Ch 123 Middle and inner ear

Question 1

otitis media species differences

Answer 1

• dogs: consequence of a descending bacterial ingress as a sequela of chronic otitis externa
• cats: an ascending cause is thought to be responsible for interrupting middle ear drainage into the pharynx

Question 2

List the components of the tympanic cavity

Answer 2

• Epitympanum (dorsal component) - Smallest, largely occupied by incus and part of malleus
• Mesotympanum (middle component) - True tympanic chamber. Bound laterally by the tympanic membrance and posteriorally by the cochlear membrane. Promontory on medial aspect
• Hypotympanum (ventral component) - Largest, sitting within the tympanic bulla
• Two membranes are found within the mesotympanic chamber: the tympanic membrane and the secondary cochlear (or round) membrane. membranes separate the chamber from the external acoustic meatus laterally and the inner ear medially

Question 3

anatomy

Answer 3

• opening to the auditory tube, eustachian, is found in the rostral mesotympanic chamber > connecting the tympanic chamber with the nasopharynx
• On the medial aspect of the middle chamber, level with the tympanic membrane, is found the bony promontory that accommodates the cochlear structure.

nerves
- facial nerve, it enters the facial canal within the petrous temporal bone and emerges caudal and medial to the tympanic bulla at the stylomastoid foramen
- vestibulocochlear nerve
- cranial nerve (CN) IX (glossopharyngeal)

tympanic artery
- derived from the maxillary artery and enters via a small foramen caudal to the temporomandibular join

Question 4

List the ossicles of the middle ear

Answer 4

• Malleus - articulates with the pars tensa laterally and the incus medially
• Incus - articulates with the malleus laterally and stapes medially
• Stapes - articulates with the incus medially and the fibrocartilaginous ring around the oval window medially

Question 5

What is the major anatomical difference of a cats bulla as compared to a dog?

Answer 5

Double chamber, separated by septum:
- Larger ventrocaudomedial chamber of hypotympanum
- Smaller rostrolateral compartment of mesotympanum and epitympanus

Bony promontory is more exposed, or more sensitive, to iatrogenic trauma

Question 6

What muscle causes opening of the auditory tube during swallowing?

Answer 6

Tensor veli palatini

Question 7

What is the bony labrinth?

Answer 7

A perilymph filled cavity in the temporal bone that communicates with the middle ear through the vestibular and cochlear windows

Question 8

What are the three sections of the membranous labyrinth?

Answer 8

Vestibule
- Middle portion containing the saccule and utricle

Cochlea
- Bony spiral ‘seashell’ structure containing the cochlear coil
- Coil originates at the cochlear window and is divided by the cochlear duct into the scala vestibuli and the scala tympani
- Flow of the duct contains the Organ of Corti

Semicircular canals
- Anterior, posterior and lateral
- Each has an ampulla arranged at right angles to each other
- The saccule and utricle are found at the confluence of the canals

Question 9

How does the inner ear function in relation to sound perception?

Answer 9

• Ossicles transmit sound waves to inner ear causing movement of endolymph within the cochlea.
• Soundwaves are converted to nerve impulses by the hair cells in the organ of Corti and transmitted to the brain via the cochlear nerve fibres

Question 10

What structures within the inner ear contribule to vestibular function?

Answer 10

Semicircular canals
Saccule
Utricle

Question 11

What are the three routes of infection of the middle ear?

Answer 11

• Extension from external ear through tumpanum
• Extension from nasopharyn through auditory tube
• Haematogenous

Question 12

List inflammatory diseases of the middle ear

Answer 12

Polyps
Topical agents causing a sterile inflammation (antiseptics, ceruminolytics)
Cholesteatoma and cholesterol granuloma

Question 13

List forms of congenital inner ear abnormalities that result in deafness

Answer 13

Collapse of scala media in Dalmatians
Neuroepithelial degeneration in Rottweilers
Changes in the organ of Corti in Pointers

Question 14

polyp presentation

Answer 14

• contained within the tympanic cavity: clinically silent, cause vestibular signs or Horner’s syndrome
• extend via the auditory tube into the nasopharynx may be large enough to interfere with swallowing, respiratory stertor, nasal dsicharge, dysphagia
• external auditory meatus cause otorrhea and purulent discharge.

