Renal nutcracker syndrome

The symptoms and severity of renal nutcracker syndrome can vary from person to person. Some people may not have any symptoms (especially children), while others have severe and persistent symptoms. Symptoms are often worsened by physical activity.^[1][2]

The most common signs and symptoms may include:^[1][2][4]

• 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][4] 

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.^[1][2] The following may increase the risk of developing NCS as a result of compression of the left renal vein:^[1][4][2]

• 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)

People with NCS usually do not have a family history of the syndrome. Although more than one family member may rarely have the syndrome, this is thought to be a coincidence and not the result of a genetic predisposition.^[1][2]

A diagnosis of NCS may first be suspected based on the characteristic signs and symptoms. Other conditions that cause similar symptoms are often first ruled out. The diagnosis is ultimately confirmed by results of various imaging studies, including:^[1][4]

• 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.^[4] In general, for people with mild hematuria or with mild and tolerable symptoms, conservative management is recommended.^[4] This generally consists of regular surveillance and observation. This is because many patients will have complete resolution of symptoms without any significant intervention.^[1][2] Medical therapy may be recommended to improve orthostatic proteinuria and/or renal perfusion.^[4]

Surgery may be considered in the following instances:^[4]

• 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.^[3] The use of a combination of surgical techniques is increasingly being recognized as a means to alleviate symptoms of NCS.^[4]

The "usual course" of renal nutcracker syndrome (NCS) is not clear and it remains under-diagnosed because symptoms vary from person to person. In some cases, more commonly in children, it can resolve spontaneously. However, without treatment, it can predispose a person to left renal vein thrombosis (a blood clot in the vein) and kidney damage. In cases presenting with hematuria, it can lead to anemia requiring blood transfusion and its associated complications.^[4]

For those treated surgically with open repair (which may refer to various techniques other than stenting), there reportedly are excellent long-term outcomes. On the other hand, while less-invasive endovascular stent placement appears to offer good results in the short term, long-term outcomes in a more diverse population are still being studied, and stents have a risk of migration. Improvement in the technology for venous stents is expected and may result in endovascular treatment of more cases in the future.^[5]

The exact prevalence of renal nutcracker syndrome is unknown. This is partly because there has been no standard diagnostic criteria, and partly because symptoms can vary (or be absent) among people with the condition.^[4] While it has been described as "rare" in the medical literature, some have suggested its incidence is likely underestimated.^[6][7][8][9]