Ch 123 - Middle and Inner ear Flashcards

1
Q

List the components of the tympanic cavity

A
  • 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
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2
Q

What are the main components of the tympanic membrance?

A
  • Pars flaccida dorsally
  • Pars tensa ventrally, much larger. Manubrium of malleus is embedded in dorsal pars tensa
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3
Q

Where is the aural opening of the auditory (eustachian) tube located?

A

Rostral mesotympanic chamber

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4
Q

List the ossicles of the middle ear

A
  • 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
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5
Q

What ligaments hold the ossicles in place?

A
  • Lateral ligament of the malleus
  • Dorsal ligament of melleus and incus
  • Annular ligament of the stapes
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6
Q

What muscles are responsible for movement of the ossicles?

A
  • Tensor tympani muscle - pulls malleus medially, increasing the tension and convexity of the tympanic membrane
  • Stapedius muscle - Tenses the stapes to limit its movement

Act to dampen sound vibrations

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7
Q

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

A

Double chamber:
- Larger ventrocaudomedial chamber of hypotympanum
- Smaller rostrolateral compartment of mesotympanum and epitympanus

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

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8
Q

What muscle causes opening of the auditory tube during swallowing?

A

Tensor veli palatini

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9
Q

What is the bony labrinth?

A

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

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10
Q

What are the three sections of the membranous labyrinth?

A

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
- Floow 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

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11
Q

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

A

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

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12
Q

What structures within the inner ear contribule to vestibular function?

A
  • Semicircular canals
  • Saccule
  • Utricle
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13
Q

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

A
  • Extension from external ear through tumpanum
  • Extension from nasopharyn through auditory tube
  • Haematogenous
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14
Q

List inflammatory diseases of the middle ear

A
  • Polyps
  • Topical agents causing a sterile inflammation (antiseptics, ceruminolytics)
  • Cholesteatoma and cholesterol granuloma
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15
Q

What breed is overrepresented with secretory (serous) otitis media

A

CKCS

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16
Q

List forms of congenital inner ear abnormalities that result in deafness

A
  • Collapse of scala media in Dalmatians
  • Neuroepithelial degeneration in Rottweilers
  • Changes in the organ of Corti in Pointers
17
Q

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

A

10-degree ventrocaudodorsal view of tympanic chambers

18
Q

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

A
  • If there is extension into the inner ear, changes on CSF consistent with bacterial meningitis can be seen
19
Q

What is BAER testing?

A

Brainstem Auditory Evoked Responses

20
Q

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

A

At least 4-6 weeks

21
Q

What are some appropriate ABx choices while awaiting culture results?

A
  • Aminoglycosides (gentamicin) topically (systemically can cause ototoxicity)
  • Fluoroquinolones topically and/or systemically
22
Q

What is the reported recurrence of polyps with traction?

A
  • Nonendoscopic traction 57%
  • Endoscopic traction, transtympanic curettage and post-op corticosteroids - 13.5%
  • Traction of nasopharyngeal polyp with prednisolone - 10%
23
Q

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

A
  • Failure of medical management
  • Neuro signs requiring tympanic decompression
  • Neoplasia
24
Q

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

A
  • Platysma
  • Sphincter colli
  • Digastricus
  • Myelohyoid
  • Hyoglossus
  • Styloglossus
25
Q

What nerve and artery should be avoided during a VBO?

A
  • Hypoglossal nerve
  • Lingual artery
26
Q

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

A

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

27
Q

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

A
  • 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
28
Q

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

A
  • Inability to open mouth
  • Neuro signs
  • Lysis of temporal bone