Answer: Sinonasal adenocarcinoma, intestinal type

Histology: Histologic evaluation reveals the presence of highly infiltrative malignant glands in a desmoplastic stroma. The glands are lined by stratified columnar cells with elongated nuclei. In areas, the tumor is associated with pools of extracellular mucin.

Discussion: Primary adenocarcinomas of the sinonasal tract are broadly subclassified into salivary gland and non-salivary gland types. The salivary gland adenocarcinomas arise from the mucinous glands that populate the submucosal of the sinonasal tract, and the non-salivary adenocarcinomas take origin from the surface mucosa. The non-salivary types are further subdivided into intestinal and non-intestinal types based on their morphologic resemblance (or lack of it) to glandular neoplasms of the intestinal tract. The intestinal types of sinonasal adenocarcinomas can mimic the full spectrum of colonic neoplasia – from villous adenoma to conventional intestinal adenocarcinoma to intestinal colloid carcinoma. The distinction between intestinal and non-intestinal sinonasal adenocarcinomas is important as many of the non-intestinal types are well differentiated and clinically indolent. In contrast, the intestinal types, particularly those that resemble invasive colonic adenocarcinomas, are aggressive tumors that are often lethal.

Sinonasal intestinal-type adenocarcinoma also shares the same immunohistochemical profile as colonic adenocarcinomas. Specifically, both tumors are immunoreactive for CK20 and CDX2; and both are non-immunoreactive for CK7. Because of this striking morphologic and immunohistochemical overlap, the only reliable way to exclude a metastasis from the intestinal tract is a thorough clinical history and clinical examination.