Middle and inner ear Flashcards
In a study by Wainberg 2019 in JAVMA, what were the complication rates for unilateral, stage bilateral, and single session bilateral VBO in cats? Cats treated with single session bilateral VBO were more likely to have what complication? The risk for permanent Horner syndrome, head tilt and facial nerve paralysis were increased in which cases?
9%, 29%, 47%.
Cats treated with single session bilateral VBO were more likely to have respiratory complications and surgery related death.
The risk of permanent Horner’s syndrome (20%), head tilt (22%), and facial nerve paralysis (8%) was increased in patients with these conditions pre-operative.
What minimally invasive approach to VBO in cats was described by Moissonnier 2022 in JAVMA?
Transoral
What bony structure is shown in the feline middle ear of the attached image from Mehrkens 2022 in JFMS? What is the surgical relevance?
Osseous septum that separates the epitympanum from the hypotympanum. This septum must be broken down to ensure complete debridement of the middle ear.
In a study by McGrath 2022 in JFMS, what was the median survival time in cats with SCC of the ear canal, middle or inner ear?
168 days with surgery, 85 days without (combination of medical management, radiation therapy, chemo, etc). No significant difference between surgically and medically managed patients.
Label the structure of the feline inner ear as seen endoscopically in a study by Enright 2023 in JFMS.
What are the three chambers of the middle ear?
1) Epitympanum: contains the incus and part of the malleus.
2) Mesotympanum: bounded by the tympanic membrane laterally. The bony promontory is on the medial aspect.
3) Hypotympanum: situated within the tympanic bulla ventrally.
Where does the tympanic plexus receive its innervation?
Parasympathetic: glossopharyngeal nerve.
Sympathetic: cranial cervical ganglion via the carotid plexus.
What are the two parts of the tympanic membrane?
The pars flaccida and pars tensa.
Where is the opening of the auditory tube?
The rostral mesotympanic chamber.
What are the bones/ossicles of the middle ear?
Malleous, incus, and stapes.
What are the muscles reponsible for movement of the ossicles?
Tensor tympani, stapedius.
The facial nerve is exposed in what aspect of the tympanic cavity?
Dorsal aspect, because the petrous temporal canal through which it travels on its way to the stylomastoid foramen is incomplete.
What is the vascular supply to the middle ear?
Tympanic artery, a branch of the maxillary artery.
What are the primary anatomic differences between the bulla of the dog and cat?
Cat has a much more distinct separation of the chambers of the bulla (larger ventral hypotympanum, and smaller rostrolateral epi/mesotympanum). Bony septum almost completely separates the two components.
The tympanic plexus distributes widely across the bony promontory and may be more exposed, or more sensitive, to iatrogenic trauma.
What are the three sections of the inner ear?
Vestibule, cochlear, semicircular canals.
The inner ear communicates with the tympanic membrane via the vestibular (oval) and cochlea (round) windows.
What nerve innervates the inner ear?
The vestibulocochlear nerve.
What are the three routes via which bacterial ingress to the middle ear can occur causing septic otitis media?
1) External auditory meatus (most common in dogs).
2) Auditory tube.
3) Hematogenous.
What are the most commonly encountered bacterial organisms in canine middle ear disease?
Staph, pseudomonas, malassezia.
What is the most common cause of septic otitis media in cats?
Ascending infection via the auditory tube associated with episodes of viral nasopharyngeal infection.
What are the treatment options for septic otitis media?
1) Conservative therapy (only if the underlying otitis externa can be resolved, and there is not evidence of extension to the CNS).
Involves myringotomy, lavage, and antimicrobials.
2) Surgery
In what location should a myringotomy be performed?
Caudal, to avoid damage to the attachment of the malleus.
What empiric antimicrobial therapy may be appropriate for treatment of septic otitis media?
Requires activity against staph and pseudomonas. Combined topical and systemic treatment recommended for 4-6 weeks.
Topical aminoglycosides or fluoroquinolones typically used. Topical aminoglycosides do not appear the same ototoxity as when used systemically.
Malessezia not normally treated unless the only growth.
From where do middle ear polyps originate?
