Radiology

THI!l authors believe that nephrotomography is an extremely accurate procedure and that most errors are due to poor radiographic and procedural technique or faulty interpretation. Before a kidney mass can be considered a benign cyst by nephrotomography, all the following characteristics must be clearly demonstrated. The lesion must be avascular with an adequate vascular phase, show a completely radiolucent zone with respect to the dense nephrograrn, exhibit sharply marginated contours in its entire circumference, and be very thin-walled and perfectly smooth. If all these criteria are not fulfilled (and the mass is not clearly malignant) then renal arteriography should be performed for further evaluation. Rigidity in requiring the presence of all these criteria is necessary if a high degree of accuracy is to be obtained. All lesions not clearly benign by nephrotomography must be considered malignant until proved otherwise. The characteristic findings in malignant tumours are the reverse of those described for benign lesions. Kidney carcinoma shows abnormal vascularity, is not completely radiolucent during the nephrogram phase, is poorly marginated and shows a lobulated contour. The evaluation of the thickness of the wall of the lesion ls emphasized in this report. A thick-walled, cyst-like mass can represent a necrotic carcinoma, and lack of awareness of this fact has in the past been the cause of serious error. A true Cyst has a very thin wall. In fact, it can barely be perceived on tomography. When seen it resembles a fine pencil line. On the other hand, if the wall is thicker or simulates the line made by a thick white crayon, then the lesion cannot be considered a simple benign cyst.