Pinna Anatomy

The pinna, or auricle, consists of the flat part of the auricular cartilage, covered by skin on both sides. The convex surface is haired, even in some hairless breeds such as the Chinese Crested dog. Most of the concave surface is glabrous in cats and is variably haired in dogs, depending on the breed. In the most hirsute breeds such as the Cocker Spaniel the area around the ear canal opening is glabrous. The proximal part of the auricular cartilage folds into different tubercles and ridges and forms the ear canal opening, which includes the anthelix (medial), tragus (lateral), and antitragus (caudal) (Figure 12-1). (See also Chapter 1.)

Figure 12-1 Right pinna of a cat, concave surface.

Nineteen muscles attached on the skull and the auricular, annular, and scutiform cartilages allow the independent and complex pinnal movements observed in dogs and cats. The evolutionary role of pinnae is not clear. It may be related to sound collection (mobility of the pinna) or to prevention against foreign bodies (pendulous ears); it may even play an ornamental role.

Aural Hematoma

Aural hematomas can form within (intrachondrally) or along (subparachondrally) the cartilage of the pinna. They are considered more common in pendulous-eared breeds, but any dog or cat can be affected. There is no sex predilection, but affected dogs are usually middle-aged or older.

Clinically, aural hematomas result in large fluctuant swellings of various sizes, but usually they affect most of the ear pinna above the anthelix. During the first days, the swelling is warm to hot to the touch, and the overlying skin is erythematous. The animal is greatly bothered by the increased weight of the ear and sometimes seems to experience pain. Aspiration fluid obtained within hours of hematoma formation is sero-hemorrhagic and usually rich in fibrin. The presence of fibrin can prevent aspiration of any fluid later in the disease. The normal evolution of a hematoma is resorption of the fluid and healing. Fibrosis is always a major feature of the aural hematoma healing process, especially if left untreated. The pinna becomes thick, hard, and permanently distorted as the fibrosis in the wound contracts. Because aural hematoma is rarely seen in dogs and cats with major trauma to their pinna, minor ear trauma and/or pruritus is more likely a precipitating factor than a primary cause. Most studies reveal the following:¹

In one study, results were in favor of an autoimmune cause.² Joyce and Day could not confirm these results, even though they did find histopathologic evidence of cartilage degeneration associated with fibrovascular granulation tissue filling the cartilage defect.¹ They presumed that their samples (incisional biopsies of affected pinna) reflected the end process of cartilage degeneration that might have been caused by the mediators released by macrophages earlier in the process. These considerations are in favor of a process, most probably immune-mediated, that began several weeks before the aural hematoma was observed by the owner. Diagnosis of aural hematoma is usually straightforward and is based on history, clinical presentation, and fluid collection. Because the disease is self-limiting and heals spontaneously, some owners may choose not to treat their animal. Nevertheless, the hematoma greatly bothers the animal. Cosmetic considerations are also in favor of surgical treatment.

Several surgical techniques have been described. Fluid drainage (aspiration, indwelling drain, partial or whole-length incision) and flushing are effective in relieving the animal but usually result in post-treatment deformity of the ear pinna. Griffin found that surgical procedures aiming at prevention of immediate relapse by compression (without necrosis) and at restoration of the pinna’s initial shape and carriage are the most cosmetically effective and have the least recurrences.³ This can be achieved by several techniques. The most commonly used are multiple mattress sutures placed after incision or multiple punch holes made through the skin (see Chapter 19). Mattress sutures may also be placed through a soft but rigid device (several types are marketed that usually contain foam).

Because the healing of aural hematomas is highly fibrotic, glucosteroids are flushed into the hematoma cavity. They are also given orally with antibiotics, at least until the sutures are removed and the incision has healed.² Even though trauma is probably only a precipitating factor, it should be avoided as much as possible to prevent relapses. It is mandatory to identify and correct the cause. Otitis externa and pinnal skin diseases are most commonly encountered (Figure 12-2).⁶

Figure 12-2 Fibrosis and folding of the pinna of a 13-year-old cat with a history of aural hematoma that was left untreated.

Pinnal Trauma

The most common causes of pinnal trauma are pruritus or fight wounds; they also may be related to common dog habits such as earth digging and chasing other animals (Figure 12-3). Complications at the surgery site, including infection and tearing of the stitches, are common where ear cropping is still allowed. Pinnal trauma is usually associated with prolific bleeding. Routine wound cleaning and topical hemostatic application (peroxide, epinephrine, or collagen) are usually sufficient treatment. In severe cases, cauterization under anesthesia and/or compressive bandage might be necessary. Due to the thin edges of the pinna, laceration of the ear margin can be a permanent sequel.

