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

• For all rectal sections along the course of the superior rectal artery and the inferior mesenteric artery
• In the lower third additionally via lymphatic pathways along the middle rectal and internal iliac arteries to lymph nodes in the area of the levator ani muscles and the ischiorectal fossa

Descending colon, retroperitoneum, and rectum

• Course of the descending colon from cranial to caudal with close anatomical relationship to the spleen (left colic flexure), omental bursa (dorso-medial to the left colic flexure), left kidney, and tail of the pancreas (cranial section of the descending colon)
• Course of the root of the sigmoid mesocolon from the left iliac fossa medially, crossing the common iliac vessels, ureter, and ovarian or testicular vessels
• Course of the ureter on the psoas muscle, crossing it from lateral and cranial to caudal and medial.

The Denonvilliers' fascia envelops the posterior wall of the bladder, the seminal vesicles, and the posterior wall of the prostate in men.