[Radio-transparent renal calculi and epithelial tumours. Contribution of ultrasound and CT scan to the diagnosis (author's transl)].

The aetiological diagnosis of lacunae detected by urography is uncertain in 10 to 20% of cases. Uric acid calculi larger than 2 cm in diameter can be demonstrated by ultrasonography, where they show as echogenic areas with conical shadows. Computerized tomography has wider possibilities: uric acid calculi are extremely dense and clearly visible, clots are not enhanced by contrast media, and the enhancement of epithelial tumours is of the avascular type.