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Compendium June 2004 (Vol 26, No 6)

Feline Inflammatory Polyps and Ventral Bulla Osteotomy

by D. Michael Tillson, DVM, MS, DACVS, Kristyn E. Donnelly, DVM

    Abstract

    Feline inflammatory polyps are benign growths that most likely originate in the middle ear and eustachian tubes. Depending on which path polyps take when exiting the middle ear and eustachian tube, patients may present with otitis, nasopharyngeal signs, or both. A patient's condition may be acute or chronic. Recurrence rates are minimized when tympanic bulla osteotomy is used to successfully remove the polyp and its inflammatory contents. Ventral bulla osteotomy is the preferred surgical approach. Horner's syndrome and otitis interna are common complications with this procedure; however, they should be minimized with careful surgical technique.

    Feline inflammatory polyps are known by many names, such as middle ear, otopharyngeal, and nasopharyngeal polyps. These benign, fibrous, pedunculated masses have a variety of clinical manifestations, including acute dyspnea and otitis externa. After lymphoma, feline inflammatory polyps are the second most common cause of nasopharyngeal disease and should be considered a top rule out when a mass emanates from within the ear canal.1 Inflammatory polyps tend to occur in younger cats (i.e., usually younger than 2 years of age); however, these polyps have been reported in cats that were a few weeks to 15 years of age.2 No breed or sex predilection has been identified, and polyps tend to be unilateral. Although the cause is still unknown, both infectious and congenital causes have been theorized. The origin of inflammatory polyps is unknown; however, a middle ear or eustachian tube origin has been speculated.

    Historical and Clinical Signs

    Because less than half of cats with polyps have grossly visible disease, a diagnosis of feline inflammatory polyps often begins with observing relevant clinical signs. Clinical signs are usually related to the extension of the mass(es) into the nasopharynx and/or external ear canal. Cats with nasopharyngeal polyps may present with dysphagia or upper respiratory signs such as stertorous respiration, nasal discharge, sneezing, voice change, or dys­pnea.2 Signs of secondary infection such as nasal discharge, rhinitis, and sinusitis may also be present. A retrospective study of 31 cats with nasopharyngeal polyps found upper airway obstruction in 30 cats.3 Cats with polyps that impinge on the auditory system present with very different clinical signs. Polyp extension into the external ear canal appears clinically as dark ceruminous discharge, head tilt, head shaking, or a visible mass in the ear canal.2 Signs of otitis media or interna such as head tilt, nystagmus, and disequilibrium may also be present.

    Gross Appearance and Histopathology

    Nasopharyngeal masses tend to be pink and pedunculated and have variable ulcerations. External ear polyps are oval to elliptical, are often red, pink, or white, and glisten because of a mucosal covering.4 Polyps that have not extended through the tympanic membrane may distort or discolor the tympanic membrane before ­perforation. Feline inflammatory polyps are typically composed of stratified squamous to pseudostratified ciliated columnar epithelium that covers a core of fibrovascular connective tissue containing scattered lymphocytes, plasma cells, and macrophages.4,5

    Cause

    The cause of feline inflammatory polyps is still unknown. Both the temporal relationship between polyp formation and inflammation and the site of origin remain unproven. Two common theories link polyps to congenital or infectious causes. The young age of most affected cats suggests that feline inflammatory polyps are aberrant growths, remnants of the branchial arches. Based on histopathology and clinical signs, however, polyps appear to be produced in response to inflammation (see Histopathology section). Pasteurella multocida and b-hemolytic Streptococcus were the two most common bacterial isolates in a clinical study of 12 cats with inflammatory polyps.1 Klebsiella, Achromobacter, and Bordetella spp have been isolated as well.3,6 However, one study found bacteria in only 3 of 29 cats with polyps.3 Whether inflammation and infection are primary or secondary to this disease is still unclear.3 It has been postulated that microorganisms migrate from the nasopharynx into the middle ear. In support of this idea, feline calicivirus has been isolated from some polyps and the nasopharyngeal region, although the direct relationship has not been determined.4,7 Experimental ligation of the auditory canals leads to polyp formation as well.7,8

    A related matter that is still in question is the exact origin of feline inflammatory polyps. This distinction is important to determine the best surgical approach. Some sources cite the origin of polyps as the mucosa of the nasopharynx, eustachian tube, or middle ear.8,9 Others suggest that feline inflammatory polyps originate solely within the middle ear or auditory tube close to its junction with the tympanic cavity. Polyps then exit the tympanic cavity via either the eustachian tube (to the nasopharynx) or the tympanic membrane (to the external ear canal).1,2,4,5

