Otitis is a common problem in dogs and cats, accounting for up to 15% of veterinary visits. Surgical treatment of chronic otitis has been attempted in dogs since the early 1800s, and has become more aggressive over the last twenty years with the general acceptance of total ear canal ablation and bulla osteotomy to treat "end stage" otitis.

Improving Results of "Conservative" Surgical Treatments

Surgery is generally considered for animals in which medical therapy has failed, which have had relapses after successful treatment, in which hyperplastic changes have developed, or in those animals which have malformations, neoplasia, or para-aural abscesses. The long term results of the more conservative surgeries, such as lateral wall resection, are often less than optimal. In one study of 281 dogs, lateral wall resection failed in 35% of dogs, and resulted in only partial improvement in an additional 13% (Tufvesson, 1955). The largest study examining failed lateral wall resections (Lane and Little, 1986) attributed the poor results of surgery to one or more of the following causes:

i)  Underlying otitis media,

ii)  Irreversible changes to the residual medial wall of the vertical canal,

iii)  Failure to provide adequate drainage of the horizontal canal,

iv)  Strictures of the horizontal canal, and

v)  Miscellaneous disorders of the aural integument, horizontal canal, and middle ear.

Assuming that technical errors in lateral wall resection are avoided, I propose that better results with lateral wall resection could be achieved by:

i)  Selecting patients in which there are minimal changes in the aural epithelium, or those in which the changes are reversible,

ii)  Aggressively pursuing and treating concurrent otitis media, and

iii)  Treating any underlying skin disease to prevent ongoing inflammation and hyperplasia of the aural epithelium.

The challenges for the surgeon therefore must include:

i)  Determining the primary cause of the ear disease,

ii)  Accurately assessing the extent of disease of the vertical and horizontal ear canals,

iii)  Determining if the middle ear is involved in the disease process, and

iv)  Selecting the appropriate surgical procedure(s) based on the extent of disease.

Determining the primary cause of ear disease is often difficult, particularly in cases of chronic otitis complicated by severe secondary infections. Potential primary causes include parasites, foreign bodies, allergies, keratinization disorders, autoimmune diseases, and systemic diseases such as juvenile cellulitis. A diagnosis of the primary cause of otitis is often vital to the success of more conservative surgical treatments, such as lateral wall resection. In the author's experience, animals with intractable, non-parasitic otitis frequently have inhalant or dietary allergies. In these cases, hyposensitization and elimination diets, respectively, can sometimes reverse or prevent ongoing hyperplastic changes to the remaining medial wall of the vertical canal and occlusion of the horizontal canal. Conversely, failure to control these underlying conditions often results in progressive inflammation and occlusion of the horizontal ear canal. Such cases present for total ear canal ablation months to years after lateral wall resection.

Accurate assessment of the extent of vertical and horizontal canal disease is vital when selecting a surgical procedure to treat chronic otitis. The examination is best performed with the animal anesthetized. Sterile saline flush and a suction apparatus should be used to clear debris from the ear canals. Samples are taken from the ear canal for cytology and culture and sensitivity testing. The canal is carefully examined for patency and the presence of any masses.

The Dilemma of Diagnosing Otitis Media

Otitis media frequently complicates chronic cases of otitis externa. Diagnosing otitis media is often difficult. The "gold standard" for a diagnosis of otitis media is histopathologic evidence of inflammation of the tissues of the middle ear. This is impractical unless a decision to proceed with middle ear surgery has already been made. A diagnosis of otitis media cannot be made based on clinical signs, as they are similar to those of otitis externa in most cases. Spreull's (1964) criteria for the diagnosis of otitis media are a ruptured tympanic membrane in the presence of otitis externa. However, the tympanic membrane can be intact in animals with concurrent otitis externa and media (Little, Lane, Pearson, 1991). In addition, visualization of the tympanic membrane via otoscopy is difficult when severe ear canal hyperplasia and discharge are present. Palpation of the tympanic membrane with a blunt probe has been advocated for these cases in the past; however, a study (Little, Lane, 1989) showed that this technique was very inaccurate and led to membrane rupture in a substantial number of cases. Impedance audiometry (tympanometry) is a very accurate test of tympanic membrane integrity in cadavers, but this technique is not always possible in canine ears which are inflamed, narrowed, or occluded.

Radiography is recommended as a means of diagnosing otitis media before surgical exploration of the middle ear. Radiographic changes which indicate middle ear disease include opacification of the tympanic cavity, thickening, lysis, or irregularity of the bulla wall, and changes in size or contour of the bulla. Radiographic changes of the middle ear are highly sensitive in the diagnosis of otitis media. However, in one study (Remedios, Fowler, Pharr, 1991) there was a 25% incidence of false negative radiographic findings. A second study (Love et al, 1995) showed that computed tomography was slightly more sensitive than radiography for diagnosing otitis media, but early middle ear changes were not detected with either modality.

Treatment Options

The choice of treatment for chronic otitis is based on an accurate assessment of the extent of disease. If more conservative surgical treatments are to be successful, surgery should be considered early in the disease process, rather than as a "last resort".

