Adrenal scintigraphy

Abstract

Adrenal scintigraphy has been clinically feasible since the development of /sup 131/I-19-iodocholesterol in 1970. This agent has been supplanted by the current agent of choice, 6-iodomethyl-19-norcholesterol. Patients receive Lugol's iodine to block the thyroid gland and receive 1 to 2 mCi of radiocholesterol intravenously. Imaging is accomplished 4 to 7 days postinjection with the gamma camera. Adrenal percent uptake determinations similar to thyroid uptakes may be accomplished with the aid of a digital computer and standard percent uptake curves derived from phantom studies. Adrenal suppression scans were developed to enhance differences between the normal and abnormal adrenal cortex in certain clinical conditions. Patients receive dexamethasone prior to radiotracer injection, and serial scans beginning 2 to 3 days postinjection are obtained. In the normal adrenal scintigram, the right adrenal gland is higher than the left and appears slightly hotter. The left adrenal has an oval configuration, while the right adrenal has a truncated or circular configuration in most subjects. Knowledge of the patient's clinical hormonal status is necessary for proper scintigraphic interpretation. With documented glucocorticoid excess, symmetrical visualization is due to adrenal hyperplasia, usually secondary to Cushing's disease. Unilateral visualization indicates the presence of an adenoma or a postsurgical adrenal remnant;more » and bilateral nonvisualization is typically due to carcinoma. On dexamethasone suppression scans in primary aldosteronism and adrenal androgenism, adenomas demonstrate unilateral or markedly asymmetrical uptake. Patients with micro- and macronodular hyperplasia typically demonstrate bilateral breakthrough in contrast to normal subjects in whom there should be no visualization while on dexamethasone suppression.« less