Diseases of the External Ear Canal, Middle and Inner Ear; Management and Surgery
Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine
Utrecht, The Netherlands
Clinical Signs of Ear Diseases
Clinical signs associated with outer ear diseases are head shaking, scratching, otic pain (otalgia) and otic discharge (otorrhea). In some cases, aural hematomas (othaematoma) can be seen. Clinical signs associated with middle ear disease are often subclinical or very subtle, especially in cats or reflects concurrent otitis externa, especially in dogs. Otalgia (otic pain), lethargy, inappetence and pain on opening of the mouth are more suggestive of middle ear involvement. Neurologic signs like facial nerve paresis or paralysis or Horner's syndrome may be present. Peripheral vestibular ataxia (head tilt, horizontal or rotary nystagmus, circling or falling toward the side of the lesion) is usually the most obvious sign of inner ear disease. Hearing loss usually goes unnoticed until complete deafness is recognized.
Clinical Examination of the Ears
When confronted with animals with clinical signs of ear disease, clinical examination should include a general physical, dermatologic, neurologic (cranial nerves) and otoscopic examination. For complete visualization of the tympanic membrane and prior to therapy, ear flushing is necessary. In some cases material should be obtained from the horizontal part of the ear canal for cytologic examination, culture and susceptibility testing. After flushing, masses can easily be identified and samples can be taken for histopathology. Increased opacity and hyperemia of the tympanic membrane may be present with otitis media. A paracentesis can be performed in dogs with an intact tympanic membrane to obtain samples for culture and susceptibility testing and cytologic examination. Radiographs of the bullae may be useful although not very sensitive; ventrodorsal, lateral oblique and open-mouth views are most helpful. Advanced imaging with CT and MRI is necessary in most cases for proper evaluation of the middle ear (and inner ear to some extent) however. When objective information on hearing capacity is needed, brainstem-evoked response audiometry can be performed.
Otitis externa is common in dogs and cats and has numerous causes, usually classified as primary, predisposing or perpetuating factors. Primary factors directly cause otitis externa and include parasites, foreign bodies, inflammatory polyps, tumors, hypersensitivities, endocrine abnormalities and keratinization disorders. Predisposing causes of otitis externa make the ear canal more susceptible to inflammation and secondary infection, while perpetuating factors exacerbate and maintain the disease even after the primary factors are eliminated and include secondary bacterial and/or yeast infection and otitis media.
In chronic cases, elimination of underlying factors however, usually doesn't end the inflammatory process. Management should then be aimed at thoroughly cleaning and drying the ear canal and administering appropriate topical therapy for a longer period of time, sometimes even a life-long treatment is necessary. Ointments with broad-spectrum antibiotics and corticosteroids should be used with careful attention to complete filling of the entire ear canal and tapering off the frequency of treatment based on clinical effect and control otoscopy. Total ear canal ablation is reserved for unresponsive or proliferative chronic otitis externa.
Otodectes cynotis is the most common parasite affecting the ear canal of especially young dogs, cats and ferrets. This highly infectious disease is transmitted by direct contact. Pruritis can be significant; accumulation of dark brown to black cerumen is usually noted. The diagnosis is made by observation of the mites on otoscopy or on microscopic identification (mineral oil cytology). Various commercially prepared topical medications are available for the treatment of otocariasis of which selamectin has recently been proven save and effective. Considering the lifecycle of the parasite, treatment should be repeated after 3 weeks.
Acute inflammation, scratching at the ear and head shaking are usually noted in acute cases of foreign body associated otitis externa. Common causes are grass awns, foxtails, dirt, sand or toys. In chronic cases, suppurative inflammation is seen and even otitis media as a result of migration can occur. The diagnosis can be made on otoscopy after flushing the ear canal. With special forceps the foreign body usually can be removed with aid of otoscopy. Severe edema of the epithelial lining of the ear canal can prevent visualization of foreign bodies. Treatment with ointments with antibiotics and corticosteroids can be necessary to reduce the edema before a foreign body can be detected and removed or after removal to treat secondary infection and inflammation.
Polyps in cats, originating from the mucosal lining of the middle ear, auditory tube and nasopharynx, have been associated with rhinitis and otitis resulting from various bacterial and viral agents. A congenital origin has been suggested as well. Polyps in the external or middle ear mimic signs of otitis externa, otitis media or otitis interna. Otoscopy after flushing may reveal a visible pink or gray smooth, spheric mass occluding the canal. Cytologic or histologic examination of biopsies will reveal the nature of the tissue when diagnosis is not straightforward. Recurrence is uncommon with simple traction-avulsion after an incision in the vertical ear canal. Ventral bulla osteotomy is reserved for patients with recurrence of polyps after this procedure.
