answer 73

Mineralized Type I Disk Extrusion (Canine)

5y Jack Russell Terrier with a 2‐week history of progressive pelvic limb ataxia and paraparesis neuroanatomically localized to L6–caudal. Vertebral column radiographs (not shown) revealed the dog had eight lumbar vertebrae. Images d and e are at the level of the L6–7 intervertebral disk. Images f and g are at the level of the midbody of the sixth lumbar vertebra. The L6–7 intervertebral disk is T2 hypointense and narrow (a,b: arrow).

• A large mass of T1 and T2 hypointense mineralized disk material has extruded from the L6–7 space, causing elevation and compression of the terminus of the conus medullaris and associated nerves of the cauda equina (a,b,d,e: arrowhead).
• The conus and cauda equina are in a more normal position cranial to the disk extrusion, but mixed signal intensity within the conus on both T1 and T2 images suggests hemorrhage (f,g: arrowhead).
• Local contrast enhancement adjacent to the extruded disk material is indicative of a traumatic inflammatory response (c: arrowhead).

A hemilaminectomy performed at L6–7 confirmed the presence of extruded disk material within the extradural space.

Question 74

Answer 74

Mineralized Type I Disk Extrusion (Canine)

5y FS Miniature Dachshund with acute‐onset right pelvic limb lameness following a racing competition. Neuroanatomically localized as a right‐sided L4–L6 radiculoneuropathy. Image a is a dorsal plane T2 image through the caudal lumbar intervertebral foramina. Images b and c are parasagittal T2 images through the right and left caudal lumbar intervertebral foramina, respectively. Image d is a transverse T2 image at the level of the L5–6 intervertebral disk space.

• Focal T2 signal void in the right L5–6 intervertebral foramen represents extruded disk material lodged within the foramen (a,b,d: arrow).
• The contralateral intervertebral foramen has normal signal intensity by comparison (a,c,d: arrowhead).

A hemilaminectomy was performed at L5–6, and disk material was removed from the right intervertebral foramen. Impingement of the disk material on the right fifth lumbar spinal nerve root resulted in neuritis and explains the neurologic signs (e: arrowhead).

Question 76

Answer 76

Hydrated Disk Extrusion (Canine)

10y FS Poodle with peracute tetraparesis with no apparent inciting cause.

• There is T2 hyperintense, T1 hypointense material distributed in the ventral aspect of the vertebral canal at the level of the C3–4 intervertebral disk space, which focally elevates and compresses the spinal cord (a,b,d,e: arrowhead).
• The ventral margin of the spinal cord has a double arching “seagull” wing appearance that has been ascribed to high liquid content disk extrusion (d: arrow).
• Focal linear contrast enhancement likely represents reactive dural enhancement (c,f: arrowhead).

Ventral slot decompression surgery was performed and a large volume of clear fluid was encountered along with more solid material that was composed of atypical chondroid‐like cells and a small amount of matrix

Question 77

Answer 77

Synovial Cyst (Canine)

5y MC American Staffordshire Terrier with acute‐onset pelvic limb paresis.

• There is a well‐ demarcated T1 hypointense, T2 hyperintense, thin‐walled cystic mass in the epidural space adjacent to the ventral margin of the left L3–4 facet articulation, consistent with a noncompressive synovial cyst (a–d: arrow­ head).

Clinical signs in this dog were from a T12–13 intervertebral disk extrusion (not shown).

Question 79

Answer 79

Meningeal Cyst with Arachnoid Communication (Canine)

9y M Borzoi with 1‐year history of pelvic limb paresis. Image a was acquired as part of a CT myelogram.

• There is a large, well‐demarcated, thin‐walled, ovoid cystic mass in the right epidural space at the level of the first thoracic vertebra (a: arrow).
• Intense and uniform contrast enhancement within the cyst documents direct communication with the subarachnoid space.
• A faint extradural contrast blush is also evident to the left of the spinal cord (a: arrowhead).
• he large cyst is T1 hypointense and T2 hyperintense, consistent with imaging characteristics of normal cerebrospinal fluid (b,c: arrow). The uniform attenuation and intensity of the large cyst is consistent with a type I spinal meningeal cyst that contains no neural tissue.
• The smaller structure to the left of the spinal cord is hypointense on both T1 and T2 images, which is more consistent with a type II cyst containing neural tissue (b,c: arrowhead).

