Discriminating renal nutcracker syndrome from asymptomatic nutcracker phenomenon using multidetector computed tomography.

Purpose: To retrospectively evaluate the ability of computed tomographic (CT) findings to discriminate nutcracker syndrome (NCS) from asymptomatic nutcracker phenomenon (NCP) and to investigate the diagnostic value of CT findings in diagnosis of NCS.

Methods: From January 2014 to April 2015, 216 patients who underwent initial urographic CT were included. Initially, 216 patients were categorized as "nutcracker" or "normal," based on the following CT criteria: (1) the presence of beak sign and (2) hilar-aortomesenteric left renal vein diameter ratio >4. Patients who satisfied both of these criteria were diagnosed with nutcracker. The nutcracker was then divided into "NCS" and "asymptomatic NCP" based on the presence of characteristic symptoms. CT findings in sagittal and axial scans of corticomedullary phase were evaluated. Multivariate analysis was used to identify significant factors among 30 NCS, 51 asymptomatic NCP, and 135 normal patients. Diagnostic performance and threshold using receiver operating characteristic (ROC) curve were calculated.

Results: A total of 131 males and 85 females, with mean age of 38.6 years (range 18-89 years), were included. Multivariate analysis demonstrated superior mesenteric artery (SMA)-aortic angle (p < 0.001) and visualization of a dilated collateral vein with reflux (p = 0.001) were independent factors for distinguishing NCS from asymptomatic NCP. The combination of SMA-aortic angle <25° and visualization of a dilated collateral vein with reflux provided the greatest diagnostic accuracy (area under the ROC curve, 0.841).

Conclusions: The combination of SMA-aortic angle and visualization of a dilated collateral vein with reflux in multidetector CT can be useful to differentiate NCS from asymptomatic NCP.