Surgical Conditions of the Ear in Dogs and Cats



Surgical Conditions of the Ear in Dogs and Cats

Dr S. M. Boyd

BVSc MMedVet (surg.)

Johannesburg Specialist Veterinary Centre

A large number of conditions that affect the ear do not require surgical intervention; however surgery may be required in the presence of severe recurrent ear disease that is refractory to treatment, neoplasia or lack of owner compliance in the treatment regime. End stage ear canals do require surgical intervention and three surgical procedures have been well described in the definitive treatment of Otitis Externa (OE) in both dogs and cats. The aim of all of them is similar: to improve ventilation and drainage of the ear canal and to remove the source of the infection.

Anatomy of the Ear Canal:

The external ear canal is a cartilage tube that extends from the external auditory meatus on the skull to the external pinnae. It consists of a short vertical canal and a slightly longer horizontal canal which ends at the tympanic membrane. It is lined by epithelium that is continuous with the skin and therefore prone to the same conditions and allergies that the skin suffers from. Allergies are reported to account for the vast majority of inflammatory ear conditions that we see, especially in the dog.

The tympanic bulla or middle ear lies on the medial aspect of the ear drum and contains the auditory ossicles. It also has the sympathetic nerve running through it and the hypoglossal nerve and external carotid artery running directly ventral. The facial nerve runs just ventral to the horizontal ear canal and is very prone to injury during surgery and with chronic disease. The last structure that may be damaged during surgery is the Retroglenoid vein which lies rostral to the tympanic bulla. This causes significant haemorrhage at the time of surgery, but has no long term ill-effects.

In cats the tympanic bulla has two distinct compartments, a larger ventro-medial one and a smaller dorso-lateral one. A major difference in cats, is that the sympathetic nerve runs through the bulla without the protection of a nerve tunnel and this increases the likelihood of Horner’s syndrome post ear canal surgery.

The medial portion of the ear canal is the inner ear which lies in the petrous part of the temporal bone. When this is affected more serious clinical and neurological signs may be present. These signs are seldom improved following surgery due to the permanent damage to the associated nerve tracts.

Otitis Externa (OE):

Otitis Externa is a frequent reason for visitations to a veterinarian and not necessarily an indication for surgery. The prevalence of OE is in the region of 5-20% of dogs seen in general practice. Certain breeds, especially those with drooping ears, are especially susceptible. Another surprisingly predisposed breed is the German Shepherd Dog, who despite their wide, upright ear conformation, suffer from a high degree of OE. This is largely due to their predisposition to skin allergies, like food hypersensitivity and atopy.

The causes of OE were well described by August in 1988, however in depth research has shown that the role of allergies in the predisposition to ear canal problems, has been largely underestimated. Other primary causes include parasites, foreign bodies, autoimmune disease and neoplasia. Predisposing factors are the conformation of the ear canal, maceration, treatment errors, obstruction and anal gland disease. The last category is perpetuating factors and these are bacteria, yeasts, ear pathology and Otitis Media. This separation is however useful in the diagnosis and medical treatment of ear conditions. It reminds us that to treat the presenting clinical signs without attempting to diagnose the underlying cause will ultimately result in recurrence of the condition and infections that are eventually refractory to medical management.

Diagnostic procedures:

There are various options when it comes to making a causal diagnosis in OE. Every case that is presented should have the minimum of an ear smear and otoscopic exam performed. In cases where the animal’s ears are painful or it is a difficult animal with which to work, sedation may be required. The purpose of the otoscopic exam is to assess the degree of stenosis and mucosal pathology present within the ear canal, to look for any parasites or foreign bodies, to assess the integrity of the tympanic membrane and lastly to identify any gross pathology like neoplasia. It is an extremely useful and easily accessible tool in any veterinary practice.

Ear smears are done in order to try and categorise the perpetuating causes like bacteria or yeast infections, as knowing that these are present will help in getting the clinical signs under control.

If recurrent infections are occurring in the same patients, then it is well advised to have survey radiographs of the external ear canals and tympanic bullae done. The standard views are a dorso-ventral, lateral and an open mouth bulla view. The latter is more correctly described as a rostal 30º ventral – caudodorsal oblique view. Sedation or general anaesthetic is usually required for these. Although radiographs are extremely useful in deciding whether there is calcification of the external ear canal or other signs like chronic narrowing that indicate end-stage ear canal disease, it must be remembered that 25% of dogs with middle ear disease have a normal appearance on radiographs.

Culture of swabs taken from the external ear canals is often futile due to the large number of commensal organisms that inhibit the ear canal. Culture of the middle ear via a myringotomy procedure is much more specific and effective, as this is a more isolated cavity. Myringotomy together with a saline flush of the middle ear can be extremely effective in alleviating clinical signs of Otitis Media, whilst at the same time allowing collection of valuable diagnostic samples.

Where more information is required relating in particular to the middle and internal ear canals, the modalities of MRI and CT are greatly beneficial.

