The kidneys are a pair of organs in the back that filter blood and make urine. They are important for regulating fluid, minerals, acidity of the blood and stimulating bone marrow growth. They are subject to different types of problems ranging from genetic disorders affecting individual cells to large structural abnormalities. One structural abnormality is called a cyst. Cysts are divided into simple and complex, and have a classification system to help predict the chances of cancer and guide therapy.
Simple Cysts
Non-cancerous cysts are known as simple cysts. An article in 2000 in the medical journal "Nephrology Dialysis Transplantation" noted that 50 percent of people over age 50 have a simple cyst. According to the Kidney Cancer Institute, a simple kidney cyst is a liquid filled round space located within the kidney. Its wall or lining is thin and without irregularities. There is nothing but fluid inside the cyst, which is usually clear to yellow. These have no risk of becoming cancerous. Their cause is unknown. They usually do not cause symptoms, but if they grow large enough they may cause dull pain or a fever. In rare cases they may burst, causing severe pain, or get infected.
Complex Cysts
A complex cyst is a cyst that is not regular like a simple cyst. For example it may have calcifications. This means that the cyst contains the mineral calcium, which can be see on radiographs such as X-rays or CT scans. They may also have walls called septa or septations, which can be thick or fine. Many septations or thick walls suggest a greater possibility of kidney cancer. Growth of a cancer is also suggested if the cyst has a blood supply or contains blood.
Cyst Classification
Cysts are classified by the Bosniak classification of renal cystic disease. The categories include I, II, IIF, III and IV. Category I cysts are simple and benign with no irregularities. On the other end of the spectrum is category IV which contains blood or other soft tissues. Category I has a less than 2 percent chance of being cancer and category IV has a 92 percent chance.
References
- "Nephrology Dialysis Transplantation"; The simple renal cyst; Anna-Maria Nahm, Eberhard Ritz; 2000
- Kidney Cancer Institute: Kidney Cyst
- MayoClinic.com: Kidney Cysts
