Ear

Chapter 50


Ear



Aural conditions in cats are common. Many of these have underlying causes that will respond effectively to medical management, but in some cases surgery is indicated either as the primary treatment option or due to failure to respond to other treatment regimens. The approach to aural disease, the surgical diseases that affect the feline ear, and the surgical management of these diseases will be discussed in the following chapter.



Surgical anatomy


The ear is a sensory organ that receives and transforms the vibrations perceived as sound into neural impulses conveyed to the brain. The ear is composed of the pinna, external ear canal (comprising vertical and horizontal ear canals), the middle ear, and the inner ear (Fig. 50-1).




Pinna


The pinna is a broad skin-covered extension of the external ear canal cartilages that helps to collect and localize the origin of sound waves. It is also important in non-verbal communication between cats and other animals, including humans. Ear position, in association with other changes in facial expression, can convey feelings such as fear, anger, happiness, and curiosity.


The size and shape of the pinna varies according to breed, although less so in the cat than the dog. Most cats, except Scottish Folds, have erect pinnae unless they are diseased. The pinna is triangular in appearance with the base of the triangle attached to the head. It has a relatively hairless and more glabrous rostralateral concave surface and a haired caudomedial surface. The auricular cartilage of the pinna is elastic with small perforations through which blood vessels pass. Rupture of these blood vessels may lead to an aural hematoma.



External ear canal


The external ear canal opening is formed by the auricular and scutiform cartilages. The large auricular cartilage is cone shaped from its origin at the annular cartilage to the external auditory meatus, and it then flares to form the pinna. The helix is the edge of the pinna and the scapha is the center. The antihelix is a ridge with a prominent tubercle on the medial aspect of the auricular cartilage at the opening of the vertical canal. The tragus is the lateral rim of the opening to the external ear canal. The antitragus is caudal to the tragus and separated from it by the inter-tragic notch. The tragohelicine fissure lies between the tragus and helix. The funnel-shaped cavum conchae forms the vertical canal and, along with the tragus, antitragus, and antihelix, the external auditory meatus. As the auricular cartilage approaches the horizontal canal it is replaced by the annular cartilage. The annular cartilage ends just before the tympanic membrane and the osseous external auditory meatus, which is an extension of the temporal bone containing the cochlea and peripheral vestibular apparatus. This canal ends at the tympanic bulla and the external acoustic meatus.


There are numerous muscles of the external ear canal and groups of muscles act to move the ear in particular directions. These groups are rostro-auricular, caudo-auricular and ventro-auricular. The innervation of the external ear is provided by cervical and cranial nerves. Sensory input is via the branches of the 2nd cervical nerve dorsally (greater occipital nerve) and ventrally (transverse cervical and greater auricular nerves) and the facial nerve and mandibular branch of the trigeminal nerve.


Blood supply to the labyrinth is provided by the vertebral artery via its basilar branches and blood supply to the rest of the ear is from the external carotid artery and its branches (caudal, intermediate, lateral, medial, and deep auricular arteries) and the superficial temporal artery via the rostral auricular artery. Blood is drained by satellite veins.


The skin of the ear canal contains sebaceous glands, which produce an oily substance, and ceruminous glands (modified apocrine glands), which secrete a milky white fluid that turns brown on exposure to air. The combined product of these glands is cerumen. Cerumen, along with trapped debris, is carried away from the tympanic membrane by migration of the epithelial cells lining the canal. The functions of cerumen are: to protect the ear canals and tympanic membrane by entrapping microorganisms and their products and mechanically removing them; to keep the ear canals moist, allowing normal desquamation of the epithelium; to contribute to the barrier function of the epidermis; and to have an antibacterial action mediated via sebaceous gland-derived fatty acids.



Middle ear


The tympanic membrane is part of the mechanism of hearing. Vibrations detected by the tympanic membrane are transmitted via the ossicles (malleus, incus, and stapes) to the vestibular (oval) window. The tympanic membrane slants downward and inward obliquely, so that it forms an angle of 30–45° with the floor of the horizontal canal. This may be a mechanism to allow a larger tympanic membrane to fit in a given size of ear canal, thus decreasing the acoustic pressure in the ear canal needed to produce perceptible vibrations in the cochlea. However, this anatomic arrangement means that debris tends to accumulate at the junction of the ventral horizontal ear canal and the tympanic membrane.


The tympanic membrane is a concave, semi-transparent epithelial structure. The umbo is the most depressed part and is formed where the tip of the manubrium of the malleus pulls the tympanic membrane medially. The tympanic membrane is divided into two parts. The pars flaccida is the smaller, dorsal opaque portion that is pink, loosely attached, and contains small blood vessels. The pars tensa is the large gray, semi-transparent ventral portion. In cats, it may be difficult to appreciate the pars flaccida as it is much smaller. Epithelial migration begins with the germinal epithelium at the umbo, and therefore this area should not be damaged during myringotomy.


