Medullary sponge kidney

Unenhanced CT scan of abdomen in a patient with hematuria shows bilateral punctate calcifications in the region of the medullary rays consistent with medullary nephrocalcinosis in a patient with dilated distal collecting tubules--medullary sponge kidney

Plain film of abdomen in patient with MSK and resultant nephrocalcinosis.  Note that the calcifications seem to be grouped in the region of the experted renal pyramids where the tubular ectasia is located.  Stasis in these dilated tubules results in stone formation and predisposed to stone migration and subsequent ureteral obstruction.