**Core Concept**
ACTH-independent Cushing syndrome refers to a condition where excess cortisol production is not due to an overproduction of adrenocorticotropic hormone (ACTH) from the pituitary gland. This can be caused by various factors, including adrenal tumors, ectopic sources of ACTH, or other mechanisms that stimulate cortisol production.

**Why the Correct Answer is Right**
The correct answer is one of the options listed below. To determine the correct answer, we need to evaluate each option and identify the ones that are ACTH-independent.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is an ACTH-dependent cause of Cushing syndrome. ACTH-dependent Cushing syndrome can be caused by a variety of factors, including pituitary adenomas, ectopic ACTH-producing tumors, or familial Cushing syndrome.
* **Option B:** This option is incorrect because it is an ACTH-independent cause of Cushing syndrome. Adrenal tumors, such as adrenal adenomas or carcinomas, can produce excess cortisol without the stimulation of ACTH.
* **Option C:** This option is incorrect because it is an ACTH-independent cause of Cushing syndrome. Ectopic sources of ACTH can stimulate cortisol production, but the correct answer is not an ectopic source of ACTH.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with Cushing syndrome, it is essential to determine whether the condition is ACTH-dependent or ACTH-independent, as this can guide further diagnostic testing and treatment.

**Correct Answer:** A.