With the advancement of medical imaging technology, more and more patients are being diagnosed with kidney cysts when they have a test like an ultrasound or CT scan for another reason.

A kidney cyst is a swelling filled with watery fluid that forms on one or both of the kidneys. Symptoms are rare and people don't usually know they have one. They can be associated with serious conditions that lead to impaired kidney function, but usually they're what we refer to as simple cysts, which don't normally cause complications.

Kidney cysts can occur in a variety of genetic diseases in adults and children, but simple renal cysts are commonly observed in normal kidneys. Simple kidney cysts are more likely to develop as a person ages. About a quarter of people who develop these cysts are 40 years or older and around half are 50 years or older.

Kidney cysts do not usually cause symptoms, but if they grow large enough, some may cause a dull pain in the back or upper abdomen. If they cysts get infected, patients may develop a fever, pain, and tenderness. They can also cause severe pain in the back or side if they burst. A cyst that blocks the normal flow of urine may cause the kidney to swell, referred to as hydronephrosis.

If a simple kidney cyst is causing symptoms or obstructing urine flow, it may need to be punctured and drained. In some cases, where a cyst is large enough, surgery may be required to remove it.

A complex kidney cyst is a cyst that has a more irregular shape or thicker walls than a simple cyst. Generally, the larger and more complex the cyst is, the greater the risk of cancer. Complex cysts are, therefore, carefully monitored and, if they appear suspicious, may need to be removed.

Many physicians use the Bosniak classification of renal cysts and uses certain characteristics of the cysts to place them into one of five categories. Bosniak categories I and II are generally simple cysts and do not require further testing. A repeat an ultrasound can be done at six to 12 months to assure stability and a correct diagnosis.

Bosniak Category IIF cysts are more complex and need a follow-up imaging to document stability. The absence of change over time supports benign disease, while progression suggests cancer. Observation can prevent many unnecessary surgeries as most cysts do remain stable.

Many recommend that all Bosniak Category III lesions undergo surgical removal and evaluation, as 40 to 50 percent will be cancer. With this approach, there are still a significant number of unnecessary surgeries. Some recommend close follow-up with magnetic resonance imaging to avoid this. MRI is especially useful for characterizing the inside of a cyst after ultrasound and CT scanning are still not definitive.

Category IV lesions will require surgical removal of the kidney. Approximately 85 to 100 percent of these are cancer. If detected and treated early, greater than 90 percent of those diagnosed with renal cancer still confined to the kidney are alive and disease-free five years after diagnosis. Five-year disease free survival is 60 to 70 percent for those whose disease has grown outside the kidney.
Survival rates are very low if the disease has spread beyond the kidney.

If you have been diagnosed with a kidney cyst, discuss the test results with your doctor. You should expect to do repeat testing with an ultrasound, CT scan or MRI at a later date, usually in six months. This interval can be stretched out if the cyst remains stable. And remember to follow-up regularly to save you from undue worry and anxiety.