Colon, Posterior View

Description

Posteriorly, the large intestine is traced from the right iliac fossa as the ascending colon runs superiorly toward the hepatic flexure, crosses the upper abdomen as the transverse colon, then descends along the left flank as the descending colon before curving medially into the sigmoid colon in the left lower quadrant. Haustra segment the colonic wall along its length, and the distal sigmoid lies anterior to the sacrum as it approaches the rectum. The descending colon appears fixed against the posterior abdominal wall, consistent with its retroperitoneal course, while the sigmoid remains more mobile on its mesocolon. A focal intraluminal lesion is marked near the rectosigmoid region. That distal location is a common site for adenomatous polyps and colorectal carcinoma, and it is where a change in stool caliber, obstructive symptoms, or iron deficiency anemia often prompts evaluation. Surgical planning often hinges on appreciating the posterior relationships of the descending colon to the left kidney and ureter, and of the rectosigmoid to the sacral promontory and pelvic brim during mobilization. This view also supports teaching of why diverticular disease clusters in the sigmoid colon, where intraluminal pressures are higher and the wall is prone to outpouchings at points of vascular penetration. A frequent source of perforation. Use this artwork for posterior abdominal wall teaching in gross anatomy and GI blocks, for colorectal cancer screening materials that localize lesions to the rectosigmoid, or for operative and radiology-facing content discussing retroperitoneal fixation and safe planes of dissection during left colectomy or sigmoidectomy. Anatomical accuracy verified by SciePro's Medical Advisory Board.