CT and MR Imaging of the Adrenal Glands in Cortisol-secreting Tumors

Cushing's syndrome (CS), first described by the neurosurgeon Harvey Cushing in the 1930s, is the result of chronic glucocorticoid excess. In patients with adrenocorticotropic hormone (ACTH)-dependent CS, bilateral hyperplasia of the adrenal cortex occurs, while in those with ACTH-independent primary CS, either adrenocortical tumors or primary adrenal hyperplasia can be observed. Cortisol-secreting adrenocortical tumors are more frequently adenomas, while adrenal carcinoma accounts for only 5% of cases. Unfortunately, no reliable endocrinological tests are available and no specific tumor markers exist to differentiate between benign and malignant adrenal tumors, so both computed tomography (CT) and magnetic resonance (MR) imaging studies are currently required to localize and define adrenal lesions. Additional information to conventional imaging can be obtained using F-18-fluoro-2-deoxyglucose (FDG)-positron emission tomography (PET)/CT, while percutaneous image-guided fine-needle aspiration cytology (FNAC) in some cases has shown a high accuracy in detecting malignancy and in confirming adrenal metastases. New PET tracers with selective affinity for the adrenal tissue are still under evaluation. Multidetector CT scan, with the combination of unenhanced and dynamic scans, represents the single most accurate modality for the detection and the characterization of adrenal adenomas. In these lesions, chemical-shift MR imaging produces a typical loss of signal intensity on out-of-phase breath-hold gradient-echo images in lipid-rich adenomas. For these lesions there is no difference between CT and MR imaging, while MR chemical shift imaging is very helpful in identifying the additional small group of adenomas where intracellular lipid content is minimal.