Anatomical Landmarks of the colon The Caecum is the widest p | ISB (MRCS) International surgical boards

Anatomical Landmarks of the colon

The Caecum is the widest part of the colon, its diameter is about 7.5 to 8.5 cm, and it has the thinnest muscle coat, this means its the most vulnerable to perforation and the least vulnerable to obstruction.

The Ascending colon is relatively unremarkable, being fixed in the retroperitoneum, the transverse colon is relatively more mobile, it is tethered by the gastrocolic ligament and by the colonic mesentery, the greater omentum also attaches to the anterior and upper aspects of the transverse colon, these three attachments explains the charactaristic triangular appearance of the transverse colon when viewed from inside by colonoscopy (see figure below)

The splenic flexure marks the transition between the transverse and descending colon, and it is held by the Lienocolic ligament to the spleen, this ligament is sometimes dense and short making mobilisation during colectomy somewhat more difficult, the splenic flexure is also a watershed area between two vascular supplies, namely the superior mesenteric and inferior mesenetric arterial networks, making this region vulnerable to vascular injury, this area is referred to as Griffiths point.

The sigmoid colon is very mobile, and it has the narrowest diameter in the colon making it the most vulnerable part to become obstructed, although its usually positioned in the lower left quadrant; its extreme mobility and redundancy sometimes makes it to lie largely in the lower right quadrant, therefore such diseases like diverticulitis may present with right lower quadrant pain.

The rectosigmoid junction is approximately at the level of the sacral promontory, which is the anterior projection of the first sacral vertebra, for ease of notion, the rectosigmoid junction is the point at which the three tinea coli converge into one continuous outer longitudinal muscle coat of the rectum.

The sigmoid colon marks another vascular watershed area, known as Sudek's point, which marks the area between the inferior mesenteric and internal iliac arteries.