Objective: Our objective was to investigate whether the quantitative measurement of venous phase enhancement on CT can distinguish a pheochromocytoma from an adrenal adenoma.
Materials and methods: A pathology database was retrospectively appraised over a period of 7 years and revealed 43 histopathologically proven adrenal adenomas and 34 pheochromocytomas. The lesion densities were measured on the 60-second venous phase CT on all adrenal lesions to assess venous phase enhancement values.
Results: Venous phase enhancement of 85 HU or greater afforded a sensitivity, specificity, positive predictive value, and negative predictive value of 88.2%, 83.7%, 81.1%, and 90%, respectively (p < 0.0001). The positive likelihood ratio was 5.42. Venous phase enhancement of ≥ 85 HU was detected in 30 (88.2%) pheochromocytomas (p < 0.001) and in seven (16.3%) adenomas. Venous phase enhancement of < 85 HU was detected in four (11.8%) pheochromocytomas and in 36 (83.7%) adenomas. Of the pheochromocytomas imaged with a triphasic protocol (n = 15), 66.7% (n = 10) met both absolute and relative percentage washout criteria for the diagnosis of a lipid-poor adenoma (p > 0.1).
Conclusion: A significant subset of pheochromocytomas mimics adenomas on absolute or relative percentage washout calculations. However, nodules with venous phase enhancement of 85 HU or more are much more likely to be pheochromocytomas than adenomas, regardless of whether the lesion shows absolute or relative percentage washout compatible with a lipid-poor adenoma. The typical values of absolute and relative percentage washout of adrenal adenoma should be interpreted along with the venous phase enhancement value to avoid potential misdiagnoses.
Keywords: CT; adenoma; adrenal; pheochromocytoma.