O-RADS adnexal lesion reference
The O-RADS categories for both the ultrasound and MRI systems, with malignancy risk and management. They are separate systems with separate definitions, which is the detail most often lost when a report just says 'O-RADS 4'.
Reference, not a calculator. This page is a reference, not a calculator. The O-RADS ultrasound algorithm branches on lesion morphology, a four-point colour score, several size cut-offs and a set of named classic benign appearances, and the categories drive decisions up to and including surgery. The category definitions and management are worth having to hand; a decision tree we were only mostly sure of is not.
O-RADS Ultrasound
| Category | Malignancy risk | Definition | Management |
|---|---|---|---|
| O-RADS 0 | Incomplete | Incomplete evaluation — the study cannot characterise the lesion. | Repeat or alternative imaging. |
| O-RADS 1 | 0% (normal) | Normal premenopausal ovary: follicle 3 cm or less, or a corpus luteum 3 cm or less. | No follow-up. A physiological structure is not a lesion. |
| O-RADS 2 | <1% | Almost certainly benign. Simple cyst under 10 cm; unilocular non-simple cyst with a smooth inner wall under 10 cm; bilocular cyst with a smooth septation and no solid component under 10 cm; typical haemorrhagic cyst, dermoid or endometrioma under 10 cm; typical paraovarian cyst, peritoneal inclusion cyst or hydrosalpinx of any size. | Depends on the entity and menopausal status; several need no follow-up at all. |
| O-RADS 3 | 1 to <10% | Low risk. Unilocular or bilocular smooth cyst (simple or non-simple) 10 cm or more; typical haemorrhagic cyst, dermoid or endometrioma 10 cm or more; unilocular cyst with an irregular inner wall (<3 mm height), any size; multilocular cyst under 10 cm with a smooth inner wall and colour score 1-3; solid smooth lesion of any size with colour score 1. | Ultrasound specialist or gynaecology; management varies by entity. |
| O-RADS 4 | 10 to <50% | Intermediate risk. Multilocular cyst without a solid component that is 10 cm or more with a smooth inner wall and colour score 1-3, has colour score 4, or has an irregular inner wall and/or septation; unilocular cyst with a solid component and 1-3 papillary projections (or a non-papillary solid component); bilocular or multilocular cyst with a solid component and colour score 1-2; solid smooth lesion with colour score 2-3. | Gynaecological oncology referral or MRI for further characterisation. |
| O-RADS 5 | 50% or more | High risk. Unilocular cyst with four or more papillary projections; bilocular or multilocular cyst with a solid component and colour score 3-4; solid smooth lesion with colour score 4; solid irregular lesion of any size or colour score; ascites and/or peritoneal nodules. | Gynaecological oncology referral. |
Colour score
| Score | Flow |
|---|---|
| 1 | No flow |
| 2 | Minimal flow |
| 3 | Moderate flow |
| 4 | Very strong flow |
Subjective, assessed on the most vascular part of the lesion. It is not a quantitative measurement, and it changes the category for multilocular and solid smooth lesions.
O-RADS MRI
| Category | Malignancy risk | Definition | Management |
|---|---|---|---|
| O-RADS MRI 1 | n/a | Normal ovaries, no adnexal lesion. | No follow-up. |
| O-RADS MRI 2 | <0.5% | Almost certainly benign — a lesion with characteristic benign features on MRI. | No further imaging in most cases. |
| O-RADS MRI 3 | ~5% | Low risk — unilocular cyst with proteinaceous or haemorrhagic (non-endometriotic) fluid; multilocular cyst without enhancing solid tissue; or enhancing solid tissue with a low-risk time-intensity curve. | Gynaecology; often follow-up rather than surgery. |
| O-RADS MRI 4 | ~50% | Intermediate risk — enhancing solid tissue with an intermediate time-intensity curve. | Gynaecological oncology. |
| O-RADS MRI 5 | ~90% | High risk — enhancing solid tissue with a high-risk time-intensity curve, or peritoneal disease. | Gynaecological oncology. |
Reporting notes
- O-RADS ultrasound and O-RADS MRI are separate systems with separate category definitions. State which you applied — 'O-RADS 4' alone is ambiguous.
- MRI is the designated problem-solver for a sonographically indeterminate adnexal lesion, and reclassifying an O-RADS US 4 downward is one of its main uses.
- The colour score is a subjective four-point scale assessed on the most vascular part of the lesion, not a quantitative measurement.
- Menopausal status changes management for several categories even where the category itself is unchanged.
Related
Source. Strachowski LM, et al. Radiology 2023;308(3):e223079 (O-RADS US v2022); Thomassin-Naggara I, et al. JAMA Netw Open 2020;3(1):e1919896 (O-RADS MRI). View the ACR document
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