What is a cystic nephroma, and what are its CT and MRI features?
A cystic nephroma is a rare benign cystic renal neoplasm. In adults, it most commonly occurs in women in the fifth through seventh decades of life. It also occurs in young boys in the first decade of life. On CT and MRI, a well-circumscribed cystic renal lesion is typically seen, usually with multiple variably enhancing internal septations, and sometimes with herniation into the renal collecting system ( Figure 35-6 ), which is a characteristic feature. Solid enhancing components, hemorrhage, venous extension, regional lymphadenopathy, and distant metastatic disease are generally not seen. However, surgical resection is generally performed because it is extremely difficult to distinguish a cystic nephroma from a cystic RCC.