Cysts are enclosed, sac-like structures that contain liquid or semisolid substance. In general, cysts can be present in any part of the body. They are named according to their location in the body; for example cysts on the skin are called sebaceous cysts, whereas those present in the nerve roots and liver are referred to as tarlov cysts and liver cysts respectively. Likewise, renal cysts are the cysts present in the kidney. It is common to have more than one renal cysts, which in maximum cases, are benign (not dangerous). However, the severity of the symptoms may vary according to the underlying causes of the condition. Classification There are several types of renal cysts, classified based on the appearance of the fluid-filled lesions. The most common types are simple and complex renal cysts. The former type is small, which appears round, spherical, or oval in shape with smooth and thin wall. Usually, simple renal cysts are harmless and asymptomatic without any clinical implications. People who are above 50 years have a higher risk of developing renal cysts. It is estimated that more than 50 percent of people over 50 years have one or more renal cysts. More than one simple cysts may be present in an individual. Simple renal cysts are called hyperdense, if there is the presence of blood on the walls of the cysts. Bilateral renal cysts refer to the presence of simple cysts in both the kidneys. In the complex type, the cysts are characterized by irregularities in the wall lining. Complex cysts may have septations (walls within the same cyst), calcifications (deposition of calcium), and enhancements (a part of the cysts receives blood supply). Causes and Symptoms Renal cysts can be present at birth (congenital) or acquired later due to obstruction in the kidney tubules. It may be caused due to underlying diseases and disorders. For example, these cysts are more common among people with polycystic kidney disease, medullary cystic disease, medullary sponge kidney, and chronic renal failure. Those who undergo frequent dialysis (especially hemodialysis) are susceptible to renal cysts development than others. Tapeworm infestation may also lead to the formation of cysts in the kidney. In majority of the cases, they cause no significant symptoms. In fact, many people with renal cysts are not aware of their condition. Some of the symptoms that may be developed due to complicated renal cysts are kidney pain, difficulty in urination, frequent urination, presence of blood tinge in urine, hypertension, and pain in the belly, sides, and back. In case of renal cysts caused by tapeworm infestation, the symptoms usually accompany the presence of tapeworm segments and/or eggs in urine and stool. At times, the cysts may lead to complications like kidney infections and cancer. Diagnosis and Treatment Renal cysts are identified by conducting imaging tests such as ultrasound, CT (computed tomography), and magnetic resonance imaging (MRI) scan. There are no specific treatments for small and benign renal cysts. In fact, therapeutic intervention is not necessary for asymptomatic kidney cysts. If there are any noticeable signs and symptoms of renal cysts, then the physician may conduct imaging tests in order to detect any changes in the cyst size. In case of a growing or cancerous renal cyst, surgical removal is suggested for the patient. Another effective treatment option for complicated renal cysts is the percutaneous sclerotherapy, which is conducted by injecting sterile alcohol, particularly ethanol.