Harry W. Boothe, DVM, MS, DACVS
Effective management of the patient with severe otitis externa often involves a combination of medical and surgical therapy. Decisions which need to be made concerning surgical management of severe otitis externa include when to perform surgery, which procedure is most appropriate and how to maximize success following otic surgery. Otic surgical procedures include: lateral ear resection, vertical ear canal ablation, and total ear canal ablation with bulla osteotomy. Specific manifestations of severe (advanced) otitis externa used to illustrate surgical decision-making include calcification of the ear canal cartilages, granulomatous proliferations of the ear canal, and periotic abscessation.
When To Perform Surgery
In general, otic surgery should be performed when there has been incomplete or temporary response to appropriate non-surgical management. Only with total ear canal ablation with bulla osteotomy, is surgery, by itself, curative. In selected cases, less invasive surgery (lateral ear resection or vertical ear canal ablation) combined with appropriate long-term medical management may help prolong the function of the ear while reducing patient discomfort. Once a decision has been made to perform surgery, there is little information to suggest that specific preoperative or perioperative antimicrobial therapy is indicated. Culture and susceptibility testing of samples obtained at surgery from the external ear canal (lateral ear resection and vertical ear canal ablation) or the middle ear canal (total ear canal ablation with bulla osteotomy) may be more representative if preoperative or perioperative antimicrobials are not used for a few days immediately prior to surgery.
Which Procedure To Perform
The type of ear surgery to perform is based on the extent and severity of otic disease present. Determine the extent and severity of otic disease by performing otoscopic and radiologic (including computerized tomography [CT]) examinations. Rupture of the tympanic membrane on otoscopic exam or evidence of otitis media on radiologic (CT) exam is usually an indication for performing a total ear canal ablation with bulla osteotomy. Palpation of the external ear canal will determine the presence of calcification or proliferation of the otic cartilages. Calcification of otic cartilages is usually an indication for performing a total ear canal ablation with bulla osteotomy.
Owner's expectations also may impact the decision as to which procedure to perform. Those clients that are seeking otic surgery to avoid the need to treat their pet's ears again should be advised that a total ear canal ablation with bulla osteotomy is their best alternative. Functional hearing loss after total ear canal ablation with bulla osteotomy may be complete; however, little change from the pet's preoperative state may be noted. This probably reflects the marked loss of hearing due to the chronic, severe otitis externa.
Lateral Ear Resection
Lateral ear resection is the least invasive surgical procedure of the external ear canal. This procedure has been used in veterinary patients for over 40 years. Lateral ear resection is indicated in the patient with chronic non-proliferative otitis externa that has failed to respond adequately to appropriate medical management. Lateral ear resection may also be used to gain access for excisional biopsy of masses involving the vertical ear canal. The goal of lateral ear resection is to provide access to the horizontal ear canal. The medial wall of the vertical ear canal and the entire horizontal ear canal remain after lateral ear resection.
Following surgical preparation of both sides of the pinna, ear canal and lateral periotic region, drape the site to expose the entire pinna. Measure the level of the horizontal ear canal by inserting a forceps or probe into the vertical portion of the ear canal. Create a "U"-shaped skin incision so that its width just exceeds that of the vertical canal and its length extends approximately 2 cm below the junction of the vertical and horizontal ear canals. Dissect the skin flap and leave it attached dorsally to assist in the cartilage incision. Bluntly and sharply dissect the subcutaneous tissue and the parotid salivary gland to expose the lateral wall of the vertical ear canal. Using scissors, create parallel incisions in the lateral cartilage to the level of the horizontal canal. Start the rostral incision at the tragohelicine incisure, and start the caudal incision at the intertragic incisure. Most canine ear canals curve slightly rostrally; hence, both cartilaginous incisions should curve slightly rostrally to maximize exposure of the horizontal canal. Deflect the incised flap of vertical canal ventrally, trim it to the appropriate size, and suture the edges of the cartilaginous flap to the skin. Carefully appose the skin and ear canal epithelium with monofilament, nonabsorbable sutures (e g, 3-0 polypropylene).
Vertical Ear Canal Ablation
The vertical ear canal ablation also has the goal of providing access to the horizontal ear canal, but it results in excision of the entire vertical ear canal. Indications for performing a vertical ear canal ablation are similar to those for lateral ear resection, but also include proliferative (granulomatous) otitis externa involving only the vertical ear canal, neoplasia of the vertical ear canal only, and possibly traumatic separation of the auricular and annular cartilages. Because this procedure results in removal of more diseased tissue compared to the lateral ear resection and has reduced postoperative pain, vertical ear canal ablation may be preferable to the lateral ear resection procedure. The vertical ear canal ablation procedure may also be technically easier to perform than a lateral ear resection since creation of a more precise opening to the horizontal canal is accomplished more consistently.