    Experimentally ligating the auditory tube causes mucociliary dysfunction, mucous hypersecretion, and otitis media with effusion, which is frequently complicated by bacterial colonization.8 Furthermore, granulation tissue in the middle ear may cause the respiratory epithelium to undergo metaplasia, resulting in stratified squamous epithelium, which may form a polyp.8 In a study by Trevor and Martin,5 all cats with inflammatory polyps had a tympanic cavity filled with polyp material. In further support of polyps originating in the middle ear, the lowest recurrence rate occurs when bulla osteotomy is performed.1,5 The origin of the polyp stalk is presumably removed with this procedure. Simple traction-avulsion techniques have much higher rates of regrowth.2,8

    Diagnosis

    Upper respiratory tract infections (e.g., due to feline calicivirus and rhinotracheitis), nasal foreign bodies, neoplasia, otitis externa/media/interna, and mycotic disease should be included in the differential diagnosis of feline inflammatory polyps. Diagnosing inflammatory polyps begins with oral and auditory examinations using general anesthesia. On occasion, the soft palate is displaced ventrally by a polyp as it emerges from the auditory tube into the pharynx. A Snook hook or retroflexed endoscope may help visualize masses dorsal to the soft palate.

    Polyps may also be seen exiting the external auditory meatus. They can be visualized with an otoscope or a videootoscope. The tympanic membrane should be examined for bulging, perforation, or inflammation. A myringotomy may be performed to obtain a culture.10

    Radiographic analysis is warranted to diagnose polyps. Diagnostic quality views of the tympanic bulla and surrounding structures require anesthesia. Ventrodorsal, oblique lateral, and frontal open-mouth ­projections are useful in evaluating the tympanic bulla. Findings such as a proliferative periosteal response, thickening or irregularity of the bulla wall, or soft tissue opacity within the bullae are consistent with potential long-standing middle ear disease (Figure 1). Changes on routine views correlate with 75% of known positives, leaving 25% of cases of otitis media undiagnosed based on radiographs alone.4 This must be considered given that polyps may not cause otitis media until late in the disease process.3,9,11 Kapatkin and Matthiesen3 found that 84% of cats with polyps had a radiographic middle ear change. Lateral views are best for nasopharyngeal polyps, which are visualized as a soft tissue opacity in the nasopharynx.

    Both computed tomography (CT) and magnetic resonance imaging (MRI) allow better evaluation of the bulla than do radiographic skull films.4,8 They provide a much clearer view of the tympanic bulla and surrounding tissues (Figure 2). Thickening of the osseous bullae as well as soft tissue opacities is much more easily seen than with radiography. MRI is capable of showing soft tissue changes of the tympanic bulla, fluid accumulation, and cystic growths.

    Many surgeons advocate ventral bulla osteotomy regardless of obvious radiographic involvement of the middle ear because polyps potentially originate from the bulla. This is supported by the low recurrence rate after ventral bulla osteotomy.5 We believe, given the likelihood that polyps originate from the middle ear, that even if bulla abnormalities are not seen using radiography, MRI, or CT, surgical intervention in an affected middle ear can be recommended with confidence.

    The definitive diagnosis of feline inflammatory polyp is made histologically from surgical biopsy ­samples.

    Treatment

    Medical management has been routinely ineffective at eliminating polyps and has been best used in conjunction with surgical removal (i.e., medical management of residual otitis media). Surgically managing inflammatory polyps remains the preferred choice of treatment with minimal recurrence. Surgical options for removing inflammatory polyps include traction-avulsion, ventral bulla osteotomy, myringotomy, lateral ear resection, ear canal ablation combined with lateral bulla osteotomy, and, in a limited role, laser debulking and sterilization of the middle ear.4 Ventral bulla osteotomy provides the best access to the middle ear, from which polyps are thought to originate.1,2,10 Lateral bulla osteotomy with total ear canal ablation is another option, but it is probably unwarranted because cats are left without an external ear canal.4 Ventral bulla osteotomy, which is the most common and successful (i.e., recurrence rate: 2%) surgery for polyp removal, is discussed in detail in this ­article.2

    Treating cats with inflammatory polyps without radio­graphic evidence of otitis media remains controversial. In these cases, careful traction can be used to remove inflammatory polyps from the external ear canal or nasopharynx. The soft palate should be retracted with a stay suture or spay hook to allow visualization of the polyp. On occasion, the soft palate must be incised down its midline to increase visualization. The polyp should be grasped with right angle or alligator forceps and gentle traction applied until it is avulsed from its origin. Hemorrhage is generally minimal.4 A similar method can be used to extract polyps that em­anate from the external ear canal. This method re­mains controversial because the polyp base is often left behind, promoting recurrence. Naso­pharyngeal polyp removal by traction, in conjunction with prednisolone (1 to 2 mg/kg/day for 14 days, followed by a tapered withdrawal for 2 weeks) resulted in a recurrence rate of only 11% in cats.4 External ear polyps had a recurrence rate of 50% after removal by traction.4 These statistics are not surprising considering that most polyps appear to originate within the middle ear. Surgical procedures should extract the entire polyp, including its base and all associated debris to minimize the chance of recurrence; because of the local anatomy, however, this cannot be done without risks.2

