Imaging Algorithm

Clearly benign - no follow-up

• Homogeneous adrenal lesion with noncontrast CT density <= 10 HU.
• Macroscopic fat: classic myelolipoma.
• Clear signal drop on chemical-shift MRI, consistent with lipid-rich adenoma.
• Simple cyst, chronic hemorrhage, or benign calcified lesion with stable benign appearance.
• Modern guidance does not require a size cutoff when benign adenoma imaging criteria are fulfilled.

1-4 cm indeterminate lesion

• Check prior imaging first. Stability for at least 1 year strongly favors benignity.
• If homogeneous, HU 11-20, and < 4 cm: consider immediate additional characterization or interval CT/MRI in 12 months.
• If < 4 cm but HU > 20 or heterogeneous: discuss / characterize with adrenal protocol CT or MRI.
• If known extra-adrenal malignancy: consider adrenal protocol CT, FDG-PET/CT, biopsy, or surgery based on staging impact.

>= 4 cm or suspicious

• Heterogeneous lesion or HU > 20: multidisciplinary review; surgery is often favored in fit patients.
• If surgery is not performed, repeat noncontrast CT or MRI in 6-12 months.

Adrenal CT / MRI

Adrenal protocol CT

• Use when noncontrast CT density is > 10 HU and morphology is not definitively benign.
• Typical protocol: noncontrast, enhanced venous/equilibrium, and delayed images.
• Adenoma washout: absolute washout >= 60% or relative washout >= 40%.
• Discordant washout, growth, heterogeneity, or suspicious clinical context should remain indeterminate.

Adrenal CT Washout CalculatorOpens pcheng.org adrenal CT calculator

Chemical-shift MRI

• Useful when CT is indeterminate or when radiation avoidance is preferred.
• Signal drop on opposed-phase images supports intracellular lipid and lipid-rich adenoma.
• Lack of signal drop does not exclude adenoma; lipid-poor adenoma remains possible.

When still indeterminate

• Compare with prior imaging whenever available.
• Use growth, heterogeneity, HU, washout, and cancer history to decide follow-up versus referral.
• Biopsy is generally reserved for selected patients with known extra-adrenal malignancy when the result will change management.

Refer, Follow, Or Stop

Refer / surgery

• Indeterminate mass > 4 cm, heterogeneous, irregular, HU > 20, or enlarging.
• Younger patients, pregnant patients, and patients with concerning imaging should be discussed early with a multidisciplinary team.

Follow-up if not resected

• Indeterminate lesion: repeat noncontrast CT or MRI at 6-12 months.
• Concerning growth: > 20% increase in maximum diameter plus at least 5 mm absolute growth favors resection.
• If growth is below threshold, another 6-12 month follow-up may be considered.

Sources

• 2023 ESE adrenal incidentaloma guideline
• ACR adrenal white paper summary
• 2024 review of adrenal incidentaloma updates
• Original combined PDF