Case series of collapsed simple renal cysts potentially simulating cystic malignancy at CT

The radiological differential diagnosis for complex renal cysts seen at CT generally includes cystic malignancy or renal abscess. We have encountered five cases of complex-appearing renal cysts at CT where serial imaging and clinical outcome favored a diagnosis of a collapsed benign simple renal cyst. We present these cases to broaden the differential diagnosis for complex renal cysts seen at CT, highlighting the importance of careful correlation with prior imaging to assist in correct recognition of collapsed simple cysts and potentially allowing for conservative management or surveillance.