PART 1: TUMOR, RESECTION -
PART 2: ROOF OR ORBIT, EXCISION -
The ectodermally derived Schneiderian epithelium, which lines the nasal and paranasal sinuses, had been categorized by Hyams1 into three histologically distinct types of sinonasal papillomas; the most recent World Health Organization nomenclature2 refers to these generically as Schneiderian papillomas, suffixed by the following types: exophytic (previously fungiform, everted, squamous), inverted, and oncocytic (previously cylindrical cell, columnar cell) papillomas.
Oncocytic Schneiderian papilloma (OSP), is the rarest of the 3 subtypes, accounting for 3% to 5% of all sinonasal papillomas1,3. The majority of OSP present beyond the 5th decade of life, without sex predilection. They almost always occur unilaterally. A predilection for the maxillary sinus is apparent in several series1,3-6, though the lateral wall, maxillary or ethmoid may be affected as well.
The gross appearance of OSP is varied: ranging from a fleshy pink to a dark red brown, typical of oncocytic neoplasms of other sites. Microscopically, the tumor is characterized by an exophytic or endophytic proliferation of tall, columnar epithelium that is at least 2 cell layers thick. The cells contain abundant granular eosinophilic cytoplasm. The cytoplasmic tinctorial quality stems from presence of numerous mitochondria, the defining characteristic of oncocytes3. The epithelium classically contains numerous microcysts, often filled with neutrophils. OSP may often occur in mixed form, with areas of inverted papilloma6. The pathogenesis is unclear, but HPV has not been identified in OSP to date7-9.
The main differential diagnostic considerations for OSP are rhinosporidiosis and low-grade papillary adenocarcinoma9. The intraepithelial mucin-filled cysts in OSP, because of their spheroidal nature and mucicarminophilia, are often mistaken for rhinosporidiosis. In rhinosporidiosis, however, the organisms are not limited to the epithelium but also involve the stroma and, moreover, never induce a diffuse oncocytic change in the epithelium. OSP is also occasionally mistaken for a low-grade papillary adenocarcinoma. However, the presence of intact basement membranes, the lack of nuclear pleomorphism, mitotic activity, perineural invasion, and the absence of extensive bone destruction on radiographs in OSP are features that point to the benignity of the tumor. Furthermore, the stratified oncocytic epithelium of OSP is in distinct contrast to the single-layered, non-oncocytic epithelium seen in a low-grade papillary adenocarcinoma9.
OSP, like other schneiderian papillomas, are technically benign but locally aggressive and can undergo malignant transformation. Recurrence rates have been reported to be up to 40%1-3,9 which is similar to that of inverted papilloma (IP), though the relative rarity of OSP has prevented an adequately powered comparison between these types.
Carcinoma arising in OSP is extremely rare with only 16 cases reported1,3,10-13. However, since OSP is itself rare, the resulting rates of malignant transformation have been reported to be as high as 17% in OSP6. Again an accurate comparison to the malignancy rate in IP (generally considered 5-10%2) cannot be made. Invasive squamous cell carcinoma is the most frequently reported malignancy arising in OSP (8 out of the 16 reported cases of carcinoma ex OSP)1,10,11. However, three of the reported cases of malignancy were high-grade mucoepidermoid carcinomas3,11. Other carcinoma types include, papillary 'transitional cell' carcinoma, sinonasal undifferentiated carcinoma, and small cell carcinoma10-13.
Contributed by Henry Armah, MD, PhD and Raja Seethala, MD