Nonvisualized ("phantom") renal calyx: causes and radiological approach to diagnosis.

A calyx which fails completely to opacify on excretory urography (phantom calyx) is often the harbinger of serious underlying renal disease. Causes of a phantom calyx include tuberculosis, tumor, calculus, ischemia, trauma, and congenital anomaly. The pathologic basis for the radiographic findings in each of these entities is described and an overall approach to diagnosis is set forth.