**Core Concept**
Adrenal adenomas are benign tumors of the adrenal gland, and computed tomography (CT) is a crucial imaging modality for their diagnosis. Characterizing adrenal adenomas relies on specific CT features that distinguish them from malignant lesions or other pathologies.

**Why the Correct Answer is Right**
Adrenal adenomas typically exhibit low attenuation values on non-contrast CT scans due to their high lipid content. This feature is a result of the tumor's composition, which includes a high proportion of lipids. The low attenuation values are a key characteristic used to differentiate adrenal adenomas from other adrenal masses, such as malignant tumors or pheochromocytomas. The presence of a thin, smooth capsule surrounding the adenoma is another distinctive feature.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is a common CT feature of adrenal adenomas. The high lipid content of the tumor leads to low attenuation values on non-contrast CT scans.
**Option B:** This option is also incorrect as it is a characteristic of adrenal adenomas. The thin, smooth capsule surrounding the tumor is a distinguishing feature.
**Option C:** This option is incorrect as it is not a typical CT feature of adrenal adenomas. The absence of a distinct capsule or the presence of a thick, irregular capsule would raise suspicion for a malignant tumor.

**Clinical Pearl / High-Yield Fact**
When interpreting CT scans of the adrenal gland, it is essential to remember that the presence of a thin, smooth capsule and low attenuation values on non-contrast scans are strong indicators of an adrenal adenoma. This can help avoid unnecessary further evaluation or biopsy.

**Correct Answer:** C.