Surgical approaches

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Chronic otitis externa

M in a labrador retriever dog a case for surgery

Surgical approaches in the management of chronic otitis externa

CHRIS LITTLE

THIS, the third in a series of articles on otitis externa in the dog and cat, briefly reviews the pathological changes which occur in chronic otitis to explain the rationale for surgery, and then goes on to discuss a variety of surgical approaches which aid the management of the condition. The previous articles covered the primary causes and investigation of otitis externa (January 1996, pp 9-16) and medical treatment (February 1996, pp 66-71). PATHOGENESIS OF CHRONIC OTITIS Otitis externa has many aetiologies which all seem to converge into a final common pathway as the condition becomes chronic. It appears that inflammation within the ear canal, irrespective of its cause, initiates self-trauma. The aural microclimate becomes warmer than usual, while exudation from the integument is retained because of the peculiar anatomy of the ear. Ideal conditions are thus created for yeasts and bacteria to multiply. Retained moisture damages the stratum comeum and is a potent stimulus for the development of otitis externa. The proliferating microflora release enzymes, such as proteases and lipases, and toxic products which together with keratin and cell debris damage the integument still further. Meanwhile, self-trauma continues. The character of the cerumen alters as a result of the persistent inflammation, disrupted adnexal gland function and, most probably, lipolysis. The integument becomes thickened which further impedes proper ventilation and drainage from the ear canal.

If these circumstances persist, the deterioration seems to become inexorable with the result that the aural integument and its microflora are irreversibly altered and the ear cannot return to health.

PATHOLOGY OF CHRONIC OTITIS Chronic otitis extema results in profound changes to the integument of the ear. The epidermis becomes thickened, acanthotic and frequently hyperkeratotic. Occasionally, the lumen of the canal will become completely plugged by keratin debris. The dermis also thickens as otitis externa progresses, leading to stenosis of the lumen of the ear canal. Sebaceous and sweat ('ceruminous' or 'apocrine') glands, which appear as quite insignificant structures in healthy ears, become grossly dilated. Inflammatory cells, particularly neutrophils and lymphoid cells, accumulate in the dermis, sometimes in the glands themselves. Foamy macrophages and giant cells may also be found in and around the glands. Another

Ear from a dog euthanased because of severe chronic otitis externa and media. The specimen has been sectioned along its long axis. Note the stenosis of the external ear canal and soft tissue within the middle ear. The tympanic membrane (arrow) is grossly thickened

In Practice * SEPTEMBER 1996

351

k Chris Little graduated from

Glasgow University in 1981. He spent three years in general practice and three years at the University of Bristol School of Veterinary Science where he obtained a PhD for studies concerned with chronic ear disease in the dog. He now teaches at the University of Glasgow Veterinary School where his principal interests are small animal cardiology and internal medicine.

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Principles of surgery in the management of otitis externa

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ZEPP'S MODIFIED LATERAL WALL AURAL RESECTION

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Irreversible narrowing of the ear canal associated with hyperplastic proliferation of the integument Chronic or unresponsive ulceration of the integument of the ear canal

Neoplasia involving the ear canal External ear canal from a dog with chronic end-stage otitis. The lumen of the canal has been virtually obliterated by hyperplastic thickening of the

Otitis externa accompanied by unambiguous evidence of chronic disease of the middle or inner ear

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The primary indication for lateral wall resection is the presence of irreversibly diseased integument lining the lateral aspect of the vertical ear canal, as illustrated in this diagram 352

2In lflractice 0 S c PT E M e E R 1 9 9 6

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Radiographic assessment Radiography can play a useful part in the assessment of cats and dogs with known or suspected aural disease, particularly where it is chronic or is failing to respond to therapy. The general indications for radiography are listed on the right.

Techniques Dorsoventral (or ventrodorsal) view of the caudal skull A dorsoventral (or ventrodorsal) view of the caudal skull is particularly useful for examining the horizontal part of the external ear and the middle ear cavities. Rare-earth screens are used wherever possible. Both ears are radiographed to enable comparisons to be made between them. The patient is sedated or anaesthetised and positioned either in dorsal or ventral recumbency. The head is extended and positioned so that the hard palate lies parallel to the film. Rotation about the midline is minimised by the careful use of sandbags or other aids. The central X-ray beam is directed at right angles to the film to pass through an axis connecting the horizontal ear canals. The atlanto-occipital and temporomandibular joints mark the caudal

Indications Chronic or recurrent external ear disease Suspected middle ear disease * Suspected inner ear disease, particularly if accompanied by signs of external or middle ear disease * Upper respiratory signs accompanied by signs of aural disease * Congenital or acquired lesions to the soft palate or nasopharynx * Suspected or known neoplasia involving the ear * Abscesses or discharging sinuses on the head and neck where para-aural abscesses must be ruled *

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Positioning a dog for a dorsoventral radiograph of the caudal skull

