Medullary sponge kidney (MSK) is a congenital disorder, meaning it is present at birth. MSK occurs when small cysts (sacs) form either on tiny tubes within the kidney (known as tubules) or the collecting ducts (a channel where urine is collected for removal). These cysts can reduce the outward flow of urine from the kidneys. One or both kidneys can be affected.
MSK is considered a rare disorder. The exact cause is not known and the vast majority of cases do not show a family history. Women are affected by MSK more frequently than men.
MSK is usually a benign disorder without any symptoms, but it can lead to other problems, such as urinary tract infections and kidney stones, as a result of the urine flow being blocked. In many cases, MSK does not cause symptoms or problems, but when it does it usually happens during adulthood. If problems do occur, it can cause pain in the side and back (known as flank pain), abdomen, or groin. Other symptoms can include painful or burning urination, cloudy urine, blood in the urine (hematuria), fever, chills, and nausea. These symptoms depend on the cause and severity of urinary blockage. Kidney failure occurs in about 10% of people with MSK.