What is the Renal Vein?

Renal veins are blood vessels that carry deoxygenated blood out of the kidney to the inferior vena cava. They lie anterior to the corresponding renal arteries and join with the inferior vena cava at close to ninety degree angles. The inferior vena cava is a major vein that carries blood to the right atrium, where the blood is sent off to become reoxygenated.

A normal human body has two kidneys, each equipped with a renal vein differentiated by “left” and “right,” according to which kidney the vein emerges from. The kidneys are organs located in the posterior abdominal cavity that serve roles of absorption, balancing the body’s water level, and filtering out waste to be excreted in the form of urine. The kidneys receive oxygen and nutrients via the oxygen rich blood that enters the kidneys through the renal arteries. The arterial blood is then relieved of unwanted minerals and metabolites in small filtration and reabsorption units in the kidney called nephrons, after which point it is excreted. The blood is then passed through small venules, which connect and empty into interlobar veins.

Two branches of veins, the anterior branch and the posterior branch, combine to create the singular renal vein that arises from each kidney. The anterior branch collects blood from the anterior, or front, region of the kidney and the posterior branch draws from the posterior, or back, region. These veins frequently have a branch that draws blood from the ureter, a tube-like organ that arises from the middle of each kidney and transports urine from the kidney to the urinary bladder.

The right renal vein accepts blood solely from these sources, whereas the left one also receives blood from several other veins to feed into the inferior vena cava. This is due to the inferior vena cava’s asymmetrical location on the right side of the body. The left inferior phrenic vein, left suprarenal vein, left 2nd lumbar vein, and the left gonadal vein. In men, the gonadal vein is the left testicular vein and in women it is the left ovarian vein.

Nutcracker syndrome, also known as renal vein entrapment syndrome and mesoaortic compression of the left renal vein, occurs when the abdominal aorta and the superior mesenteric artery put pressure on the left renal vein. This obstructs the flow of blood and presents symptoms of abdominal pain, nausea, and left testicular pain in men. Nutcracker syndrome also presents with hematuria, or red blood cells in the urine, and variocele, or abnormally enlarged veins in the scrotum. This condition is usually treated with a stent or renal vein reimplantation.

Another disease that can affect these blood vessels is renal vein thrombosis, wherein a blood clot forms in the vein, thus obstructing the outflow of blood from the kidney. This disorder usually presents with hematuria and decreased urine excretion. The patient is usually prescribed anticoagulation medication and, on rare occasions, the clot may be surgically removed.