Mesocolon

At a glance

English

Mesocolon

Latin (TA2)

Mesocolon

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the mesocolon

The mesocolon is the mesentery of the large intestine: a sheet of peritoneum enclosing fat, blood vessels, lymphatics and nerves, by which the colon is held to the posterior abdominal wall. Its parts are named after the segment of colon they hold: the ascending and descending mesocolons, the transverse and sigmoid mesocolons, together with the mesoappendix for the appendix and the mesorectum for the upper rectum.

Classic teaching treated these as separate pieces. The transverse and sigmoid mesocolons were described as long, free folds that let those loops of colon move, while the ascending and descending parts were said to have disappeared, the colon there being plastered flat onto the back wall. More detailed study during colectomy has shown that the mesocolon is in fact one continuous structure from the ileocaecal junction down to the rectum. Over the ascending and descending colon it persists as a flattened layer fused to the back wall, separated from the kidney and other retroperitoneal organs by a thin fascial plane. At the flexures and at both ends it merges with neighbouring folds.

The transverse mesocolon has a horizontal root running across the head and body of the pancreas and the descending duodenum, and divides the abdomen into a supracolic and an infracolic compartment. The sigmoid mesocolon has an inverted-V root over the left iliac vessels and the left ureter. Between the layers run the colic branches of the superior and inferior mesenteric arteries, the marginal artery, and the matching veins and lymph nodes.

Recognising the mesocolon as a single continuous sheet changed bowel cancer surgery. In complete mesocolic excision, surgeons follow the plane between the mesocolon and the back wall to remove the bowel with its whole, intact mesentery and its lymph nodes, an approach linked to better local control. A long, free sigmoid mesocolon also explains why that loop is prone to twisting (volvulus).

Function and supply

Begins at

Its root runs along the posterior abdominal wall, from the ileocaecal region on the right, across the pancreas, down the left side and into the pelvis.

Ends at

Attaches to the mesenteric border of the colon throughout its length, continuing as the mesoappendix and mesorectum.

Function

Suspends and anchors the colon, and carries the arteries, veins, lymphatics and nerves that serve it.

Blood supply

Carries the ileocolic, right colic and middle colic branches of the superior mesenteric artery and the left colic and sigmoid branches of the inferior mesenteric artery.