Imaging of the pituitary gland in Cushing's disease

Objective: To evaluate the sensitivity of computed tomography (CT) and magnetic resonance imaging (MRI) of the pituitary gland in detecting pituitary adenomas in patients with Cushing's disease. Methods: Twenty-five patients aged 8-55 years (average age 30 years), clinically and biochemically diagnosed as having Cushing's disease, were evaluated with a contrast-enhanced CT scan and MRI of the pituitary gland. Contrast-enhanced CT scans of direct 2-mm-thick coronal sections were performed. Pre- and post-enhanced MRI of the pituitary gland was performed on a 1.5-tesla superconducting magnet, taking 2-mm-thick sections in the sagittal and coronal planes. Results: MRI revealed adenomas in 16 patients (12 microadenomas and 4 macroadenomas). Twelve (75%) adenomas were delineated more clearly on post-gadolinium MRI scans. Nine (56%) adenomas were better delineated on coronal images. Out of 16 adenomas identified on the MRI, only 5 were seen on the CT scan. All patients underwent trans-sphenoid surgery and the MRI findings were confirmed. Conclusion: Contrast-enhanced MRI is the preferred modality for the detection of ACTH-secreting adenomas, which are difficult to visualize on CT scans due to their small size. A focal hypointense lesion is the commonest finding on T-1-weighted images and, if identified on coronal sections, is the most sensitive diagnostic criterion. However, a negative MRI does not exclude the presence of a microadenoma.