Abstract
An 83-year-old male was admitted to our hospital with diarrhea. Colonoscopy revealed a 20-mm-sized protruding rectal lesion with surrounding edematous change. Magnifying crystal violet staining showed type Ⅳ pit pattern on the tumor surface. A biopsy from the tumor showed a low-grade tubulovillous adenoma, while a biopsy from the border of the tumor showed a moderately differentiated adenocarcinoma. Abdominal computed tomography (CT) demonstrated the rectal tumor and was suggestive of lymph node swelling outside the rectal wall. Surgical resection was performed. The final pathological diagnosis was adenocarcinoma, por2, 45×45mm, pA, sci, INFc, ly1, v3, pPM0, pDM0, pRM1, and pN2. Although the tumor surface was a tubulovillous adenoma, the entire tumor was an invasive carcinoma which presented as a unique growth pattern, with a poorly differentiated carcinoma permeating the deepest portion.