The tympanic membrane has four layers. The outermost layer is a continuation of the lining of the external ear canal. Medial to this is the fibrous stratum that consists of two layers of collagen fibers. The inner layer is composed of modified respiratory epithelium, which lacks goblet cells and cilia normally found in respiratory epithelium. The tympanic membrane is thin in the center and thicker at the periphery, where the fibrous layers thicken to form the tympanic annulus. If the tympanic membrane is perforated, it will heal by proliferation of the fibrous layer, which results in a thickened, opaque membrane in contrast to the normal translucent structure.


The normal barrier function of the tympanic membrane is impaired with acute inflammation and this may lead to transtympanic migration of bacteria with resulting otitis media, and absorption of topical medication with resulting ototoxicity. With chronic inflammation, the tympanic membrane becomes thickened and this is less of a concern.


The middle ear is an air-filled cavity lined by a pseudostratified ciliated columnar epithelium containing goblet cells, which is continuous with the pharynx via the Eustachian tube. It is separated from the external ear canal by the tympanic membrane. There are mucus-producing glands in the tympanic cavity, but not in the external ear canal and thus if mucus is present in the horizontal ear canal, it must have originated in the tympanic cavity, which indicates a defect in the tympanic membrane. The tympanic cavity is not sterile and bacteria found in the tympanic cavity are similar to those found in the nasopharynx and not the external ear canal.


The middle ear cavity contains three parts: the dorsal epitympanic recess (or attic), the tympanic cavity proper, and the tympanic bulla (Fig. 50-2).



The epitympanic recess is located dorsally and is the smallest chamber. It contains two of the three ossicles, the malleus and incus, and the facial nerve canal. The ossicles have synovial articulations with each other, with fibrous ligaments for support.


The tympanic cavity proper (mesotympanum) is adjacent to the tympanic membrane and contains the stapes and part of the malleus. The stapes is attached to the vestibular (oval) window, which communicates directly with the inner ear. The manubrium of the malleus attaches to the fibrous layer of the pars tensa, and may be seen through the normal tympanic membrane as the stria mallearis. The manubrium of the malleus is much straighter in the cat compared to the C-shape in the dog.


The tympanic bulla (hypotympanum) is the largest of the three compartments of the tympanic cavity, and is located in the ventromedial part of the tympanic cavity. In cats, a bony shelf separates the tympanic cavity proper from the tympanic bulla almost completely, with a small defect in the shelf located just lateral and caudal to the round window in the medial caudal part of the tympanic cavity proper. This makes access to the tympanic bulla from the tympanic cavity proper via a myringotomy difficult.


The bony eminence (promontory) is on the medial wall of the tympanic cavity proper, directly opposite the mid-dorsal region of the tympanic membrane. It may occasionally be visible through the tympanic membrane. The oval (vestibular) window is dorsal to the cochlear promontory and is covered by the stapes. Medial to the promontory is the round (cochlea) window of the inner ear. The cervical sympathetic nerves run through the tympanic cavity proper, coursing submucosally across the promontory, and thus they are susceptible to damage when performing a myringotomy or middle ear lavage.


The medial wall of the tympanic cavity proper also contains the Eustachian tube opening rostrally. The Eustachian tube is lined by ciliated pseudostratified columnar epithelium that includes goblet cells. The Eustachian tube is normally collapsed, but will inflate when the pressure in the tympanic cavity and medial aspect of the tympanic membrane is equalized with the pressure on the lateral surface of the tympanic membrane. The tensor veli palatini muscle supports the lateral wall of the auditory tube and contraction of this muscle and the levator veli palatini keeps the pharyngeal opening of the Eustachian tube open.



Inner ear


The inner ear is composed of the cochlea, vestibule, and semicircular canals which are housed in a membranous labyrinth, surrounded by a bony labyrinth in the petrous temporal bone, located deep to the tympanic bulla dorsomedially.


Vibrations from the tympanic membrane are transmitted from the malleus to the incus and then stapes. The stapes then transmits this vibration to the inner ear via the vestibular (oval) window and movement of the fluid in the inner ear (perilymph) converts mechanical energy (vibrations) to electrochemical energy (nerve impulses), which is then transmitted to the auditory cortex in the temporal lobe of the cerebral cortex. The cochlear (round) window is located at the caudal end of the promontory. It is covered by a mucous membrane and communicates with the inner ear. The round window functions as a pressure relief valve, bulging into the tympanic cavity as the pressure rises in the inner ear.


