Anatomy - Intersphincteric resection, open, with transanal colon pull-through and transverse coloplasty pouch

• Splenic flexure attached to the diaphragm by the phrenicocolic ligament
• Descending colon situated in secondary retroperitoneal position
• Transition between descending and sigmoid colon in the left iliac gutter
• Sigmoid colon situated intraperitoneally (→ sigmoid mesocolon)
• Transition between sigmoid colon and rectum anterior to the 2^nd/3^rdsacral vertebra

The rectum is divided into thirds. The level of their borders is measured with the rigid endoscope and referenced to the anocutaneous line. Distal third at 0-6cm, middle third at 6-12cm, proximal third at 12-16cm

• The pelvic parietal fascia covers the pelvic wall with its vessels, autonomic nerves and plexus of the presacral veins/nerves
• The rectosacral fascia and visceral pelvic fascia meet proximal to the anorectal transition
• The visceral fasciae comprise the proper pelvic fascia (encasing the posterior and lateral mesorectum) and the anterior Denonvilliers fascia

• Anastomoses between branches of the superior and inferior mesenteric artery (middle and left colic artery respectively) near the splenic flexure (anastomosis of Riolan).
• Left hemicolon, sigmoid colon and upper rectum supplied by the inferior mesenteric artery and its branches: left colic artery, sigmoid arteries with Drummond marginal artery, superior rectal artery.
• Proximal third of the rectum supplied by the superior rectal artery dividing posteriad into two terminal branches; middle third by the middle rectal artery (paired, each originating from the internal iliac artery); and the distal third by the inferior rectal artery (paired, each originating from the internal iliac artery). The middle rectal arteries course in the so-called lateral ligaments of the rectum and are divided in total mesorectal excision.
• Venous blood from the left hemicolon flows via veins of the same name into the area drained by the portal vein.
• Venous drainage of the proximal and middle third via the inferior mesenteric vein (draining into the portal vein), while venous blood from the distal third returns via the area drained by the inferior vena cava.