DIFFERENTIATION OF ADRENAL ADENOMAS FROM NONADENOMAS USING CT ATTENUATION VALUES

OBJECTIVE. The purpose of our study was to determine whether unenhance d CT attenuation value, enhanced CT attenuation value, or lesion size can be used to differentiate adrenal adenomas from nonadenomatous adre nal masses. MATERIALS AND METHODS. We retrospectively assessed the CT scans of 135 adrenal masses in 124 patients with a variety of adrenal masses. There were 93 cortical adenomas (85 nonhyperfunctioning adenom as, four Gushing's adenomas, and four primary aldosteronism adenomas). The nonadenomas consisted of 34 metastases, four cortical carcinomas, and four pheochromocytomas. The scattergrams and mean values of the s ize and attenuation values on enhanced and unenhanced scans were corre lated with the final diagnoses. Results were also subjected to receive r operating characteristic analysis. RESULTS, Forty-one adenomas and 2 0 nonadenomas had unenhanced CT. The mean attenuation value of the 41 adenomas was significantly lower (p < .001) than that of the nonadenom as (2.5 H +/- 14 compared with 32 H +/- 6.4). The lowest unenhanced CT attenuation value of the nonadenomas was 18 H; therefore, the sensiti vity:specificity ratio for the diagnosis of adenomas was 85%:100% at a threshold value of 18 H. At this threshold, the positive predictive v alue was 100% and the negative predictive value was 77%. For the 85 ma sses with enhanced CT, the mean attenuation of the 60 adenomas was als o significantly lower (p < .01) than for the 25 nonadenomas (47 H +/- 24 compared with 62 H +/- 21). The lowest enhanced CT attenuation valu e of the nonadenomas was also 18 H, but the sensitivity:specificity ra tio was only 10%:100% at this threshold value of 18 H. Although the me an diameter of the adenomas was significantly lower (p < .001) than fo r the nonadenomas (2.4 cm +/- 0.9 compared with 4.5 cm +/- 2.5), there was sufficient overlap between the two groups at the smallest sizes t hat a threshold value for a highly specific diagnosis of adenoma was n ot present. The area under the receiver operating characteristic curve for unenhanced CT attenuation values (0.98 +/- 0.02) was significantl y greater than the area for enhanced CT values (0.68 +/- 0.06, p < .00 1) and the area for size (0.79 +/- 0.04, p <.001). CONCLUSIONS. Unenha nced CT attenuation values can characterize an adrenal mass as a benig n adenoma with high specificity and acceptable sensitivity. Adrenal ma sses cannot be characterized using enhanced CT attenuation values or l esion size.