CT features of a simple renal cyst include which of the following?

• A. Sharp demarcation, smooth/thin wall, homogeneous fluid, no contrast enhancement
• B. Irregular thick wall with septations and enhancement
• C. Calcifications within wall
• D. Heterogeneous density with solid components

Answer: (A)

Simple renal cysts on CT are fluid-filled, benign lesions that appear as well-defined, sharply demarcated structures with a smooth, thin wall. The contents have water attenuation and look homogeneous, and there is no enhancement after IV contrast because the cyst fluid is avascular. This combination—clear borders, thin wall, uniform fluid density, and lack of enhancement—is what sets a simple cyst apart from more complex or solid renal lesions. If you see an irregular thick wall, septations with enhancement, or solid components, that suggests a complex cyst or tumor and warrants further evaluation. Wall calcifications can occur with some complex cysts but are not typical of a benign simple cyst, and heterogeneous density with solid parts clearly points away from a simple cyst.