The Ovarian-Adnexal Reporting and Data System (O-RADS) gives pelvic imagers a shared lexicon, a risk category, and a recommended next step for adnexal lesions. Applied well, O-RADS ultrasound reporting is more consistent for referring clinicians, follow-up is less haphazard, and intermediate-risk masses are less often overcalled or undercalled. This article is a practical walkthrough of ACR O-RADS US descriptors, categories, management principles, and common reporting pitfalls for OB/GYNs, radiologists, and sonographers.
What O-RADS Ultrasound Classification Is For
O-RADS is an ACR system for ovarian and adnexal findings, in the same family as other structured reporting tools such as BI-RADS category 4 on breast ultrasound and TI-RADS for thyroid nodules. A companion O-RADS MRI score is used when ultrasound leaves a lesion indeterminate. Use O-RADS US to characterize adnexal cysts and masses in average-risk patients, not as a substitute for acute diagnoses such as torsion, ectopic pregnancy, or tubo-ovarian abscess, where management follows the acute condition rather than an elective risk score.
O-RADS Lexicon: Descriptors That Drive the Score
Assign descriptors first, then the category. If the study cannot characterize the lesion, the correct assignment is incomplete evaluation, not a guessed lower score.
Cystic versus solid morphology
- Unilocular cyst: one locule, no solid component.
- Multilocular cyst: septa present, still no solid component.
- Cystic and solid: any papillary projection or other solid tissue.
- Solid: predominantly solid tissue (a commonly used O-RADS threshold is about 80% solid).
Describe inner walls and outer contours as smooth or irregular. A papillary projection is solid tissue 3 mm or greater arising from a wall or septum. Size should be measured in three dimensions when it will change category or follow-up, with the largest diameter stated clearly.
Classic benign patterns
Call a classic diagnosis only when the pattern is typical:
- Simple cyst: anechoic, thin smooth wall, no septa or solid tissue, no internal flow, posterior acoustic enhancement.
- Typical hemorrhagic cyst: reticular fibrin strands or a retracting clot, without internal vascularity.
- Typical endometrioma: homogeneous ground-glass echoes without internal flow.
- Typical dermoid: hyperechoic components with acoustic shadowing, hyperechoic lines and dots, or a fat-fluid level.
If the pattern is not classic, do not force a benign label. Score by morphology plus Doppler instead.
Color score and extraovarian findings
Optimize color Doppler for slow flow before deciding that a component is avascular. The IOTA-style color score used in O-RADS US is:
- 1: no flow
- 2: minimal flow
- 3: moderate flow
- 4: very strong flow
Also document ascites, peritoneal thickening or nodules, and whether the finding is ovarian, paraovarian, or tubal. Hydrosalpinx, peritoneal inclusion cysts, and pedunculated fibroids should be recognized so they are not scored as ovarian neoplasms.
O-RADS Risk Categories and Next Steps
When more than one lesion is present, the report category is the highest applicable score. Risk ranges below are the system's assigned strata. Confirm current ACR O-RADS US criteria at the time of reporting, because lexicon details and management recommendations have been refined since the original release.
- O-RADS 0: Incomplete evaluation. Recommend additional imaging, typically transvaginal ultrasound if only transabdominal views were obtained, or MRI when ultrasound cannot be completed.
- O-RADS 1: Normal ovary, including a follicle or corpus luteum. No additional imaging of the ovary on that basis.
- O-RADS 2: Almost certainly benign (generally cited as less than 1% risk). Classic simple cysts and typical hemorrhagic cysts, endometriomas, and dermoids below commonly used size thresholds often land here. Management is usually expectant, with optional follow-up based on size and menopausal status.
- O-RADS 3: Low risk (generally 1% to less than 10%). Larger classic lesions and some smooth multilocular or smooth solid lesions without worrisome Doppler features. Ultrasound follow-up or gynecology referral is typical, depending on the lesion and the patient.
- O-RADS 4: Intermediate risk (generally 10% to less than 50%). Morphology or vascularity is not reassuring. Specialist ultrasound, O-RADS MRI, and gynecology or gynecologic oncology referral are the usual pathways.
- O-RADS 5: High risk (generally 50% or higher). Irregular solid tissue, strong flow in solid components, ascites, or peritoneal nodules in the appropriate context. Prompt gynecologic oncology referral is the priority.
Classic lesions at or above about 10 cm are generally up-classified relative to smaller typical lesions, even when the internal pattern looks classic. Match the recommendation to menopausal status, symptoms, and whether the finding is incidental. Acute pain still needs a diagnosis for torsion, hemorrhage, or infection even if morphology looks benign.
Reporting Pearls and Common Pitfalls
- State laterality, relevant measurements, the O-RADS category, and a brief lexicon-based justification in one readable impression.
- Do not call internal debris solid unless it has a real contour. Color Doppler is what separates clot and fibrin from true solid tissue.
- Typical hemorrhagic cysts are expected before menopause. The same appearance after menopause is not treated as a classic physiologic lesion.
- A technically limited study is O-RADS 0. Incomplete visualization is not O-RADS 2.
- Look outside the ovary. Extraovarian disease and non-ovarian mimics change both the category and the clinical message.
- If ultrasound remains indeterminate, say so and recommend O-RADS MRI or expert ultrasound rather than stretching a 2 or 3.
Transvaginal ultrasound is first-line imaging for most ovarian cysts because it defines unilocular versus solid architecture and Doppler better than CT. MRI is the problem-solving test when the ultrasound category is intermediate or the lesion is incompletely characterized, not a routine add-on for every simple cyst.
Consistent O-RADS reporting depends on disciplined lexicon, honest color Doppler, and a category that matches the most suspicious feature. Use current ACR O-RADS US guidance at the workstation and document a clear next step. IAME offers accredited ultrasound CME courses in gynecologic and pelvic imaging for clinicians who want structured practice with these examinations.
Frequently Asked Questions
What does O-RADS 1 mean?
O-RADS 1 means a normal ovary. Follicles and a corpus luteum are physiologic and do not require ultrasound follow-up of the ovary on that basis. It is not a cystic neoplasm category. If the clinical question is pain or pregnancy, interpret those findings in that context rather than as an elective mass score.
When is an adnexal cyst almost certainly benign?
Many adnexal cysts are physiologic or classic benign lesions and map to O-RADS 1 or 2. Concern rises with solid components, irregular contours, strong internal flow, ascites, or peritoneal nodules, which drive O-RADS 4 or 5. Counsel and refer based on the category, symptoms, and menopausal status, not on the mere presence of a cyst.
What is the best imaging for ovarian cysts?
Pelvic ultrasound, preferably transvaginal, is the first-line test to characterize ovarian cysts and supplies the lexicon features O-RADS US requires. MRI with an O-RADS MRI score is appropriate when ultrasound is incomplete or the lesion is intermediate risk. CT is not the preferred test for characterizing an isolated adnexal cyst.
What does an O-RADS 4 score mean?
O-RADS 4 is intermediate risk of malignancy on ultrasound. These lesions need a defined next step: specialist ultrasound, MRI, and timely surgical specialty referral rather than routine annual observation. Absence of symptoms does not downgrade an O-RADS 4 lesion.
How is an O-RADS 2 ovarian cyst managed?
O-RADS 2 lesions are almost certainly benign. Management is usually observation, with optional follow-up ultrasound according to size, lesion type, and menopausal status in current ACR guidance. Surgery is not the default for a typical O-RADS 2 cyst in an asymptomatic patient. Confirm the current ACR recommendation for the specific lesion you are reporting.
