Anatomy - Rectal resection according to Hartmann

• Left colic flexure fixed to the diaphragm by the phrenicocolic ligament
• Secondary retroperitoneal position of the descending colon
• Transition from descending colon to sigmoid colon in the left iliac fossa
• Intraperitoneal position of the sigmoid colon (→ sigmoid mesocolon)
• Transition from sigmoid colon to rectum before the 2nd-3rd sacral vertebra

The rectum is divided into thirds. The height of the boundaries is measured with the rigid endoscope; the reference point is the anocutaneous line:

• lower third 0 – 6 cm
• middle third 6 – 12 cm
• upper third 12 – 16 cm

• Fascia pelvis parietalis covers the pelvic wall with vessels, autonomic nerves, and presacral venous/nerve plexus
• above the anorectal junction, the meeting of the fascia rectosacralis and the fascia pelvis visceralis
• the visceral fasciae include the fascia propria organi pelvis (enveloping the mesorectum dorsally and laterally) and the ventrally located Denonvilliers' fascia

• Anastomosis between the territory of the superior mesenteric artery (A. colica media) and the inferior mesenteric artery (A. colica sinistra) near the left colic flexure (Riolan's arcade)
• Supply of the left hemicolon, the sigmoid colon, and the upper rectum by the inferior mesenteric artery and its branches, the left colic artery, sigmoid arteries with Drummond's arcade, and the superior rectal artery.
• Supply of the upper third of the rectum via the superior rectal artery, which divides dorsally into two terminal branches, the middle third from the middle rectal artery (paired, each as a branch of the internal iliac artery), and the lower third via the inferior rectal artery (paired, each as a branch of the internal pudendal artery from the internal iliac artery). The middle rectal arteries run in the so-called lateral ligaments of the rectum and are transected during total mesorectal excision.
• Venous drainage of the left hemicolon through veins of the same name into the portal vein system
• Venous drainage of the upper two-thirds via the inferior mesenteric vein (portal vein system) and of the lower third via the drainage area of the inferior vena cava