Adrenal Washout Calculator

Adrenal masses are found incidentally in approximately 3%–7% of adults (ACR 2017).

Typically, adenomas take up intravenous contrast rapidly and also lose it rapidly; malignant lesions usually wash out more slowly (ESE 2023).

Absolute washout = (E − D)/(E − U) × 100; decides when an unenhanced value is available (≥60% adenoma range; ACR 2017). Below 60%: Indeterminate.

Relative washout = (E − D)/E × 100; used when no unenhanced value is available. “Relative percent washout is used when an unenhanced CT value is not available” (ACR 2017); ≥40% adenoma range. Below 40%: Indeterminate. Leave unenhanced blank for RPW-only mode.

Protocol: if unenhanced CT shows no benign features, 60–90 seconds after contrast (portal venous) and a 15-min delayed acquisition (ACR 2017).

Chemical-shift MRI is an alternative characterization method (ACR 2017). This calculator uses ACR's 15-minute delayed acquisition; the ACR Appropriateness Criteria (2021) report diminished sensitivity with a 10-minute substitute. ESE 2023 accepts a delay of at least 10 minutes and notes that 15 minutes may be better.

Checks run in order: reject missing/non-finite HU inputs and non-finite or nonpositive entered size; hold HU outside the Radikulus −1000 to 1000 input range for input review; identify unenhanced ≤10 HU low-density features (an E < U entry adds a field-check note); hold E < U or RPW-only E ≤0 for input review; check delayed enhancement (D−U ≥10 HU) before early nonenhancement (0≤E−U<10 HU); for U>10 and E−U≥10, hold D<U for measurement review; apply the ≥4 cm washout size gate; identify D>E as no washout; then apply APW ≥60% when U exists or RPW ≥40% only when U is absent. Classification uses unrounded values. The input-review holds are Radikulus policy, not ACR diagnostic criteria.

ACR's incidental adrenal-mass guidance applies to asymptomatic adults imaged for reasons unrelated to adrenal pathology.

ESE 2023 suggests immediate additional imaging for a homogeneous mass with unenhanced HU 11–20 and size <4 cm when hormonal work-up shows no significant hormone excess; alternatively, noncontrast CT or MRI at 12 months can be performed. Washout CT can be that additional imaging. For a mass ≥4 cm with HU >20 or heterogeneous appearance, ESE suggests multidisciplinary discussion; ≥4 cm with HU 11–20 falls under its individualized approach (R.2.4–R.2.6).

This calculator uses ACR's APW ≥60% / RPW ≥40% thresholds. ESE 2023 lists RPW >58% as favoring benignity, based on a single study requiring caution and further validation (Table 4).

ACR also recognizes benign calcified masses, such as an old hematoma or prior granulomatous calcification; this requires imaging characterization and is not inferred from HU alone.

For an isolated mass ≥4 cm without diagnostic benign features and without cancer history, ACR recommends surgical resection without biopsy after biochemical evaluation (ACR 2017; ACR Appropriateness Criteria 2021).

Determine hormonal status and exclude pheochromocytoma before biopsy or resection (ACR 2017; ESE 2023).

ESE 2023 recommends against adrenal biopsy unless there is a history of extra-adrenal malignancy. Before biopsy is considered, the lesion must be hormonally inactive, particularly with pheochromocytoma excluded; imaging must not have conclusively characterized it as benign; and histology must alter clinical management (R.2.7, R.6.3.5).

Assess symptoms and signs of adrenal hormone excess (ESE 2023, R.3.1). A 1-mg overnight dexamethasone suppression test is recommended for adrenal incidentalomas; it may not be warranted in frail patients with limited life expectancy (R.3.2). Exclude pheochromocytoma with plasma free metanephrines or urinary fractionated metanephrines for lesions not typical of a benign adenoma, including unenhanced HU >10; testing is also advised when no unenhanced CT is available (R.3.9). Use the aldosterone/renin ratio with hypertension or unexplained hypokalemia (R.3.10). Imaging does not determine whether an adrenal mass is hyperfunctioning (ACR 2017).

ESE considers omitting metanephrines reasonable with clear CT adenoma features (≤10 HU); it suggests this probably also applies to unequivocal chemical-shift MRI, while noting no published supporting data (R.3.9 reasoning).

Without cancer history or diagnostic benign features, ACR considers 12-month follow-up for an initially detected 1–2 cm mass; for >2 to <4 cm, dedicated adrenal CT may be obtained at identification. Subsequent management depends on the characterization result (ACR 2017).

ACR 2017 considers an otherwise indeterminate mass stable for ≥1 year very likely benign. For an indeterminate mass not resected after initial assessment, ESE 2023 suggests repeat noncontrast CT or MRI after 6–12 months and resection if maximum diameter increases by >20% and by ≥5 mm (R.5.2).

For indeterminate lesions in patients with a history of extra-adrenal malignancy, ESE suggests FDG-PET/CT (if not done already), resection or biopsy when proving malignancy would alter management; otherwise it recommends imaging follow-up at the same interval as imaging for the primary malignancy (ESE 2023, R.6.3.4).

ACR 2017 (PET/CT): “In oncology patients, an enlarging adrenal mass, an indeterminate adrenal mass on adrenal CT, and an adrenal mass ≥4 cm should proceed with PET/CT or biopsy because the presumed diagnosis is metastatic disease.”

Without cancer history, when a dedicated adrenal CT protocol cannot establish a specific benign diagnosis, 6- to 12-month follow-up CT to document stability, or resection, may be considered depending on the clinical context (ACR 2017).

In a single-center cohort, the ACR 60% APW and 40% RPW thresholds misclassified 35.9% and 35.2%, respectively, of 142 lesions with unenhanced attenuation >10 HU. These percentages describe overall misclassification in that subgroup, not the proportion of malignancies missed (Schloetelburg et al., Eur J Endocrinol 2022;186:183–193; published online 2021; PMID 34813495).

ACR 2017 white paper (PMID 28651988) remains the current ACR adrenal incidental-findings guidance; ACR lists 'Adrenal masses (revision)' under Topics Under Development (checked 27 Oct 2026).

For ACR's isolated-mass pathway, ‘isolated’ means no other metastatic disease identified. Central necrosis increases the likelihood of metastasis in an oncology patient; work-up may not alter management with multiple metastases, inability to receive treatment, or limited life expectancy. ACR suggests 120 kVp without tube-voltage modulation for density measurement; virtual unenhanced dual-energy CT measurements require equipment- and protocol-specific evidence (ACR 2017).

Which washout decides the result?

Absolute washout = (E − D)/(E − U) × 100; decides when an unenhanced value is available (≥60% adenoma range; ACR 2017). Below 60%: Indeterminate. Relative washout = (E − D)/E × 100; used when no unenhanced value is available. “Relative percent washout is used when an unenhanced CT value is not available” (ACR 2017); ≥40% adenoma range. Below 40%: Indeterminate. Leave unenhanced blank for RPW-only mode.

When should the CT scan be performed in the adrenal protocol?

See Adrenal protocol CT for scan timing and the ACR/ESE comparison.

How does a 4 cm adrenal mass affect washout interpretation?

See ACR management and endocrine evaluation guidance for size-dependent ACR guidance and Imaging eligibility and guideline differences for the ESE comparison.