The sigmoid colon is the continuation of the descending colon.
After the distal descending colon has curved medially it enters the pelvis, where it gains a mesentery and is then called the sigmoid colon. It measures approximately 15 cm in length.
The sigmoid colon continues as the rectum when it loses its mesentery, at approximately S3.
- superiorly: loops of small intestine
- posteriorly: left internal iliac artery and vein, left ureter, piriformis muscle, sacrum, sacral plexus
- arterial: two-to-four sigmoid arteries (branch of inferior mesenteric artery)
- venous: similarly named veins drain into the inferior mesenteric vein
- sympathetic: inferior mesenteric plexus
- parasympathetic: via pelvic splanchnic nerves (from S2-S4)
Lymphatics travel with vessels to the inferior mesenteric group.