    If radiographic evidence of middle ear disease is present, ventral bulla osteotomy should be performed.1,2-6,10 Because polyps likely originate from the middle ear, ventral bulla osteotomy is probably justified in all cases of inflammatory polyps.2,5 Lateralization via an otoscopic examination (for an otic polyp) or imaging technique (i.e., radiography, CT, MRI; for an inflammatory polyp) is appropriate before ventral bulla osteotomy. Bradley and Noone9 performed ventral bulla osteotomies in three of five cats that presented with nasopharyngeal polyps. In these three cats, polyps did not recur, whereas polyps recurred in both cases in which simple traction was applied via an oral approach.9 In one study of 12 cats, polyps did not recur when ventral bulla osteotomy was performed based on radiographic evidence of otitis and histologic confirmation of inflammatory polyps.1 Kapatkin and Matthiesen3 performed bulla osteotomies on 23 of 31 cats. Four of five cats in which regrowth occurred did not have an initial bulla osteotomy. ­Kapatkin and Matthiesen3 as well as Boothe6 concluded that, even without radiologic evidence of otitis media, bulla osteotomy may be justified in all cats during polyp removal to eliminate otitis and prevent recurrence.

    Surgery

    To perform ventral bulla osteotomy, the patient should be intubated and placed in dorsal recumbency with cervical support to extend the neck and maximize the surgical area. The cervical, intermandibular, and facial areas should be clipped and aseptically prepared. The rounded ventral aspect of the tympanic bulla (bound by the wing of the atlas [C2], caudal border of the mandible, and larynx) can be palpated in most cats. A 3- to 5-cm incision should be centered between the wing of the atlas and angular process of the mandible (i.e., paramedian) and made directly over the bulla.14 Dissection should be continued through the platysma and sphincter colli muscles. The mandibular salivary gland and bifurcation of the facial and lingual veins (if visible) should be retracted from the field. Blunt dissection should be continued between the digastric muscle laterally and styloglossus and hyoglossus muscles medially. The hypoglossal nerve, located medial to the hyoglossal muscle, should be identified and the lingual artery retracted medially. The external carotid is dorsolateral to the bulla and should not be in the field. Senn and/or Gelpi retractors should be used to carefully retract soft tissue and improve visualization. A periosteal elevator should be used to remove overlying soft tissue from the ventral surface of the bulla.

    The bulla should be entered through the larger ventromedial compartment. Osteotomy can be performed using a 1/8-inch Steinmann pin and a hand chuck or an air drill. If a Steinmann pin is used, the osteotomy should begin with a small pin and progress to larger pins until the opening is large enough to accommodate rongeurs (e.g., Kerrison, Lempert). Thick mucus or other debris is often encountered at this point.

    Once the osteotomy of the ventral aspect of the tympanic bulla is complete, the dorsolateral compartment should be entered because that is where most polyps originate.2 The ventral portion of the septum should be removed at its lateral-most aspect to avoid the sympathetic fibers coursing over the oval promontory and reduce the risk of causing Horner's syndrome. The septum can be removed in a fashion similar to the original entry into the tympanic cavity (i.e., with a drill and pin). Once both compartments have been entered, appropriate cultures should be taken, including those for mycoplasma.12

    Thumb forceps and a small curette should be used to remove the polyp, epithelial lining, and accumulated material while avoiding iatrogenic trauma to the nerves. Small curettes and Freer periosteal elevators should be used to remove all polypoid material and associated attachments. The excised tissues should be submitted for histopathologic analysis. The site should be thoroughly lavaged with warm saline before closure. Although drain placement is controversial, we place a 1/4-inch Penrose drain in the bulla with an egress site adjacent to, but not incorporated within, the original incision. The external ear and/or oropharynx should be examined to ensure full removal of the polyp. Otoscopic and pharyngeal examination can help ensure complete removal. Traction may be necessary to remove the remaining polypoid material. The wound should be bandaged until the drain is removed in approximately 3 days. An Elizabethan collar may be needed. Appropriate antibiotic therapy, based on culture and susceptibility, should be administered for approximately 3 to 5 weeks.