Positioning a dog for rostrocaudal open mouth view optimised for evaluation of the middle ear cavities

Dorsoventral view of the caudal skull of a normal cat. Note the air-shadows of the external ear canals and the complex appearance of the middle ear cavities

Open mouth view of a normal cat. The middle ear cavity is divided into two compartments

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In Practice e SEPTEMBER 1 996

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and rostral limits of the relevant radiographic field. The X-ray beam should be collimated to avoid unnecessary radiation scatter. Rostrocaudal open mouth view A rostrocaudal open mouth view is probably the most useful one for the assessment of the middle ear cavities. However, accurate positioning of the patient is crucial if radiographs of diagnostic quality are to be obtained. Once again, rare-earth screens are valuable and both ears should be included in the radiograph to allow comparison between them. The patient must be anaesthetised and positioned in dorsal recumbency. The head is flexed so that the hard palate forms an angle of about 10 to 150 with the vertical. The mouth is opened and the mandible is made to form an angle of 10 to 150 with the vertical in the contrary direction. The tongue is drawn as far forward as possible and secured in place between the lower canine teeth. Rotation of the skull about the vertical axis must be avoided. This positioning is maintained using radiolucent aids such as bandages. The central ray of the X-ray beam is directed perpendicular to the film to pass through an axis connecting the commissures of the mouth. The limits of the relevant radiographic field are delineated by the atlantoaxial joint and the dorsal limits of the mandibular rami. Immediately prior to making the exposure the endotracheal tube must be removed, taking especial care to avoid altering the patient's position. Once the exposure has been made it is equally important to reintubate the patient immediately to avoid obstruction of the airway. Lateral view A lateral view is occasionally useful, in particular when lesions in the nasopharynx are thought to accompany aural disease, for instance in young cats with naospharyngeal and/or aural polyps. The patient must usually be sedated or anaesthetised. Positioning is straightforward with the patient in lateral recumbency and the head extended. The sagittal plane of the skull is orientated parallel to the radiographic film. The beam is centred over the tympanic bullae; the area of interest encompasses the pharynx and caudoventral skull. The endotracheal tube may be removed but where a lesion might obstruct the airway this is usually not advisable.

Ipterpretatlon Interpretation of these radiographs is principally founded upon familiarity with the radiographic anatomy of the healthy ear and comparison between the two ears of a patient. The external ear normally provides a soft tissue density only, through which the air shadow of the ear canal can be visualised. Lesions within the horizontal canal are principally recognised by narrowing or obliteration of this air shadow. When the external ear has been subjected to recurrent or long-standing inflammatory disease the air shadow In Practice a SEPTEMBER 1996

will be narrowed. In addition, calcification or true ossification of the annular and, more rarely, the proximal auricular cartilages, may occur. This change will be radiographically obvious. The petrous temporal bone and middle ear cavity have a complex radiographic appearance. Feline-middle ear The open mouth view in a healthy individual gives a very clear illustration that the feline middle ear is divided into two compartments, dorsolateral and ventromedial; each is delineated by a sharply defined bony outline while the air-filled cavities are dark. Dorsal to these cavities the dense bone surrounding the labyrinth of the inner ear can be identified. Dorsoventral views of the cat's middle ear show that the smaller cavity lies rostrolateral to the larger compartment. Other features which may be obvious include the tympanic ring, which is frequently very radio-opaque, and the complex density of the promontory which appears to straddle the two compartments.

Canine middle ear The canine middle ear displays a simple hemispherical outline to the hypotympanum on the open mouth view. This is formed by the thin, but dense, bone of the bulla. More dorsally, the appearance of the petrous temporal bone is complex, particularly on the medial aspect where the labyrinth is housed. Between these two regions an incomplete bony shelf, corresponding to the junction between the hypotympanum and the mesotympanum, may be seen. Dorsoventral or ventrodorsal projections of the canine petrous temporal bone show a rather dense structure with a slightly oval outline. The landmarks which are most often recognised lie outside the middle ear; namely, rostrally, the retroglenoid process, caudal to the middle ear cavity the jugular and mastoid processes, and laterally the osseous portion of the external ear canal.

Continued on page 356 355

Rostrocaudal open mouth view of the ears of a normal dog. Note the thin dense outline of the tympanic bullae and the complex appearance of the more dorsomedial aspects of the petrous temporal bone

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Continuedfrom page 355

Ventrodorsal view of the caudal skull of a dog with unilateral right-sided otitis externa, otitis media and cholesteatoma of the middle ear. The middle ear cavity is enlarged and shows a hazy sclerotic density (Reproduced, with permission, from The Veterinary Record 128, 319-322)

Pathological changes Changes to the radiographic appearance of the middle ear will only be recognised if pathological lesions at this site are quite severe; the absence of such changes is no indication that this area is free of disease. When major soft tissue pathology is present, the middle ear cavity frequently assumes a hazy appearance and the intricate bone detail may be lost. Sclerosis and irregular thickening of the wall of the tympanic bulla is also seen in some cases. Less commonly, new bone may be deposited ventral,

rostral and lateral to the tympanic bullae and the ipsilateral temporomandibular joint may become involved. Tumours within the middle ear space, cholesteatoma, and osteomyelitis of the petrous temporal bone may also cause such changes, or may lead to complete disfiguration of the outline to the tympanic bulla. Wherever the radiographic appearance of the middle ear is radically altered severe disease should be suspected and the prognosis may be adjusted accordingly.

