American Board of Internal Medicine (ABIM) Certification Practice Exam

In patients with suspected pituitary adenoma causing Cushing syndrome, when should a pituitary MRI be ordered?

1. After documenting adrenal insufficiency

2. Only if hypercortisolism is suspected

3. After hypercortisolism and Cushing syndrome are diagnosed

4. As a routine follow-up test

The correct answer is: After hypercortisolism and Cushing syndrome are diagnosed

Ordering a pituitary MRI after hypercortisolism and Cushing syndrome have been diagnosed is a critical step in the evaluation of patients with suspected pituitary adenoma. Cushing syndrome, characterized by excess cortisol production, can stem from various sources—including adrenal tumors, ectopic ACTH secretion, or pituitary adenomas (Cushing's disease). A definitive diagnosis of hypercortisolism is necessary before pursuing further imaging because the MRI is specifically used to visualize the pituitary gland to identify any aberrations that may indicate an adenoma. This imaging supports the clinical suspicion of pituitary etiology after confirming that a patient exhibits the clinical features of Cushing syndrome, such as weight gain, hypertension, and characteristic striae, as well as biochemically elevated cortisol levels. In summary, the timing of the MRI is important—while initial screening for hypercortisolism involves biochemical testing, the MRI is best reserved for when the diagnosis of Cushing syndrome has been confirmed, ensuring that the imaging results will be interpreted in the context of a clear clinical picture. This approach optimizes the patient's diagnostic pathway and facilitates targeted management if an adenoma is identified.