Nutcracker phenomenon

It results most commonly from the compression of the left renal vein between the abdominal aorta (AA) and superior mesenteric artery (SMA), although other variants exist. The name derives from the fact that, in the sagittal view, the SMA and AA (with some imagination) appear to be a nutcracker crushing a nut (the renal vein).
There is a wide spectrum of clinical presentations and diagnostic criteria are not well defined resulting in frequently delayed or incorrect diagnosis. This condition is not to be confused with superior mesenteric artery syndrome, which is the compression of the third portion of the duodenum by the SMA and the AA.

This Computed tomography for a 52-year-old woman with mild episodic gross hematuria revealed compression of the left renal vein between the superior mesenteric artery (SMA) and the aorta (Ao) before the vein merges into the inferior vena cava (IVC). This compression caused marked dilatation of the distal part of the renal vein (RV). The renal venous congestion caused hematuria, presumably through the rupture of submucosal veins into the renal pelvis. No treatment was given. Entrapment of the renal vein is a known cause of hematuria.