Nutcracker syndrome

What is nutcracker syndrome?

Nutcracker syndrome is also known as left kidney vein entrapment syndrome. It is believed to be secondary to compression of the left kidney vein as it passes through the angle between the abdominal aorta and the superior mesenteric artery.

Nutcracker syndrome is secondary to compression of the left renal vein as it passes between the abdominal aorta and SMA, resulting in outflow obstruction and left renal vein hypertension.

Patients may present with left flank pain and hematuria. Associated left perirenal or periureteral varices, a left varicocele in men, or left pelvic and vulvar varices in women may be encountered.

Nutcracker syndrome is an uncommon cause of pelvic pain and flank pain, with associated hematuria, orthostatic proteinuria, varicocele in men, and ovarian and pelvic varices in females.

Classic nutcracker syndrome occurs when the left renal vein is compressed anteriorly when the vein passes between the superior mesenteric artery and the aorta. Less commonly the left renal vein is compressed posteriorly at the point where the vein passes between the aorta and vertebral body.

Other rare causes of compression of the left renal vein are listed below. These include expanding abdominal aortic aneurysm, pancreatic neoplasm, left renal ptosis, fibrous bands, and the gravid uterus.

Regardless of the source of left renal vein compression, compression of the left renal vein at this anatomical location can result in chronic kidney damage secondary to left renal vein hypertension due to the unique relationship of the left renal vein to the left gonadal vein and the superior mesenteric artery and abdominal aorta.

Untreated severe cases may result in thrombosis of the left renal vein.

Uncommon Causes of Left Renal Vein Compression Causing Nutcracker Syndrome

  • • Abdominal aortic aneurysm
  • • Pancreatic neoplasm
  • • Retroperitoneal neoplasm
  • • Paraaortic lymphadenopathy
  • • Left renal ptosis
  • • Gravid uterus
  • • Abnormally high left renal vein position
  • • Overarching testicular artery
  • • Lordosis
  • • Retroperitoneal fibrosis
  • • Loss of retroperitoneal fat during fasting

The pathophysiology of nutcracker syndrome is believed to be the result of hypertension of the compressed left renal vein causing venous reflux with secondary variceal formation in the renal pelvis and ureter.

The finding of micro and/or macro hematuria and associated proteinuria is thought to be caused by the rupture of the thin septum that lies between abnormally dilated renal sinuses and the renal calyces.

The amount of hematuria can be significant and lead to anemia. The proteinuria associated with nutcracker syndrome is often orthostatic and is thought to be due to altered release of angiotensin II and norepinephrine.

The flank and pelvic pain associated with nutcracker syndrome is thought to be secondary to dilation of pelvic veins and from reflux from pelvic varicosities.

What are the Symptoms of Nutcracker syndrome?

Common presentations include hematuria (resulting from varices within the kidney pelvis and ureter), left-sided varicocele, and left flank discomfort.

The classic presentation of nutcracker syndrome is left-sided flank and pelvic pain with associated unilateral hematuria and orthostatic proteinuria.

The pain and urinary abnormalities may be made worse with exercise and lordosis of the thoracolumbar spine. Left-sided varicocele in males and pelvic varicosities in females may be the only physical findings and cystoscopy to confirm unilateral left-sided hematuria.

Radiographic evaluation of the left renal vein and inferior vena caval manometry may be required to confirm the diagnosis.

How is Nutcracker syndrome diagnosed?

Diagnosis is established by performing a left kidney venography or a magnetic resonance angiography.

Pelvic, scrotal, testicular, and rectal examination are indicated in all patients suspected of suffering from nutcracker syndrome. Complete blood count to rule out anemia, urinalysis to confirm hematuria and proteinuria, and renal function tests to rule out renal compromise are indicated in all patients suspected of suffering from nutcracker syndrome.

Diagnostic cystoscopy is useful in confirming unilateral left-sided hematuria and ruling out other causes of the patient’s symptoms (see Differential Diagnosis to follow). Doppler ultrasound imaging can help clarify the diagnosis of left renal artery compression and identify dilated gonadal veins and varices.

Computed tomography and magnetic resonance imaging may also help identify compression of the left renal vein as well as gonadal vein dilation and pelvic and gonadal varices. Contrasted computed tomography of the left renal vein may identify a positive beak sign which suggests severe compression of the vein at its aortomesenteric course.

Phlebography with intra-venocaval manometry may allow identification of abnormally high venous pressure gradients between the left renal vein and the inferior vena cava, which is highly suggestive of nutcracker syndrome.

Differential Diagnosis

The differential diagnoses of nutcracker syndrome include left renal malignancies, left renal calculi, left ureteral calculi, arteriovenous malformations of the left kidney, primary varicocele, primary pelvic congestion, glomerulonephritis, endometriosis, and spinal and musculoskeletal pathologies causing flank and back pain.


In cases of recurrent or persistent pain, surgical treatment is considered (e.g., endovascular stenting, kidney vein reimplantation, and gonadal vein embolization).

The goal of the treatment of nutcracker syndrome is the relief of left renal vein hypertension.

If the patient has experienced significant recent weight loss before the diagnosis of nutcracker syndrome, conservative management consisting of dietary interventions to promote weight gain with the goal of increasing retroperitoneal fat to improve the position of the left kidney to decrease compression and tension on the left renal vein should be considered.

Endovascular interventions including stenting of the left renal vein may provide improvement of pain and renal symptoms in selected patients, although surgical interventions to lessen tension and decrease compression on the left renal vein may be required to provide long lasting relief.


A failure to diagnose other causes of the patient’s pain symptomatology or to identify serious conditions responsible for venous vein compression such as pancreatic neoplasm can result in serious harm to the patient.

Hematuria can result in significant anemia that may require immediate treatment to stabilize the patient to allow diagnostic testing and definitive treatment.

Clinical Pearls

The diagnosis of nutcracker syndrome should be suspected in any patient suffering from unexplained micro and/or macro hematuria and proteinuria as well as in any patient suffering from varicocele or pelvic varices.

A failure to diagnose and treat nutcracker syndrome can result in serious loss of renal function.


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