Nutcracker syndrome is a rare condition characterized by compression of the left renal vein. The left renal vein carries filtered blood away from the left kidney. In Nutcracker syndrome, the vein is either compressed between two arteries (the abdominal aorta and superior mesenteric artery) or between one artery and the bones of the spine. The exact reason for the compression is unclear. In some children with the condition, it is thought to be related to changes in body proportion that accompany growth and development.
Some people with Nutcracker syndrome do not develop symptoms and signs. Others may have hematuria (blood in the urine), abdominal pain, flank pain, varicocele in men, protein in the urine, or fatigue.