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Table 1 Imaging findings differentiating common adrenal pathologies in AIs

From: Adrenal incidentalomas: imaging challenges—role of MDCT scan versus MRI in evaluating adrenal incidentalomas

Finding Benign adenoma ACC Pheochromocytoma Metastases
Size Mostly less than 4 cm Mostly greater than 4 cm Variable Variable
Growth rate Stable or slow growth (< 0.8 cm/year) Significant growth (> 1 cm/year) Slow growth Significant growth (> 1 cm/year)
Shape and margins Round or oval with well-defined margins Irregular shape and margins. Variable Variable
Composition Homogenous Heterogeneous (hemorrhage, necrosis) Heterogeneous (necrosis) Heterogeneous (hemorrhage, necrosis)
CT unenhanced attenuation ≤ 10 HU (or > 10 HU for lipid-poor adenomas) >10 HU > 10 HU > 10 HU
CT percent washout (PW) APW > 60%, RPW > 40% APW < 60%, RPW < 40% APW < 60%, RPW < 40% APW < 60%, RPW < 40%
MRI-CSI (out-of phase) Signal loss (except in lipid-poor adenomas) No change in signal intensity No change in signal intensity No change in signal intensity
FDG uptake (PET) Low (some can have low to moderate uptake) High Low (malignant pheochromocytomas show high uptake) High
  1. ACC adrenocortical carcinoma, HU Hounsfield units, APW absolute PW, RPW relative PW, CSI chemical-shift imaging, FDG fluoro-deoxyglucose [Chatzellis and Kalsas, 2019]