Adrenocortical carcinomas and adrenal pheochromocytomas: Mass and enhancement loss evaluation at delayed contrast-enhanced CT

PURPOSE: To retrospectively measure the adrenal gland attenuation and the percentage loss of adrenal land enhancement at delayed contrast medium-enhanced computed tomography (CT) in patients with adrenocortical carcinomas and pheochromocytomas and to compare these data with those in patients with adenomas and metastases. MATERIALS AND METHODS: The study protocol was approved by the ethics committee, which waived informed consent. Eleven patients with proved adrenocortical carcinoma, 17 with proved pheochromocytoma, 23 with adrenal adenoma, and 16 with metastasis to the adrenal gland underwent helical CT. Nonenhanced CT was followed by contrast-enhanced CT I minute and 10 minutes later. Attenuation and enhancement loss values were calculated. RESULTS: The mean attenuation of adenomas (8 HU +/- 18 [standard deviation]) was significantly lower than those of adrenocortical carcinomas (39 HU 14), pheochromocytomas (44 HU 11), and metastases (34 HU 11) on nonenhanced CT scans (P <.001). Although the mean attenuation values for nonadenomas (ie, adrenocortical carcinomas, pheochromocytomas, and metastases) were significantly higher than the value for adenomas on the 1-minute contrast-enhanced CT scans (P <.001), there was more overlap in attenuation between adenomas and nonadenomas on contrast-enhanced scans than on nonenhanced scans. On the 10-minute delayed contrast-enhanced scans, the mean attenuation of adenomas (32 HU 17) was significantly lower than the mean attenuations of carcinomas (72 HU 15), pheochromocytomas (83 HU +/- 14), and metastases (66 HU +/- 13) (P <.001). At optimal threshold values of 50% for absolute percentage of enhancement loss and 40% for relative percentage of enhancement loss at 10 minutes, both the sensitivity and the specificity for the diagnosis of adenoma were 100% when adenomas were compared with carcinomas, pheochromocytomas, and metastases. CONCLUSION: The enhancement loss in adrenocortical carcinomas and pheochromocytomas is similar to that in adrenal metastases but significantly less than that in adrenal adenomas. The percentage change in contrast material washout is a useful adjunct to absolute CT attenuation values in differentiating adrenal adenomas from adrenocortical carcinomas and pheochromocytomas.