The vestibular system mediates the control of posture and movements of the body and eyes relative to the external environment. Sensory information from vestibular, somatosensory, and visual receptors and motor information from the cerebellum and cerebral cortex are integrated and processed centrally allowing appropriate co-ordination of the relevant muscle movements. The vestibular system is divided into a peripheral component located in the inner ear and a central component, located in the central nervous system (CNS). Three major CNS areas receive projections from the peripheral sensory receptors of the vestibular system: the cerebral cortex, the spinal cord, and the cerebellum.



General considerations



History


A detailed and logical history is of paramount importance and, in common with other problems that are considered more purely ‘dermatological’, will guide the selection of additional diagnostic tests and may go a long way to providing a diagnosis.


Important findings to determine include details of the onset, duration, and progression of the clinical signs and a consideration of whether the disease is unilateral or bilateral. Unilateral disease is more consistent with foreign bodies, ear tumors, and polyps, whereas generalized dermatopathies are more likely to be bilateral. Seasonal disease suggests allergic reactions, which is an important cause of ear disease in cats. The age of the patient may also guide the diagnosis, as young animals are more likely to have mites, young adult animals are more prone to allergies, and older animals more prone to tumors and immune-mediated disease. The owner’s approach to parasite control should be ascertained as fleas and mites commonly affect the head and neck.


Other health matters are also important. Recently rescued cats may have unknown underlying medical disorders, free-roaming cats are at increased risk of contagious diseases, and viral status may be important as chronic otitis media is often linked to chronic upper respiratory tract virus infection and retrovirus infection.


The owner’s normal treatment regime, response to prior treatment, and compliance with treatment should be determined.


The owner may report head shaking, ear twitching, fits of ear scratching, particularly after manipulation of the ear, change in eating habits, change in behavior, and vocalization. Clinical signs may be unilateral or bilateral, persistent or intermittent, and acute or chronic. Pain when eating may indicate otitis media that has extended to involve the tissues around the tympanic cavity and temporomandibular joint. A history of upper respiratory tract disease, e.g., sneezing, ocular discharge, and nasal discharge may be present in cats with ascending otitis media.



Clinical signs


Clinical signs of external ear canal disease include otorrhea, head shaking, and scratching at the ear. External ear canal or middle ear disease may cause pain on opening the mouth and facial nerve paralysis.


Clinical signs of middle ear disease include shaking the head and pawing at the ear. An intermittent and temporary tilt of the head, caused by irritation, pain, and discomfort rather than neurologic dysfunction, may be seen.


Involvement of the facial nerve will result in paralysis of the lip or ear, widened palpebral fissure, reduced palpebral reflexes, and drooling. Involvement of the cervical sympathetic trunk will result in Horner syndrome (miosis, ptosis, enophthalmos, and protrusion of the nictitans gland) and involvement of the parasympathetic fibers in the facial nerve may result in keratoconjunctivitis sicca. An ophthalmologic examination may show signs of CNS disease in cats with central vestibular syndrome.


Clinical signs of vestibular disease include a head tilt towards the affected side or wide excursions of the head if the disease is bilateral, asymmetric ataxia, typically with leaning, stumbling, falling or rolling to the affected side, or symmetric ataxia if both sides are equally affected, and spontaneous horizontal or rotatory nystagmus, with the fast phase away from the affected side. Nausea and vomiting may be seen due to vestibular input to the vomiting center in the brainstem. Peripheral vestibular disease should be differentiated from central vestibular disease (Table 50-1). Rarely, extension of inner ear disease into the CNS may cause brainstem dysfunction. Neurologic signs indicating middle ear involvement may be seen in 25% of cats with external ear canal tumors.



Involvement of the inner ear may cause deafness (sensorineural deafness), as may obstruction of the external ear canal, rupture of the tympanic membrane, disruption of the ossicles, and middle ear disease (conductive deafness). Conductive deafness is usually not complete and there may be differences between the ears in a hearing impaired animal.


Involvement of the nasopharynx is uncommon, but signs such as gagging, upper respiratory tract dyspnea, and stertor may be seen, with thick discharge draining from the Eustachian tube or the presence of a nasopharyngeal polyp.


Marked pain on palpation of the base of the ear canal and on traction of the pinna may be seen in animals with otitis media.



Diagnostic procedures


Examination of the patient, using various means, is indicated to answer the questions listed in Box 50-1.




Physical examination


Examination of the ear should be performed in any cat with skin disease and conversely, a dermatologic examination should be performed in any cat with ear disease, as most dermatopathies will also affect the ear. A general examination of the patient is needed to determine if the ear disease is the only abnormality, or if there are concurrent medical or dermatologic problems. Otitis may occur as a paraneoplastic syndrome, e.g., in cats with mast cell disease.


