Nutcracker Syndrome: Compression of Left Renal Vein by Superior Mesenteric Artery
Nutcracker syndrome is the clinical condition caused by compression of the left renal vein between the superior mesenteric artery anteriorly and the aorta posteriorly. 1
Pathophysiology and Anatomy
- The left renal vein becomes entrapped between the superior mesenteric artery (SMA) and the aorta, leading to left renal venous hypertension 2
- This anatomical compression is also known as the "nutcracker phenomenon" when it's an incidental finding, and "nutcracker syndrome" when it causes clinical symptoms 3
- The compression results from a decreased angle between the aorta and SMA, which can be associated with low body mass index 3
- The condition can sometimes occur secondary to SMA syndrome (duodenal compression by the SMA) 4
Clinical Presentation
- Common symptoms include left flank pain, hematuria (microscopic or macroscopic), and proteinuria 1
- Patients may develop pelvic congestion due to collateral venous drainage through gonadal veins, leading to varicoceles in males or pelvic congestion syndrome in females 2, 1
- Other symptoms may include orthostatic hypotension, especially in pediatric patients 1
- The condition has a female predilection, typically occurring in the third to fourth decade, though it tends to be diagnosed earlier in men 3
- Low BMI is a common characteristic in affected patients 3
Diagnostic Approach
- Diagnosis requires a high index of suspicion, especially in patients with unexplained left flank pain, hematuria, and normal urological evaluations 1
- Imaging studies are essential for diagnosis:
- Doppler ultrasound can demonstrate increased peak systolic velocity at the site of compression compared to the renal hilum (ratio typically >7) 2
- CT angiography can visualize the compression of the left renal vein between the SMA and aorta 3
- Venography with pressure measurements showing a renocaval pressure gradient (typically >3 mmHg) can confirm the diagnosis 2, 5
- MR angiography may also be used 1
Management Options
- Conservative management is appropriate for mild cases and especially in children, who may outgrow the condition as they develop 1
- Medical management with ACE inhibitors can help manage orthostatic hypotension in pediatric patients 1
- Surgical interventions for persistent, severe symptoms include:
- Left renal vein transposition (considered the standard surgical approach) 2
- External stenting of the left renal vein with reinforced polytetrafluoroethylene 5
- Renal autotransplantation for recalcitrant cases 1
- Endovascular stenting as a less invasive alternative 1
- Laparoscopic placement of an exovascular stent (newer technique) 1
Treatment Considerations
- Evaluation of the clinical significance of radiologic left renal vein compression remains challenging 2
- Patient selection for intervention should be based on symptom severity and persistence 2
- Varicoceles associated with nutcracker syndrome may require independent repair even after successful treatment of the primary condition 2
- Patients with progression to occlusion of the left renal vein may need alternative therapeutic approaches 2