Nutcracker Phenomenon/Syndrome

Nutcracker syndrome is a vascular compression disorder. The left renal vein courses in between the Aorta and Superior Mesenteric Artery(SMA). If the descent of the SMA is to steep and the aorto-mesenteric angle to acute (normal angle is 38–65°) this could lead to left renal vein compression and Nutcracker syndrome/phenomenon. The difference between Nutcracker syndrome and phenomenon is the presence of symptoms.


  • Hematuria (Macro/microscopic  rupture of thin-walled varices, due to elevated venous pressure, into the collecting system)
  • Proteinuria
  • Left-sided flank/lower abdominal/pelvic pain
  • Varicose veins
  • Urinary frequency
  • Left-sided varicocele (or pelvic varices)
Normal distance between Aorta and SMA with LRV coursing through


There are 2 types of Nutcracker compression

Classic or anterior type which is compression of the LRV between the Aorta and SMA

Posterior which is when the anatomical variant of retrocaval LRV (when the left renal vein goes posterior to the IVC) and is compressed between the IVC and vertebrae.


Sonographically there will be an acute aortomesenteric angle >36°

Measure the compression ratio = P-C/C (P = pre-compressed vein C= compressed vein, CR >2.25 is indicative of NCS). Image the vessels in sagittal and transverse

Sagittal image showing very narrow angle between aorta and sma
Aorta with normal aortomesenteric distance
Transverse image showing the impinged Left renal vein
LRV with color doppler

Nutcracker Phenomenon (asymptomatic patient)

Left renal compression without symptoms Nut Cracker Phenomenon

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