Dorsoventral view of the caudal skull of a dog with bilateral chronic otitis extema and media. Calcification of cartilages of the external ears is evident and the middle ear cavities appear sclerotic

Dorsoventral view from a cat with middle ear disease. The affected middle ear cavity, shown on the right,

appears denser than normal. The fine internal anatomy of the middle ear is also obscured

Open mouth view from a dog with unilateral rightsided otitis externa and media. The affected middle ear is denser than the healthy one

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where the ear itself is not obviously stenosed; and lesions to the proximal ear canal or middle ear, where access to these tissues would be improved substantially by such surgery. It has been clearly demonstrated that lateral wall resection will cause a modest but significant reduction in the relative humidity and surface temperature of the aural environment. These changes should render the tissues less hospitable to opportunist bacterial or fungal pathogens. Provided that the lateral wall resection is carefully performed and heals without contracture, a neat and patent ostium to the horizontal ear canal will be created; drainage of the proximal ear will obviously be enhanced under these circumstances. Surgical technique No special preparation is required for a patient undergoing lateral wall resection. However, this is an elective procedure and, when the ear is infected, preoperative

treatment of the patient for a few days using appropriate antibiotics is likely to improvfthe outcome. It may also be helpful to instil a ceruminolytic agent, such as a 5 per cent solution of sodium bicarbonate (Robinson and Hawke 1989), into the ear several hours before the operation is performed in order to facilitate lavage and preoperative preparation of the ear. The patient is anaesthetised and placed in lateral recumbency with the candidate ear uppermost; a sandbag under the neck aids optimal positioning. Both surfaces of the entire pinna are closely clipped, together with a wide surgical field rostral, caudal, ventral and dorsal to the ear. Hair is removed as far as possible from the aural

canal. Preparation and disinfection of the skin and aural canal must be performed thoroughly because the site is likely to be heavily colonised by bacteria and yeasts. However, it must also be appreciated that the aural integument may be fragile and very susceptible to

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Technique for lateral wall resection of the ear canal (demonstrated on a cadaver for clarity). (A) Placement of skin incisions. The horizontal incision is made about 2 to 3 cm ventral to the ventral limit of the vertical canal. Further incisions are made perpendicular to this initial incision. The rostral one (to the left of the picture) connects the rostral end of the first incision to the tragohelicine incisure, while the caudal one (to the right) runs parallel, connecting the caudal aspect of the first incision to the intertragic incisure. (B) Exposure of the aural cartilages. The auricular cartilage supports the vertical ear canal; the horizontal canal is largely supported by the annular cartilage. The outer end of annular cartilage is telescoped inside the proximal aspect of the auricular cartilage, forming an obvious landmark. Recognition of the junction between these two cartilages (annular ligament) is crucial to good surgical technique. (C) The lateral wall of the vertical ear canal has been reflected ventrally about the annular ligament. A part of the lateral wall will be retained to form a baffle plate. The ostium of the horizontal ear canal can be seen. (D) Placement of rostral and caudal anchoring sutures at the external ostium of the horizontal canal. Care should be taken to avoid any constriction at this site. (E) Final appearance of the ear

