Microscopic findings of the resected specimen (H-E staining, ×200). A: The sigmoid colon cancer, penetrating to the urinary bladder, did not invade the surrounding muscular layer as the tumor progressed. Adjacent to the sigmoid tumor, the normal colon mucosa was depressed sharply (arrows) with a thin-walled muscular layer (arrowhead), indicating that the colon cancer had arisen from a colon diverticulum. B: The sigmoid and urinary sides of the tumor were connected via the colovesical fistula. In the fistula, the cancerous tissue was completely covered with fibrous tissue, indicative of no exposure to the intraperitoneal space to cancerous tissue.