The «nutcracker phenomenon» was defined by De Schepper in 1972 as a left renal vein compression between the superior mesenteric artery (SMA) and the aorta. The vein passes in front of the aorta and posteriorly to the SMA in a position just above the transverse duodenum. The condition is analogous to the superior mesenteric artery syndrome, where compression of the third part of duodenum between SMA and aorta results in duodenal obstruction. Left renal vein compression syndrome («nutcracker phenomenon») appears in individuals in whom the angle between SMA and aorta is decreased. Posterior renal ptosis owing to loss of perirenal adipose tissue associated with prominent lordotic lumbar curve may cause stretching of the left renal vein over the aorta.
Clinically, the phenomenon is associated with hematuria, abdominal pain, varicocele formation, and possibly infertility. The abdominal pain or flank pain is exacerbated by sitting, walking, standing or riding in shaking vehicles, known as the gonadal vein pain syndrome. Hematuria is a result of abnormal communication between submucosal venous plexus and the pyelocalyceal system presumably induced by venous hypertension.
The diagnosis of «nutcracker phenomenon» is best established by selective renal phlebography. Compression usually results in dilata tion of the renal vein, slow wash out of contrast medium from the vein, and in severe cases, collateral venous drainage. Collateral circulation occurs through suprarenal, gonadal, lumbar and periureteral veins and the azygous venous system. Contrast enhanced CT scan shows compression of the left renal vein between the aorta and SMA, distention of the vein proximal to the site of compression and sometimes abnormal venous collaterals.
Therapy of the condition is controversial and depends on the clinical situation. For some authors massive, recurrent hematuria, pain or varicocele are indications for surgical bypass treatment.