Examination of the pinna for primary lesions, such as macules, papules, plaques, pustules, and alopecia, as well as secondary lesions such as scale and crusts should be performed to help identify the nature of the pinnal disease.


The external ear canals are palpated for thickening, calcification, exudate, and pain or discomfort. The external auditory meatus is examined for the presence of exudate, masses, and foreign material. Pain on palpation of the ear canal and fluid within the canal increase the suspicion of otitis media associated with chronic otitis externa.


The oropharynx should be examined because of the close association of pharyngeal disease and middle ear disease, particularly from nasopharyngeal polyps and palatine defects. Pain on palpation of the tympanic bulla or on opening the mouth may be seen with middle ear disease.


A neurologic examination should be performed to examine for the presence of abnormalities that might indicate middle ear or inner ear disease, such as vestibular signs (ataxia, nystagmus, head tilt, and circling or falling to the affected side), facial paresis, Horner syndrome, and keratoconjunctivitis sicca. An ophthalmologic examination may reveal evidence of inflammatory CNS disease.



Otoscopy


Otoscopy should be performed on every animal with otitis externa. Many cats may require sedation or anesthesia for a complete examination. If a ruptured tympanic membrane is suspected, ideally the examination should be performed under general anesthesia so that a cuffed endotracheal tube may be placed to prevent aspiration of fluid and discharge from the Eustachian tube into the pharynx.


Both ears should be examined, even in animals with unilateral signs, as bilateral disease of different severities may be present. The less affected ear should be examined first and a new otoscope cone should be used for each ear. If a large amount of discharge is present, the ears may need to be flushed before examination can be conducted. In animals with marked erythema, proliferation, stenosis or ulceration, administration of topical or systemic corticosteroids for seven–14 days may be needed to decrease the inflammation and pain and open up the external ear canals so that a full examination may be performed. The use of a video-otoscope (Fig. 50-3A), rather than a hand-held otoscope (Fig. 50-3B) has a number of advantages to consider (Box 50-2).




To examine the ear, the tip of the otoscope cone should be introduced into the ear canal pointing ventrally, with concurrent upward and outward traction on the pinna. There is a ridge of cartilage on the dorsal surface of the ear canal where the vertical canal meets the horizontal canal, and the otoscope must be passed below this ridge, while pulling on the pinna.


The lining of the normal ear canal is pink and glistening with few hairs and the dermal blood vessels should be apparent. One of the first signs of inflammation in the ear canal is inability to see these vessels as a result of thickening of the epidermis or dermal edema. In the presence of inflammation, the epidermis becomes reddened. Excessive waxy secretions and ceruminous gland hyperplasia may be seen which creates a cobblestone appearance to the lining, which may progress to polyp formation. Defective epithelial migration, as a result of damage to the tympanic membrane or inflammation of the ear canal, leads to the accumulation of cerumen, which may therefore indicate previous or current ear canal disease. Recurrence of cerumen after removal indicates continued external ear canal disease. Cerumen in cats tends to be moist and is seldom dry and flaky as it can be in dogs.


The presence, location, and degree of inflammation, stenosis, ulceration, and proliferative changes should be noted. The size of the vertical and horizontal canals and the type, location, and quantity of debris or exudate should also be noted. The consistency, color and amount of any exudate should be determined. Samples should be collected for cytology and culture and sensitivity testing.


Ulceration of the ear canal is often associated with a Gram negative infection, e.g., Pseudomonas, but may also be caused by inappropriate cleaning with cotton-tipped applicators. Foreign bodies such as plant awns, impacted wax, and concreted otic preparations may be present. Plant awns should be removed with forceps and impacted wax and otic preparation should be softened with ceruminolytic agents and removed by flushing or with endoscopic forceps. Masses in the external ear canal should be biopsied with forceps.


The tympanic membrane is assessed for presence, integrity, color, and texture. If the tympanic membrane cannot be assessed due to debris in the external ear canal, this should be cleaned thoroughly to allow inspection of the tympanic membrane. If the tympanic membrane cannot be assessed due to stenosis of the canal, then a number of tests may be used to assess its presence and integrity. A small diameter (3.5 or 5 French) red rubber catheter may be inserted into the ear canal until it stops and then gently removed and advanced to get a feel for the rigidity of the ‘stop’. The ‘stop’ will be ‘spongy’ if the ear drum is intact and more rigid if it is not intact, and the catheter is therefore contacting the medial wall of the tympanic bulla.


