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The nutcracker syndrome (NCS) results most commonly from the compression of the left renal vein (LRV) between the abdominal aorta (AA) and superior mesenteric artery (SMA), although other variants exist. The name derives from the fact that, in the sagittal plane and/or transverse plane, 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, which frequently results in 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.

The signs and symptoms of NCS are all derived from the outflow obstruction of the left renal vein. The compression causes renal vein hypertension, leading to hematuria (which can lead to anemia) and abdominal pain (classically left flank or pelvic pain). The abdominal pain may improve or worsen depending on positioning. Since the left gonadal vein drains via the left renal vein, it can also result in left testicular pain in men or left lower quadrant pain in women, especially during intercourse and during menstruation. Another clinical study has shown that nutcracker syndrome is a frequent finding in varicocele affected patients and possibly, nutcracker syndrome should be routinely excluded as a possible cause of varicocele and pelvic congestion. In women, the hypertension in the left gonadal vein can also cause increased pain during menses. NCS can also be due to other causes such as compression by pancreatic cancer, retroperitoneal tumors, and abdominal aortic aneurysms.

Nutcracker syndrome is diagnosed through imaging such as doppler ultrasound (DUS), computed tomography (CT), magnetic resonance imaging (MRI), and venography. The selection of the imaging modality is a step wise process. DUS is the initial choice after clinical suspicion based on symptoms. CT and MRI are used to follow up afterwards, and if further confirmation is necessary, venography is used to confirm.

Treatment depends on the severity and symptoms. In addition to conservative measures, more invasive therapies include endovascular stenting, and gonadal vein embolization. The decision between conservative and surgical management is dependent on the severity of the symptoms. Conservative management is used if the patient is a child and the hematuria is mild. In contrast, more severe symptoms such as reduced renal function, flank pain, and anemia are managed with surgical interventions.

Conservative management is advised in children as further growth may lead to an increase in tissue at the fork between the SMA and AA, providing room for the LRV to pass blood without obstruction. Treatment in this case involves weight gain to build more adipose tissue, decreasing the compression. Venous blood may also be directed towards veins formed as a result of the higher blood pressure, which may contribute to symptomatic relief for individuals as they age. 75% of adolescent patients have been found to have their symptoms resolved after two years. Medications that decrease blood pressure such as ACE inhibitors can also be used to reduce the proteinuria.

Endovascular interventions involve the use of stents to improve blood flow in the area of LRV impingement. Following catheterization, venography is done to visualize the vasculature and can provide confirmatory diagnosis of NCS prior to stenting. Following stenting, 97% of patients have had improvement of symptoms by sixth months following the procedure, and long term follow up showed no recurrence of symptoms after 66 months. Although less invasive, risks involved include incorrect placement of the stent as well as stent dislodging and migration to the right atrium. Furthermore, patients must be on anticoagulation therapy after stenting for three months.