Figure 12-3 Hypothrichosis due to intense ear scratching caused by otitis externa.

Dermatophytosis is another possible consequence, which is often associated with a history of cat fighting or soil digging. Both cat claws and soil can be a source of various dermatophytes. The trauma associated with contact facilitates the inoculation of the fungi. This may happen during a fight or if the pinna is scratched with a soil-covered paw during digging or shortly after.

Blood sampling from the ears of dogs and cats has been recently developed in order to monitor blood glucose. Pinnal lesions may result from frequent sampling. The local ischemia associated with the vascular problems commonly associated with diabetes mellitus probably predisposes diabetic patients to pinnal complications.

Pruritic Dermatoses

Pruritus is probably the most common cause of pinnal lesions in dogs and cats. The origin of the pruritus can be the pinna itself, as in arthropod-related dermatoses, atopic dermatitis, or contact dermatitis.⁴ Nevertheless, pinnal pruritus is most commonly caused by otitis externa (e.g., otodectic mange, foreign body, Malassezia otitis externa, atopic dermatitis) or facial diseases (e.g., intertrigo, food allergy, atopic dermatitis, conjunctivitis).⁴ Pruritus results in pinnal alopecia, excoriation, and crusting.

Sarcoptic Mange

Sarcoptic mange is a cosmopolitan, transmissible, nonseasonal, highly pruritic, generalized dermatosis of dogs caused by Sarcoptes scabiei var cani. It is contagious among dogs and can cause transient lesions on humans because sarcoptic mange is a zoonosis. Other variants of Sarcoptes scabiei are found on most mammalian species.

The pinna is one of the favorite habitats of the mite. Early pinnal lesions are abundant, with yellowish crusts that adhere between hairs. The entire border of the pinna may be involved. Pruritus is usually intense and results in pinnal trauma, hair loss, excoriation, and erythema. Because the pathogenesis of scabies involves a hypersensitivity reaction, some dogs may experience only mild pruritus. An anergic form is described where affected animals are almost nonpruritic in spite of the presence of hundreds of mites.⁵ More commonly, clinical signs of scabies can be more subtle or have a different localization in dogs treated for fleas and ticks with drugs used against acarids (permethrin, other pyrethroids, fipronil, amitraz) that are not completely efficient due to their spectrum, the formulation used (spot-on, collars, shampoo), the amount used, or the frequency of application.

Differential diagnosis includes otodectic dermatitis, trombiculosis, pediculosis, cheyletiellosis, contact dermatitis, Malassezia dermatitis, and atopic dermatitis. Definitive diagnosis is based on finding Sarcoptes scabiei mites. Multiple skin scrapings are sometimes necessary and should involve at least both pinnae and both elbows. Pinnae should be sampled preferentially in areas where thin crusts are present. They feel like sand when the pinnal margins are palpated between the fingers. Nevertheless, mites can be difficult to find. If sarcoptic mange is suspected, a complete treatment should be instituted regardless of skin scraping results.

The pinnal-pedal reflex is often positive. When the pinnal margin is scratched with a fingernail, a reflexive rear leg scratch is initiated. Most pruritic conditions of the pinna and even pruritic otitis externa can also induce a positive response. False-negative reactions are also encountered.

Treatment for scabies should involve the whole body, even if lesions are localized. Systemic treatments (selamectin, ivermectin) are usually preferred because they are easy to use, have minimal side effects, and are environmentally safe. In case of treatment failure or for cost considerations, especially in kennels, acaricidal rinses are a good alternative (lime sulfur, amitraz, rotenone, phosmet). Hair clipping is mandatory if the hair coat is thick and/or long. Lime sulfur rinses can be used on young dogs.

Notoedric Mange

Notoedric mange is a nonseasonal, transmissible, pruritic dermatosis of cats caused by Notoedres cati. It can cause transient lesions on most mammals, including dogs and humans. All in-contact cats, especially littermates, are more or less affected. The incidence is reported to have greatly decreased, and notoedric mange is considered rare in most countries. The distribution is epizootic; in a given country, it can be seen commonly in one region and rarely in another.

