Renal nutcracker syndrome (NCS) is a condition that occurs when the left renal vein (the vein that carries blood purified by the left kidney) becomes compressed. Signs and symptoms can vary from person to person. Some people may not have symptoms, while others develop severe and persistent symptoms. Symptoms may include blood in the urine (hematuria), orthostatic proteinuria, flank pain and/or abdominal pain.

Some cases of mild NCS in children may be due to changes in body proportions associated with growth. It is less clear why NCS occurs or causes symptoms in adults. Treatment ranges from surveillance (in less severe cases) to various types of surgery. The surgical technique depends upon each person's anatomy and how likely it is to relieve symptoms.

• Blood in the urine (hematuria) which can occasionally cause anemia requiring blood transfusions.
• Abdominal or flank pain that may radiate to the thigh and buttock. Pain may be worsened by sitting, standing, walking, or riding in a vehicle that shakes.
• Varicocele in men - almost always occurring on the left side.
• Chronic fatigue syndrome and fatigue symptoms.
• Pelvic congestion syndrome, causing symptoms such as chronic pelvic pain, pain during intercourse, painful or difficult urination, painful menstrual cramps during periods, and polycystic ovaries.
• Orthostatic proteinuria.
• Orthostatic intolerance (feeling light-headed or having palpitations when standing upright).

NCS is generally divided into 2 types: anterior and posterior.

1. Anterior NCS, which is the most common form, occurs when the normally-placed left renal vein (the vein that carries blood purified by the left kidney) is compressed between two arteries (the abdominal aorta and the superior mesenteric artery).
2. Posterior NCS generally occurs when the left renal vein is compressed between an artery (usually the abdominal aorta) and the bones of the spine.

Some cases of mild NCS in children may be due to changes in body proportions associated with growth. The reason NCS occurs or causes symptoms in adults is less clear. The following may increase the risk of developing NCS as a result of compression of the left renal vein:

• Pancreatic tumors
• Swelling of the para-aortic lymph nodes (a group of lymph nodes in front of the base of the spine)
• Retroperitoneal tumors
• Abdominal aortic aneurysm
• Left renal vein duplication, and an abnormally placed right renal artery
• Nephroptosis of the left kidney - when the kidney drops down into an abnormal position in the pelvis while a person goes from sitting to standing
• Lordosis
• Low body mass index (BMI)

• Doppler ultrasonography (DUS)
• Computed tomography angiography
• Magnetic resonance angiography
• Venography
• Intravascular ultrasound
• Cystoscopy

The best treatment for each person with renal nutcracker syndrome (NCS) is a controversial topic. In general, for people with mild hematuria or with mild and tolerable symptoms, conservative management is recommended. This generally consists of regular surveillance and observation. This is because many patients will have complete resolution of symptoms without any significant intervention. Medical therapy may be recommended to improve orthostatic proteinuria and/or renal perfusion.

Surgery may be considered in the following instances:

• Gross hematuria (when urine is visibly discolored by blood)
• Severe symptoms (flank or abdominal pain, anemia, autonomic dysfunction, impairment of renal function)
• If conservative management is not effective after a specific period of time, depending on the patient's age (generally after 24 months in patients under 18, and after 6 months in adults)

The surgical technique depends upon each person's anatomy and how likely it is to relieve symptoms. The use of a combination of surgical techniques is increasingly being recognized as a means to alleviate symptoms of NCS.