Editing Colon and rectum (section)

== '''Venous drainage''' ==

** Follows the arterial supply
** '''SMV'''
*** Originates in the distal small bowel mesentery, where ileal and caecal branches join
*** Lies to the right of SMA
**** If not, may indicate intestinal malrotation
*** At the lower margin of the pancreas, the right gastrocolic vein (Henle trunk) and then the inferior pancreaticoduodenal veins enter from the right
*** Forms PV behind neck of pancreas with splenic vein
*** Trunk of Henle (right gastrocolic vein)
**** Confluence of RGEV with one or more colic veins +/- anterior superior pancreatic vein
**** Drains to SMV at a mean distance of 2.2cm from the inferior border of the pancreas
**** Present in 90%, but variable
** '''IMV'''
*** Formed as the continuation of the superior rectal vein as it crosses the pelvic brim
*** Identified at the level of the ligament of Treitz, just to the left of the DJ flexure
*** Continues along the base of the mesentery after the ligament of Treitz, and into the splenic vein
*** Can be divided to achieve extra colonic length for low pelvic anastomoses
*** '''Superior rectal vein'''
**** Drains the upper two thirds of the rectum
**** Internal venous plexus of anorectum - within the anorectal columns, draining into superior rectal veins (PV system)

**** Can see varicosities in this system in portal hypertension

** '''Internal iliac veins'''
*** '''Middle and inferior rectal veins''' - drain to systemic circulation
**** Explains the higher rate of lung metastases seen in low rectal cancers