Pathology of the Head and Neck

Nasal Cavity and Paranasal Sinuses Chapter 2 47cysts. The invagination of the mucosa may result in thepresence of apparently discontinuous cell masses lyingdeep to the epithelial surface, but the basement membraneis intact and may be shown in continuity with thatof the surface epithelium [226]. An inverted growth isthe hallmark of inverted papilloma, but varying degreesof papillary growth may be seen at the surface [54]. Thesurface is characteristically lined by a respiratory typeof epithelium; nevertheless, foci of surface keratinisationare occasionally present [122]. A few regular mitosesmay be found in the basal and parabasal layers. Althoughthe nuclei may show mild nuclear irregularitiesand hyperchromatism, no disturbances of the cellularpolarity are found. An abundant and oedematous connectivetissue stroma is a common feature of invertedpapillomas. It usually contains macrophages and neutrophils,but eosinophils may also be present. This inflammatoryinfiltrate may also be present between theepithelial cells, within the dilated lumens of invaginatedcrypts, and within the numerous microcysts that usuallyoccur in the respiratory epithelium. Seromucinousglands are absent, but branching gland ducts are oftenpresent. The tumour grows by extension to involve thecontiguous sinonasal epithelium.If treated only by local surgical excision, recurrenceoccurs in up 75% of cases. Therefore, lateral rhinotomyand medial maxillectomy are advisable for tumours ofthe lateral nasal wall [236]. Carcinoma develops in about10–15% of inverted papillomas [122, 211, 236]. Carcinomamay coexist with inverted papilloma at the initialpresentation or originate subsequently [122, 273].According to the experience of Michaels and Hellquist[171], carcinoma does not usually develop in the courseof recurrences of inverted papilloma. In the presenceof severe atypia or marked keratinisation in an invertedpapilloma malignant transformation is always suspected(Fig. 2.4b). In these instances the entire specimenshould be thoroughly examined to exclude an associatedcarcinoma. Most associated carcinomas are squamous[204], although other types may also occur such asverrucous carcinoma [192].2.9.1.4 Oncocytic PapillomaabFig. 2.4. a Inverted papilloma: prominent invaginating cryptslined by hyperplastic respiratory epithelium are supported by oedematousconnective tissue. b Squamous cell carcinoma ex invertedpapilloma: remnants of benign invaginating crypts are seen betweeninvasive cords of squamous epitheliumICD-O:8121/1Oncocytic papilloma, also known as “columnar” or “cylindric”cell papilloma [226], is the least common type ofschneiderian papilloma. It constitutes less than 5% of allsinonasal papillomas [18, 122, 173, 262]. Both sexes areequally affected. Bilaterality has not been documented.Tumours are in general small, although occasionally mayreach various centimetre measurements in their greatestdimension. They are composed of exophytic frondsand endophytic invaginations lined by pseudostratifiedor multilayered columnar cells with prominent oncocyticfeatures. The cells have uniform hyperchromaticnuclei and abundant eosinophilic, occasionally granular,cytoplasm that contains abundant mitochondriaand stains for the mitochondrial enzyme cytochromeC oxidase [59]. Goblet cells are not found. Cilia may beoccasionally encountered on the superficial epitheliallayer. Intraepithelial microcysts containing mucin andneutrophils are usually present. These microcysts arelarger than the similar structures also seen in invertedpapilloma. The tumour resembles inverted papilloma inits sites of occurrence, the lateral wall of the nasal cavityand the maxillary antrum. The rate of recurrence isconsidered to be 36%, which is lower than in invertedpapilloma. The low frequency of this tumour makes itdifficult to evaluate its true malignant potential, whichseems to be similar to that of inverted papilloma [262].Atypical hyperplasia and carcinoma in situ changescan be occasionally found (Fig. 2.5). Surgical excisionwith wide margins is the treatment of choice. Invasivesquamous cell carcinoma, high-grade mucoepidermoid