Answer: Sinonasal intestinal type adenocarcinoma

Histology: The tumor has a distinct resemblance to colonic carcinoma. The tumor forms large glands and papillary structures characterized by columnar, hyperchromatic, stratified nuclei with apical mucin. More solid areas with high mitotic activity and rounder nuclei are also present. Further questioning reveals that the patient does not have a history of colorectal carcinoma, and is a woodworker.

Discussion: Sinonasal intestinal type adenocarcinoma is morphologically essentially identical to colonic adenocarcinoma. Distinction is made by the clinical history; namely, the lack of a history of colonic carcinoma, (which only infrequently metastasizes to the sinonasal tract) and a positive history of woodworking with its inherent dust exposure. Additionally, sinonasal intestinal type adenocarcinomas are often CEA negative, in contrast to colonic adenocarcinomas. Mucoepidermoid carcinomas would feature squamoid areas and do not demonstrate typically the well-developed goblet cells of the sinonasal intestinal type adenocarcinoma. Low-grade adenocarcinomas of the sinus lack the pleomorphism, high mitotic rate, and intestinal appearance of these tumors.

The histology of sinonasal intestinal type adenocarcinomas essentially recapitulates the spectrum of intestinal tract pathology. Well-differentiated papillary forms can resemble normal small bowel, other forms have an adenomatous appearance, and other higher-grade lesions are morphologically identical to colonic adenocarcinoma with extensive necrosis. The typical presentation is in the sinuses (ethmoid is most common) or nasal cavity as a nasal polyp or refractory chronic sinusitis. These tumors are locally aggressive; only 10 percent metastasize but progressive local disease results in death in approximately 60 percent of patients.