Brian Shuch, MD, director of the UCLA Kidney Cancer Program, discusses renal cysts. These are very common, especially in individuals over the age of 50, and are usually asymptomatic. Most cysts do not impair kidney function and are not caused by genetic factors. There are different types of cysts, including simple cysts filled with low-density water, cysts filled with protein or high-density material, and hemorrhagic cysts filled with old blood. Complex cysts have thick walls or solid elements. Most cysts do not require treatment, but large, simple cysts causing symptoms may be drained. Moderately complex cysts are closely monitored, whereas very complex cysts may need treatment. Dr Shuch advises seeking expert opinion if a cyst is deemed complex.