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

Egyptian Journal of Radiology and Nuclear Medicine

Table 1 Imaging findings differentiating common adrenal pathologies in AIs

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

ACC adrenocortical carcinoma, HU Hounsfield units, APW absolute PW, RPW relative PW, CSI chemical-shift imaging, FDG fluoro-deoxyglucose [Chatzellis and Kalsas, 2019]