Diseases of the Pinna
Congenital Deformation of the Pinna. Congenital deformation of the pinna is rare in dogs and cats, and when it occurs correction is not always needed, although faulty ear carriage may be seen as a loss of value of the dog. Veterinarians in the Netherlands do not encourage surgical intervention when the pinnae are in principle healthy, and cropping of the pinnae without medical indication is prohibited. Further information may be found elsewhere ().
Inflammation. Lesions of the pinna may be part of more generalized skin disease (). They can be bacterial, fungal, parasitic, immune mediated, or vascular (drug mediated) in origin (). These disorders are not age dependent, and hence young dogs and cats are not excluded. Bacterial folliculitis of the pinna with focal areas of alopecia has been described in dogs, and dermatophytosis of the pinna with focal alopecia and extensive crusts can be found in cats (). Nonpruritic areas of alopecia in dogs should be scraped for demodectic mites. Pruritus and crusting of the pinna can be caused by Sarcoptes mites in dogs and Notoedres mites in cats ().
Trauma. Trauma of the pinna can occur at any age. A tear in the pinna is usually the result of a fight with another dog or cat. The cat’s claws and the dog’s canine teeth are the sharp instruments that cause this trauma. The resulting bleeding can be impressive, and the veterinarian must act immediately to induce primary wound healing.
In young dogs it is often possible to place several sutures without local or general anesthesia. A small, fresh tear (up to 1 cm in length) can be sutured after cleaning and removal of some of the surrounding hair. The skin on the concave side of the pinna is apposed and sutured with interrupted sutures, starting at the edge of the pinna. Then the skin on the convex side is apposed and sutured in the same way. The cartilage is not included in these sutures. Bleeding stops during suturing, but a resistant artery may have to be ligated separately. The use of de-layed-solubility suture material is preferred so that the sutures do not have to be removed.
Most cats will not submit to suturing without severe resistance, and hence they, as well as dogs with larger lacerations, should be anesthetized. When the wound is not fresh and inflammation is apparent, surgical correction is postponed and the inflammation treated first. Surgical correction then begins with debridement of the wound edges. Suturing follows the same procedure as in fresh wounds.
Othematoma. Othematomas occur at all ages. The bleeding occurs between the carti-lagenous layers of the pinna and is usually considered to result from trauma, such as caused by shaking the head or scratching. Kuwashara () has suggested an immune-mediated disease as the underlying cause. Surgical intervention is necessary because without treatment the pinna will shrivel, and subsequent ossification of the cartilage will cause continuous irritation. Also, shriveling of the pinna may cause obstruction of the external orifice of the ear canal and thus induce chronic otitis externa.
The purpose of surgery is to remove the blood clot and press the layers of the pinna together long enough to effectuate reunion of the layers. A reliable method consists of suturing through all layers of the pinna, placing sutures over its entire surface. Interrupted mattress sutures of monocryl are excellent for this purpose and should be left in place for 2 weeks.
Abscesses. In cats, a penetrating wound inflicted by the claw of another cat usually causes abscesses of the pinna. The cat is depressed and febrile, and the ear is obviously painful. The skin over the abscess should be opened and the pus removed by gentle compression, followed by flushing with 0.9% sodium chloride solution. A broad-spectrum antimicrobial agent should be administered systemically for 10 days. In the young cat no complications are expected.
Tumors of the Pinna. Tumors of the pinna occur at all ages in dogs and cats but are very rare in young dogs and cats ().
Diseases of the External Ear Canal
The external ear canal in puppies and kittens is closed during the first days of life. In puppies the external meatus of the ear canal begins to open at the age of 2 weeks. According to our hearing tests in four puppies, the ear canals are functionally open at die age of 25 or 26 days.
Congenital Deformations of the Ear Canal. Congenital deformations of the ear canal (usually atresia) are rare and are usually unilateral and therefore not often detected before fistulas occur. Unilateral deafness is well masked in the kitten and puppy. When atresia of the ear canal is found without clinical signs, it is advisable to refrain from intervention. Abscesses of the middle ear require drainage, followed by antimicrobial therapy for 10 days.
Otitis Externa. In young dogs and cats otitis externa is most commonly caused by the parasite Otodectes cynotis. The parasite is common in groups of young cats and dogs and when found in one dog or cat in a litter all animals of the litter and the mother should be examined. The mites appear to irritate the ceruminous glands in particular because excessive thick, brown cerumen always accompanies mite infestation. The mites can be detected on this dark brown background with an otoscope. The mites begin to walk when the light of the otoscope warms them. This way of detecting ear mite infestation is almost foolproof and is more reliable than microscopic examination of a cerumen sample.
Treatment begins with flushing of the ear canal. When all cerumen is washed away, the tympanic membrane is clearly visible. In most cases the wall of the ear canal is slightly irregular. Topical antiparasitic drugs are ototoxic and can only be used when the tympanic membrane is intact, so only the veterinarian should administer them. A single application is usually sufficient when reinfection is prevented. After antiparasitic treatment, the otitis is treated for 5 days by local application of an ointment containing broad-spectrum antimicrobial agents and a corticosteroid. One week after the initial treatment, the ears are reexamined. Further treatment is usually not needed.
Another cause of otitis externa in young dogs is a foreign body. This is usually a grass awn. Detection with the otoscope is easy when the otitis externa is still mild, and the plant part can then be removed via the otoscope.
Cleaning of the ear canal of young dogs and cats as part of the routine care by the owner should be discouraged. The skin of the ear canal is too tender, and regular cleaning can result in otitis externa. It should be explained to the owner that a small amount of cerumen visible at the external opening of the ear canal is normal and quite acceptable.
Diseases of the Tympanic Membrane and the Middle Ear
The tympanic membrane is composed of three layers: the epidermis, which is a continuation of the epidermis of the external ear canal; the lamina propria, or fibrous and vascular layer; and the mucosa, which is a continuation of the mucosa of the middle ear. The pathology of the tympanic membrane is usually related to the pathology of the external ear canal or that of the middle ear. Chronic irritation results in thickening of the tympanic membrane, recognized via the otoscope as a loss of transparency. This may be seen, for example, after a longstanding plug has been removed, and it is usually, especially in young dogs and cats, temporary. Middle ear disease is diagnosed more often in cats than in dogs. Reddening of the tympanic membrane is a common sign of middle ear disease. In dogs spontaneous rupture of the tympanic membrane is rare. We have diagnosed this in young dogs with purulent middle ear disease in the course of juvenile cellulitis (). When the tympanic membrane is ruptured accidentally and no middle ear disease occurs, the perforation heals in 1 to 3 weeks, depending on its size (). In cats the most common cause of rupture is a polyp in the middle ear that grows through the tympanic membrane into the external ear canal. Among 64 cats in which middle ear polyps were removed, 14 were 1 year old or younger (). After removal of the polyp, the tympanic membrane is healed and transparent within 4 weeks, at least in cases in which the middle ear disease is cured.
Otitis media without proliferative disease of the external ear canal is diagnosed by otoscopic examination. The tympanic membrane is not transparent and usually red, and it is sometimes ruptured. The discharge from the middle ear is visible in the external ear canal when there is a rupture and is mucopurulent in acute inflammation, as is the case in young animals. When the tympanic membrane is not visible, diagnosis is difficult because radiographs do not conclusively show acute middle ear inflammation.
In young animals the treatment of otitis media consists of systemic broad-spectrum antimicrobial therapy for at least 2 weeks. The inflammation is resolved when the tympanic membrane appears to be normally colored and transparent.
Selections from the book: “Veterinary pediatrics: dogs and cats from birth to six months”. Johnny D. Hoskins. (2001)