Adnexal lesion — MRI (O-RADS MRI)

MRIACR O-RADS MRI (2020/2022)

Problem-solving MRI of an adnexal lesion that is indeterminate on ultrasound (O-RADS US 4–5 or sonographically indeterminate).

Applies to

Sonographically indeterminate adnexal lesion characterized on multiparametric MRI

Does not apply to

Lesions confidently classified on ultrasound (report O-RADS US)
Post-hysterectomy patients — no myometrium reference for the time-intensity curve (score conservatively)
Peritoneal disease better explained by a separate known primary (do not apply O-RADS)

What to report

Tap an item to check it off while dictating.

1.Peritoneum
Assess for peritoneal, omental, or mesenteric nodularity or irregular thickening (± ascites) — this alone assigns O-RADS MRI 5, even without a visible adnexal mass.
Pitfall: Ascites alone does not trigger a 5; nodularity or irregular thickening is required.
2.Fat content
Macroscopic fat indicates a mature teratoma. A typical Rokitansky nodule is acceptable, but a large volume of enhancing non-fatty solid tissue (immature teratoma) raises the score.
3.Solid tissue and its signal
Identify enhancing solid tissue. Solid tissue that is homogeneously dark on T2 AND dark on high-b-value DWI is fibrous (benign).
Pitfall: Smooth wall/septal enhancement is not 'solid tissue'; irregular wall, papillary projections, or mural nodules are.
4.Cyst characteristics
Locularity (a multilocular cyst without solid tissue is at least O-RADS 3) and fluid type (simple/endometriotic vs hemorrhagic/proteinaceous/mucinous). A purely cystic lesion cannot score above 3.
5.Time-intensity curve (DCE)
Place ROIs on the solid tissue and the outer myometrium on DCE (temporal resolution ≤ 15 s). Classify the curve: low-risk (no plateau) → 3, intermediate (plateau, ≤ myometrium) → 4, high-risk (steeper than myometrium) → 5.
Pitfall: Without DCE, enhancement ≤ myometrium at 30–40 s is O-RADS 4 and > myometrium is 5 — a non-DCE study cannot yield a 3.
6.Size, laterality, menopausal status
Report size and side; menopausal status and size affect scoring of complex unilocular cysts.

Scores & calculators

O-RADS MRI score

ACR O-RADS MRI (2020/2022)

Risk stratification of an adnexal lesion on MRI (ADNEX MR / O-RADS MRI). Solid-tissue lesions are scored by the dynamic contrast-enhanced time-intensity curve relative to the outer myometrium.

Peritoneal / omental / mesenteric nodularity or irregular thickening

AbsentPresent (± ascites)

Lesion

Complex unilocular cyst — menopausal status & size

Premenopausal and ≤ 3 cmPremenopausal and > 3 cm, or postmenopausal

Enhancing solid tissue — time-intensity curve (DCE) or enhancement vs myometrium

Complete the inputs to see the result.

Ellipsoid volume

Volume of an ellipsoid lesion or organ from three orthogonal diameters.

Length

Width

Height

Complete the inputs to see the result.

Ellipsoid formula V = (π/6) × L × W × H. 1 cm³ = 1 mL.

Sources

O-RADS MRI risk stratification system — Sadowski EA, Thomassin-Naggara I et al. Radiology (2022)

Content review: Content pending clinical review · 2026-07-10

Educational reference for trained clinicians. Verify every result against the cited original guideline before use. Not a substitute for clinical judgment or medical advice.