    Surgical Complications

    Potential complications following bulla osteotomy include Horner's syndrome, vestibular disturbances, polyp regrowth, otitis media, hemorrhage, wound drainage, hypoglossal nerve damage, damage to auditory ossicles and vascular structures, and facial nerve paralysis. Manipulating pharyngeal tissue that has nasopharyngeal polyps warrants postoperatively monitoring respiratory quality. Careful surgical technique and recognizing anatomic landmarks should minimize the risk of these ­complications.

    Horner's syndrome has been observed in most cats after polyp excision.12 Horner's syndrome, which is characterized by ptosis, miosis, enophthalmos, and elevation of the third eyelid, is most likely caused by damage to the oculosympathetic trunk during polyp removal and curettage. In most cases, it resolves within weeks to months. In a study by Faulkner and Budsberg,1 83% of cats were affected with Horner's syndrome, 25% of which were affected in the long term. In another study, three of five cats had Horner's syndrome that resolved in 7 to 14 months.9 Kapatkin and Matthiesen3 diagnosed Horner's syndrome in 22 of 23 cats that had a ventral bulla osteotomy. All cases eventually resolved.

    Overzealous curettage of the bulla that damages the round and oval windows or vestibulocochlear apparatus results in vestibular disturbances. This manifests clinically as head tilt, ataxia, and nystagmus and appears to be less common than Horner's syndrome, with a reported incidence of 4% to 42%.1,3 Vestibular signs can be minimized with meclizine (12.5 mg PO q24h) until signs resolve.15 Facial and hypoglossal nerve paralyses are uncommon complications of ventral bulla osteotomy.

    Summary

    Feline inflammatory polyps are benign masses that most likely originate in the middle ear and/or auditory tubes that extend into the nasopharynx and external ear canals. Diagnosis should be based on history, diagnostic imaging, and direct visualization. The most reliable method of permanently removing inflammatory polyps is ventral bulla osteotomy. Knowing the surgical anatomy of the feline middle ear is essential to perform a successful ventral bulla osteotomy with minimal iatrogenic complications.

    See Surgical Anatomy box .

    Downloadable PDF

    1. Faulkner JE, Budsberg SC: Results of ventral bulla osteotomy for treatment of middle ear polyps in cats. JAVMA 26:496-499, 1990.

    2. Pope ER, Constantinescu GM: Feline respiratory tract polyps, in Bonagura J (ed): Kirk's Current Veterinary Therapy XIII. Philadelphia, WB Saunders, 2000, pp 794-796.

    3. Kapatkin AS, Matthiesen DT: Results of surgery and long-term follow-up in 31 cats with nasopharyngeal polyps. JAAHA 26:387-392, 1990.

    4. Muilenburg RK, Fry TR: Feline nasopharyngeal polyps. Vet Clin North Am Small Anim Pract 32(4):839-849, 2002.

    5. Trevor PB, Martin RA: Tympanic bulla osteotomy for treatment of middle ear disease in cats: 19 cases (1984-1991). JAVMA 202(1):123-128, 1993.

    6. Boothe HW: Ventral bulla osteotomy: Dog and cat, in Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 4. Baltimore, Lippincott, Williams & Wilkins, 1998, pp 109-111.

    7. Parker NR, Binnington AG: Nasopharyngeal polyps in cats: Three case reports and a review of the literature. JAAHA 21:473-478, 1985.

    8. Little JL: Nasopharyngeal polyps, in August JR (ed): Consultations in Feline Internal Medicine, ed 3. Philadelphia, WB Saunders, 1997, pp 310-315.

    9. Bradley RL, Noone KE: Nasopharyngeal and middle ear polypoid masses in five cats. Vet Surg 14(2):141-144, 1985.

    10. White RA: Middle ear, in Slatter DH (ed): Textbook of Small Animal Surgery, ed 3. Philadelphia, WB Saunders, 2003, pp 1760-1767.

    11. Little CJ, Lane JG: The surgical anatomy of the feline bulla tympanic. J Small Anim Pract 27:371-378, 1986.

    12. Smeak D: Ventral bulla osteotomy in cats. Proc 12th Annu Vet Symp ACVS:122-124, 2002.

    13. Hudson LC, Hamilton WP: Atlas of Feline Anatomy for Veterinarians. Philadelphia, WB Saunders, 229-234, 1993.

    14. Smith MM, Waldron DR: Atlas of Approaches for General Surgery of the Dog and Cat. Philadelphia, WB Saunders, 1993, pp 115-117.

    15. Plumb DC: Meclizine. Veterinary Drug Book, ed 4. Ames, Iowa State University Press, 2002.

    References »

    NEXT: Hypernatremia in Critically Ill Cats: Evaluation and Treatment

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