A cyst is a fluid-filled sac. There are two types of kidney cysts.

Polycystic kidney disease (PKD) runs in families. In PKD, the cysts take the place of the normal tissue. They enlarge the kidneys and make them work poorly, leading to kidney failure. When PKD causes kidneys to fail - which usually happens after many years - people need dialysis or kidney transplantation. About half of people with the most common type of PKD end up with kidney failure. PKD also causes cysts in other parts of the body, such as the liver.

Symptoms of PKD include

• Pain in the back and lower sides
• Headaches
• Urinary tract infections
• Blood in the urine

Doctors diagnose PKD with imaging tests and family history. Treatments include medications, and, when people with PKD develop kidney failure, dialysis or kidney transplants.

Acquired cystic kidney disease (ACKD) usually happens in people who are on dialysis. Unlike PKD, the kidneys are normal sized, and cysts do not form in other parts of the body. People with ACKD already have chronic kidney disease when they develop cysts. ACKD often has no symptoms. In most cases, the cysts are harmless and do not need treatment.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases