Right sided descending and sigmoid colon: its embryological basis and clinical implications.

Anatomical variations of the colon are described by various authors, but the occurrence of right sided descending and sigmoid colon is rare and has not been reported. We found that the anomalous right-sided descending and sigmoid colon had four parts. The proximal segment of the first part consisted of the descending colon extending across the midline from the splenic flexure to the portion supplied by the left colic artery. The distal segment was supplied by the superior sigmoid artery. The second and third parts formed a loop in the right lumbar region anterior to the lumbar cecum. The fourth part was in the lesser pelvis, extending from right sacroiliac joint to the third sacral body. Parts two, three, and four were supplied by the inferior sigmoid artery, which arose from the right side of the inferior mesenteric artery. The ascending and transverse colon was normally placed. This is a rare anomaly that has not been reported so far in adults and is of immense importance to interventional radiologists and colorectal surgeons. The embryological basis of such an anomaly is defective fixation occurring as early as the 12th-17th week of intrauterine life.