Ch 123 Middle and inner ear Flashcards
otitis media species differences
- 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
List the components of the tympanic cavity
- 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
anatomy
- 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
List the ossicles of the middle ear
- 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
What is the major anatomical difference of a cats bulla as compared to a dog?
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
What muscle causes opening of the auditory tube during swallowing?
Tensor veli palatini
What is the bony labrinth?
A perilymph filled cavity in the temporal bone that communicates with the middle ear through the vestibular and cochlear windows
What are the three sections of the membranous labyrinth?
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
How does the inner ear function in relation to sound perception?
- 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
What structures within the inner ear contribule to vestibular function?
Semicircular canals
Saccule
Utricle
What are the three routes of infection of the middle ear?
- Extension from external ear through tumpanum
- Extension from nasopharyn through auditory tube
- Haematogenous
List inflammatory diseases of the middle ear
Polyps
Topical agents causing a sterile inflammation (antiseptics, ceruminolytics)
Cholesteatoma and cholesterol granuloma
List forms of congenital inner ear abnormalities that result in deafness
Collapse of scala media in Dalmatians
Neuroepithelial degeneration in Rottweilers
Changes in the organ of Corti in Pointers
polyp presentation
- 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.
What radiographic view of the bulla is most uselful for identifying fluid changes?
10-degree ventrocaudodorsal view of tympanic chambers
How may CSF be helpful in work-up of otitis?
If there is extension into the inner ear, changes on CSF consistent with bacterial meningitis can be seen
What is BAER testing?
Brainstem Auditory Evoked Responses
CT/MRI
- 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
What is the reported recurrence of polyps with traction?
- 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
How long should ABx be administered for otitis media/interna?
At least 4-6 weeks
What are some appropriate ABx choiced while awaiting culture results?
Aminoglycosides (gentamicin) topically (systemically can cause ototoxicity)
Fluoroquinolones topically and/or systemically
What are the indications for surgical management of middle ear disease?
- Failure of medical management
- Neuro signs requiring tympanic decompression
- Neoplasia
VBO
- 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
What muscles need to be dissected during the approach to a VBO?
Platysma
Sphincter colli
Digastricus
Myelohyoid
Hyoglossus
Styloglossus
What nerve and artery should be avoided during a VBO
Hypoglossal nerve
Lingual artery
What can be palpated externally to aid in the ventral approach to the bulla in a dog?
The paracondylar (jugular) process
- Bulla is 5-10mm rostral and medial to this prominence
complications VBO (5)
- 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%
dog VBO
- 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
What is the recommended surgery for a cholesteatoma?
What is the prognosis?
- 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
What factors are assoc with higher risk of recurrence with cholesteatomas?
Inability to open mouth
Neuro signs
Lysis of temporal bone
Rigid normograde rhinoscopyassisted
traction-avulsion removal
of small middle ear polyps from the
auditory tube in five cats
Claire WD Oorsprong 2023
A normograde rhinoscopy-assisted traction-avulsion (RATA) removal
of these small polyps
short term outcome only
Anatomic structures of the canine middle ear visible during endoscopic examination through a ventral
or lateral approach
Emily C. Viani 2022
Transoral
ventral tympanic bulla osteotomy in cats:
13 cases (2016–2019)
Pierre H. M. Moissonnier 2022
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
Retrospective study of the
presentation, diagnosis and
management of 16 cats with
otitis media not due to
nasopharyngeal polyp
Nicola Swales 2018
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
Experience level as a predictor of
entry into the hypotympanum during
feline total ear canal ablation and
lateral bulla osteotomy
Lea R Mehrkens 2021
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.
Comparison of complications and outcome
following unilateral, staged bilateral, and single-stage
bilateral ventral bulla osteotomy in cats
Wainberg 2019
liptak
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%
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
