Inter-method agreement between wash-in and wash-out computed tomography for characterizing hyperattenuating adrenal lesions as adenomas or non-adenomas

To investigate inter-method agreement between wash-out and wash-in computed tomography (CT) to determine whether hyperattenuating adrenal lesions are characterized as adenomas or non-adenomas. We evaluated 243 patients who underwent wash-out CT for a solid enhancing hyperattenuating (i.e., > 10 Hounsfield unit [HU]) adrenal mass of ≥ 1 to < 4 cm. Wash-out (absolute percentage wash-out [APW]; relative percentage wash-out [RPW]) and wash-in values (enhancement ratio [ER]; relative enhancement ratio [RER]) were analyzed by two independent readers. Diagnostic criteria of wash-out CT for adenoma were APW ≥ 60% or RPW ≥ 40% (conventional method). Three different criteria for wash-in CT were set: ER ≥ 3.0; RER ≥ 200%; and RER ≥ 210%. Concordance rate and inter-method agreement between wash-out and wash-in CT were investigated using Gwet's AC1. For all lesions, concordance rates between wash-out and wash-in CT were > 83%. AC1 between conventional method and ER ≥ 3.0 or between conventional method and RER ≥ 200% were identically 0.843 for reader 1 and 0.776 for reader 2. AC1 between conventional method and RER ≥ 210% were 0.780 for reader 1 and 0.737 for reader 2. For lesions of > 10 to ≤ 30 HU, concordance rates between wash-out and wash-in CT were > 89%. AC1 between conventional method and ER ≥ 3.0 or between conventional method and RER ≥ 200% were identically 0.914 for reader 1 and 0.866 for reader 2. AC1 between conventional method and RER ≥ 210% were 0.888 for reader 1 and 0.874 for reader 2. In approximately 90% of patients with a hyperattenuating adrenal lesion of ≥ 1 to < 4 cm and >10 to ≤ 30 HU, wash-out CT with 15-min contrast-enhanced images may be replaced by wash-in CT. An enhancement ratio of ≥ 3.0 or a relative enhancement ratio of ≥ 200% appears to be appropriate as the threshold of wash-in computed tomography (CT) comprising unenhanced and 1-min contrast-enhanced CT. Measurement of enhancement ratio or relative enhancement ratio was reproducible. We found good agreement between wash-in and wash-out CT for determining whether hyperattenuating adrenal lesions of ≥ 1 to < 4 cm and >10 to ≤ 30 Hounsfield unit would be characterized as adenomas.