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frictional injury. In addition, care must be taken to avoid traumatising the tympanic membrane. Once skin disinfection has been completed it is advisable to douche the ear with physiological saline - this action will remove agents which might otherwise irritate the skin and provoke self-trauma in the crucial hours after the operation has been completed. Landmarks for accurate surgery must be identified before the procedure is begun. At the ear canal opening the tragohelicine and intertragic incisures are located forming rostral and caudal notches, respectively, on the lateral aspect of the cavum concha. The ventral limit of the vertical ear canal should also be identified by palpation. A blunt probe passed down the vertical ear canal may be helpful here. The first skin incision is made about 2 to 3 cm ventral to the ventral limit of the vertical canal. It is about 2 cm in length, orientated horizontally. Two further incisions are made perpendicular to this initial incision. The rostral one connects the rostral end of the first incision to the tragohelicine incisure, while the caudal one runs parallel, connecting the caudal aspect of the first incision to the intertragic incisure. The long skin flap thus formed is dissected free and reflected dorsally. Next, the soft tissues overlying the lateral aspect of the ear canal are freed, principally by blunt dissection. This area is frequently quite vascular; careful haemostasis, though time-consuming, will be rewarded because it is easier to complete the surgery with accuracy when the field is clear of blood. The auricular and annular cartilages are identified. Recognition of the ligamentous tissue uniting these two cartilages (the 'annular ligament') is crucial to good technique. The outer end of the annular cartilage is telescoped inside the proximal aspect of the auricular cartilage forming an obvious landmark. Ventral to the ear at this level lies the parotid salivary gland. Using a scalpel a short incision, directed vertically, is made in the most rostral part of the auricular cartilage starting at the annular ligament. A second short incision is made in the most caudal part of the auricular cartilage directed vertically from the annular ligament. The scalpel is exchanged for a pair of Mayo scissors and these incisions are extended vertically to the cavum concha. Thus, the rostral incision connects the rostral aspect of the annular ligament to the tragohelicine incisure and the caudal one connects the caudal aspect of the annular ligament to the intertragic incisure. The lateral wall of the vertical ear canal is at this stage free except for the annular ligament which forms a hinge about which the tissue is reflected ventrally. A portion of this tissue is retained (see below). Careful swabbing and irrigation of the surgical field are usually necessary at this point. The ostium of the horizontal ear canal should now be visible. Once identified, the first two sutures are placed. A curved cutting needle and 3-0 monofilament nylon are recommended. The first suture is placed to bring the skin rostral to the ear into apposition with the most rostral part of the ostium formed by the annular cartilage. The suture should pass through the cartilage itself because experience shows that the integument overlying the cartilage will otherwise often tear. The second suture apposes the skin caudal to the ear with the most caudal part of the ostium created by the annular cartilage. These two sutures determine the shape of the new aural opening; inaccurate placement may affect the outcome

adversely. 358

At this point, the portion of the lateral wall of the ear canal which was retained and reflected ventrally is used to form a so-called 'baffle plate' to optimise drainage from the horizontal ear canal. This is kept as wide as the horizontal ear canal and fashioned to about 2 cm in length. Sutures apposing skin to the ventrorostral and ventrocaudal corners, again passing through the cartilage, are placed first. The borders of the baffle plate and adjacent skin are then brought into apposition. The skin surrounding the ostium of the horizontal ear canal is highly mobile and hirsute - the baffle plate is created to prevent this skin from obstructing the new opening of the ear. Finally, the two vertical incisions are closed using simple interrupted sutures. Once again it is usually wise to pass the suture material through the auricular cartilage. Postoperative care is routine but should include analgesia and systemic antibiotics for at least five days. While routine bandaging of the head is not usually necessary, Elizabethan collars are often useful. Sutures are removed 10 to 14 days postoperatively.

Hazards * When the operation site is prepared and draped, antiseptic agents should be kept well away from the ipsilateral eye and towel clips must be positioned with care to avoid traumatising the eye. * Irrigation of the ear canal could lead to the introduction of ototoxic agents into the middle ear if the tympanic membrane is traumatised. To prevent any risk of this, it is wise to avoid probing deeply into the horizontal ear canal with instruments, no matter how blunt. Concentrated antiseptic agents should also be avoided. * Haemorrhage frequently occurs during dissection of the soft tissues lateral to the ear. Haemostasis is not difficult but may require that individual small vessels are isolated and ligated. * The parotid salivary gland lies ventral to the horizontal ear canal and could conceivably be damaged during the procedure. However, in the author's experience the danger of a salivary mucocele or fistula forming postoperatively has been exaggerated. * Wound dehiscence is not uncommon following lateral wall resection. Where it occurs, obvious inciting causes such as self-trauma must be identified and dealt with. Except where severe secondary infection has developed the site should be debrided and resutured promptly. Results and complications Although lateral wall resections have long been used as an aid in the management of otitis externa, the technique frequently gives unsatisfactory results. In three surveys examining outcomes in a total of 348 dogs (Tufvesson 1955, Blakely 1957, Gregory and Vasseur 1983), results were described as good in only about half of the dogs; over a third of the dogs were not helped by the surgery. Arguably one of the principal reasons for the poor results following aural resection procedures is that, until recently, surgeons tended to treat otitis as a purely surgical problem affecting the external ears alone and failed to address the underlying disorder(s) which had initiated the condition. Although this theory might seem attractive, there are no hard data to support it, however. Some factors which are known to contribute to disappointing results following lateral wall resection are listed in the table on page 361. In Practice v SEPTEMBER 1996

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Concurrent otitis media

Inadequate drainage from the horizontal ear canal Irreversible pathological change affecting the residual vertical ear canal Stenosis or other pathological change affecting the horizontal ear canal

Miscellaneous (retained sutures, unrecognised neoplasia, etc)

