Dog Ear Anatomy and Issues

• This document describes the anatomy, issues, and treatment related to a dog's ears

External Ear

• Composed of the pinna and external auditory canal (or external acoustic meatus).
• Captures and conducts sound vibrations to the eardrum, which separates the external ear from the middle ear.
• Pinna consists of cartilage covered with thick skin and has two sides, the rostral and dorsal.
• Auricular concha is formed in continuity with the pinna.
• Numerous muscles derived from the facial nerve move the pinna.
• External acoustic meatus is a horizontal canal composed of a cartilaginous part surrounded by auricular adipose tissue and a bony part hollowed out in the tympanic part of the temporal bone.
• The facial nerve innervates the musculature and the trigeminal nerve's branches innervate the integument.

Middle Ear

• Air-filled cavity located between the petrous and tympanic parts of the temporal bone connecting to the nasopharynx.
• Lined with mucous, the tympanic cavity containing the ossicles is divided into three sections.
• The superior section contains the ossicles, the intermediate section has the tympanic membrane and the opening of the auditory tube on its lateral wall.
• The lower or ventral section forms a recess inside the tympanic bulla.
• Tympanic membrane separates the external ear from the tympanic cavity.
• The thin oval tympanic membrane is attached to malleus.
• The tympanic cavity is separated from the inner ear by a bony wall with two windows containing the vestibule and the cochlea.
• Ossicles transmit vibrations from the tympanic membrane, malleus, to the perilymph of the inner ear through the oval window (vestibule).
• Auditory tube connects the middle ear to the nasopharynx draining secretions and balancing pressures across the tympanic membrane.

Inner Ear

• Consists of a membranous labyrinth filled with endolymph inside space of the petrous part of the temporal bone: the bony labyrinth.
• Vestibular part of the membranous labyrinth: responsible for balance, containing the utricle, saccule, and three semicircular canals communicating with the utricle.
• Cochlear part of the membranous labyrinth: hearing organ composed of a coiled conduit.
• Bony labyrinth: contains the vestibule that houses the utricle and saccule, semicircular canals housing the semicircular ducts, the cochlea housing the cochlear duct, the vestibular ramp, and the tympanic ramp.

Otitis Externa

• Inflammation of the external ear (pinna and external auditory canal) stopping at the tympanic membrane.
• Common condition representing 7.5 to 16.5% of consultations in dogs.
• Erythematous: earliest stage with edema and erythema of the ear canal wall without increased cerumen production with head shaking and scratching.
• Erythemato-ceruminous: most frequent, shows thickening of canal wall, glandular hyperplasia, increased cerumen, pruritus, excoriations, with possible proliferation of Malassezia or bacteria, and frequent middle ear involvement.
• Suppurative: often corresponds to a chronic otitis with presence of degenerated neutrophils and numerous bacteria.
• Middle ear complication is very frequent.

Otitis Media

• Inflammation of the middle ear (tympanic membrane, ossicles, Eustachian tube, and tympanic bullae).
• Frequent complication of otitis externa, present in about 16% of acute and 80% of chronic cases.
• Observation of tympanic breach confirms diagnosis; however, middle ear otitis can occur with an intact tympanum if earlier breach permitted germ passage in tympanic bullae.
• Imaging is often needed due to ear canal changes that prevent otoscopy.
• Claude Bernard-Horner syndrome may suggest otitis media in cases of neurological signs.
• Study in "Veterinary Dermatology" (2014): sought an objective clinical score for evaluating the severity of external otitis and treatment response.
• The Otitis Index Score (OTIS) was studied using scales from 0 (absence) to 2, 3, or 5 (most severe).
• Scores were based on clinical and cytological criteria.
• Evaluated by the veterinarian and owner: erythema, swelling, erosion/ulceration, ear canal discharge, pain, pruritus, odor, tympanum integrity, response to treatment, and otitis type.
• Evaluation of pruritus and pain involved placing a marker on a Visual Analog Scale (VAS) from "does not scratch" to "scratches all the time" and from "no pain" to "extremely painful."
• No significant difference between the vertical and horizontal portions of the ear canal; one evaluation or both results seem representative.
• Pain and pruritus scores correlated poorly with lesion scores.
• Higher pruritus scores were linked to OEC, and higher pain scores were linked to suppurative otitis.
• OTIS3 parameters (erythema, swelling, erosion/ulceration, and discharge) are most reliable for assessing lesions; an OTIS3 score that is greater than or equal to 4 defines external otitis with 100% specificity and 91.1% sensitivity.
• OTIS3 that is less than or equal to 3 defines dogs without external otitis, with 91.9% specificity and 100% sensitivity.
• OTIS3 seems reliable, easily implemented for assessing severity, and treatment efficacy.

