An ultrasonographic classification for diverse clinical symptoms of pediatric nutcracker phenomenon

The nutcracker phenomenon (NCP) is the significant compression of the left renal vein (LRV) by the aorta and superior mesenteric artery (SMA), and found in the patients with so-called idiopathic renal bleeding, orthostatic proteinuria and severe orthostatic intolerance. The purpose of this study is to investigate clinical implications among these disorders possibly related to the NCP.

We analyzed 93 pediatric patients (56 with idiopathic renal bleeding, 14 with massive orthostatic proteinuria and 23 with severe orthostatic intolerance), and the findings of 64 patients were compared on both digital subtraction angiography (DSA) and ultrasonography (US) to obtain a new US classification of the NCP with seven grades.

US grades of the NCP were well-correlated with DSA findings (rs = 0.797, p < 0.0001). LRV stenosis was a typical finding in patients with idiopathic renal bleeding. LRV occlusion was observed in 70% for severe orthostatic intolerance, and in contrast in 18% and 14% for idiopathic renal bleeding and massive orthostatic proteinuria, respectively. Collateral veins on color Doppler US as well as a mirror image of the SMA in the aorta on conventional US were found as subsidiary signs of LRV occlusion. Extreme dilatation of the LRV was present in 44% for massive orthostatic proteinuria and in 7% for idiopathic renal bleeding (p < 0.0001).

Anew US classification is useful for the diagnosis of the NCP in diverse clinical symptoms.