A Case of Atypical Cap Polyposis which was Difficult to Differentiate from Rectal Cancer

概要

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A 30-year-old man consulted a local doctor because of melena and prolapse of mass. He did not have a habit of straining during defecation. Colonoscopic examination revealed a large polyp covered by mucous exudates in the lower rectum. A biopsy specimen was found to consist of granulation tissue and no malignant tissue. However, because there was some possibility of malignancy, transanal tumor resection was performed in our hospital. On histopathology, the polyp was found to consist of inflamed mucosa with elongated tortuous crypts that were attenuated towards the mucosal surface, and granulation tissue, the so-called "cap", was observed on the surface of the mucosa. Therefore, cap polyposis was diagnosed. The etiology of cap polyposis is still unknown and there is no specific treatment. We report this rare case with a review of the literature.