MODIFIED VERTICAL CANAL ABLATION Indications The integument on the medial aspect of the vertical ear canal may. like that on the lateral aspect, be irrevocably diseased beftore any attempt is made to include surgery in the management of an animllal with chronic otitis. Where this has occurred, Zepp's modiftied lateral wall aural resection is probably not the most appropriate technique and, if attempted. would be associated with a high tailure rate. In an efflort to overcome this difficulty more radical ablation procedures have been used. Vertical carn.al ablation takes various forms. The technique the aLithol- uses ablates the entire vertical ear canial except for a small portion oft the laterial aspect of the canal which, as in Zepp s resection, is retainied to form-l a baffle plate ventral to the new aditus of the horizontal ear canal. Vertical canal ablation is straiclhtforwarld. It enables radical excision of the tissues of the vertical Carl canial in cases where these are irreversibly diseased in the absence of severe disecase involving the mor-e proximlal tissues of the ear.

Surgical technique The aniimal is prepared as described for Zepp's resectionl. The preparation may be rather more difficult and timeconsuming, however, since stenosis of the vertical canal of these ears is likely to be particularly extensive. The initial incision is made around the cavumn conch.L. On the medial aspect the incision divides the auricularcartilage at the base of the pinna from that part which contributes to the aural canal. More laterally, over the tragus, the incision is made through skin alone. A second incision begins at the caudal commissure of the ear ad jacent to the intertragic incisure and is directed ventr-ally to term-linate just below the ventral limit of the vertical canal, forming an inverted 'L shape. A skin flap is thereby created which can be undermined anid reflected rostrally. Alternatively, this incisioni canl simply run ventrally from the midpoint of the first incision (creating a 'T' shape and two skin flaps). The entire vertical ear canal is mobilised, using blunt dissection wherever possible, to separate it f-om the soft tissues later-al and medial to it. The annular- ligament uniting the annular and auricular cartilages must be identified. This landmark delineates the outer limit of the horizontal ear canal which will form-l the new opening to the ear. A baffle plate to support the new ostium )of the ear canal, analogous to that used in Zepp's resection, will be created. This is fashioned fr-omi the lateral wall of the vertical ear canal Usinlg the proximiial part of the aIuricular cartilage. It is hinged about the annula ligament to lie ventr-al to the opening of the ear canial. Dorsal to the horizontal ear canal the aninular and auricular- carIn Practice e SEPTEMBER 1 996

Vertical canal ablation is indicated where irreversible changes have developed in the integument of the vertical ear canal but the horizontal canal remains relatively healthy, as illustrated in this diagram

tilages are separated by sev ering the aninular ligamnent (some Ssurgeons prefer to retain a small plate of the auricuLla- cartilage her-e to forimi a seconid baffle plate dor-sal to the neCW OStiuIll of the car canial). Closure ol the skin is achieved using simple interrupted sutures of 3-0 moniofilamiieint nylon and paying p articul'ar attention to the proxvision c)f a well dilated ostiuLmI to the residual ear cianal. Irrespectixve of xxhich ori cinal iicision w as chosen, the skin is closed so that the suturle line tcakes the for-mii of an inxerted L' angled caudodor-sally. This results in more norm-lal eair carriage aLlter- SUrgery, particularly in prick-eared dogs. Somile plastic sUIreCrIy may be helpful to achiex e optimum11 cosmiietic results. Most surgeons prefcr to close dead space b) including0Z the soft tissues deep to the skin flap in the skin sutui-es. This axvoids thc usC of bul-ied absorbable sutures which might be prone to sepsis. Aftercar-c is slimilar to that foI Zepp s resection1. Owners must be instl-ucted to clip the halir reCularly fr01om a.round the nexxwly fashionied ear canal opening to imaintain optimal xventilation. Hazards The hazar-ds arisine dul-illn X ertical canial ablation arc akin to those described foi lateral w all rcsectionl. Results and complications In the aLuthor- s cxpericnice, the comnplications associaLted xxith the xvcrtical ablation procedurc are similalr- to thosc described for lateral wall resectioni. The technique is, howexver, no\x little used because, where the eair is x ery scerely altered, total car- canial ablation combined with latertal bulla osteotomy (see below) has become popular. Nexvertheless, in onc suLIrxeC of thc ICSIltS froim 75 Operal0tiOnlS, anl outstandina success rlate and a Irecluccd incidene of complications coImparcd xxith Zepp's resection (including less pain, less exudation aind less Tran1ulation during the postoperatix e period) were

repor-ted (Sniemering 1980). 361

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suffering from unremittingy pain anld often the only alternative course for them would be euthanasia.

