What are the diagnostic criteria for polycystic ovaries (PCOS) on ultrasound in a female patient?

Ultrasound Diagnostic Criteria for Polycystic Ovaries

The gold standard ultrasound criterion for diagnosing polycystic ovarian morphology is ≥20 follicles per ovary (measuring 2-9mm in diameter), which demonstrates 87.64% sensitivity and 93.74% specificity. 1

Primary Diagnostic Thresholds

Follicle Number Per Ovary (FNPO) is the most accurate ultrasonographic marker and should be prioritized when technically feasible. 1

• ≥20 follicles per ovary (2-9mm diameter) is the recommended threshold, with superior diagnostic accuracy (AUC 0.905) compared to other markers 1
• This threshold is substantially higher than the older Rotterdam 2003 criterion of ≥12 follicles, which has been shown to result in overdiagnosis due to high false-positive rates in healthy women 2, 3
• FNPO demonstrates less within-study and between-study variability compared to alternative markers 1

Alternative Diagnostic Markers

When accurate follicle counting is not possible due to technical limitations or image quality, use these alternatives in order of preference: 1

Ovarian Volume (OV):

• >10 mL (10 cm³) threshold serves as a robust alternative 1, 4
• Demonstrates 81.48% sensitivity and 81.04% specificity in adults 1
• Lower diagnostic accuracy (AUC 0.856) compared to FNPO but remains clinically useful 1

Follicle Number Per Single Cross-Section (FNPS):

• ≥9 follicles in a single cross-section provides intermediate diagnostic accuracy 2
• Shows 81.07% sensitivity and 82.70% specificity 1
• Can be used when counting throughout the entire ovary is unavailable 1

Technical Requirements for Optimal Imaging

Transvaginal ultrasound with ≥8 MHz transducer frequency is mandatory for optimal resolution in adults. 1, 5

• Higher transducer frequency (≥8 MHz) significantly improves diagnostic accuracy compared to <8 MHz 1
• Studies using ≥8 MHz transducers show diagnostic odds ratio of 106.83 versus 34.09 for FNPO 1
• Document three dimensions and calculate volume of each ovary 6
• Ensure no corpora lutea, cysts, or dominant follicles ≥10mm are present, as these invalidate the assessment 6

Age-Specific Considerations

Critical Pitfall: Ultrasound should NOT be used as a first-line diagnostic tool in adolescents. 1, 5

• Avoid ultrasound in patients <8 years post-menarche or <20 years old due to poor specificity (high false-positive rates from normal multifollicular ovaries) 1, 5, 6
• In adolescents, rely primarily on clinical and biochemical hyperandrogenism plus menstrual irregularity persisting 2-3 years beyond menarche 5
• If ultrasound is performed in adolescents, ovarian volume shows 81.84% sensitivity and 83.54% specificity, but interpretation requires extreme caution 1

Diagnostic Algorithm

Step 1: Use transvaginal ultrasound with ≥8 MHz transducer in adults (≥18 years, >8 years post-menarche) 1, 5

Step 2: Count total follicles (2-9mm) throughout the entire ovary using systematic scanning 1, 2

• If FNPO ≥20 in either ovary → Polycystic ovarian morphology confirmed 1, 5

Step 3: If accurate follicle counting is impossible, measure ovarian volume 1, 6

• If OV >10 mL in either ovary → Polycystic ovarian morphology confirmed 1, 5

Step 4: If neither FNPO nor OV can be reliably assessed, use FNPS 1

• If ≥9 follicles in single cross-section → Suggests polycystic ovarian morphology 2

Critical Clinical Pitfalls to Avoid

Polycystic ovarian morphology alone does NOT diagnose PCOS. 5, 6

• Up to one-third of reproductive-aged women without PCOS have polycystic ovarian morphology on ultrasound 5
• PCOS diagnosis requires at least 2 of 3 Rotterdam criteria: oligo/anovulation, clinical/biochemical hyperandrogenism, and polycystic ovarian morphology 5, 4
• Other conditions must be excluded (thyroid disease, hyperprolactinemia, Cushing's syndrome, androgen-secreting tumors, congenital adrenal hyperplasia) 5, 7

Do not use the outdated ≥12 follicle threshold from 2003 Rotterdam criteria. 2, 3

• This lower threshold results in overdiagnosis with poor specificity 2, 3
• Recent meta-analysis confirms ≥20 follicles provides optimal balance of sensitivity and specificity 1

Presence of an IUD does not interfere with ovarian imaging. 6

• The IUD sits within the endometrial cavity while ovaries are separate lateral pelvic structures 6
• Acoustic shadowing from the IUD does not extend to the ovaries 6

Geographic and Diagnostic Criteria Variations

Diagnostic accuracy varies by PCOS diagnostic criteria used: 1

• Rotterdam criteria show higher sensitivity (89.81%) but slightly lower specificity (89.79%) for FNPO 1
• NIH 1990 criteria show lower sensitivity (81.76%) but higher specificity (91.06%) for FNPO 1
• Asian studies preferentially use Rotterdam criteria (71% of studies), while North American studies exclusively use NIH criteria (100% of studies) 1