Generally, benign lesions are rounded and homogenous whereas most malignant lesions appear lobulated and inhomogeneous. Pheochromocytoma and adrenomyelolipoma may also exhibit lobulated and inhomogeneous features. Additional information can be obtained from CT by assessment of contrast wash-out after 15 minutes, which is >50% in benign lesions but <40% in malignant lesions, which usually have a more extensive vascularization.
MRI also allows for the visualization of the adrenal glands with somewhat lower resolution than CT. However, as it does not involve exposure to ionizing radiation, it is preferred in children, young adults, and during pregnancy. MRI has a valuable role in the characterization of indeterminate adrenal lesions using chemical shift analysis, with malignant tumors rarely showing loss of signal on opposed-phase MRI.
Fine-needle aspiration (FNA) or CT-guided biopsy of an adrenal mass is almost never indicated. FNA of a pheochromocytoma can cause a life-threatening hypertensive crisis. FNA of an adrenocortical carcinoma violates the tumor capsule. FNA should only be considered in a patient with a history of nonadrenal malignancy and a newly detected adrenal mass. FNA should be carried out only after careful exclusion of pheochromocytoma and if the outcome will influence therapeutic management
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