Appearance of the right ear of a nine-year-old male Japanese chin with longstanding recurrent suppurative end-stage otitis externa. The proximal ear

TOTAL EAR CANAL ABLATION COMBINED WITH LATERAL BULLA OSTEOTOMY

canal was stenosed. This animal'rz vvc ennelitinn anmai onuo WAC was>

successfully managed by total ear canal ablation and lateral wall resection

Indications When otitis externa is severe and protracted or relapses repeatedly the integument lining the entire ear canal is likely to be irreversibly diseased. Moreover, in a. very substantial proportion of such cases, perhaps the mlajority, the middle ear is also secondarily involved in this chronic process. The most proxiimial part of the external ear- canal is the osseous portion contained within the external auditory process of the temporal bone. The aural integument at this site is very firmly united to the underlying bone so that complete removal by curettage following ablation of the aural cartilages alone may bc impossible; experience shows that sepsis develops quite frequently, often months after the original surgery. For these reasons, when radical surgical treatment is required foi external ear disease many surgeons now use a combined approach - namely, total ear canal ablation comnbined with a lateral bulla osteotomy (TECA/LBO). This technique facilitates completc ablation of the ear canal, including the osseous portion together with curettate of the middle ear cavity. Many of the animals chosen f-or TECA/LBO will have previously had other aural surgery which has failed to cure their condition. TECA/LBO is a radical andi irneversible procedure which efflectively destroys the ear. Such surgery must neter be resorted to in a cavalier fashion; it is important that efforts are made to elucidate the under-lying, mechanismi fotr the otitis (radiography will trequently contribute to the assessment of these patients) and to treat this first by appropriate medical means whenever practical. Nonetheless, TECA/LBO has provided a very valuahle therapeutic route for the mana-ement of animals with severe aural disease. These animals are frequently

Chronic 'end-stage' otitis externa where the proximal ulcerated Severe or recurrent otitis externa

ear

canal is obviously stenosed

or

recurrently

accompanied by unambiguous evidence of middle or inner ear

d'isease

Para-aural abscess Neoplasia of the ear involving the horizontal ear canal and/or the middle

362

ear

cavity

Surgical technique For animals with chr-onic puurulent discharge fiom the aural canal, preoperatise preparationi should ideally begin with an appropriate course oft systemic antibiotics chosen on the basis ot cytology and/or culture and sensitivity tests. The use of celruminolytic agents prior to surgery is unlikely to be of much benefit simply becaLuse ear canal stenosis w ill usually prevent them being introduced sufficiently far downi the ear canal. The patient is anaesthetised and placed in lateral recumiibency with the candidate ear- uppermost. Further preptaration is akin to that required for the aural resection procedures. including clipping of hair and thorough lavage of the ear canial. Once acTain, care should be exercised to avoid introducing ototoxic agents inlto the middle ear space. Familiarity with the anatomiiy of this region is v ital to the surgeon embarkingt on a TECA/LBO. Landmar-ks which shoLuld be located before commiiiiencement are the caVuim concha. the ventral limits of the vertical ear canal. the vertical rallLus of the mandible, and the tympaniic bulla. Anatomical landmarks on the skull adjacent to the middle ear cavity should be revised; these are showsn on page 363. Where no surgery has been performed on the ear prcviously. the initial incisionis are similar to those used foi the modified tvertical canal rcsection. The first incision cncircles the cavumn concha anid, on the medial aspect. cutS through the auL-icular cartilage to divide the pinna trom the ear canal lust dorsal to the tubercle of- the anthclix. The second incision is made over the lateral aspect of the vertical ear canal; starting fromii about 2 cm ventral

Diagram illustrating the tissues which will be resected during total ear canal ablation and lateral bulla osteotomy. Thorough curettage of the proximal ear canal and of the middle ear cavity is essential for success. The facial nerve, shown here as a spot, can represent a hazard during surgery

In Practice a SEPTEMBER 1 996

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Important bony landmarks on the skull adjacent to the middle ear cavity

to its lower limit, it courses dorsally up to the tragus. Thus the initial skin incision forms either a 'T' or an inverted 'L'. The skin flaps are reflected. Next, using a combination of blunt and sharp dissection the auricular cartilage is freed from the soft tissues until the annular ligament is identified. Careful haemostasis is vital so that visibility within the surgical field remains good. Branches of the rostral auricular artery and vein must sometimes be ligated during this dissection. Once the annular cartilage has been located it becomes imperative to stay close to the cartilage as careful blunt dissection continues medially towards the external acoustic process of the temporal bone. The confined surgical field around the horizontal ear canal tends to impair visibility which will be adequate only provided good haemostasis is maintained. Retraction of the soft tissues by a competent assistant will be helpful. A headtorch is a valuable aid. The facial nerve exits the skull at the stylomastoid foramen just caudal to the ear canal. It then courses rostroventrally in the soft tissues ventral to the horizontal ear canal. This structure represents a potential hazard during surgery. In most cases it should be identified and gently retracted ventrally. A loop of Penrose drain is particularly effective here as an atraumatic retractor (White and Pomeroy 1990). Occasionally, the facial nerve will be encased in a mass of tumour, connective tissue or even new bone around the horizontal canal. In these instances it is a matter of judgement how, and to what extent, the nerve should be mobilised. Once the osseous acoustic process of the temporal bone is reached the ear canal is transected. The soft tissues overlying the tympanic bulla ventral to the meatus are reflected using a periosteal elevator or small bone chisel. The same small bone chisel or Rongeurs are used to create an opening into the lateral aspect of the bulla. This is enlarged to incorporate the osseous ear canal and a large proportion of the lateral wall of the bulla. Careful and meticulous curettage of the ear canal is pursued so that all the integument is completely removed. The middle ear is also thoroughly curetted, where necessary, but instruments are not introduced dorsally into the epitympanum to avoid trauma to the oval or round windows. Debris, including chips of bone, must be removed from the tympanum itself; this usually requires repeated flushing with saline. Prior to closure the local tissues are irrigated with an appropriate antibiotic solution. Some In Practice * SEPTEMBER 1996