Otitis Pathogenesis

• Otitis has many causes and factors.
• Predisposing factors are not directly responsible for otitis but increase its likelihood if a primary cause is present and may be due to ear conformation, lifestyle, or inappropriate topical products.
• Drooping ears or ear canal hypertrichosis, or intense ceruminous gland function, increase susceptibility as they promote infections and reduce earwax.
• Acquired or congenital ear canal stenosis, as in Shar Peis or brachycephalic breeds, predisposes dogs
• Increased earwax can result from overactive ceruminous glands, and brachycephalic breeds can have larger, more active ceruminous glands.
• Neoplasia is the primary cause of ear canal obstruction in dogs; tumors of sebaceous glands, histiocytomas, and mastocytomas affect the pinna, while ceruminous gland tumors typically affect the ear canal.
• Systemic Illness: Immunosuppression, debilitating disease, or fever can alter the ear's environment, promoting opportunistic infections, such as with allergic dermatitis and generalized pyoderma.
• Inappropriate Topical Treatments: Self-medication with unsuitable products can foster otitis by causing inflammation or ulceration due to the canal's fragility
• Trauma: Injuries like bite wounds can disrupt the ear's epidermis, encouraging bacterial colonization of the ear canal and cotton swabs can cause microtrauma that leads to inflammation.

Otitis Primary causes

• Parasites: Most parasitic external otitis is caused by Otodectes cynotis; it is a common cause, at 5-10% of canine otitis cases. The parasite is a small mite (1 mm) that lives in the ear canal, feeding on cerumen and debris.
• Otacariosis: mainly found in collective animal environments, is transmitted by close contact, and mothers may infect puppies.
• Clinical signs: significant ear canal inflammation causing intense itchiness with a characteristic abundant, brownish, flaky cerumen.
• Confirmed parasitic diagnosis: observed using otoscope or microscope.
• Treat all animals: All animals in contact with the infected animal should be treated given that it’s extremely contagious.
• Hypersensitivity: Allergic dermatitis causes recurring or chronic otitis; ear inflammation is a clinical sign of atopic dermatitis in 55% of patients as food allergies can also trigger skin manifestations (65%-80% cases).
• Hypersensitivity diagnosis is confirmed via strict diet.
• Topical dermatitis: a frequent cause, are attributed to neomycin, propylene glycol, and multiple ear cleansers.
• Foreign objects: often unilateral, causes intense pain, head shaking, and head tilt, typically caused by plant awns, which progress into ear, injure tympanum, and cause otitis media.

Perpetuating Factors

• Exacerbating factors that can come on secondarily to the root cause may be the only ones identifiable, and if treated, the primary infection is treated while fading into the past.
• Bacteria: frequently identified alongside inflammation, primarily staphylococcus but also streptococcus and pseudomonas.
• Yeasts: the most commonly contracted is Malassezia, and can be identified by its unique "Perrier bottle" formation during an ear canal evaluation, although difficult to link it to an underlying cause.

Tympanic Changes

• Is very crucial, as internal damage could cause otitis media and further prolong a treatment plan, requiring a video otoscope to be viewed clearly.
• Cleaning: Is very important- you must use a commercial ear wash to remove debris and cells before treatment.
• Treatments are specifically for Otitis Acute, often anti-inflammatory- but can differ.

Otitis Treatment

• Acute: Parasitic or due to the presence of a foreign body resolve fast whereas the implementation of a topical anti-inflammatory treatment is required.
• Chronic: Is rare for cats and is attributed to ear mites, in which no other causes are identified.
• Inflammation of the External Ear: Most prevalent, and is caused by bacterial or fungal infections of skin.

Cat Ear Infection Treatment

• Ear infections can be identified via an erythema test from a microscopic exam, or if there's pus present.
• Cats are more prone to ear ototoxicity than dogs, meaning that you should only proceed with extreme caution to avoid damaging epidermal layers.

Diagnostic Procedures

• Comprehensive Assesment: Evaluate the entire ear's condition, which includes a visual exam of the pavilions and the palpation of the relative consistency.
• Palpatation or Pain is: Strong indicator of Otitis.
• Otoscopic Exam: Can further reveal foreign material as well as inflammation.
• Imagerie: Best used to detect irreversible damage that won't respond to simple treatment.
• Scanners: Most versatile for middle and inner evaluation.
• MRI: Best for internal softness and neurological disorders attributed to internal otitis.
• Surgery: Effective at managing irreversible damage due to bacterial or fungal infections/inflammation.

Cat Ear Infection Factors

• Parasites: Otodectes, Demodex
• Hyersensitivity: Dermatitis
• Auto-Immune: Pemphigus Foliaceus
• Bacteria/Cultures: Malassezia, Candida and Aspergillus