Alternatively, positive contrast ear canalography (see below) or tympanometry may be used. A warmed, colored solution (e.g., fluorescein or povidone-iodine) may be infused via the ear canal in the conscious patient; the appearance of this fluid at the external nares or the patient snorting it through the oropharynx indicates that the tympanic membrane is not intact and the fluid has passed via the Eustachian tube into the pharynx. However, this carries the risk of introducing potentially ototoxic substances into the middle ear. A simpler method in the anesthetized patient is to lavage the external ear canal with warm saline and, if bubbles of air rise through the fluid when the animal breathes, then the tympanic membrane is not intact.


Otitis media may be present when the tympanum is discolored gray or brown. An intact tympanum does not rule out otitis media, although with otitis media the tympanic membrane does not usually have a normal opacity and color, and a ruptured tympanic membrane is not an absolute indicator of otitis media in the absence of other abnormal findings. Bulging of the membrane towards the observer may indicate fluid accumulation in the middle ear and retraction of the tympanic membrane suggests a partially filled middle ear with obstruction of the Eustachian tube.


It is not possible to differentiate a thickened tympanic membrane caused by chronic inflammation from a thickened tympanic membrane caused by previous or current otitis media without advanced imaging, a myringotomy, or surgical exploration via bulla osteotomy. Animals with otitis media and an open ear drum often have a copious malodorous liquid discharge on otoscopy, with magnetic discharge along the floor of the horizontal canal.



Clinical pathology


Both cytology and culture have a role to play in the diagnosis of ear disease and these tests are complementary to each other. Many infections are polymicrobial with mixed infections of bacteria (cocci and rods) and yeast. Cytology may reveal Malassezia, which would not be reported if only bacterial culture was performed. Conversely, culture may show bacteria that were not identified on cytology as mucus may protect them from cytology stains. Bacteria may be obtained from many samples, but the presence of a host inflammatory response on cytology suggests that organisms cultured are pathogens rather than contaminants.



Cytology


Cytologic examination of otic exudate is a simple, practical, and cheap diagnostic test that provides rapid results to help identify the primary cause and perpetuating factors in animals with ear disease. Cytologic examination of exudate should be repeated while treating the disease and it should not be assumed that the changes present at previous examinations are representative of the current status of the ear canal.


The main use of cytology is to identify and characterize microbial overgrowth or infection, which then guides therapeutic decisions and allows response to therapy to be monitored. Bacterial overgrowth is uncommon in cats compared to dogs and therefore culture is indicated when bacteria are seen. Cytology may identify the primary cause of otitis in some cases, although this is less important than other dermatologic testing.


Samples should be taken from both ears and should be taken before use of any cleaning agent or therapy. A cytology sample may be obtained by using a cotton-tipped applicator inserted gently into the external ear canal. Samples obtained from the deeper horizontal canal are more clinically relevant than samples obtained from the vertical canal, although this is best performed with the animal under anesthesia. In cats with otitis media, samples obtained from the tympanic cavity are more representative. The swab is then rolled onto a clean glass microscope slide, evenly distributing a thin layer of material. Cerumen has a high lipid content and briefly heating the slide will fix the material to the slide and avoid loss of the sample in the stain solvent. A simple, rapid in-house stain using a modified Wright’s stain (e.g. DiffQuick) is adequate. A Gram stain is more time consuming and may not be necessary as most cocci found in the ear are Gram positive and most rods are Gram negative. If parasites are suspected, mounting the otic exudate in a few drops of mineral oil on a slide followed by a coverslip is suitable and this should be performed in all cats with otitis externa. Examination for Demodex should similarly be performed in adult cats with pruritic otitis externa as this condition is uncommon but certainly underdiagnosed.1


It is tempting to make conclusions about the etiology of the ear disease (e.g., parasites, bacteria or yeast) based on the color, texture, and smell of the discharge, but these observations are not reliable and the diagnosis should rest on more objective tests.


The normal cerumen is waxy and yellow and, due to the high lipid content, does not take up stain and therefore a cytology slide from a normal ear should be almost colorless. Normal cornified squamous epithelial cells and desquamated keratinocytes may be seen. Small numbers of resident bacteria may be identified in 71% of cats,2 usually Gram positive cocci: coagulase negative Staphylococcus spp., coagulase positive Staphylococcus spp., and Streptococcus spp. Rods are rarely found in the normal ear canal, with the exception of Corynebacterium.2,3 Bacteria found in the presence of leukocytes should be considered an abnormal finding. Malassezia is a normal resident of the feline ear canal, being found in 23% to 83% of normal cats,2,4 but it is also an opportunistic pathogen and is found in 64% of cats with otitis externa.5 Abnormal findings include increased numbers of Malassezia organisms (greater than 12 organisms per high dry [×40 objective] field).6 Less than two organisms is considered normal and two to 11 is considered a gray zone. This cut off has a specificity of 100% and sensitivity of 63% for Malassezia infection in cats.