surgeons prefer to anchor a Penrose drain in the middle ear at the time the wound is closed. This drain does not follow the line of excision but exits the tissues ventral to the bulla. The soft tissues are closed using a few interrupted sutures of a synthetic absorbable material. The skin incision is closed using 3-0 monofilament nylon to form either a 'T' or an inverted 'L'; the latter wound conformation aids ear carriage in prick-eared dogs and in cats. Potent analgesics must be administered during the first 48 hours following surgery and the animal hospitalised for a similar length of time. Postoperative care is otherwise straightforward. A five- to 10-day course of systemic antibiotics will usually be required. Stitches are removed 10 to 14 days after surgery. Where TECA/LBO surgery is carried out as a revision of previous aural surgery, the incision is usually made around the margins of the remaining integument of the ear canal. Dissection is frequently more difficult in these cases but follows the same principles. Closure of the wound in these instances may also present some difficulties. Fortunately, the skin rostral and caudal to this location is highly mobile so that a neat cosmetic result can invariably be achieved.

lntraoperative view during total ear canal ablation and lateral bulla osteotomy (rostral to the left). The confined surgical field hampers visibility. Good haemostasis and retraction of the soft tissues by a competent assistant will contribute to a successful outcome 363

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Hazards TECA/LBO surgrely is associated with several mlajor h.azards. In the main, these have been outlined in the disCuLsioin above. Additionial hazards peculiar to this procedurl-c aIeC as follows. * QLlite severe haemorrhagc frequently occurs when the Ilteiral bulla osteotomny is performed and there aIe two repor-ts of' ain aniaial hav ing died as a ressult of this (Smneak and D)ehoff 1986, Mason and otheris 1988). The retroglenoid xein which emerees friom a foramen rostral to thc OSSCOuS canal (as illustrated on the previous page) is the most commllon source of haemorrhage. It is xcry difficult to isolate aind ligate this vessel but blood loss cani be stopped by alpplying firm pressure with a swab ftor sexceral minlutes. The f'oramiien may also be packed with bone wax. Other vascular structui-es which might conceciably bc damilaged during surgery include the commiiiion, exter-nial and interna-Il carotid ariteiics, as VxclI as the superficial tempor-al and inter-nial maxillar v eins. * The hyoid CappCaratus attaches to the skull caludal to the osseous ea.r canial. Care should be taken to axvoid this st tIlctLI re. * Proxvidcd thc facial

ncrx e is idetitified and hlindlcd caret'ully. without undue traction, postoperative nerve deficits will tcnd to bc inifrequenit aind of short dul-ation. * Complete removal of the integrumnent lining the moist proximilal part of' the eai canal is essential to the success of this procedure. Such thorough Curettage is time'con sumIingr. Similai-ly, where the m11uCOSa of the middle ear- is obviously thickened or material such as pus or keratin debris is found here this must bc completely reiooved. Any bone f'ragments lett at this site will act as a nidus flor intfectioni. so these too must be removed. * The labyr-inth ot' the inner ear is housed in the dense, petrous (rock-like) tempoi-al bone and the two windows openingT into thi'S StluLCture are tucked away in the epitympanumI1. Provided instruments are not directed into this locale, traLumna to these structui-es should be avoided. * Modest para-aural swellinT commlil-only occuLrS postoperatively as a consequence ol' the surgical traumia. Some surgeons like to place a Penrose drain in the tissueSI to help deal with this. The author does not flind it helpful. howevexe. * Provided the preoperative prepar-ationi is coniducted carefully, all the infected tissue is removed and a course of antibiotics is ;given postoperatively. wound dehiscence is unlikely to occur. Results and complications The numerous reports that haxe beeni published as well as the author's personal experience indicate that TECA/LBO surgery can provide outstandingly good results in dogs with end-stage otitis externa. A l.arge majority (85 to 92 per cent) of the dogs to which this surgery has been applied have shown excellent or good long term results. TECA/LBO surgery has also been associated with a high incidence of postoperative complications including: intraoperative death from haemnorrhage. postoperative death or eLithanasia for a variety of reasons; sepsis and fistula formation; signs of damage to the labyrinth (ataxia, nystagmus and head tilt). which may be transient or permiianent; facial nerve partalysis or temporary neurapraxia-; wound dehiscence; and total or partial loss of hearing in dogs in which the surgery has beenl perlormed bilateially. Those surgeons whose experience 364

