Primary adenocarcinoma of the small intestine with emphasis on microvillous differentiation

A detailed ultrastructural study was made of 12 primary adenocarcinomas of the small intestine. A comparative analysis of microvilli identified three characteristic features in various proportions on the apical tumor cell surface. These were; 1) "long rootlets," which are long intravillous filamentous cores penetrating into the cytoplasm and identical to those observed in colonic adenocarcinoma; 2) a regular arrangement of uniform microvilli similar to the brush border of normal intestinal epithelium; and 3) sparse rudimentary microvillous structures. Because of the rarity of adenocarcinoma in the small intestine no previous study defined these ultrastructural characteristics. The results of the present study suggest that the diverse ultrastructural findings may be related to different stages of tumor cell maturation and that the neoplastic state may increase the variation and range of microvillous differentiation regardless of capacity of mucin secretion by the tumor cells. For diagnostic purposes, brush borders as well as two other microvillous features may serve to identify adenocarcinoma of mucosal origin of the small intestine, if an ultrastructural study discloses these three features.