Bacteria identified on cytology may be normal flora, bacterial overgrowth in the debris and on the epithelial surface, or true infection. Semiquantitative cytologic criteria may help to identify the clinical importance of bacteria. Four or fewer bacteria per high dry field may be considered normal, five to 14 is of unknown importance, and 15 or more is abnormal.6 This cut off has 100% specificity and 63% sensitivity in cats. The presence of a large number of leukocytes, which are not usually found in normal cerumen, particularly if they contain phagocytosed bacteria, also provides evidence in support of true infection, although leukocytes may be seen in other forms of ear disease, e.g., immune-mediated dermatopathies.


Cytology may also identify parasites such as Otodectes cynotis, which is responsible for up to 50% of all cases of otitis externa in cats, as well as other mites such as Demodex, Notoedres cati, and Neotrombicula autumnalis.


Cytology may also be used in the evaluation of masses involving the external ear canal.7 In one study of 27 masses from 25 cats, fine needle aspirate cytology showed a good level of agreement with the final histologic diagnosis and was able to differentiate all inflammatory polyps from other tumors. However, cytology was less useful in differentiating between benign and malignant neoplasia, being correct in 22 out of 27 masses (81.5%).7



Culture


Culture is needed to identify the species of bacteria and the antimicrobial sensitivity of the isolates. However, culture should be used in conjunction with cytology to avoid making therapeutic decisions based on isolation of bacteria of no clinical relevance. Culture and sensitivity testing may not be a cost-effective and relevant test, because clinical response to topical therapy may not correlate with in vitro sensitivity as topical agents reach very high concentrations in the ear canal.


In cats with otitis media, the most common bacterial pathogen is Staphylococcus intermedius, although other organisms including streptococci spp, Pseudomonas, Proteus, Bordetella, Bacteroides, Fusobacterium, and Mycoplasma have been reported.8 Bacterial resistance is not usually a problem in feline otitis media compared with the situation in dogs. Bacteria of the same species isolated from the middle ear and the horizontal ear canal may display different antibiotic sensitivity patterns in up to 80% of cases.9


Dermatophyte culture is recommended in cats with otitis externa, particularly if they are young, free-roaming or have been recently acquired from a rescue shelter.





Diagnostic imaging


Diagnostic imaging is often useful in the diagnosis of ear disease, mainly to investigate those parts of the ear that cannot be visualized directly on examination. Diagnostic imaging of the thorax and (other potential sites of metastasis) should be performed if neoplasia is suspected. Diagnostic imaging should be performed before otoscopy and certainly before administration of any medication or lavage fluid into the ear canal as these may mimic findings of otitis externa or media and lead to a false positive diagnosis.


The selection of the most appropriate diagnostic imaging technique depends on the particular question being asked and the differential diagnoses being considered.10 For instance, in an animal with otitis externa with suspected otitis media, radiography or CT is appropriate, with CT having a role to play even if radiographs do not reveal any abnormality. In a cat with a suspected nasopharyngeal polyp, a CT has greater sensitivity for detection of a mass in the middle ear and nasopharynx, although these areas can still be imaged with radiographs. An MRI scan has the greatest sensitivity, particularly for acute otitis media, but assessment of the bony structures of the middle ear is difficult with MRI. In a cat with signs of vestibular disease, an MRI provides the most useful information for evaluation of inner ear structures, but a CT may be useful to assess the middle ear if otitis interna arose from otitis media.



Radiography


Radiography is the mainstay of diagnostic imaging for the ear in most private practices. It is cheap and relatively easy to perform and produces a global view of the region being examined. However, great care must be taken to use good technique and positioning to get radiographic images of diagnostic quality. This usually means general anesthesia for positioning. The greatest disadvantage is superimposition of overlying structures, which is a particular problem when imaging the head.


Projections include lateral, dorsoventral or ventrodorsal, latero 20° ventral-laterodorsal oblique, rostro 10° ventral-caudodorsal closed-mouth oblique11 and rostro 30° ventral–caudodorsal open-mouth oblique.12 The ventrodorsal view is better for evaluating a patient with otitis externa, although positioning is easier for the dorsoventral view. Of the two rostroventral-caudodorsal oblique projections, the 10° closed-mouth oblique is more accurate and easier to perform, although there is no difference in the accuracy of these views for the detection of fluid in the middle ear.13


Radiographs are useful for evaluating the osseous tympanic cavity and evaluating the external ear canals for chronic changes, such as stenosis and mineralization. In otitis externa, radiographic findings include stenosis or mineralization of the wall of the ear canal and soft tissue opacity within the canal, representing a mass or debris.


