Lipid-Poor Adrenal Lesion: Differentiation of Benign from Malignant Disease by Using Imaging Features on Routine Contrast-Enhanced CT

Objective: To assess the effectiveness of CT imaging features of lipid-poor adrenal lesions on routine contrast-enhanced CTs in differentiating benign from malignant masses. Methods: A retrospective study was performed on 84 lipid-poor adrenal lesions (HU >10 on unenhanced CT scans), which were sized 1-4 cm, had a proven final diagnosis, and were detected during routine contrast-enhanced MDCT studies. Of those, 58 were found in patients with an underlying extra-adrenal malignancy. Two authors determined the morphological features according to their shape, margin, density on unenhanced images, and enhancement pattern. The sensitivity, specificity, and positive and negative predictive values were also calculated for each feature which suggested benignancy, plus a combination of those features. Results: There were 46 (55%) benign and 38 (45%) malignant adrenal masses. The low-density feature (10-20 HU on unenhanced CT images) indicated as benign with a high specificity of 92%, even in patients with known malignancy. The other features (round/oval shape, smooth margin, and homogenous enhancement) showed a high sensitivity (75%-85%) but a low specificity (39%-56%) in predicting benignity. The combined features for presumed benignancy could predict a benign mass with the highest specificity of 95%. Conclusion: The small, lipid-poor, adrenal masses detected by routine contrast-enhanced CTs are likely to be benign when their internal density on unenhanced images is not higher than 20 HU and/or, especially, when a combination of all morphological features for presumed benignancy presents