FamilyDoctor.org notes that the function of the kidneys -- located in the rear of the abdomen near the spine -- is to remove waste from the blood, which is then excreted in urine. Fluid-filled growths called cysts can develop on the kidneys, often causing no symptoms unless they grow excessively large, which may cause pain in the abdomen, blood in the urine and frequent urinary tract infections. Kidney cysts have a few distinct causes.
Polycystic Kidney Disease
Polycystic kidney disease is caused by a genetic defect that causes the growth of many kidney cysts. One subtype of polycystic kidney disease is a recessive disorder, meaning a person needs to inherit two copies of the defective gene to have the disease. The recessive disorder is less common than the other type, a dominant disorder for which a person needs inherit only one copy of a defective gene to have the disease. The Merck Manuals Online Medical Library states that the recessive type of polycystic kidney disease is characterized by the growth of very large kidney cysts in infancy that can cause the abdomen to become very swollen. High blood pressure in this form of the disease eventually causes the kidney and liver to fail, often during childhood.
The dominant form of the disease is more common and is characterized by fewer kidney cysts that grow at a much slower rate compared to the recessive form. The cysts cause no problems in many people, and some are not even aware they have the disease, although it is possible for the cysts to grow large enough to cause symptoms.
Medullary Sponge Kidney
This kidney disease is present at birth, according to the National Kidney and Urologic Diseases Information Clearinghouse, and causes the development of cysts in structures called tubules in the medulla, which is the inner part of the kidney. These cysts are often small in size, but large in number and cause the kidney to take on the appearance of a sponge. Urine usually flows through the tubules, but the cysts can partially or completely block it from flowing normally, which may cause symptoms.
Age
Cysts often develop in the kidneys of people who do not have polycystic kidney disease or medullary sponge kidney. In fact, FamilyDoctor.org reports that up to 50 percent of people over the age of 50 develop at least some fluid-filled cysts in their kidneys. As a person grows older, his risk of having kidney cysts increases. However, these age-related cysts usually do not cause symptoms, and are often identified by imaging tests, such as an ultrasound, that are conducted for other reasons. Like the other cysts caused by diseases, age-related cysts that do grow very large may cause symptoms.
