Kidney cysts are closed pockets of tissue, filled with fluid, that develop in the kidneys. Multiple cysts can develop, or a single cyst. Kidney cysts can develop more or less spontaneously with no underlying cause, or they may develop as a result of a condition such as polycystic kidney disease or multicystic kidney dysplasia. The development of so-called “simple" kidney cysts (those with no underlying genetic cause) becomes more common in older people: up to 30% of those aged 70 and over have one or more cysts.
Complex kidney cysts are so-called because of their irregular shape. Another difference between simple and complex cysts is that complex kidney cysts often have “enhanced" tissue, meaning that within the cyst, there is tissue that has access to a blood supply.
Most of the time simple cysts are asymptomatic and are not harmful. Sometimes, they may cause pain if cysts enlarge to the point where they encroach on other organs. In other cases they may become infected or may bleed. It is rare for simple kidney cysts to cause any reduction in kidney function. However, there is a link between simple kidney cysts and high blood pressure, although it is unknown whether the link is a causative link or simply correlation.
Because kidney cysts are usually asymptomatic, it is common for them to remain undiagnosed. Most of the time, cysts are only found when a person undergoes a CT scan or ultrasound for another unrelated condition. No treatment is needed for kidney cysts that are present without causing any complications.