Figure 13a. Perianal mucinous adenocarcinoma in a 79-year-old man with a 20-year history of anal fistula. (a) Contrast-enhanced CT scan shows large, lobulated cystic masses in the perianal region (arrows). These hypoattenuating lesions proved to contain mucin at surgery. (b) Photomicrograph (original magnification, x100; H-E stain) shows well-differentiated neoplastic glands associated with large lakes of mucin.