Question 15

What radiographic view of the bulla is most uselful for identifying fluid changes?

Answer 15

10-degree ventrocaudodorsal view of tympanic chambers

Question 16

How may CSF be helpful in work-up of otitis?

Answer 16

If there is extension into the inner ear, changes on CSF consistent with bacterial meningitis can be seen

Question 17

What is BAER testing?

Answer 17

Brainstem Auditory Evoked Responses

Question 18

CT/MRI

Answer 18

• imaging of the surrounding bony structures (e.g., petrous temporal bone or temporomandibular joint).
• conditions that cause primarily bony changes, such as cholesteatoma: osteosclerosis, changes in the temporomandibular joint, and lysis of the petrosal bone are common

MRI
- most sensitive imaging modality for detection of nonosseous middle and inner ear disease
- demonstrated between the predicted site of lesions responsible for vestibular signs in dogs
- surrounding soft tissues and involvement of the central nervous system

Question 19

What is the reported recurrence of polyps with traction?

Answer 19

• nonendoscopic traction = 57%
• per-endoscopic transtympanic technique, plus transtympanic curettage of the bulla + oral CCS = 13.5%
• nasopharyngeal > traction with oral prednisolone resulted in recurrence of 10%

Surgery may be recommended in patients that exhibit neurologic signs (Horner’s syndrome or vestibular syndrome) > VBO usually for cat

Question 20

How long should ABx be administered for otitis media/interna?

Answer 20

At least 4-6 weeks

Question 21

What are some appropriate ABx choiced while awaiting culture results?

Answer 21

Aminoglycosides (gentamicin) topically (systemically can cause ototoxicity)
Fluoroquinolones topically and/or systemically

Question 22

What are the indications for surgical management of middle ear disease?

Answer 22

• Failure of medical management
• Neuro signs requiring tympanic decompression
• Neoplasia

Question 23

VBO

Answer 23

• bulla, located within the triangular area bounded by the mandibular symphysis, the caudal border of the mandible, and the larynx
• through the platysma and sphincter colli muscles.
• mandibular salivary gland and bifurcation of the linguofacial and maxillary veins are retracted
• digastricus and mylohyoid muscles are separated by blunt dissection
• underlying hyoglossus and styloglossus muscles
• Care hypoglossal nerve, which lies close the lingual artery
• larger hypotympanic cavity is invariably filled with tenacious mucous secretion
• bony septum
• risk for damage to the tympanic plexus ( Horner’s syndrome) locate osteotomy site as far laterally as possible to avoid contact with the bony promontory
• Curettage should never be performed over the promontory or near the round window or ossicles

prognosis for resolution of middle ear polyps in cats is reported to be excellent

Question 24

What muscles need to be dissected during the approach to a VBO?

Answer 24

Platysma
Sphincter colli
Digastricus
Myelohyoid
Hyoglossus
Styloglossus

Question 25

What nerve and artery should be avoided during a VBO

Answer 25

Hypoglossal nerve Lingual artery

Question 26

What can be palpated externally to aid in the ventral approach to the bulla in a dog?

Answer 26

The paracondylar (jugular) process - Bulla is 5-10mm rostral and medial to this prominence

Question 27

complications VBO (5)

Answer 27

- Horner's syndrome 68% (19% permanent) - vestibular signs 30% (22% permanent) - respiratory 9-47% (single vs bilateral) - facial n 13% (8% permanent) - recurrence 6.2%

Question 28

dog VBO

Answer 28

- Notably, no large series of otitis media managed successfully by ventral bulla osteotomy have been reported in dogs - ventral aspect of the canine bulla is much less prominent

Question 29

What is the recommended surgery for a cholesteatoma? What is the prognosis?

