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 | n/a (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 10 cm or less; a classic benign lesion 10 cm or less (haemorrhagic cyst, dermoid, endometrioma, paraovarian cyst, peritoneal inclusion cyst, hydrosalpinx); typical corpus luteum. | Depends on the entity and menopausal status; several need no follow-up at all. |
| O-RADS 3 | 1 to <10% | Low risk. Simple cyst over 10 cm; classic benign lesion over 10 cm; unilocular non-simple cyst with a smooth inner wall; 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 10 cm or more, or any multilocular cyst with colour score 4; a lesion with solid components and fewer than four papillary projections; solid smooth lesion with colour score 2-3. | Gynaecological oncology referral or MRI for further characterisation. |
| O-RADS 5 | 50% or more | High risk. Four or more papillary projections; a solid irregular lesion; ascites and/or peritoneal nodularity. | 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 — a lesion with no enhancing solid tissue, or 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. ACR O-RADS Ultrasound v2022 and O-RADS MRI. View the ACR document
This is a reference implementation of a published guideline, for use by qualified clinicians. It does not account for patient-specific factors and is not a substitute for clinical judgment or a formal radiology consultation. See our full disclaimer.