3 November 2010 – Case of the Week #189
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Case of the Week #189
A 58 year old man had a large, rectosigmoid colonic polyp excised.
What is your diagnosis?
Tubulovillous adenoma with microcarcinoids
The small islands of cells were immunoreactive for synaptophysin.
Microcarcinoids within adenomatous polyps of the colon have only recently been described (Am J Surg Pathol 2006;30:1531). They range up to 1.5 mm in size, and are located between the crypts and the muscularis mucosae. They are composed of nests, cords, tubules and clusters of large epithelial cells with abundant cytoplasm, usually eosinophilic and granular, and round central nuclei with stippled or dusty chromatin. There is no desmoplasia, no atypia and no mitotic activity. Tumor cells are immunoreactive for chromogranin, synaptophysin, neuron-specific enolase or other neuroendocrine markers.
Microcarcinoids have previously been described in ulcerative colitis (J Clin Pathol 2003;56:963) and other chronic inflammatory disorders, where they may be due to reactive hyperplasia of colonic endocrine cells.
The differential diagnosis includes mixed adenoma-carcinoids. In these tumors, the carcinoid component is substantial, in contrast to the incidental microcarcinoid tumor in this case that did not alter the polyp architecture. Microcarcinoids may be interpreted as incipient adenocarcinoma, particularly if the polyp exhibits high grade dysplasia. Finally, due to their incidental nature, the microcarcinoids may not be identified.
These microcarcinoids appear to have benign behavior, with no recurrences identified to date.
Nat Pernick, M.D., President
and Liz Parker, B.A., Associate Medical Editor
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
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