Animals which have minimal changes in the vertical and horizontal canals are candidates for lateral wall resection. If the tympanic membrane is concurrently ruptured, the clinician must decide between conservative treatment (flushing the middle ear and treating with antibiotics) and surgical exploration of the middle ear. Flushing the middle ear combined with antibiotic treatment gave an 80% success rate in one series (Spreull, 1964), but multiple anesthetics and flushings over a two week period were required. Results of combining lateral wall resection with ventral bulla osteotomy have not been published. In a series of 18 dogs treated at University of Pennsylvania, these combined procedures produced a satisfactory result in 12 dogs. Unsatisfactory results in 6 dogs were attributed to i) Ongoing disease of the horizontal ear canal, or ii) persistent otitis media. The author feels that lateral wall resection/ventral bulla osteotomy is a viable alternative to total ear canal ablation provided that: i) The horizontal canal is patent, and ii) Concurrent skin disease is controlled.

Cases with extensive disease of the vertical canal require either vertical canal ablation or lateral wall resection and removal of proliferative tissue on the medial wall of the vertical canal. This procedure is performed with electrocautery after the lateral wall resection is completed. Hyperplastic tissue is removed flush with the surface of the medial wall of the vertical leaving a flat, raw surface which epithelializes within two weeks.

Alternative treatments to total ear canal ablation have been described for dogs with severe horizontal canal disease; both techniques involve salvaging the horizontal ear canals. Sis (1963) described vertical canal and partial horizontal canal ablation. The remaining horizontal canal was sutured to the skin and stented with a polytetrafluroethylene implant. Recently McAnulty (1995) descried salvaging the ear by reconstructing the horizontal canal with an angularis-oris based buccal flap lined by oral mucosa. The flap was used to replace the ventral two-thirds of the horizontal ear canal, and the procedure was combined with a ventral bulla osteotomy. The role for these alternatives to total ear canal ablation remains to be completely defined.

Total Ear Canal Ablation: Managing Complications

Complications from total ear canal ablation (TECA) include wound breakdown, facial nerve paralysis, deafness, fistula formation, and ongoing skin disease affecting the pinna. Wound breakdown is not an unexpected complication, as it is often impossible to convert the area of the TECA into a clean wound before closure. The role of appropriate perioperative antibiotics in reducing postoperative wound breakdown is not known. In the author's experience, wound breakdown is best managed by initial debridement and lavage; the wound should then be left to heal by second intention.

Damage to the facial nerve is sometimes unavoidable. The nerve can be entrapped in fibrous or osseous tissue surrounding the horizontal canal. However, facial nerve paralysis can occur from the over-zealous use of electrocautery in the area of the horizontal canal. Lubrication of the ipsilateral cornea is required for several weeks until the animal learns to retract the globe using the retractor bulbi occularis muscle (innervated by the abducens nerve), thus prolapsing the nictitans and spreading the tear film across the cornea.

Fistulas can develop weeks to even years after total ear canal ablation and bulla osteotomy. The reported incidence of fistula formation is 3 to 15%. Fistula formation is associated with incomplete removal of diseased tissue or epithelium lining the cartilaginous or bony ear canal, or the tympanic bulla. Surgical treatment of fistulas involves removal of the retained diseased tissue and drainage of the middle ear. Re-exploration using either a ventral or lateral approach is reported. The author prefers a lateral approach along the fistula, as it facilitates identification and removal of annular cartilage or epithelial remnants present lateral to the external acoustic meatus. A concurrent lateral bulla osteotomy is performed.

Conclusion

When treating chronic otitis, the clinician must recognize the connection between skin disease, disease of the ear canal, and disease of the middle ear. The results of more conservative ear surgeries are related more to the nature and extent of the ear disease rather than the performance of a specific procedure. The challenge for the clinician thus lies in accurate assessment of the extent of disease, and selecting the appropriate procedure for a given ear.

References

1.  Lane, J.G. & Little J.L. (1986) Surgery of the canine external auditory meatus: a review of failures. Journal of Small Animal Practice 27, 247.

2.  Little, C.J.L., Lane, J.G. (1989) An evaluation of tympanometry, otoscopy and palpation for assessment of the canine tympanic membrane. The Veterinary Record 124, 5.

3.  Little, C.J.L., Lane, J.G. & Pearson, G.R. (1991) Inflammatory middle ear disease of the dog: the pathology of otitis media. The Veterinary Record 128, 293.

4.  Love, N.E., et al. (1995) Radiographic and computed tomographic evaluation of otitis media in the dog. Veterinary Radiology and Ultrasound 36, 375.

5.  McAnulty, J.F., Meinen J.B. (1995) Horizontal ear canal reconstruction: Does it have a role in the treatment of dogs with end-stage otitis externa? Veterinary Surgery 24, 432.

6.  Remedios, A.M., Fowler, J.D. & Pharr, J.W. (1991) A comparison of radiographic versus surgical diagnosis of otitis media. Journal of the American Animal Hospital Association 27, 183.

7.  Sis, R.F. (1963) Reconstruction of the canine ear with polytetrafluoroethylene implants. Journal of the American Veterinary Medical Association 143, 295.

8.  Spreull, J.S.A. (1964) Treatment of otitis media in the dog. Journal of Small Animal Practice 5, 107.

9.  Tufvesson, G. (1955) Operation for otitis externa in dogs according to Zepp's method. American Journal of Veterinary Research 16, 565.