High Diagnostic Accuracy of Arterial Phase CT in Differentiating Pheochromocytoma in Good/Poor Washout Adrenal Masses.

Introduction: Differentiating pheochromocytomas from other adrenal masses based on computed tomography (CT) characteristics remains challenging, particularly in lipid-poor lesions with variable washout patterns. This study evaluated CT features for distinguishing pheochromocytomas in good and poor washout subcohorts.

Methods: We prospectively analyzed 72 patients with unilateral lipid-poor adrenal masses. CT protocol included basal, bolus-tracked arterial, early venous (45 seconds postarterial), and delayed (15 minutes postarterial) phases. Masses were categorized into good and poor washout groups. Histopathology provided the final diagnosis. CT characteristics and calculated indices were compared between pheochromocytomas and other masses in each washout category.

Results: The cohort included pheochromocytomas (n = 35), adrenocortical carcinoma (ACC; n = 15), lipid-poor adenomas (n = 13), and metastatic infiltration/infection (n = 9). In the good washout group, pheochromocytomas (n = 15) showed larger diameters (6.00 vs 3.45 cm, P = .001), higher necrosis frequency (73.3% vs 30%, P = .049), and greater arterial attenuation (173.2 vs 74.5 HU, P < .001) compared to adenomas (n = 9). Arterial attenuation provided a high discriminatory value [area under the curve (AUC): 0.967], with 100% sensitivity at 87.6 Hounsfield unit (HU) and 100% specificity at 139.9 HU. In the poor washout group, pheochromocytomas (n = 20) exhibited higher arterial attenuation (99.2 vs 59.2 HU, P < .001; AUC: 0.844) compared to ACC (n = 14), metastatic infiltration (n = 9), and adenomas (n = 4), with 85% sensitivity and 78% specificity at 73.3 HU. Normetanephrine-secreting/nonsecretory pheochromocytomas showed higher arterial enhancement than metanephrine-secreting ones (132.0 vs 90.5 HU, P = .020) within the poor washout group.

Conclusion: Arterial phase attenuation on CT has good diagnostic accuracy for differentiating pheochromocytomas from other adrenal masses in both good and poor washout categories, potentially guiding hormonal workup.