[737] Squamous Morules in Colon Polyps: Endocrine Differentiation in an Under-Recognized Mimic of Invasive Carcinoma

Safia N Salaria, Elizabeth Montgomery, Christina Arnold. Johns Hopkins, Baltimore

Background: Squamous morules encountered in colorectal adenomas are groupings of monotonous cells showing both squamous and endocrine differentiation, the latter not well-recognized. On our consult service, adenomas with squamous morules are often submitted with a concern for invasive carcinoma, or not recognized/reported. To further characterize this important carcinoma mimic, we studied the clinicopatholigic features of squamous morules.
Design: The study group consisted of prospectively identified colon polyps with squamous morules.
Results: We prospectively identified 10 colon polyps with squamous morules from 10 patients (5 men) ranging in age from 28-82 years (mean, 60 years). Eight were consultation cases; 2 were prospectively identified in our material. Indications for colonoscopy were known in 7 patients: screening colonoscopy (3), GI bleed (3), and diarrhea (1). The polyps involved the right (4), transverse (1), and left colon (4), and the site was not specified in one case. The average polyp size was 19 mm, and most were tubulovillous adenomas (7). Associated findings included prolapse change (10), fibrosis (4), high grade dysplasia (3), and serrated features (3).
The individual cells of squamous morules were cuboidal with abundant eosinophilic, dense cytoplasm. The nuclei were montonous and round with “salt-and-pepper” chromatin. Pleomorphism, hyperchromasia, and mitotic activity were absent. Squamous morules often had a quasi-infiltrating architecture (10), occasional lumen formation (7), a connection to adjoining adenomatous epithelium (8), and a fibrotic background (4). The majority of squamous morules were multifocal (7), extending over an average length of 0.4 cm. The morules displayed synpatophyin reactivity, variable chromogranin reactivity, and a negligible Ki-67 index.
In the 8 cases with a submitted diagnosis or impression, the squamous morules were interpreted as invasive carcinoma (2), not reported (3), or appropriately recognized as squamous morules (3). The two cases misinterpreted as invasive carcinoma showed quasi-infiltrative architecture, fibrotic background reminiscent of desmoplasia, and associated high grade dysplasia.
Conclusions: We report squamous morules with endocrine differentiation as an important mimic of invasive carcinoma. Squamous morules were found in polyps sharing the following core features: large size, tubulovillous features, prominent prolapse changes, fibrotic background, and, occasionally, high grade dysplasia and serrated features. Awareness of the unique morphology of squamous morules is important to avoid misdiagnosing carcinoma.
Category: Gastrointestinal

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 104, Monday Morning


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