Clinical experience with 75Se selenomethylcholesterol adrenal imaging

The results of quantitative adrenal imaging using 75Se selenomethylcholesterol in sixty-two subjects are analysed. The adrenal area was localized by a renal scan, lateral views of which enabled adrenal depth to be estimated. The first nineteen cases were scanned with a rectilinear scanner and the remaining forty-three cases imaged with a gamma camera. Quantitation of adrenal uptake was performed on computer-stored static images obtained 7 and 14 days post-injection of 75Se selenomethylcholesterol (3 and 6 days in the first ten cases studied). Normal uptake was found to be 0.07-0.30% of the administered dose. Overall predictive accuracy of the type of adrenal disorder of thirty-two patients with Cushing's syndrome ws 90.6%, this included twelve cases of Cushing's disease (mean uptake 0.58%), seven ectopic ACTH syndromes (mean uptake 0.69%), five unilateral adenomata (mean uptake 0.93%), three post adrenalectomy regrowths (mean uptake 1.37%), three adrenal carcinomas (mean uptake 0.01%), one congenital hyperplasia (mean uptake 3.4%) and one unilateral nodular hyperplasia. Overall predictive accuracy of the cause of Conn's syndrome in twenty-two cases was 86.4%; this included thirteen cases of bilateral hyperplasia (mean uptake 0.34%), eight unilateral adenomata (mean uptake 0.47%) and one patient with mineralocorticoid excess in whom the cause has not been confirmed. The mean uptake in the normal adrenal in cases of unilateral adenoma was 0.19% (range 0.07-0.30%). Causes of unsatisfactory adrenal imaging are examined. The procedure is recommended as the localizing and lateralizing technique of choice in Cushing's syndrome except where due to adrenal carcinoma, and as an important non-invasive technique in Conn's syndrome for the lateralization of adenoma.