Milk of calcium cysts masquerading as renal calculi

Milk of calcium renal cysts contain a colloidal suspension of calcium crystals. By routine radiography and sonography in supine position this rare condition may be misinterpreted as renal lithiasis for which an unnecessary surgical intervention may be performed as it happened in our two cases that are presented here. Postoperatively, the characteristic finding of half-moon contour on upright abdominal plain views was lacking in one case, but in both cases computed tomography revealed the typical calcific suspension layering. However, upright plain views and computed tomography are not routinely performed in patients in whom a renal stone has initially been considered. This entity should be considered in the differential diagnosis of renal paracalyceal calcifications of obscured origin.