What is a medullary sponge kidney (MSK)?
MSK is a disorder characterized by dilated collecting ducts (precalyceal ducts) that may or may not contain calculi and/or nephrocalcinosis, and classic “papillary blush” or “paint brush” linear striations on intravenous urography (IVU) or CT urography. This characteristic appearance is the result of pooling contrast material within dilated collecting ducts in the tips of the renal papilla.
Although the prevalence in the general population is unknown, it is well represented among kidney stone patients (12% to 20% of calcium stone formers). MSK is incidentally diagnosed when IVU is performed for flank pain or indications other than renal colic. It can be seen in 1 in every 200 IVUfs and is more frequent in women than men. Because conventional CT has almost completely replaced IVU, the diagnosis of MSK may now be made less often since the finding of medullary nephrocalcinosis on CT are suggestive, but is not diagnostic, of MSK. A multidetector-row CT using high-resolution three-dimensional volume rendering late urographic images is required for a diagnosis of MSK by CT.
The disease may affect one, both, or only portions of the kidneys and is characterized by dilation (3 to 8 mm) of medullary collecting ducts, which in 50% of patients contain calcium deposits or stones and is the most common presentation of this disease. However, usually patients with MSK are asymptomatic and therefore remain undiagnosed for life. Other associated symptoms include macrohematuria and microhematuria and UTI.