The tympanic bulla is a thin-walled gas-filled structure with well-defined, smooth borders. Sclerosis of the wall of the tympanic bulla may be seen in older animals or following resolution of middle ear disease. The external acoustic meatus is rounded with distinct smooth margins.


In otitis media, soft tissue opacity in the tympanic cavity (representing fluid or a soft tissue mass), sclerosis of the wall of the bulla or petrous temporal bone, bony proliferation of the bulla or petrous temporal bone, lysis of the bony wall of the tympanic bulla, and signs of concurrent otitis externa may be seen. Lysis of the adjacent calvarium may be seen with aggressive tumors. Radiographs are remarkably insensitive for the diagnosis of middle ear disease in the absence of osseous changes.


Contrast radiography may be of use on occasion. Positive contrast canalography, after instillation of a water contrast iodinated solution into the external ear canal, may be used to assess the integrity of the tympanic membrane and to assess the integrity of the external ear canal, e.g., in patients with suspected ear canal avulsion or stenosis, and the success of any repair.14–16 Water soluble iodine-containing contrast medium (1–2 mL) is instilled into the ear canal with the patient either in lateral recumbency, or, preferably in ventral recumbency so that a dorsoventral projection may be used to compare both external ear canals at the same time. In normal canine ears, positive contrast canalography was more sensitive than otoscopy in identifying iatrogenic tympanic membrane perforation.16 Positive contrast sinography may also be used in patients with chronic draining tracts after total ear canal ablation or accidental trauma to the ear canal (See Fig. 50-9B).


Inner ear disease rarely produces signs visible radiographically.



Ultrasound


Ultrasonography is not commonly used, but has several potential advantages, as it is relatively quick, non-invasive and may be used in conscious patients.17 In a normal animal, air in the external ear canal and middle ear prevents transmission of ultrasound waves, but if the external ear canal is filled with fluid, e.g., saline, or if the middle ear contains soft tissue or fluid as a result of disease, then these structures may be examined. In one study ultrasonography was more accurate than radiography in the detection of fluid in the middle ear in feline cadavers, although both modalities were inferior to CT.18



Computed tomography


CT is more sensitive than radiography for examination of the ear, particularly the middle ear, and for assessment of other structures such as the draining lymph nodes. CT can also differentiate between soft tissue and fluid within the middle ear and intravenous contrast will allow the vascularity of a lesion to be identified. The principles of interpretation and diagnostic imaging findings with the various disease processes are similar to radiography, but findings are more readily identified on transverse CT images as there is no superimposition of structures compared to radiographs. CT may therefore be of use for detection of soft tissue changes, delineation of tumors and detection of subtle bony lysis and proliferation.


Caution should be exercised when evaluating the thickness of the tympanic bulla wall in animals with fluid in the middle ear, as the thickness of the wall of a fluid-filled bulla appears greater than that of an air-filled bulla, due to a volume averaging artifact.19


CT evaluation of the peripheral vestibular system is useful if radiographs have not provided a diagnosis, if a mass lesion such as a polyp or tumor is considered likely, or if the patient is a potential surgical candidate. However, CT is less useful for the evaluation of the central vestibular system.


CT has been found to be a more sensitive but less specific modality for the diagnosis of middle ear disease, although neither modality was able to detect early lesions associated with otitis media/interna when there was no osseous involvement.20 Another study showed that CT and radiographs have a similar sensitivity for detection of otitis media.21 Sensitivity is increased if a smaller slice thickness is chosen.10 Otitis interna is difficult to diagnose with CT except where there is marked destruction of the inner ear.



Magnetic resonance imaging


MRI produces images with better soft tissue contrast than radiography or CT and is indicated if peripheral or CNS disorders are suspected, such as tumors, inflammatory lesions, or abscesses associated with ear disease.22 However, osseous lesions of the middle ear are difficult to assess with MRI and MRI requires general anesthesia. MRI is superior to radiography in the detection of middle ear disease in cats.23


MRI provides superior soft tissue resolution that aids the diagnosis of neoplastic and inflammatory diseases of the central vestibular system.


MRI findings of middle ear disease include medium signal intensity material in the tympanic bulla (TB) on T1W (isointense to brain tissue) and hyperintense on T2W and enhancement of inner margin of TB post-contrast. Soft tissue will enhance with gadolinium whereas fluid will not.


MRI findings of otitis interna are lack of signal intensity of the labyrinthine fluid on T2W sequences24 and meningeal enhancement on post-contrast T1W sequences.25




Additional tests






Surgical diseases of the pinna



Trauma


Wounds to the pinna are relatively common after cat fights, but they have also been reported in cats with frostbite. These wounds are classified according to the depth of the wound. The wounds may involve: skin on one side of the pinna; skin on one side of the pinna and cartilage; and full thickness defects involving skin on both sides of the pinna and cartilage.


