Renal Veins and Portal Veins

 Systemic Veins A retroaortic left renal vein, located either at the same level as a normal renal vein or more caudally, occurs in about 5% of the population. Circumaortic left renal veins consist of a true vascular ring and also occur roughly in about 5%, findings detected with contrast enhanced CT. Gadolinium enhanced 3D MRA
detects a retroaortic and circumaortic left renal veins with roughly the same frequency. An abdominal aortic aneurysm can compress a retroaortic left renal vein and result in renal vascular congestion and induce hematuria. Although at times called a nutcracker phenomenon, this term is best avoided to prevent confusion with other similarly named conditions.
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This is radiology images of Retroaortic left renal vein. Frontal (A) and oblique (B) 3D CT reconstructions reveal the left renal vein (arrows) posterior to a tortuous aorta.

Portal Venous System
            Congenital portal venous absence is rare; most occur in females and tend to be associated with liver tumors and other congenital abnormalities. With an absent portal vein, intestinal
and splenic venous blood bypasses the liver and drains directly into systemic veins. Some of these patients develop hepatofugal drainage of a large inferior mesenteric vein into systemic veins.
            Congenital portal vein duplication or an accessory portal vein is also rare. Some of these mimic a liver hilar tumor. At times direct portography shows an accessory smaller vein located parallel to the main portal vein and draining into the right liver lobe; some of these accessory portal veins drain the coronary veins, thus modifying results obtained after a transjugular intrahepatic portosystemic shunt (TIPS) and preventing coronary vein embolization.
             A portal vein located cranial to the gallbladder bed and feeding the right anterior segment is associated with rightward deviation of the ligamentum teres.A portal vein located anterior to the duodenum (and thus prepancreatic in location) is associated with malrotation and polysplenia. Computed tomography and magnetic resonance imaging (MRI) reveal a vascular structure anterior to the head of the pancreas.
              Aberrant gastric venous drainage is common and accounts for some of the unusual liver enhancement patterns detected.Veins of Retzius are intestinal veins draining directly into vena cava or its branches—usually the gonadal or renal veins—rather than into portal vein branches. Whether they represent a normal variant or should be considered congenital anomalies is conjecture. These veins can be identified if searched for, including with CT arterial portography.
              Ultrasonography can detect portocaval anastomoses in infants; these vessels probably represent continued ductus venosus patency. Normally the superior mesenteric vein lies to the right and anterior to the superior mesenteric artery. A reversed position of these two vessels suggests but is not pathognomonic of midgut malrotation. An aberrant right gastric vein supplies segment 4 of the liver and is a cause of a pseudolesion during contrast-enhanced CT or CT portography. An aberrant left gastric vein is less common and is identified on postcontrast CT along the hepatogastric ligament. These veins provide a partial collateral pathway for the portal system.
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Radiology images of Congenital absence of portal vein in an 11-year-old boy. A: Transverse magnetic resonance (MR) imaging shows the splenic vein (arrows) joining the superior mesenteric vein and emptying into the inferior vena cava. B: An MR angiogram identifies the superior mesenteric vein (arrow) draining into inferior vena cava.
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