Discussion

Diagnosis

Composite intestinal adenoma-microcarcinoid (CIAM).

Discussion

CIAM is a rare gastrointestinal lesion consisting of a conventional adenoma interspersed with small foci of monotonous cells with neuroendocrine or squamoid features. The cells may be present individually or grouped as nests and trabeculae and they are typically situated within the basal aspect of the lamina propria, yet some extend into the muscularis mucosae. CIAM is discovered incidentally during histologic examination of polypectomy specimens and is most prevalent in the colorectal region, with a few cases described in the stomach and small intestine. Aside from CIAM in the stomach, there is no standardized size criterion. CIAM is distinct from mixed-adenoma carcinoids, which are characterized by a substantial neuroendocrine cell population that disturbs the overall architecture of the polyp, making them visible on endoscopy. CIAM has an overall favorable clinical course, with only one documented case with neuroendocrine metastasis to a lymph node.

The etiology of CIAM remains unknown. Several cases have been described in patients with chronic inflammatory disorders of the gastrointestinal tract, such as ulcerative colitis. As a result, some have suggested that these lesions arise in response to chronic inflammation. Additional hypotheses propose adenomas and microcarcinoids differentiate from a common cell of origin or that neuroendocrine metaplasia is induced by the adenoma.

It is important to recognize CIAM since diagnostic pitfalls can drastically alter clinical management. The most significant pitfall leads to misdiagnosis of the lesion as an adenocarcinoma. This occurs in lesions characterized by infiltrative single cells or in lesions with mucosal prolapse and a desmoplastic-like reaction. The use of immunohistochemistry, specifically synaptophysin and chromogranin, identifies cells with neuroendocrine differentiation and Ki-67 expression will be low. Lastly, these cells stain strongly for β-catenin and may show p63 and CK5/6 positivity.

References

Kim, M.J., et al., Composite intestinal adenoma-microcarcinoid in the colon and rectum: a case series and historical review. Diagn Pathol, 2017. 12(1): p. 78.

Lin, J., et al., Composite intestinal adenoma-microcarcinoid. Am J Surg Pathol, 2012. 36(2): p. 292-5.

Pulitzer, M., et al., Microcarcinoids in large intestinal adenomas. Am J Surg Pathol, 2006. 30(12): p. 1531-6.

Salaria, S.N., et al., Composite intestinal adenoma-microcarcinoid clues to diagnosing an under-recognised mimic of invasive adenocarcinoma. J Clin Pathol, 2013. 66(4): p. 302-6.

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