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 |