-Cochlea: 

-Stria vascularis produces endolymph

-"intermediate cells" (melanocytes) maintain K+ potential in endolymph

-MITF is essential for the development of the cochlea

Albinos can hear:

-Melanin production is not essential

-Otitis externa is an acute or chronic inflammation of the external ear canal, developing anywhere from the tympanic membrane to the pinna.

-It is the most common disease of the ear canal in dogs and cats, and is much more common in dogs than in cats.

-It can range from a mild to a severe disease and it sometimes extends to the middle ear.

There are three areas which regroup the causes of otitis externa.

Predisposing factors increase the risk of development of the disease.

Primary factors directly cause the otitis.

Perpetuating factors prevent the resolution of otitis externa once it develops.

Predisposing factors

Anatomy: pendulous pinnae, hairy, stenotic canals, long, steeply-sloping canals

Maceration: wetting due to swimming, bathing/hosing, high humidity.

Trauma: usually from inappropriate cleaning

Concurrent systemic disease: pyrexia

Tumours, polyps, cysts: more common in cats

Primary factors

Parasites: Otodectes cynotis, Sarcoptes, Demodex, Neotrombicula, ticks

Fungi: Dermatophytosis

Allergies: atopic dermatitis, diet, contact

Foreign bodies: grass seeds, grass awns,

Abnormal epidermal turnover or sebum production: seborrhea, endocrinopathy, nutritional problems, sebaceous adenitis

Primary keratinisation defects: idiopathic seborrhoea

Autoimmune disease: pemphigus foliaceus

Miscellaneous: juvenile cellulitis

Perpetuating factors

Bacteria: S. intermedius, Pseudomonas aeruginosa, Proteus

Fungi: Malassezia pachydermatis

Topical treatments: inappropriate use of topical treatments

Progressive ear pathology: ulceration, glandular hypertrophy and atrophy, thickened, folded canals

Otitis media

This can be performed at an early stage to increased drainage and ventilation of the external ear canal.

It should be used in cases where otitis has recurred despite appropriate medical management.

The horizontal canal must be intact for this surgery to be effective, and irreversible canal stenosis and end-stage otitis can lead to failure of the procedure.

This involves the complete removal of all external ear tissue except the pinna, and also the removal of infected tissue within the middle ear.

It is a salvage procedure that should only be performed in otitis externa cases that are chronic and endstage.

It can also be performed if otitis externa is still present following a lateral wall resection.

-Middle ear consists of an air-filled tympanic cavity, three auditory ossicles, and tympanic membrane

-Tympanic membrane is a semitransparent membrane divided into the pars flaccida and pars tensa.

-The tympanic cavity consists of a small epitympanic recess, a large ventral bulla and the tympanic bulla proper.

-On the medial wall of the tympanic cavity is the promontory, which houses the cochlea.

-The cochlear (round) window is located in the caudolateral portion of the promontory, covered by a thin membrane.

-The vestibular (oval) window is located on the dorsolateral surface of the promontory, covered by a thin diaphragm over which the footplate of the stapes is attached.

-The auditory tube is a short canal that extends from the nasopharynx to the rostral portion of the tympanic cavity proper.

-The auditory ossicles are the bones that transmit and amplify air vibrations from the tympanic membrane to the inner ear. 

-Inner ear is housed in a bony labyrinth in the petrous portion of the temporal bone.

-The bony labyrinth contains the membranous labyrinth with its sensory organs responsible for hearing and balance.

-The external ear is composed of auricular and annular cartilage. -The auricular cartilage of the pinna becomes funnel-shaped at the opening of the external ear canal.

-The vertical ear canal runs for about 1 inch, then forms the horizontal ear canal, which is composed of auricular and annular cartilage. 

-Cavalier King Charles Spaniels have been described to have a unique disease resulting in the formation of a buildup of highly viscous mucus within the middle ear

-The diagnosis of PSOM has been made based only on visualization of a bulging tympanic membrane and mucus in the middle ear post-myringotomy

-Treatment involves removing the mucus plug and flushing the middle ear (a procedure called a myringotomy), followed by medication with corticosteroids and antibiotics.

-Treatment may need to be repeated more than once before it's successful

-PSOM has a good prognosis

-Proliferative and necrotising otitis externa (PNOE) is a very rare disease affecting the ear canals and concave pinnae of kittens

-treatment options for PNOE are limited

 -spontaneous regression of PNOE after 12–24 months

-tacrolimus is effective for this condition

-Pathogenesis of PNOE is currently being explored.

-Severe acanthosis of the epidermis and hair follicles is one of the primary histological features.

-Epidermal and follicular hyperplastic changes are also observed in the feline dermatitis associated with viral infections

-Polymerase chain reaction analysis and immunohistochemical staining  have ruled out infection by herpesvirus, calicivirus or papillomavirus.

-It has been demonstrated that apoptosis of keratinocytes and infiltration of CD3+ T cells into the epidermis occurs in PNOE

-Brainstem Auditory Evoked Response (BAER) testing

-used by many breeders and pet owners as a hearing test for dogs and cats

-BAER is an electrodiagnostic test that determines if brainstem and hearing function is present in a patient.

-BAER testing is done on canines at least 35 days old.

-A signal equivalent to between 70 and 105 dB nHL (normal hearing level)

-Ceruminous cystomatosis is a skin disease of the ear in cats.

-Likely congenital (present from birth) or degenerative (progressive, often irreversible deterioration) and senile (weaknesses or diseases of old age) change

-Ceruminous cysts in the ear canals of cats originate in the ceruminous glands of the meatic lining (ceruminous glands are modified sweat glands and are generally more prevalent in the upper half of the meatic horizontal canal)

-characteristic bluish-black cystic lesions on the concave pinna, tragus region, and the vertical auditory meatus of one or both ears.

-Cysts can extend to the level of the horizontal canal

-genetic predisposition in Persians and Himalayans.

-can cause mild to severe symptoms of secondary otitis externa and media caused by the obstructive effect of the cysts interfering with normal self-cleaning

- CO-2 laser treatment 

Primary: The cause. What is the cause of the ear infection? Big tumor? Food allergy? Environmental allergy? Combination of both? This is *important*. If you don't know this answer, you will never fix the ear for good. 

Secondary: What is the infection type? Yeast vs. bacteria vs. both. Bacteria-rods vs. cocci vs. both. Cultures are helpful, but cytology is more helpful. What do you see? I have a few rules for when and why I culture an ear. 

Perpetuating: Big momma here. This is the stuff that makes the battle an uphill one. Biofilm, chronic inflammatory changes of the ear tissue, stenosis, otitis media, antimicrobial resistance, loss of epithelial migration, calcification of the external ear cartilage. If you have a lot of perpetuating factors in your way, the ear gets closer to being end-stage. Hard to get over some of these humps without more drastic measures like flushing, myringotomy, middle ear culture.

Predisposing: Genetics and ear carriage. These are risk factors for ear disease. Are you a gross Basset Hound with ears that hang to the center of the Earth? Or does the dog swim every day? Predisposing factors add a little fuel to the primary fire. But, they don't start the fire. 

-Head tilt

-Asymmetrical ataxia

-Circling to the side of the lesion

-Torticollis

-Horizontal or rotatory nystagmus- quick phase from the

 side of the lesion

-Positional ventral strabismus

-Deafness

[image]

-Most commonly: neomycin, propylene glycol

-Acute exacerbation of otitis

-Persistence of otitis

-Inflammatory cells (neutrophils) when neutrophils not originally present

-variably present

• Stapes attaches to the oval window
• [image]