CT diagnosis of circumcaval ureter.

Variability in the normal course of the ureter makes it difficult to differentiate a normal variant from a congenital anomaly or deviation caused by a mass. CT can be useful in making this distinction. We present five cases of circumcaval ureter in which contrast-enhanced CT, by showing the ureter passing posterior and medial to the inferior vena cava (IVC), provided the definitive diagnosis. In addition, we studied the position of the inferior vena cava in the midlumbar region in 100 consecutive contrast-enhanced CT scans and compared the results with the position of the IVC in our five cases of circumcaval ureter plus one case of circumcaval ureter taken from the literature. Whereas only 6% of the normal patients had an IVC lateral to the right pedicle of the third lumbar vertebra, all of the patients with a circumcaval ureter and the one case in the literature had the IVC lateral to the pedicle. Therefore, the finding of a laterally placed IVC on CT is suggestive but not pathognomonic of circumcaval ureter. Contrast-enhanced CT can be used to prove the diagnosis of circumcaval ureter, and lateral placement of the IVC on non-contrast-enhanced CT suggests the diagnosis.