Kidney Cysts

Kidney cysts are fluid-filled sacs that form within or on the surface of the kidneys. They are among the most common renal lesions, found in approximately 50% of people over age 50 on imaging studies. Most kidney cysts are simple cysts - round, thin-walled, fluid-filled structures that are benign and typically do not cause symptoms or require treatment. However, some cysts can be complex, with thick walls, internal septations, or solid components that may indicate a more serious condition, including a small risk of malignancy. Simple kidney cysts are thought to arise from the accumulation of fluid within the renal tubules, possibly due to obstruction or weakened tubular walls. They are usually discovered incidentally during imaging studies performed for other reasons. Simple cysts are classified as Bosniak Category I on imaging and have virtually no risk of becoming cancerous. Complex cysts (Bosniak Categories II-IV) have features that raise concern for malignancy and require closer monitoring or intervention. Most simple kidney cysts do not require treatment unless they become large enough to cause symptoms such as flank pain, urinary obstruction, or infection. Treatment options include observation, percutaneous aspiration and sclerosis (injecting a sclerosing agent to prevent fluid reaccumulation), or laparoscopic marsupialization (surgically creating a window in the cyst wall to drain it). Complex cysts may require surgical excision, partial nephrectomy, or close surveillance depending on their Bosniak classification. Regular follow-up imaging is recommended for complex cysts to monitor for changes.