Treatment options:

The full medical approach to the treatment of OE is beyond the scope of this talk; however some of the principles are discussed. Firstly treating with polypharmacy ear drops and ointments is only beneficial if we know which organisms we are targeting. In some cases these topical treatments may even be harmful, especially if they are ototoxic in the presence of a ruptured tympanic membrane or if they add to the debris within the ear canal and further compromise the drainage and aeration that these diseased ear canals desperately require. I many instances the dog’s ears are extremely painful and sensitive, so patient cooperation is not always guaranteed. Lack of owner compliance is also a common problem, especially in chronic cases where owners are disillusioned by the lack of cure with this condition. Once ear canals are not responding to medical management for any of the above reasons, surgical intervention is usually required.

Surgical Procedures:

As mentioned earlier in the article, the purpose of surgical intervention is to improve ventilation and drainage of the ear canal and to remove the source of the infection. The most commonly used surgical procedures include a lateral ear canal ablation, vertical ear canal ablation, ventral bulla osteotomy (VBO) and lastly a total ear canal ablation (TECA) together with a lateral bulla osteotomy (LBO):

Lateral Ear Canal Resection – This is the removal of the lateral wall of the vertical ear canal in order to facilitate air flow and drainage and allow better access to the rest of the ear canal for topical treatment applications. The modified version where a cartilage drainage plate is created to prevent hair growth around the opening is known as the Zepp’s procedure. The procedure, although popular is rarely successful as it often fails to remove the underlying cause. One exception to this is in the presence of an isolated lesion on the lateral wall of the vertical canal.

Vertical Ear Canal Ablation – This is similar to the above procedure, but requires dissection and resection of the entire vertical canal. Again its indications are limited to those conditions that only affect the vertical canal. It does create a much better cosmetic appearance than that of a lateral wall resection.

Ventral Bulla Osteotomy – This procedure is designed to provide drainage at the most ventral portion of the tympanic bulla. The indications are for primary conditions of the middle ear where an intact ear drum and a normal external ear canal exist and for failed TECA procedures. It requires technically difficult dissection, especially in the dog. In cats is the procedure of choice for removing inflammatory polyps and the entire lining of the tympanic bulla.

Total Ear Canal Ablation and Lateral Bulla Osteotomy – This is a salvage procedure, but is by far the most effective surgical treatment for end-stage ear canal disease. End stage ear canals have the following characteristics: hyperplasia of the epithelium, hypertrophy of the glands, collapse and/or stenosis of the horizontal part of the ear canal, calcification of the peri-auricular soft tissue. Many of these cases also have a ruptured tympanic membrane and concurrent otitis media. By removing the entire lining of both the external ear canal and the tympanic bulla, TECA/LBO provides a definitive cure for these animals. It is however a complicated procedure with serious potential complications if it is performed by someone who is not totally familiar with the anatomy of this area.

Described complications of this surgical procedure include: fascial nerve palsy, vestibular syndrome, Horner’s syndrome (in cats), chronic recurrent draining sinus tracts and poor carriage of the external pinnae. Fascial nerve palsy is characterized by a decreased palpebral reflex, widened palpebral fissure, drooping of ear or lip, excessive drooling and blepharospasm. In some instances it may be transient and can be caused by ear canal disease without any form of surgical intervention, so complete clinical and neurological examinations prior to surgery are essential.

Vestibular syndrome is another serious condition characterized by a head tilt, circling to the affected side, falling or rolling to the affected side, nystagmus in a direction away from the affected side, as well as asymmetric ataxia, positional strabismus and abnormal postural reactions. Once again, this condition may be present prior to surgery and it is essential that the veterinarian does not miss the early signs. One other point that is important is that owners be warned that surgery, although effective for relieving the majority of clinical signs associated with OE, may not reverse neurological signs that were present prior to the surgery.

In summary, external ear canal disease is not a simple pathological process with a quick-fix treatment option. Correct diagnosis of the underlying problem is essential in order to formulate a treatment protocol. In the event that patient’s clinical signs are refractory to treatment, then various surgical options are available and can, in most instances, be curative provided they are performed by a competent surgeon and the correct procedure is selected for the problem at hand.

References:

August JR 1988 Otitis externa. A Disease of Multifactorial Etiology. Veterinary Clinics of North America (SAP) 18:731-741.

Foster AP, De Boer DJ 1998. The Role of Pseudomonas in Canine Ear Disease. Compendium for Continuing Education for the Practicing Veterinarian 20(8): 909-919.

Fossum TW, Small Animal Surgery 2007 - edition 3 . Chapter 17. Surgery of the Ear: 289-316.

Henderson JT, Radasch RM 1995 Total Ear Canal Ablation with Lateral Bulla Osteotomy for the Management of End-stage Otitis in Dogs. Compendium for Continuing Education for the Practicing Veterinarian 17: 157-164

Hoskinson JJ 1993 Imaging Techniques in the diagnosis of Middle ear Disease. Seminars in Veterinary Medicine and Surgery (Small Animals) 8: 10-16.

Krawinkel DJ Ear Section 14. In Slatter D Textbook of Small Animal Surgery Edition 3: pg 1737-1773.

Taibo RA Otology: Clinical and Surgical Issues 2003. Sponsored by Royal Canin. Entire book.

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