Nutcracker syndrome

Nutcracker syndrome is a condition characterized by compression of the left renal vein where it courses between the aorta and superior mesenteric artery. Anatomical variations in vascular structures and other conditions such as pancreatic or retroperitoneal tumors can also cause left renal vein compression.[1] The term “nutcracker” suggests compression from two opposing structures, but otherwise does not describe symptoms or anatomical locations. Because this condition can mimic low back pain from musculoskeletal causes, and because the diagnostic process is complex, the true prevalence is unknown.

Though a fairly large body of literature describing nutcracker syndrome exists, the condition appears to be relatively unknown outside the field of urology.[2] Providers evaluating and/or caring for patients with low back pain would be wise to understand the pathophysiology, clinical presentation, diagnostic criteria, natural history, and treatment options for this condition. Below is a brief, though far from exhaustive synopsis of these key components. For further information, I recommend reviewing the 2 publications referenced below from which this information was synthesized.

Pathophysiology
• Left renal vein compression resulting in venous stasis in the left renal vein and distal communicating veins
• Non-hereditary
• Varicoceles can form in men
• Varicosities in the left renal vein, or communicating veins in the pelvis, vulva, or proximal thigh
• Pelvic varicosities can influence piriformis syndrome via congestion around the sciatic nerve coursing under the piriformis muscle.
• Left adrenal gland and the duodenum can be affected resulting in reduced cortisol secretion and gastrointestinal symptoms
• Abnormally low abdominal fat content or hyperlordosis can lead to left renal vein compression in those who would otherwise not experience this phenomenon

Clinical presentation (variable but can include)
• Occurs at any age from children to elders
• Hematuria due to increased pressure in renal vein. Hematuria is sometimes increased with upright positions (orthostatic hematuria)
• Flank/low back, or pelvic pain with potential radiation to the buttock and posteromedial thigh can incorrectly suggest musculoskeletal pain
• Pain location and aggravation by activity or certain positions can mimic musculoskeletal symptoms
• Pain exacerbated by sitting, walking, standing, incorrectly suggesting musculoskeletal pain
• Chronic fatigue from adrenal insufficiency
• Epigastric pain, nausea, and/or weight loss when duodenal entrapment co-occurs
• Symptoms increased by hyperlordosis, which can incorrectly suggest musculoskeletal pain

Diagnosis
• No diagnostic gold standard exists
• Other diagnoses, including musculoskeletal, should be ruled out or otherwise deemed less likely
• Doppler ultrasound is the least invasive method of evaluating renal vein size, though findings suggesting nutcracker syndrome do not confirm a diagnosis
• Angiographic methods and computed tomography can reveal venous dilation and varicosities, though anatomic variation can potentially lead to misdiagnosis and
• Abnormal pressure values greater than 3 mm Hg between renal veins using venography is the most reliable, though a costly and invasive diagnostic procedure

Natural history
• Many patients are asymptomatic and never develop symptoms. Symptoms represents those with nutcracker phenomenon, rather than nutcracker syndrome
• Some patients experience spontaneous resolution, perhaps by developing collateral veins
• Changes in anatomic features through childhood and adolescent growth may induce self-resolution

Treatment options
• Treatment is based on symptom severity and age and typically avoided when possible due to risks associated with current invasive procedures
• Watchful waiting for at least 2 years is the recommended approach, especially for those under 18 years old
• Angiotensin inhibitors may reduce orthostatic proteinuria
• Endovascular stenting may alleviate symptoms, though stent failure and/or migration pose risks
• Nephroplexy (surgically migrating the left kidney)
• Renal auto-transplantation
• Laparoscopic extravascular stenting

Reference List
1. Kurklinsky AK, Rooke TW: Nutcracker phenomenon and nutcracker syndrome. Mayo Clin Proc 2010, 85(6): 552-559.
2. Berthelot JM, Douane F, Maugars Y, Frampas E: Nutcracker syndrome: A rare cause of left flank pain that can also manifest as unexplained pelvic pain. Joint Bone Spine 2016.