Value of nephrotomography in evaluating nonvisualized kidney in renal absence: the colon sign.

Nephrotomography is a simple, highly accurate, noninvasive procedure and is extremely helpful in differentiating a nonvisualized kidney due to renal agenesis, ectopia, or nephrectomy from other acquired renal diseases. Early recognition of the characteristic malpositioning of the colon, "the colon sign," eliminates the need for more invasive investigations.