Medullary Sponge Kidney

What is medullary sponge kidney?

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 most cases do not appear to be inherited. Problems caused by MSK include hematuria, or blood in urine; kidney stones; and urinary tract infections (UTIs). But these problems do not usually appear until the ages of 30 to 40. MSK affects about 1 person per 5,000 to 20,000 people in the United States. Researchers have reported that up to 20 percent of people who form kidney stones have MSK. MSK rarely leads to more serious problems, such as total kidney failure.

What are the kidneys and what do they do?

The kidneys are two bean-shaped organs, each about the size of a fist. They are located on either side of the spine, just below the rib cage. The kidneys filter wastes and extra fluid from the blood to produce urine. They also release hormones that help control blood pressure and that keep blood and bones healthy.

Blood flows into the kidneys through two blood vessels called renal arteries. Inside the kidneys, the arteries branch off into smaller and smaller arteries. The smallest blood vessels intertwine with tubules that start to collect wastes and extra fluid from the blood. The point where the blood vessel and tubule intertwine is called a nephron. Each kidney contains about 1 million nephrons.

Urine leaves the nephron and drips through the tubules, which connect to increasingly larger tubules, and finally to the ureters, which are tubes that carry urine to the bladder.

In MSK, abnormal sacs called cysts form in the collecting tubes in the medulla of the kidneys. The cysts keep urine from flowing freely through the kidneys. UTIs and kidney stones can develop because the urine flow is blocked.

What are the signs and symptoms of MSK?

For many people, MSK causes no symptoms. The first sign that a person has MSK is usually a UTI or kidney stone. UTIs and kidney stones share many of the same symptoms:

burning or painful urination
pain in the back, lower abdomen, or groin
cloudy, dark, or bloody urine
foul-smelling urine
fever and chills
vomiting

People who experience these symptoms should see a doctor as soon as possible.

How is MSK diagnosed?

A doctor may suspect MSK when a person has repeated UTIs or kidney stones. To confirm the diagnosis, the doctor may order an x ray called an intravenous pyelogram (IVP). In an IVP, dye is injected into a vein. The dye travels through the blood to the kidneys. As the dye is filtered into the urinary tract, it makes urine visible on the x ray and shows any blockage in the urinary tract. Cysts show up as clusters of light in an IVP.

How is MSK treated?

No treatment can get rid of cysts in the affected kidneys. Once a doctor is sure that a person has MSK, treatment focuses on curing existing infection, removing any stones, and preventing future infection and stone formation.

UTIs. To treat UTIs, the doctor may prescribe a medicine called an antibiotic that kills bacteria. A person with MSK may need to continue taking a low-dose antibiotic to prevent recurrent infections.
Kidney stones. Stone removal may require a procedure called lithotripsy, which uses sound waves to break stones into sand-like particles. The particles can then pass easily through the urinary tract with the flow of urine. Another way to remove stones is to insert a thin tube called a ureteroscope through the urethra and bladder to catch the stone and retrieve it. A person with MSK may be able to prevent more stones from forming through diet changes or taking medicine. Increasing fluid intake so the person makes more urine is also very important to reduce the risk of new stone formation.

Points to Remember

Medullary sponge kidney (MSK) is a birth defect of the tubules inside the kidneys.
Problems caused by MSK include hematuria, kidney stones, and urinary tract infections (UTIs).
MSK problems do not usually appear until ages 30 to 40.
Many people with MSK have no symptoms.
Diagnosis of MSK may require an x ray called an intravenous pyelogram (IVP).
No treatment can get rid of cysts in MSK.
Treatment for MSK focuses on curing UTIs, removing kidney stones, and preventing recurrent infections and stones.