A CASE OF DIFFUSELY INFILTRATING CARCINOMA OF THE RECTUM IN ULCERATIVE COLITIS-DIFFICULTY FOR CORRECT DIAGNOSIS IN DEPTH OF WALL INVASION-

Patients with long-standing ulcerative colitis are at a high risk of developing colorectal cancer. Risk factors for the development of colorectal cancer inclide duration and extent of the disease. We experienced a patient with long-standing ulcerative colitis associated with infiltrating carcinoma of the rectum which presented difficulty in preoperative diagnosis of the depth of wall invasion. A 33-year-old man who had been suffered from ulcerative colitis limited in the left-side colon for 15 years was found having a reddish irregular elevated lesion, 5×3cm in size, above the peritoneal reflection on colonoscopic examination. Biopsy from this lesion revealed group IV. Endoscopic ultrasonography indicated that the depth of wall invasion in this lesion limited to within the mucosa, and an early rectal cancer was diagnosed. Left hemicolectomy and rectal resection with colo-anal canal anastomosis were performed. Contrary to the preoperative diagnosis, the pathological examination revealed that well-differentiated adenocarcinoma reached to the adventitia. This case has confirmed previous reports that correct diagnosis for the depth of colorectal cancer in patients with ulcerative colitis is often difficult.