Table 1.
Imaging criteria of a benign adrenal mass
| Non-contrast CT | ≤10 HU homogenous lesions only |
| A homogeneous mass is defined as a lesion with uniform density or signal intensity throughout. The ROI measurements should include at least 75% of a lesion without contamination by tissues outside the adrenal lesion | |
| Heterogeneous lesions should not be subjected to MRI or washout CT for further characterization | |
| MRI—chemical shift | Loss of signal intensity on out-of-phase imaging consistent with lipid-rich adenoma |
| CT with delayed contrast media washout | Absolute washout >60% |
| Relative washout >40% | |
| There is no clear evidence about the best time interval. We recommend 10 or 15 min for delayed images | |
| 18F-FDG PET | Absence of 18F-FDG uptake or uptake less than liver. Certain metastasis (e.g. from renal cancer or low-grade lymphoma) may be 18F-FDG negative |
18F-FDG, fluorine-18 fludeoxyglucose; HU, Hounsfield units; PET, positron emission tomography; ROI, region of interest.
These criteria can be applied only to homogeneous masses or masses with clear features consistent with benign disease, e.g. myelolipoma.