Small linear lacerations involving one skin surface only may be left to heal by second intention after appropriate local wound management as the cartilage will splint the wound and prevent deformity of the pinna. Larger lacerations that result in two-sided or three-sided flaps should be closed primarily if possible, as second intention healing may result in malalignment or pinnal deformity as a result of wound contraction.


Wounds that involve the cartilage take longer to heal by second intention as the cartilage support is lost and healing is delayed until there is fibrous union of the cartilage. This may result in pinnal deformity. Surgical closure provides a more rapid and cosmetic result. Sutures should be placed to appose the edges of the cartilage and the skin edges, either with separate sutures in each tissue plane, or with vertical mattress sutures with deep bites in the cartilage and superficial bites in the skin.


Wounds that involve both skin surfaces and the cartilage will have a better cosmetic outcome if sutured, although these wounds may be left to heal by second intention (Fig. 50-4). Lacerations on the ear margin may widen with time as a result of contracture if allowed to heal by second intention, but if closed, wounds in this location may result in ‘cupping’ or folding of the ear margin as a result of contraction. Small wounds on the margin of the pinna may be treated with partial amputation of the pinna (subtotal pinnectomy) to avoid these cosmetic changes.



Traumatic wounds resulting in large wounds with substantial loss of tissue may be reconstructed with a distant direct flap from the adjacent skin, although the erect nature of the feline pinna makes apposition of the pinna to the skin more challenging than the same technique in a dog with a pendulous pinna.



Aural hematoma


Aural hematoma (Fig. 50-5) is a common disorder of the pinna, resulting either from trauma, which may be self-trauma due to head shaking or scratching, or external trauma, e.g., from a cat-fight wound, or from immune-mediated disease.29 In cats, otitis externa associated with ear mites is often noted and is usually unilateral. Hemorrhage results in sanguinous fluid accumulating between the cartilage and skin on the concave inner surface of the pinna, although analysis of this fluid suggests an exudate rather than frank blood.29 Further head shaking or self-trauma results in continuing bleeding and formation of a hematoma. Left untreated, the hematoma matures, leaving a sanguinous seroma, and then granulation tissue forms on the wall of the cavity. Contraction and fibrosis then result in pinnal deformity (‘cauliflower ear’) and thickening.



Therapeutic options for aural hematoma comprise: identification and, if possible, treatment of the underlying cause; prevention of further self-trauma, by using an Elizabethan collar and specific therapy for any underlying cause; drainage of the hematoma cavity; and apposition of the skin and cartilage to allow healing to progress without significant deformity.


Drainage of the hematoma may be achieved in several ways. Needle aspiration of the hematoma is the simplest method, but may not be effective if the hematoma is chronic and may need to be repeated if the hematoma recurs before the cavity has been obliterated. Corticosteroids may be used to reduce local inflammation, reduce head shaking and self-trauma, and suppress an autoimmune reaction if one is present.29,30 Although these are probably best given systemically, as administration into the hematoma cavity has the potential to maintain the separation between the cartilage and skin and prolong healing.


There are a variety of surgical options reported for aural hematoma management31–36 (see Box 50-13).



Pinnal neoplasia


Tumors arising from the ear are uncommon in cats, and usually affect the pinna and external ear canal. Benign tumors are less common than malignant tumors, although the most frequent proliferative lesion is the inflammatory polyp. Benign tumors are less likely to be ulcerated, tend to have a narrow base of attachment, are more likely to be lobulated and typically do not invade the ear cartilage.37


Clinical signs depend on the location and size of the tumor, degree of ulceration and local invasion, and the presence or absence of distant metastases. As with all tumors and suspected tumors, cytologic or histologic diagnosis of the primary tumor and assessment of regional lymph node involvement and depending on tumor type, distant metastasis, is indicated.


Many tumors of the pinna are actinically induced and therefore reducing exposure to UV light by keeping the cat indoors, by UV shields on windows and by applying infant-safe sunscreen to the pinnae and nose may prevent tumor formation.



Squamous cell carcinoma (SCC)


SCC is the most common tumor of the feline pinna (Fig. 50-6). SCC usually affects light-colored cats exposed to UVB.38 These tumors are often actinically induced as a result of DNA damage following exposure to solar radiation. Tumors are more frequent in regions with the highest solar radiation. In such regions, the incidence of cutaneous SCC has been reported to be 27 cases per 100 000 cats.39 Thin-haired and light-colored cats are at risk, with white cats being 13 times more likely to develop this tumor.39 Lesions are most common where the hair is thin and exposure to the sun is greatest, i.e., pinna, especially the concave aspect and base, eyelids and nasal planum. SCCs are discussed further in Chapter 20.


Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Ear
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