[A case of a right-sided sigmoid colon].

During dissecting practice by students at Chiba University in 1991, a rare anomaly was found in a cadaver of a 50-year-old Japanese male. The distal part of the colon, including the sigmoid colon, was excessively long and formed a loop behind the ascending colon. This anomalous colon consisted of four parts. The first part began in the left iliac fossa and passed across the lower posterior abdominal wall into the right iliac fossa; the second turned upward and ascended along the posterior surface of the ascending colon to the inferior surface of the right lobe of the liver; the third turned backward and descended to the right iliac fossa and was in contact with the posterior abdominal wall; the fourth curved medially and downward and ended in the rectum at the median line. Only the anterior surface of the anomalous colon was covered with the peritoneum, and its mesocolon was not found. The inferior mesenteric artery gave off four branches toward the distal three-fourths of the excessively long colon and the superior rectal artery to the upper part of the rectum. Since it did not directly give off any branches toward the descending colon and the first part of the anomalous colon (these portions were supplied by a marginal artery), the branch supplying the second part was considered to be equivalent to the left colic artery. Thus, the proximal half of the long colon (parts 1 and 2) can be regarded as a part of the descending colon, and the distal half as the sigmoid colon.(ABSTRACT TRUNCATED AT 250 WORDS)