MONDO_0015268 (medullary sponge kidney) (MSK) is a birth defect of the tubules - tiny tubes inside the kidneys. In a normal kidney, urine flows through these tubules as it is being formed. In MSK, tiny sacs called cysts form in the medulla (the inner part of the kidney), creating a sponge-like appearance. The cysts keep urine from flowing freely through the tubules. MSK is present at birth but symptoms typically do not occur until adolescence or adulthood. Problems caused by MSK include blood in the urine, kidney stones, and urinary tract infections. MSK rarely leads to more serious problems, such as total kidney failure. There is no cure for this condition, so treatment is aimed at removing kidney stones and treating urinary tract infections with antibiotics. Also known as: Cacchi-Ricci disease, MSK, Precalicial canalicular ectasia.