The medial borders of both pinnae are affected first, then the whole pinna is affected; the lesions then spread all over the face, eyelids, neck, and, infrequently, the perineum and feet. Generalization is unusual. Papules are early transient lesions. The skin rapidly becomes thickened and forms large wrinkles covered with thick, adherent, yellowish to silvery crusts. Pruritus is intense and results in alopecia. Severe excoriation leads to infected wounds. Lymphadenopathy is a common feature.

Differential diagnosis includes otodectic dermatitis, cheyletiellosis, food allergy, atopic dermatitis, contact dermatitis, and pemphigus foliaceus or erythematosus. Mites are more readily found on skin scrapings than Sarcoptes scabiei. Nevertheless, due to their small size, the scraping should be scrutinized under 10× objective, closed diaphragm, medium light, and after good clearing of the sample.

Many acaricidal drugs are toxic in cats, particularly organochlorates, organophosphates, permethrin, and amitraz. Avermectins (selamectin, ivermectin) and lime sulfur are effective.

Treatment of the premises is mandatory because the mite can survive for more than 2 weeks in the environment.⁵

Trombiculiasis

The six-legged larvae of the genera Trombicula (chigger mite, harvest mite) cause a seasonal (in temperate or continental climates) and pruritic papular dermatosis both in dogs and cats. Numerous species of Trombicula are associated with the disease in various countries. The more commonly recognized are Neotrombicula automnalis (Europe) and Eutrombicula alfreddugesi (America).

Mites are often found on and around the pinna. The legs, interdigital areas, ventrum, and face are often involved, too. Pruritus is almost always present. Crusts, alopecia, and erosion are present on affected areas.

The diagnosis is usually easy because the larvae are visible to the naked eye (0.5 mm), have a bright orange to red color, and are tightly adherent to the skin, usually in clusters.

Treatment should aim at killing the mites present on the animal, relieving the pruritus, and preventing subsequent infestation. If infestation is localized, topical application of an otic ointment containing steroids and an insecticide is sufficient. Otherwise, an acaricidal spray should be associated with a 5- to 8-day course of oral prednisolone (1 mg/kg). If free roaming cannot be prevented, the prevention of reinfestation is difficult. An acaricidal spray with a strong repellent effect such as permethrin is an option for dogs but is toxic in cats. In one study on a small number of animals, fipronil spray applications seemed to achieve a more effective and lasting result in dogs than in cats.⁶ Trombicula autumnalis adults are found in the outside environment. Compost areas should be enclosed so that the pet cannot access them. Treatment of other favorable areas (under trees, under the house, in bushes) with insecticides should be discouraged because of the toxicity to invertebrates (pollinating insects, honeybees) and children and the presence of residue on fruits or vegetables grown in the garden.

Louse Infestations

Pediculosis can be caused by sucking lice (Anoploura, such as Linognathus setosus in dogs) or chewing lice (Mallophaga, such as Felicola subrostrata in cats and Trichodectes canis or, in warm climates, Heterodoxus spiniger in dogs). Lice are dorsoventrally flattened wingless insects. They cause few direct lesions but usually cause intense pruritus. The whole body is often involved, but they particularly accumulate on the concave surface and base of the pinna.

Nits (louse egg cases) are usually visible, adherent to the hair. The hair coat is often matted and dirty. Lice infestation is associated with neglect (overcrowding, poor sanitation), and affected animals are often debilitated. Anemia can be associated with heavy Linognathus setosus infestation because sucking lice feed on blood. Asymptomatic carriers exhibit only mild pruritus and seborrhea sicca.

Differential diagnosis includes flea-allergy dermatitis, scabies, cheyletiellosis, Dermanyssus or Trombicula infestation, Malassezia dermatitis, allergic skin diseases, and seborrheic disorders. Acetate tape allows lice immobilization and identification by microscopic observation. Hair coat observation with the video otoscope is another possibility. Nits are visible both on macroscopic and microscopic examination. They are larger and more tightly attached to the hair than Cheyletiella eggs.

In dogs and cats, most routine insecticides are active on adult lice (spray, shampoo, powder, dips), which might explain the observed decrease in pediculosis prevalence. Nevertheless, treatments are usually ineffective on eggs and have to be applied repeatedly.

