Adrenal scintigraphy in the morphological and functional evaluation of Cushing's syndrome.
In recent years, cholesterol adrenal scintigraphy has been employed in the morphofunctional study of adrenal hypercorticism. Particularly in Cushing's syndrome, this noninvasive procedure can give a determinant contribution to distinguish ACTH-dependent from ACTH-independent forms. In our Institute, adrenal scintigraphy was performed in 77 patients with Cushing's syndrome diagnosed on clinical grounds confirmed by laboratory investigations and functional tests (17 with cortisol-secreting adenoma, 54 with pituitary ACTH-dependent bilateral adrenal hyperplasia, 2 with ectopic ACTH-dependent bilateral hyperplasia and 4 with bilateral nodular hyperplasia). Three distinct scintigraphic patterns have been identified. The 56 patients with ACTH-dependent Cushing's syndrome showed bilateral symmetric or slightly asymmetric visualization of the adrenal glands; in the 17 patients with ACTH-independent Cushing's syndrome the adrenal scintigraphy only visualized the gland harboring the adenoma; finally, a marked asymmetric visualization of the glands was observed in the 4 patients with adrenal nodular hyperplasia. These data confirm that adrenal scintigraphy is able to distinguish between ACTH-dependent and ACTH-independent Cushing's syndrome and reliably lateralizes adenomas when they are present. Moreover, the morphofunctional information obtained by this procedure, together with the high resolution morphological data by computerized tomography, allows to recognize the presence of bilateral nodular hyperplasia, an uncommon cause of Cushing's syndrome.