Removal of Middle Ear Polyp by Traction-Avulsion
After aseptic preparation of the surgical site, an incision is made in the skin in a dorsoventral direction over the palpable vertical part of the ear canal. The subcutaneous tissue and parotid gland are dissected with small scissors to free the cartilage of the vertical ear canal to the level of the junction between the auricular and annular cartilages. A vertical stab incision is made in the auricular cartilage and stay sutures are placed on both sides of the incision in the ear canal to increase visualisation and avoiding damage to the cartilage. A small closed haemostatic forceps is then introduced into the ear canal and advanced deeper over the polyp until it can be grasped as close as possible to the osseous meatus. When a firm grip has been achieved, the forceps is gently rotated and traction is applied until the polyp is removed. The middle ear cavity is flushed with warm saline and with a small curette the osseous meatus and most lateral aspect of the tympanic cavity is "palpated" to check for additional inflammatory tissue which is removed with this curette when encountered. The stay sutures are removed and the cartilage of the ear canal is closed with 4-0 monofilament suture material in an interrupted pattern. The subcutis is closed in a continuous pattern with 4-0 absorbable monofilament material and the skin is closed in a subdermal suture pattern using the same material.
Ear tumors occur in older cats and dogs. The most frequently observed clinical signs are those of a mass, otic discharge, odor, pruritis, and local pain. Neurologic signs are uncommon. Approximately 25% of malignant forms will have evidence of bulla involvement, and skull radiographs and/or computed tomography are recommended as part of the diagnostic work-up. Benign tumors like papillomas and basal cell tumors can sometimes be removed otoscopically. Malignant tumors are usually epithelial in origin and can usually be treated successfully by complete surgical resection; total ear canal ablation.
Total Ear Canal Ablation
Indications for TECA are chronic unresponsive or proliferative otitis externa or neoplasia of the ear canal. A V-shaped incision is made in the skin from the intertragic incisure to the ventral limit of the vertical ear canal and from the tragohelicine incisure to the same ventral point. The skin flap is retracted dorsally and the lateral aspect of the vertical ear canal is exposed. The cartilage and the skin of the medial wall of the ear canal are separated from the cartilage and the skin on the inner side of the base of the pinna by use of strong scissors. The vertical ear canal is now dissected to the level of the horizontal ear canal. Appropriate care should be taken to avoid the facial nerve in this area. The dissection is continued with freeing the horizontal part of the ear canal from the surrounding tissues to the level of the external acoustic meatus. The cartilaginous part is separated from the osseous part with scissors and removal of all of the skin lining the osseous external ear canal is accomplished with a small curette. The pinna is then remodeled and sutured with absorbable suture material. A Penrose drain is placed and subcutaneous tissue and skin under the pinna are closed in a routine matter. Complications are facial nerve paralysis, wound infection and dehiscence and chronic fistulation.
Otitis Media and Interna
Otitis media generally develops as an extension of otitis externa through a perforated tympanum in dogs. Cats may develop otitis media as a sequela to upper respiratory tract disease with infection ascending through the Eustachian tube into the middle ear cavity. Organisms cultured most frequently from affected middle ears include Pseudomonas species, Staphylococcus intermedius, beta-hemolytic Streptococcus, Malassezia, Corynebacterium species, Enterococcus species, Proteus species, E. coli and anaerobes. Bacteria can directly infect the middle and inner ear, or the bacteria can produce toxins that inflame the labyrinth.
Other causes of otitis media include fungal infections (Aspergillus, Candida), neoplasia, inflammatory polyps, trauma and primary tumors.
The therapy of otitis media and/or interna consists of systemically delivered broad-spectrum antibiotics. Amoxicillin potentiated with clavulanic acid or enrofloxacine are first choice antibiotics. No ototoxic topical medications should be used when the tympanic membrane is not intact to avoid ototoxicity.
Chronic unresponsive or recurrent otitis media warrants surgical intervention. Total ear canal ablation with lateral bulla osteotomy should be considered in cases with severe secondary changes of the external ear canal and concurrent otitis media or para-aural abscessation. If the external ear canal is not affected, a ventral bulla osteotomy may be performed to remove gross exudate and establish drainage from the middle ear.
Ventral Bulla Osteotomy
An incision is made parallel with the midline, centered 2-3 cm toward the affected side from halfway the mandible to the level of the atlas. The platysma muscle is incised and linguofacial vein is retracted. The incision is deepened by blunt dissection between digastricus muscle and hypoglossal and styloglossal muscles until the bulla can be palpated. A Steinmann pin can be used to make a hole on the ventral aspect, the opening can be enlarged with a small rongeur. In cats both compartments should be opened. Material is collected for culture, sensitivity testing, cytology and histopathology. The cavity is flushed and drained with a Penrose drain. Closure is routine.