The epithelium of the tympanic chamber or auditory tube.
Often preceded by an episode of upper respiratory viral infection.
What are the most common clinical signs associated with polyps?
1) Confined to bulla: clinically silent, Horner’s, vestibular signs.
2) Extend to auditory tube: interference with swallowing, obstruction of airflow.
3) Extend to auditory meatus: otorrhea, purulent discharge.
What are treatment options for polyps?
1) Medical: traction +/- prednisolone (57% recurrence without pred, 10% with). Per-endoscopic transtympanic polyp removal and curettage of the dorsolateral bulla also described with similar recurrence rate as traction and pred (14%).
What is a cholesteatoma?
Development of an epidermoid cyst in the middle ear, characterized by destructive and expanding keratinizing squamous epithelium.
Thought to originate from displaced epithelial cells from the external meatus following an episode of septic otitis media.
Are males or females more frequently affected by cholesteatoma?
Males. Brachycephalic dogs are also at increased risk.
What are the clinical signs associated with cholesteatoma?
Head shaking, pawing at the ear, pain on opening of the mouth.
What is the treatment for cholesteatoma?
Removal of the entire cystic structure with meticulous stripping of the epithelium and removal of parts of the bulla via a lateral or ventral (more common) approach.
What is the recurrence rate of cholesteatoma following surgery?
50%
Risk factors for recurrence include inability to open the mouth, presence of neurologic signs, and lysis of the temporal bone.
What is secretory otitis media?
Accumulation of mucinous material within the tympanic chamber.
Thought to occur secondary to congenital dysfunction in drainage via the auditory tube.
King charles cavaliers predisposed.
What is ciliary dyskinesia?
A congenital condition resulting in depressed ciliary function, affecting mucus removal via the auditory tube.
Leads to sterile otitis media.
What is the treatment for secretory otitis media or ciliary dyskinesia?
Placement of tympanostomy tube or ‘grommets’ in the tympanic membrane to allow ongoing drainage.
What are the most common tumours of the middle ear?
Typically extensions of neoplasms from the external ear.
Adenocarcinomas, SCC, and lymphomas can rarely arise from the tympanic membrane.
Is head tilt a common clinical finding in patients with septic otitis media?
Only in cases with extension to the inner ear.
What neurologic signs might be associated with otitis media?
- Facial nerve paralysis (10% of cases).
- Horner’s syndrome.
- Vestibular or central nervous system signs if progression to the inner ear or intracranial structures occurs.
What testing should be performed as part of the work-up of middle ear disease?
1) Physical examination: pay attention to concurrent dermatoses, palpation of regional lymph nodes and TMJ, examination of the nasopharynx.
2) Otoscopy and video otoscopy +/- myringotomy and guarded swab collection for C&S.
3) Radiography: 10 degree ventrocaudodorsal view particularly useful in cats.
4) CT/MRI.
+/- CSF analysis (if suspicion of extension to the inner ear), brainstem auditory evoked responses, impedance audiometry.
What are the landmarks for location of the bulla for VBO?
Located within the triangle bounded by the mandibular symphysis, the caudal border of the mandible, and the larynx.
Dissection occurs through the platysma and sphincter colli muscles, the diagastricus and mylohyoideus, and styloglossus and hypoglossus muscles.
Care should be taken to avoid which nerve during the surgical approach for VBO?
The hypoglossal nerve.
The bifurcation of the maxillary and linguofacial vein will also need to be retracted.
Osteotomy of the septum separating the hypotympanum and mesotympanum should be performed as far as possible in which direction to minimize the risk of damage to the bony promontory?
Lateral.
What are some complications associated with VBO?
Horner’s syndrome, vestibular signs.
If Horner’s doesn’t resolve after 6-weeks is likely to be permanent.
What is the bony landmark used to identify the location of the bulla during VBO in dogs?
Paracondylar (jugular) process. The bulla is 5-10mm rostral and 5-10mm medial to this prominence, midway between the wings of the atlas and caudal mandible.
What muscle attaches to the paracondylar process and requires retraction during VBO in dogs?
Digastricus.
