Correct!
3. Brain MRI
The dexamethasone testing is consistent with Cushing syndrome, probably ACTH-dependent. The most common etiology for Cushing syndrome is a pituitary adenoma, and thus brain MRI is indicted. 18FDG-PET scan is not indicated. 68Ga-Dotatate PET, typically used for neuroendocrine tumor assessment, could eventually play a role in this patient’s evaluation, but is premature at this point. Repeat chest CT is not indicated as the initial CT was of good quality and unrevealing. Abdominal CT is reasonable, but the most likely source for ACTH-dependent Cushing syndrome is the pituitary gland, and therefore brain MRI is the “best” answer.
Brain MRI (Figure 3) was performed and reported as normal. A corticotropin releasing hormone test suggested an ectopic source of ACTH production.
Figure 3. Brain MRI in the sagittal (A), axial (B-D) and coronal (E and F) planes shows a normal pituitary gland (arrows), sellar region (circle), and infundibulum (arrowhead).
Which of the following represents the most appropriate next step for the patient’s management? (Click on the correct answer to be directed to the sixth of twelve pages)