Prepare and drape the affected ear as described for lateral ear resection. Create a vertical skin incision directly over the vertical ear canal to the level of the horizontal ear canal. Make a circular incision surrounding the opening of the ear canal and connect the vertical incision. Make this circular incision just dorsal to the proliferative tissue which surrounds the opening of the ear canal. Take care when incising the skin and cartilage of the anthelix so as to incise just through the cartilage and not the deeper tissue. Dissect the entire vertical ear canal from the surrounding tissue to the level of the horizontal canal using blunt and sharp dissection. The horizontal ear canal begins just proximal to the junction of the auricular and annular cartilages. Excise the vertical ear canal by scalpel, creating an opening into the horizontal ear canal. When incising the ventral aspect of the cartilage, make an attempt to create a small drain board. This tends to make suturing of the horizontal canal cartilage easier and reduce the potential for stricture of the opening of the ear canal. Appose the epithelium of the horizontal ear canal as accurately as possible to the surrounding skin with monofilament, nonabsorbable sutures (e g, 3-0 polypropylene). Close the dorsal aspect of the skin incision in the shape of a "T", using the same suture material.
Surgical correction of traumatic separation of the auricular and annular cartilages results in the creation of a horizontal opening in the horizontal ear canal, similar to that which results from a vertical ear canal ablation. Locate the blind end of the horizontal ear canal (proximal end of the annular cartilage) by sharp and blunt dissection. Flush the secretion-filled horizontal ear canal, and appose the epithelium of the horizontal ear canal to the surrounding skin with sutures. Leave the vertical ear canal, which is separated from the rest of the ear canal, undisturbed. The horizontal ear canal in cases of traumatic separation of the auricular and annular cartilages tends to be shorter than that following a standard vertical ear canal ablation. Thus, tension on the suture line uniting the skin and otic epithelium tends to be greater, with postoperative stricture of the otic orifice more troublesome.
Total Ear Canal Ablation
Total ear canal ablation is the most invasive surgery of the external ear, yet it is most likely to be curative when combined with a lateral bulla osteotomy procedure. Indications for performing a total ear canal ablation include proliferative otitis externa in which the proliferations are present in the horizontal and vertical ear canals, most cases of periotic abscessation, severe, non-responsive, painful otitis externa accompanied by otitis media, calcification of the otic cartilages (especially annular cartilage), and neoplasia of the horizontal ear canal. Total ear canal ablation results in excision of the entire external ear canal. The goals of this procedure are to surgically excise all diseased tissue (infected and/or neoplastic), including epithelium of the tympanic bulla, and to eliminate the clinical signs associated with otitis externa.
Prepare and drape the affected ear as described for lateral ear resection. The skin incision and initial dissection are identical to those for the vertical ear canal ablation. Continue dissection around the entire horizontal ear canal until the junction of the annular cartilage and the skull is reached. Take great care when dissecting around the horizontal ear canal, particularly in the ossified ear canal, to avoid damaging the facial nerve. Positively identify and protect the facial nerve, which courses rostrally just ventral to the horizontal ear canal. Carefully excise the ear canal from the skull with either scalpel blade or rongeurs. Since otic epithelium continues into the bony ear canal for 5-10 mm before the tympanum is reached, this tissue must be excised as well. Use both rongeurs and a bone curette to remove all of the epithelial tissue. Use the rongeurs to remove the ventrolateral wall of the osseous bulla and bony ear canal. Access to the middle ear cavity (tympanic cavity) enables flushing and gentle curettage of this area. This step is critical to a long-term successful outcome. Close the skin in a "T"-shape.
Possible complications following total ear canal ablation include facial nerve injury (resulting in partial or complete facial paralysis), sympathetic nerve injury (resulting in Horner's syndrome), and hearing loss.
Results following otic surgery depend, to a large part, on proper patient selection, avoiding technical errors, identification and treating systemic disease(s), accurately assessing the extent of ear disease and conscientious postoperative management. Failure following lateral ear resection has been shown to be as high as 47% in one study. Long-term results following vertical ear canal ablation may be more favorable than those for lateral ear resection. Results following total ear canal ablation without bulla osteotomy have been discouraging, with recurrence of periotic abscessation being a common complication. Results following total ear canal ablation with lateral bulla osteotomy have been quite favorable.
How to Maximize Success Following Surgery
Attentiveness to technical details during surgery will usually improve long-term success. Diligently remove affected tissue, and accurately approximate tissues, particularly near the otic orifice (lateral ear resection and vertical ear canal ablation). Ear surgery is painful, and postoperative analgesics should be used routinely. Use of preoperative analgesics and intra-operative local anesthetics (e g, bupivacaine hydrochloride) will improve patient comfort in the early postoperative period. Avoid self-inflicted trauma by protecting the surgical site with bandages postoperatively. Use hot packs to minimize postoperative swelling and to facilitate removal of debris and exudates from the incision. Use systemic antimicrobial agent(s) which are based on culture and susceptibility testing results. Use appropriate systemic antimicrobial(s) for 4 to 6 weeks. Remove sutures in 10 to 14 days.
In summary, success of surgical management of severe otitis externa depends on complete patient evaluation so that the extent of ear disease is determined, selection of the appropriate surgical procedure, knowledge of the regional anatomy, attentiveness to technical detail and dedicated postoperative care. If the above steps are followed, improved results should be expected.