A rare cause of left flank pain: “the nutcracker syndrome”.

A 14 year old female refers persistent left flank pain for about 6 months, with two episodes of hematuria associated with pain, which has motivated countless medical consultations. Refers pain as more intense while standing and sitting, which is relieved clearly in the lying position. Many ultrasounds were performed showing a grade-II hydronephrosis without finding any lithiasis in the urinary tract. She consulted again for pain, a urinalysis found proteinuria and hematuria. A new ultrasound was done identifying the same findings. However in a more detailed exploration, a reduction of the caliber of the left renal vein(LRV) was identified at the level of its passage between the superior mesenteric artery(SMA) and aorta, with a significant decrease in the distance between these two vessels and a very acute aortic-SMA angle. There was dilatation of the proximal LRV without dilatation of the distal LRV. In the Doppler study there was a turbulent bluff distal to the aorto-mesenteric junction, with difference in the curves between the right and left renal veins that intensified while standing. These findings were compatible with a “nutcracker syndrome”(NS) and were confirmed with a CT. The patient was operated doing a combined renal-splenic shunt and evolved well with resolution of the symptoms.

The NS refers to the compression of the LRV at the aortomesenteric junction(AoMJ). The prevalence is unknown but is more frequent in women. The compression leads to secondary renal hypertension with development of venous collaterals. The most frequent symptom is hematuria but left flank pain is common. The key imaging findings in CT are: beak sign with dilatation of the proximal LRV, elevated ratio between the proximal LRV and the LRV at the AoMJ, aortomesenteric angle less than 41. The same findings can be identified in ultrasound. In Doppler examination an elevated distal LRV velocity and turbulence are found. Treatment ranges from conservative management to surgical intervention or placement of a stent in the LRV.

NS is an uncommon cause of left flank pain, a high grade of suspicious by both the clinician and the radiologist is needed. We must think of it specially when the pain is associated with hematuria and there is no evidence of lithiasis.

- Fong J, Poh A, Tan A, Taneja R. Imaging Findings and Clinical Features of Abdominal Vascular Compression Syndromes. American Journal of Roentgenology. 2014,203(1):29-36.