What is the O-RADS (Ovarian-Adnexal Reporting and Data System) classification?

O-RADS Classification System

The O-RADS (Ovarian-Adnexal Reporting and Data System) is a standardized ultrasound-based risk stratification system developed by the American College of Radiology that categorizes adnexal masses into six risk categories (0-5) based on their likelihood of malignancy, with each category having specific management recommendations. 1

Six Risk Categories

The O-RADS system divides adnexal masses into the following categories based on malignancy risk 1:

O-RADS 0: Incomplete Evaluation

• Inadequate ultrasound assessment due to technical factors (bowel gas, large lesion size, inability to tolerate transvaginal imaging) 1
• Management: Repeat ultrasound or alternative imaging (MRI) 1

O-RADS 1: Normal Ovary (0% malignancy risk)

• Only applies to premenopausal women 1
• Includes physiologic findings:
  • Follicles: Simple cysts <3 cm 1
  • Corpus luteum: Thick-walled cysts <3 cm with crenulated inner margins, internal echoes, and peripheral color Doppler flow 1
• Management: No follow-up required 1, 2

O-RADS 2: Almost Certainly Benign (<1% malignancy risk)

• Simple cysts (anechoic, smooth thin wall, acoustic enhancement) 1
• Non-simple unilocular cysts with smooth walls <10 cm 1
• Classic benign lesions <10 cm: hemorrhagic cysts, dermoid cysts, endometriomas, paraovarian cysts, peritoneal inclusion cysts, hydrosalpinx 1
• Validated malignancy rate: 0.6% (95% CI: 0.3-1.0%) 3
• Management: 1, 2
  • Simple cysts ≤5 cm in premenopausal women: No follow-up
  • Simple cysts >5 cm to <10 cm: Follow-up ultrasound in 8-12 weeks (postmenopausal) or 1 year (premenopausal)
  • Postmenopausal women with simple cysts >3 cm: Follow-up in 8-12 weeks

O-RADS 3: Low Risk (1% to <10% malignancy risk)

• Unilocular cysts ≥10 cm (simple or non-simple) 1
• Unilocular cysts with irregular inner wall <3 mm height 1
• Multilocular cysts <10 cm with smooth inner walls and color score 1-3 1
• Classic benign lesions ≥10 cm (dermoid cysts, endometriomas, hemorrhagic cysts) 1
• Validated malignancy rate: 3.9% (95% CI: 2.5-5.4%) 3
• Management: Gynecologist consultation 1

O-RADS 4: Intermediate Risk (10% to <50% malignancy risk)

• Multilocular cysts with smooth inner walls and color score 4 1
• Lesions with irregular inner walls or irregular septa 1
• Unilocular-solid lesions without papillary projections 1
• Unilocular-solid with 1-3 papillary projections (≥3 mm height) 1
• Multilocular-solid lesions with color score 1-2 1
• Smooth solid lesions with color score 2-3 1
• Validated malignancy rate: 43.5% (95% CI: 33.8-53.2%) 3
• Management: Gynecologist or gynecologic oncologist consultation 1

O-RADS 5: High Risk (≥50% malignancy risk)

• Unilocular-solid with ≥4 papillary projections 1
• Multilocular-solid with color score 3-4 1
• Solid lesions with irregular contour 1
• Smooth solid lesions with color score 4 1
• Presence of ascites and/or peritoneal nodules (except with physiologic or benign lesions) 1
• Validated malignancy rate: 87.3% (95% CI: 83.0-91.7%) 3
• Management: Gynecologic oncologist consultation 1

Diagnostic Performance

When O-RADS scores 4 and 5 are combined as indicators of malignancy, the system demonstrates pooled sensitivity of 95.6% (95% CI: 94.0-97.2%) and specificity of 76.6% (95% CI: 70.4-82.7%). 3 External validation studies confirm O-RADS achieves an area under the ROC curve of 0.91-0.94, with sensitivity of 96.8-99% and specificity of 70-92.8% for distinguishing benign from malignant lesions. 4, 5

Key Lexicon Components

The O-RADS system uses standardized terminology based on IOTA (International Ovarian Tumor Analysis) definitions 1:

• Unilocular vs multilocular: Single compartment vs multiple compartments with complete septa 1
• Solid components: Tissue elements >3 mm in height 1
• Papillary projections: Solid components arising from cyst wall/septation protruding into cavity 1
• Color score: Doppler flow assessment (1-4 scale) 1
• Acoustic shadowing: Attenuation artifact behind sound-absorbing structures 1

Important Clinical Considerations

For multiple or bilateral lesions, each lesion should be characterized separately, with management driven by the lesion with the highest O-RADS score. 1

The system is designed for average-risk patients without acute symptoms; it does not apply to patients with acute presentations, known ovarian malignancy history, or pregnancy. 1, 6 Individual management may be modified based on clinical judgment despite O-RADS recommendations. 1

Common pitfall: The O-RADS classification can be assigned using either IOTA lexicon descriptors or the ADNEX mathematical model, but these two approaches show only moderate agreement (Kappa: 0.47) with 46% concordance, particularly for O-RADS 2-3 and 3-4 categories. 7 Despite this variability in category assignment, both approaches demonstrate similar diagnostic performance. 7

Adding acoustic shadowing as a benign finding improves O-RADS diagnostic performance (AUC from 0.91 to 0.94). 4