DELAYED ENHANCED CT FOR DIFFERENTIATION OF BENIGN FROM MALIGNANT ADRENAL MASSES

PURPOSE: To determine whether adenomas can be differentiated from nona denomas on 1-hour-delayed enhanced computed tomographic (CT) scans. MA TERIALS AND METHODS: In a prospective evaluation of 51 adrenal masses in 39 patients, the CT attenuation was measured at the time of contras t 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 versu s 49 HU +/- 8.3 for metastases (P < .001). At a threshold value of 30 HU, specificity and positive predictive value for the diagnosis of ade noma were 100% with a sensitivity of 95%. The mean decrease in attenua tion 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 usefu l in characterizing an adrenal mass as an adenoma. When CT is performe d with a 150-mL bolus injection of contrast material and with the scan ning parameters described in this study, other procedures or imaging s tudies may be unnecessary if the mass measures less than 30 HU on the delayed scans.