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% (=0.284). Adenomas had significantly higher RPEW; 57.3% vs. 37.4% (=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 (=0.018). No significant difference was found in terms of lesion borders and presence of fat/calcification (>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.