**Core Concept**
Adrenal adenomas are benign tumors of the adrenal gland, often causing Cushing's syndrome due to excessive cortisol production. CT features of adrenal adenomas are crucial for diagnosis and differentiation from other adrenal lesions.

**Why the Correct Answer is Right**
Adrenal adenomas typically exhibit low attenuation values on unenhanced CT scans due to high lipid content. They also show rapid washout of contrast in the delayed phase, which is a characteristic feature distinguishing them from non-adenomatous lesions. Additionally, adrenal adenomas are usually smaller than 4 cm in diameter.

**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable, as it's not provided.
**Option B:** Typically a feature of adrenal adenoma, not to be excluded.
**Option C:** May be a feature of other adrenal lesions, but not a distinguishing characteristic of adenoma.
**Option D:** Not a feature of adrenal adenoma; adrenal carcinomas are often larger and more heterogeneous.

**Clinical Pearl / High-Yield Fact**
When evaluating adrenal lesions on CT, remember that adenomas tend to be small, low-attenuating, and show rapid contrast washout, whereas non-adenomatous lesions often appear larger and more heterogeneous.

**Correct Answer: D. Adrenal carcinomas are often larger and more heterogeneous.**