Answer 29

* Removal of the entire epidermal cyst with meticulous stripping of the epithelium and additional margins which include the bulla wall * Prognosis guarded, 45-50% recurrence

Question 30

What factors are assoc with higher risk of recurrence with cholesteatomas?

Answer 30

Inability to open mouth Neuro signs Lysis of temporal bone

Question 31

Rigid normograde rhinoscopyassisted traction-avulsion removal of small middle ear polyps from the auditory tube in five cats Claire WD Oorsprong 2023

Answer 31

A normograde rhinoscopy-assisted traction-avulsion (RATA) removal of these small polyps short term outcome only

Question 32

Anatomic structures of the canine middle ear visible during endoscopic examination through a ventral or lateral approach Emily C. Viani 2022

Answer 32

Question 33

Transoral ventral tympanic bulla osteotomy in cats: 13 cases (2016–2019) Pierre H. M. Moissonnier 2022

Answer 33

13 client-owned cats. Transoral ventral tympanic bulla osteotomy in cats tympanic bulla (TB) infection (10), polyps (5) no intraoperative complications Eight cats experienced postoperative complications: Vestibular 15% Horner syndrome 23% loss of appetite (2), temporary blindness (1). 7% The maxillary artery is the main source of arterial supply to the brain in cats, as there is no internal carotid artery Six months 9/13 cats were free of MED signs proposed benefits – avoidance of neurovascular structures by access from rostromedial aspect Transoral approach for ventral tympanic bulla osteotomy in the dog: a descriptive cadaveric study. Vet Surg. 2017;46(6):773–779

Question 34

Retrospective study of the presentation, diagnosis and management of 16 cats with otitis media not due to nasopharyngeal polyp Nicola Swales 2018

Answer 34

Of 16 cats, one had a total ear canal ablation, five had ventral bulla osteotomy surgery and 11 were medically managed. Of the cats that were medically managed, using either topical products, systemic antimicrobials or a combination of both, eight had complete resolution of clinical signs 72% Conclusions and relevance This small cohort shows that some cats with OM can be successfully managed medically. Surgery is invasive and may not necessarily be required if appropriate medical management is undertaken

Question 35

Experience level as a predictor of entry into the hypotympanum during feline total ear canal ablation and lateral bulla osteotomy Lea R Mehrkens 2021

Answer 35

12 feline cadavers The novice surgeon entered the hypotympanum in 3/12 (25%) procedures, compared with 9/12 (75%) procedures performed by the experienced surgeon. The experienced surgeon performed a larger osteotomy recommend a ventromedial osteotomy of approximately 10 mm in depth to ensure penetration of the septum and allow for complete curettage of the hypotympanum.

Question 36

Comparison of complications and outcome following unilateral, staged bilateral, and single-stage bilateral ventral bulla osteotomy in cats Wainberg 2019 | liptak

Answer 36

unilateral 211, staged bilateral 7, bilateral single-session 64 VBO cats post-op respiratory complications: 9% unilateral, 29% staged, 47% single-session haemorrhage intraoperative (2.1%). complications: 68.2% Horner’s (19.4% permanent); 30.1% head tilt (22.1% permanent), 13.5% facial palsy (8.0% permanent); 6.2% local recurrence bilateral single-session more likely to have severe resp compromise and sx-related death Eleven of the 34 (32%) cats with severe respiratory complications developed cardiac arrest, died, or were euthanized within 5 days after surgery pre-op Horner’s, head tilt and facial paralysis likely to have permanent post-op malignant tumors > higher local recurrence rate (44%) and shorter MST 855 days compared to nonmalignant disease local recurrence rate for cats with inflammatory polyps was 5%

Question 37

Janssens 2017 – traction avulsion via lateral approach to ear canal in 62 cats - DSH (48%) and Maine Coons (37%) over-represented - otorrhoea, ear scratching, head shaking - recurrence rate: experienced surgeion 14.3%, less experienced 35% - not significant - overall 13/62 (21%) - complications: Horner’s 11.5%, facial paralysis 3% - outcome: 47/62 (75.8%) complete recovery