This dog had a compressive C4–5 interver­ tebral disk extrusion (not shown) that was the cause of clinical signs. The meningeal cysts were considered incidental finding

Question 81

Answer 81

Chronic Muscle Denervation (Canine)

7y MC Boston Terrier with progressive left thoracic limb lameness of 4 months’ duration. Transverse images were acquired at the level of the midbody of the first thoracic vertebra and immediately caudal to the scapular spines.

• There is marked volume reduction of the left serratus ventralis (a–c: single asterisk), subscapularis (a–c: arrowhead), and infraspinatus (a–c: double asterisks) muscles, with mild increased T1 and T2 hyperintensity that is most pronounced in the serratus ventralis.
• The fat‐suppressed T1 image nullifies much of the increased signal intensity, documenting the cause as fatty infiltration (b).
• A contrast‐enhancing mass at the bottom of the images represents a peripheral nerve sheath tumor (a–c: arrow).

Question 82

Answer 82

Brachial Plexus Peripheral Nerve Sheath Tumor (Canine)

4y FS Labrador Retriever with right thoracic limb lameness. Image a was acquired at the level of the seventh cervical vertebra. Images b–e are consecutive dorsal plane images with image b through the caudal cervical spinal cord, and images ordered from dorsal to ventral.

• There is a large contrast‐enhancing mass with an intrinsic component at the level of the seventh cervical spinal segment (a,b: arrows).
• The seventh and eighth cervical spinal nerves are grossly enlarged as they exit the intervertebral foramina (b,c: 7,8).
• The left sixth cervical spinal nerve is smaller but also pathologically enlarged (d,e: 6).
• The nerves converge to form a large irregularly shaped axillary mass (d,e: arrowhead).

Imaging features of the spinal nerves and mass closely match the postmortem appearance (f: 6,7,8). A diagnosis of peripheral nerve sheath tumor involving spinal nerves C6‐C8 was confirmed histologically.

Question 84

Answer 84

Brachial Plexus Peripheral Nerve Sheath Tumor (Canine)

Adult M Husky with progressive left thoracic limb lameness of 7 weeks’ duration.

• Multiple focal areas of high signal intensity are seen in the region of the origins of left eighth cervical and first thoracic spinal nerves (a: 8,1) on a dorsal plane STIR image.
• Marked enlargement and contrast enhancement of the seventh and eighth cervical and first thoracic spinal nerves is seen on consecutive contrast‐enhanced fat‐suppressed images acquired at two slightly different oblique angles approximating the plane of the proximal brachial plexus (b,c: 7,8,1).
• The left eighth cervical spinal nerve is enlarged, T2 hyperintense, and moderately contrast enhancing near its origin on transverse images (d–f: arrowheads).

Question 86

Answer 86

Brachial Plexus Peripheral Nerve Sheath Tumor (Canine)

6y MC Labrador Retriever with progressive left pelvic limb lameness of 6 months’ duration. Images a–c were acquired at the level of the sacrum and are ordered from cranial to caudal. Images d–f are at the same level as images a–c, and images g and h are further caudal.

• An enlarged nerve is identified ventral to the left side of the sacrum, which represents a coalescence of components of the left fifth through seventh lumbar spinal nerves (a–g: white arrowhead).
• A second mass representing an enlarged left first sacral nerve originates within the spinal canal (a,d: black arrowhead) and exits into the left first sacral foramen (b,c,e–g: black arrowhead), which is grossly dilated as the result of chronic bone resorption.
• The two nerves merge to form a single mass in the sacral network of the lumbosacral plexus (h: arrow).
• Marked left‐sided pelvic muscle atrophy is also present (d–h).

The diagnosis of peripheral nerve sheath tumor was based on the CT imaging appearance, clinical signs, and the long and progressive clinical history.