What are the ultrasound criteria for diagnosing polycystic ovaries?

Ultrasound Criteria for Diagnosing Polycystic Ovaries

The most accurate ultrasound criteria for diagnosing polycystic ovaries is follicle number per ovary (FNPO) ≥20 follicles measuring 2-9mm in at least one ovary, which has a sensitivity of 84% and specificity of 91%. 1

Primary Diagnostic Criteria

Follicle Number Per Ovary (FNPO)

• Gold standard marker: FNPO is the most accurate ultrasonographic marker with the highest diagnostic performance (AUC 0.905) 2, 1
• Diagnostic threshold: ≥20 follicles measuring 2-9mm in at least one ovary 1
• Diagnostic accuracy:
  • Sensitivity: 84.32% (81.27-86.95%)
  • Specificity: 91.06% (86.44-94.21%) 2

Ovarian Volume (OV)

• Alternative marker: Should be used when accurate follicle counting is not possible 1
• Diagnostic threshold: >10 mL in at least one ovary 1, 3
• Diagnostic accuracy:
  • Sensitivity: 81.48% (76.05-85.90%)
  • Specificity: 81.04% (74.66-86.11%)
  • AUC: 0.856 2

Follicle Number Per Cross-Section (FNPS)

• Third-line marker: Used when neither FNPO nor OV can be accurately assessed
• Diagnostic accuracy:
  • Sensitivity: 81.07% (70.10-88.67%)
  • Specificity: 82.70% (75.15-88.31%)
  • AUC: 0.870 2

Technical Considerations

Ultrasound Methodology

• Preferred approach: Transvaginal ultrasound for optimal visualization 1
• Transducer frequency: ≥8 MHz recommended for maximum resolution 2
• Timing: Perform when ovaries are quiescent (no dominant follicles >10mm, corpus luteum, or cysts) 1, 3
• Measurement technique:
  • For FNPO: Count all follicles measuring 2-9mm in diameter in each ovary 3
  • For OV: Calculate using the formula length × width × depth × 0.5233 3

Special Populations

Adolescents

• Important limitation: Ultrasound should not be used for PCOS diagnosis in those with gynecological age <8 years (less than 8 years after menarche) due to high incidence of multi-follicular ovaries in this age group 1
• Alternative approach: In adolescents, diagnosis should be based on irregular menstruation and clinical/biochemical hyperandrogenism without requiring ultrasound 1

When Transvaginal Ultrasound Cannot Be Used

• Recommendation: For transabdominal ultrasound, rely only on ovarian volume (≥10 ml) due to difficulty in reliably assessing follicle count 1

Diagnostic Algorithm

1. First-line assessment: Evaluate FNPO using transvaginal ultrasound with ≥8 MHz transducer

   • If ≥20 follicles measuring 2-9mm in at least one ovary → Polycystic ovary morphology confirmed
   • If <20 follicles → Proceed to step 2

2. Second-line assessment: Evaluate ovarian volume

   • If >10 mL in at least one ovary → Polycystic ovary morphology confirmed
   • If ≤10 mL → Not consistent with polycystic ovary morphology

3. Third-line assessment (if needed): Evaluate FNPS

   • Used when technical limitations prevent accurate FNPO or OV assessment

Common Pitfalls and Caveats

• Single ovary sufficient: The presence of polycystic morphology in just one ovary is sufficient for diagnosis 3
• Avoid during hormonal contraceptive use: Hormonal contraceptives can alter ovarian appearance, potentially leading to false negatives 2
• Repeat if necessary: If a follicle >10mm is present, repeat the scan when ovaries are quiescent 3
• Asymptomatic PCO: Women with polycystic ovaries on ultrasound but without anovulation or hyperandrogenism should not be diagnosed with PCOS 3
• Diagnostic context: Remember that ultrasound findings are just one component of PCOS diagnosis according to Rotterdam criteria, which requires at least two of three criteria: oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovary morphology 1, 4

Emerging Techniques

• 3D ultrasound: May improve diagnostic accuracy but not currently required for routine diagnosis 3
• Offline analysis: May improve diagnostic accuracy for FNPO compared to real-time approaches, but limited data available 2
• Doppler ultrasound: Potential research tool but not required for standard diagnosis 3