with the technique is greatest report few postoperative complications which indicates that familiarity with the technique and meticulous curettage, as well as a very good understanding of aural anatomy, aire prerequisites for success. The results of TECA/LBO in dogs with neoplasia of the external ear canal are imuch poorer than for dogs with inflammatory ear disease. However, in one study good or excellent long term results were reported for four of six dogs in which a neoplasm of the horizontal ear canal was dealt with in this way (Matthiesen and Scavelli 1990). In cats, the commonest indication for TECA/LBO is neoplasia; because these tumours are frequently malignant the prognosis for these animals must be guLarded oI poor. Neurological complications, including Horner s syndrome and facial nerve damage, are commiion. References BLAKELY, C. L. (1957) Ottorhoea and surgical drainage 11. In Canine Surgery, 4th edn. Eds K. Mayer, J. V. Lacroix and H. P. Hodkins. Santa Barbara, USA, American Veterinary Publications GREGORY, C. R. & VASSEUR, P. B. (1983) Clinical results of lateral ear resection in dogs. Journal of the American Veterinary Medical Association 182, 1087- 1090 MASON, L. K., HARVEY, C. E. & ORSHER, R. J. (1988) Total ear canal ablation combined with lateral bulla osteotomy for end-stage otitis in dogs. Veterinary Surgery 17, 263-268 MATTHIESEN, D. T. & SCAVELLI, T. (1990) Total ear canal ablation and lateral bulla osteotomy in 38 dogs. Journal of the American Anima/ Hospital Association 26, 257-267 ROBINSON, A. C. & HAWKE, M. (1989) The efficacy of ceruminolytics: everything old is new again. Journal of Otolaryngology 18, 263-267 SIEMERING, G. H. (1980) Resection of the vertical ear canal for treatment of chronic otitis externa. Journal of the American Animal Hospital Association 16, 753-758 SMEAK, D. D. & DEHOFF, W. D. (1986) Total ear canal ablation: Clinical results in the dog and cat. Veterinary Surgery 15, 161-170 TUFVESSON, G. (1955) Operation for otitis externa in dogs according to Zepp's method. American Journal of Veterinary Research 16, 565-570 WHITE, R. A. S. & POMEROY, C. J. (1990) Total ear canal ablation and lateral bulra osteotomy in the dog. Journal of Small Animal Practice 31, 547-553 Further reading BECKMAN, S. L., HENRY, W. B. & CECHER, P. (1990) Total ear canal ablation combining bulla osteotomy and curettage in dogs with chronic otitis externa and media. Journal of the American Veterinary Medical Association 196, 84-90 GIBBS, C. (1978) Radiological refresher: The head, part IlIl Ear disease. Journal of Small Animal Practice 19, 539-545 HUANG, H-P., FIXTER, L. M. & LITTLE, C. J. L. (1994) Lipid content of cerumen from normal and otitic canine ears. Veterinary Record 134, 380-381 LANE, J. G. & LITTLE, C. J. L. (1986) Surgery of the canine external auditory meatus: a review of failures. Journal of Small Animal Practice 27, 247-2 54 LANE, J. G. & WATKINS, P. E. (1986) Para-aural abscess in the dog and cat. Journal of Small Animal Practice 27, 521531

LITTLE, C. J. L. & LANE, J. G. (1989) An evaluation of tympanometry, otoscopy and palpation for assessment of the canine tympanic membrane. Veterinary Record 124, 5-8 LITTLE, C. J. L., LANE, J. G., GIBBS, C. & PEARSON, G. R. (1991) Inflammatory middle ear disease of the dog: The clinical and pathological features of cholesteatoma, a complication of otitis media. Veterinary Record 128, 319-322 LITTLE, C. J. L., LANE, J. G. & PEARSON, G. R. (1991) Inflammatory middle ear disease of the dog: The pathology of otitis media. Veterinary Record 128, 293-296

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, 183-188 WILCOCK, B. P. (1993) Eye and ear. In Pathology of Domestic Animals, 4th edn. Eds K. V. F. Jubb, P. C. Kennedy and N. Palmer. Orlando, USA, Academic Press. pp 441-529 WILLIAMS, J. M. & WHITE, R. A. S. (1992) Total ear canal ablation combined with lateral bulla osteotomy in the cat. Journal of Small Animal Practice 33, 225-227

In Practice * SEPTEMBER 1 996

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Surgical approaches in the management of chronic otitis externa Chris Little In Practice 1996 18: 351-364

doi: 10.1136/inpract.18.8.351

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