What is medullary sponge kidney?
This is also a congenital condition, in which the collecting ducts in the medullary pyramids are dilated and ectatic, giving the medullary pyramids a brush-like or sponge-like appearance. Stones form within these ducts, which can then erode into the collecting system. The findings are seen on the excretory phase of a CTU or on an IVU. Medullary renal cysts may also be encountered. The presence of clustered calcifications in the collecting ducts in the medullary pyramids is referred to as medullary nephrocalcinosis.
The clinical importance of medullary nephrocalcinosis is that there is a very high incidence of stones passing from the renal parenchyma into the collecting systems; patients present with recurrent episodes of renal colic and stone-related complications.