Renal milk of calcium: contraindication to extracorporeal shockwave lithotripsy.

Renal milk-of-calcium (MOC) cysts are rare findings, with only approximately 60 cases reported in the literature. The diagnosis depends on the demonstration of the typical "half-moon" configuration on horizontal beam radiography; classical ultrasound finding is a gravity-dependent, echogenic shadowy material in a renal cyst. The importance of the MOC syndrome lies in its recognition and differentiation from a renal stone in order to avoid unwarranted surgery or extracorporeal shock-wave lithotripsy (ESWL). We have encountered five patients with renal MOC and present the typical clinical and radiological features in order to facilitate differential diagnosis.