Delayed enhanced CT for differentiation of benign from malignant adrenal masses

PURPOSE: To determine whether adenomas can be differentiated from nonadenomas on 1-hour-delayed enhanced computed tomographic (CT) scans. MATERIALS AND METHODS: In a prospective evaluation of 51 adrenal masses in 39 patients, the CT attenuation was measured at the time of contrast enhancement and 1 hour later. The results were compared for adenomas (n = 41) and metastases (n = 10). RESULTS: On 1-hour-delayed enhanced CT scans, the mean attenuation of the adenomas was 11 HU +/- 13 versus 49 HU +/- 8.3 for metastases (P < .001). At a threshold value of 30 HU, specificity and positive predictive value for the diagnosis of adenoma were 100% with a sensitivity of 95%. The mean decrease in attenuation during the 1-hour delay was 74% +/- 37 for the adenomas versus 31% +/- 28 for the metastases (P < .001). CONCLUSION: CT densitometry on delayed scans obtained 1 hour after contrast enhancement may be useful in characterizing an adrenal mass as an adenoma. When CT is performed with a 150-mL bolus injection of contrast material and with the scanning parameters described in this study, other procedures or imaging studies may be unnecessary if the mass measures less than 30 HU on the delayed scans.