Editing Retroperitoneum (section)

== Venous Vasculature ==

* '''Inferior vena cava'''
** Formed from the confluence of the common iliac veins, inferior and to the right of the aortic bifurcation
** '''The venous system is more variable than the arterial system; however, many venous structures run parallel with their arterial equivalent.'''
** '''Tributaries'''
*** '''Median (middle) sacral vein'''
**** Runs with its respective artery and typically '''drains into the left common iliac vein'''
*** '''Ascending lumbar veins (paired)'''
**** Drain the posterior abdominal wall and run posterior to the psoas muscle and lateral to the spinal column
**** Connect with the ipsilateral '''lumbar veins, which are variable in number and location compared with their arterial equivalents.''' '''These veins may assume a plexiform arrangement anterior to the vertebral bodies.'''
**** '''As the ascending lumbar veins enter the thorax, they become the hemiazygos vein on the left and the azygos vein on the right.'''
*** '''Gonadal veins'''
**** In males, the gonadal veins (testicular veins) receive drainage from the pampiniform plexus, which is the venous complex that emerges from the testes. '''The testicular veins ascend through the retroperitoneum medially, running lateral to the respective artery and anterior to the ipsilateral ureter.'''
***** '''The left testicular vein typically enters the inferior aspect of the left renal vein at a right angle;''' however, it may enter the IVC directly.
***** '''The right testicular vein typically enters into the right anterolateral aspect of the IVC;however, it may enter into the right renal vein in 10% of cases.'''
***** '''Clinical significance:'''
****** '''The increased length and perpendicular entry of the left testicular vein into the left renal vein may result in some element of increased back pressure and explain the higher incidence of left-sided varicoceles''' compared with the right side.
****** With the relative rarity of unilateral right-sided varicocele, '''a sudden-onset right varicocele should increase suspicion for a renal or retroperitoneal malignancy causing obstruction and poor venous outflow (e.g., right side renal cell cancer with venous thrombus). This clinical scenario should warrant retroperitoneal imaging to rule out malignancy.'''
**** The ovarian veins receive drainage from the pampiniform plexus adjacent to the ovarian hilum and travel through the infundibulopelvic ligament. '''As with the gonadal veins in males, the left ovarian vein enters the left renal vein, and the right ovarian vein empties into the anterolateral wall of the vena cava'''.
*** '''Renal veins'''
**** '''Course anteriorly to the renal arteries and empty into the lateral aspects of the vena cava at the level of L1'''
**** '''The right and left renal veins differ in length and tributaries'''
***** '''Right is shorter and typically has no tributaries'''
***** '''Left is longer and typically receives (3):'''
*****# '''The left gonadal vein at its inferior margin'''.
*****# '''At least one lumbar vein at or near the ostia of the gonadal vein.'''
*****# '''The left adrenal vein at its superior margin and in most patients inserts into the renal vein just medial to the gonadal vein.'''
*** '''Gastrointestinal venous drainage'''
**** '''Does not mirror the arterial system'''
**** '''The portal venous system receives venous blood from the bowel, spleen, pancreas, and gallbladder to be emptied into the liver'''
**** '''Splenic vein'''
***** '''Receives the venous drainage from the colon distal to the splenic flexure'''
***** '''Tributaries include''' the short gastric, left gastro-omental, pancreatic, and typically '''inferior mesenteric veins.'''
**** '''Superior mesenteric vein (SMV)'''
***** '''Receives venous drainage from the small intestine and the large intestine proximal to the splenic flexure'''.
***** Tributaries include the right gastro-omental, anterior and posterior inferior pancreaticoduodenal, jejunal, ileal, ileocolic, right colic, and middle colic veins.
**** '''The SMV combines with the splenic vein to form the hepatic portal vein'''
**** Insert figure
**** '''Portal vein'''
***** '''Splits into right and left branches, and the venous blood enters the endothelial lined hepatic sinusoids.''' '''After passing through these sinusoids, the venous blood leaves the liver through the hepatic veins'''
***** '''Hepatic veins'''
****** '''Enters the anterior aspect of the IVC before it crosses the diaphragm into the thorax'''
****** Two groups of hepatic veins: upper group, typically larger in caliber vs. lower group, which are typically smaller.
****** Occlusion can lead to Budd-Chiari syndrome, which is a form of progressive liver failure that often manifests rapidly with jaundice, ascites, abdominal pain, and hepatomegaly