Diagnostic performance of adrenal CT in the differentiation of adenoma and pheochromocytoma

Background: Differentiation of adenoma and pheochromocytoma on computed tomography (CT) may be problematic. Purpose: To investigate if adenoma and pheochromocytoma can be differentiated with adrenal CT. Material and Methods: A total of 147 pathologically proven adrenal masses (119 adenomas, 28 pheochromocytomas) that had undergone adrenal CT were retrospectively evaluated. Lesion attenuation on unenhanced phase (UEP), portal phase (PP), 15-min delayed phase (DP), absolute/relative percentage enhancement wash-out (APEW/RPEW), and qualitative features were recorded. Student’s t-test for parametric data, Mann–Whitney U test for non-parametric data, and Fisher’s exact test for categorical data were used. Diagnostic performance of CT attenuation was assessed by area under the curve (AUC) of the receiver operating characteristics. Results: APEW of adenomas was not significantly different from pheochromocytomas; 68.4% and 59% (P = 0.284). Adenomas had significantly higher RPEW; 57.3% vs. 37.4% (P = 0.004). Of pheochromocytomas, 50% met APEW >60% or RPEW >40% criteria, and therefore were misclassified as adenoma on wash-out CT. Of those, 80% (4/5) were < 3 cm. UEP, PP, and DP attenuations of pheochromocytomas were significantly higher than adenomas; however, they were overlapping. AUC for UEP, PP, and DP was 0.906, 0.784, and 0.926, respectively. Larger pheochromocytomas were more likely to contain necrosis compared to smaller pheochromocytomas and adenomas; 41.6% vs. 12.5% vs. 3%. Homogeneous enhancement was seen in 25% of pheochromocytomas and 49% of adenomas (P = 0.018). No significant difference was found in terms of lesion borders and presence of fat/calcification (P > 0.05). Conclusions: A considerable percentage of pheochromocytomas, especially smaller ones, demonstrate adenoma-like wash-out on CT. Heterogeneous enhancement, higher attenuation, and necrosis are more suggestive of pheochromocytoma.