History

A 4-year-old 4.0-kg (8.8-lb) spayed female domestic shorthair cat was evaluated because of chronic scratching of its left ear. The owner, who was a veterinarian, reported first noticing a mass in the horizontal canal of the left ear 6 months prior. Previous attempts by the owner to remove the mass otoscopically were unsuccessful.

Clinical Findings

Otoscopic examination of the left ear revealed a large (11 × 6 × 5-mm) bulbous mass within the horizontal canal that obstructed visualization of the tympanic membrane. The surface of this mass appeared red, smooth, and inflamed. In CT images of the skull, soft tissue–attenuating material was present within the left horizontal canal; the material originated from the middle ear and extended from the level of the left ear canal rostrally along the lateral aspect of the ramus of the mandible to the level of the last molar. Ventral bulla osteotomy was performed to completely excise the mass, which originated in the cranial lateral chamber of the bulla and extended across the tympanic membrane into the horizontal canal.

Cytologic Findings

Imprints made from the freshly excised mass were examined microscopically. The mass was highly cellular; there were large numbers of epithelial cells and lower numbers of inflammatory cells against a background that contained abundant erythrocytes, bare nuclei, free cilia, and cellular debris. The epithelial cells were present mostly in clusters of varying size. The cells had distinct cellular borders and ranged from low cuboidal and tall columnar cells to pear- and spindle-shaped cells on the basilar side (Figure 1). They had abundant pale basophilic cytoplasm, a basally located oval nucleus, finely stippled chromatin, and rarely a small nucleolus. The apical side of these cells often had abundant brightly eosinophilic cilia. Admixed with these cells were some oblong secretory cells that had abundant coarse basophilic intracytoplasmic granules and a round polar hyperchromic nucleus. Small lymphocytes and non-degenerate neutrophils were frequently found admixed with the epithelial cells. Occasionally, the epithelial cells were found amid a brightly eosinophilic amorphous extracellular matrix or surrounded by an amphophilic, streaming, mucous material.

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Cytologic image of an imprint of a mass excised from the left ear of an adult domestic shorthair cat that was evaluated because of chronic scratching of its left ear. The mass was first noticed in the horizontal canal of the left ear 6 months prior. Note the large numbers of ciliated (arrows) and secretory (arrowheads) epithelial cells. Wright stain; bar = 20 μm.

Citation: Journal of the American Veterinary Medical Association 252, 3; 10.2460/javma.252.3.297

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Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →

Histologic Findings

Histologically, the excised mass had a polypoid and pedunculated core of proliferative fibrovascular stroma lined superficially by simple to pseudostratified squamous nonkeratinized epithelium. There were nodular aggregates of lymphocytes and plasma cells scattered throughout the mass. At the base of the mass, there were multiple glandular structures lined by tall columnar, ciliated cells and goblet cells, which were interpreted as remnants of normal feline auricular mucoperiosteum of the middle ear (Figure 2).

Interpretation and Case Summary

Interpretation: marked hyperplasia of the auricular mucoperiosteum and lymphocytic inflammation.

Case summary: aural inflammatory polyp in a cat.

Comments

Aural inflammatory polyps are common in young cats. These polyps are nonneoplastic inflammatory lesions that originate from the auditory tube (Eustachian tube) and middle ear.¹ Similar polyps may be found in the nasopharynx as well.² Cats with aural inflammatory polyps may develop head tilt, loss of balance, nystagmus, and Horner syndrome when the polyp affects the auditory tube and otorrhea and head-shaking when the polyp protrudes through the tympanic membrane into the ear canal.¹ The cause of aural inflammatory polyps is unknown¹; it has been suggested that polyps have a congenital origin or are caused by chronic inflammation or infections. By use of molecular methods, the prevalence of feline herpesvirus-1, feline calicivirus, Mycoplasma spp, Bartonella spp, and Chlamydophila felis in normal cats and cats with nasopharyngeal and aural polyps has been investigated.² Results of that study² did not detect differences in the presence of infectious agents between the 2 groups, but the possibility that microbial nucleic acids could have been cleared prior to sample collection was not ruled out.²

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Photomicrograph of a section of the mass removed from the left ear of the cat in Figure 1. The epithelium lining the polyp and the glandular structures are composed of ciliated columnar cells and goblet cells. A lymphocyte population is present on the right of this image. H&E stain; bar = 100 μm.

Citation: Journal of the American Veterinary Medical Association 252, 3; 10.2460/javma.252.3.297

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Treatment of feline aural inflammatory polyps involves surgical removal of the mass. Aural and nasopharyngeal polyps may be removed via traction-avulsion, if amenable, although recurrence is reported in up to 57% of cases.³ When necessary, the polyp may have to be excised through a more invasive approach such as a ventral bulla osteotomy, as performed in the case described in the present report. It is recommended that cats that have an inflammatory polyp removed by traction subsequently undergo ventral bulla osteotomy to remove the epithelial lining from the tympanic cavity at the location of the mass's origin. By doing so, the recurrence rate becomes considerably lower than that achieved by traction removal alone. Postoperative treatment with an anti-inflammatory drug, such as prednisone, may slightly decrease recurrence rates following traction removal alone.

Development of Horner syndrome following removal of an aural inflammatory polyp by traction or bulla osteotomy is a frequent complication. When Horner syndrome develops, it is most commonly transient with spontaneous resolution after 2 to 3 weeks. Treatment of Horner syndrome is rarely required unless vestibular signs are present. Overall prognosis for cats following complete removal of aural inflammatory polyps is generally excellent. The cat of the present report did not develop Horner syndrome after surgery and recovered uneventfully.

Diagnosis of aural inflammatory polyps in cats is typically made on the basis of clinical findings and gross appearance of the lesion during otic examination. In the case described in the present report, the histologic findings were characteristic of a feline aural inflammatory polyp, and cellular remnants of the normal feline auricular mucoperiosteum, namely the ciliated cells and goblet cells, were captured pristinely in the cytologic sample. Sula et al⁴ have reported that the morphological appearance of the auricular mucoperiosteum in cats varies by location. The term mucoperiosteum refers to the direct apposition of epithelial and submucosa against periosteal tissues.⁴ This is a histologic feature unique to the middle ear.⁴ Ciliated epithelial cells are found overlying the petrous portion of the temporal bone medial to the tympanic membrane and the dorsolateral compartment of the auditory ossicles.⁴ Goblet cells are present in the dorsolateral compartment of the auditory ossicles as well.⁴ It has been suggested that the variable morphology of the mucoperiosteum may be related to the dual origin of this epithelium, whereby ciliated epithelial cells originate from the endoderm and nonciliated epithelial cells originate from the neural crest.⁵

Feline aural inflammatory polyp is a nonneoplastic disease that can be diagnosed on the basis of clinical and cytologic findings, with confirmation provided by results of histologic examination of samples of the mass. In the cat of the present report, the cytologic findings reflected the unique histologic features of the auricular mucoperiosteum. Ventral bulla osteotomy is the treatment of choice for aural inflammatory polyps in cats; the prognosis for affected cats that undergo that treatment is excellent.