Insect Bite Dermatitis

Insect bite dermatitis can be caused by various hematophagous insects due to the mediators or toxic products present in their saliva; it is sometimes associated with hypersensitivity reactions. Cats are more commonly affected than dogs, perhaps because they roam more and because of their “lie and wait” way of hunting. Papules, erythema, erosion, and alopecia are seen mainly on the thickened tip of the pinna. The border and the dorsal side can also be affected. In dog breeds with pendulous or broken ears, lesions are seen on the surface of the pinna where the ear folds down. In severe cases, multiple small ulcers covered with hemorrhagic crusts are present.

The causative insects vary with the season, environment, and climate.

The rabbit flea (Spilopsyllus cuniculi) can infest dogs and cats that are in contact with infected rabbits (pet, hutch, hunting). Transmission is reported to occur mainly at the time of rabbit parturition. This flea is found mainly in Europe and Australia. It stays tightly attached to its host’s skin, usually at the tip of the pinna, and should not be confused with a tick.

Mosquitoes (Aedes spp., Culex spp.), stable flies (Stomoxys calcitrans), and blackflies (Simulium spp.) may cause lesions on the pinna. The bridge of the nose and/or the periocular area can also be affected. Their presence is seasonal in endemic areas. Because they do not stay on their host, the diagnosis is often putative.

Differential diagnosis includes actinic dermatitis, trauma, canine eosinophilic pinnal folliculitis, and eosinophilic furunculosis of the face. Diagnosis is based on history and clinical signs. Lesions are often infiltrated with eosinophils and show secondary infection.

Treatment should be aimed at the lesions and at reinfestation prevention. Lesions are cleaned and topical antibiotics are applied. Steroids are often used because of the common hypersensitivity component of the disease. Steroids are not indicated if ulceration is present because they slow the healing process. Elimination of the animal’s exposure to the insects is the only effective prevention but is usually difficult to achieve. Measures include treatment of farmed or pet rabbits, prevention of free roaming, and application of a repellent. Permethrins and pyrethroids have good repellent activity, as shown with a deltamethrin-containing collar against phlebotomes, but they are toxic in cats. Vaseline mixed with citronella, DEET, or N,N-diethylmetatoluamide allows the product to stay longer on the ear tip.

Atopic Dermatitis

Erythema of the concave pinna is seen in more than 50% of atopic dermatitis cases in dogs and is the only symptom for a year or more before the development of other symptoms in at least 3% of canine cases.^10–12 Associated pruritus is intense (Figure 12-4).

Figure 12-4 Intense pruritus of the inner pinnae in a 5-year-old female atopic Labrador with secondary Malassezia dermatitis and otitis externa.

Lichenification and thickening of the concave pinna usually occur. Seborrhea and Malassezia dermatitis are common complications. This frequent feature might be explained in part by the observation made on 10 normal dogs, where mast cell counts were found to be highest in the medial and lateral pinna.⁷ Otitis externa, cheilitis, and conjunctivitis are also frequently encountered in canine atopic dermatitis and also cause pinnal pruritus and trauma.

The clinical presentation of atopic dermatitis is very different in cats. Otitis externa and the related pinnal trauma caused by pruritus are uncommon, even rare. Atopic dermatitis is a common underlying cause of the initially non-lesional pruritus of the face, neck and pinna, even though Otodectes cynotis and food allergy are the main differential diagnosis for this condition in cats.

Food Allergy

Food allergy is commonly associated with auricular disease both in dogs and cats (see Chapter 6). The pathogenesis of cutaneous nontoxic adverse reaction to food can involve immune-mediated or non–immune-mediated mechanisms. They are respectively called food allergy/hypersensitivity and food intolerance. The precise mechanisms are not elucidated in animals and are a point of controversy in humans.

In cats, facial pruritus is probably the most common presentation of food allergy. Excoriations caused by the intense self-mutilation are usually not restricted to the pinna but also affect the preauricular area, face, and neck. As opposed to canine cases of food allergy, otitis externa is rare in cats.

In one study of 51 food-allergic dogs, Rosser⁸ stated that 80% of cases had otitis externa and that it was the only symptom in 20%. Pinnal lesions mainly result from otitis externa–related pruritus (Figure 12-5). Improvements in pruritus and skin lesions during the food trial may not be obvious if the perpetuating factors of the otitis externa are not treated initially (bacteria or yeast proliferation, inflammation associated ear canal or pinna changes).

Figure 12-5 Erythema and lichenification on the inner pinnae of a female Bichon Frisé with food allergy.

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