What is the recommended imaging modality for clinical imaging of Polycystic Ovary Syndrome (PCOS)?

From the Guidelines

Transvaginal ultrasound is the recommended first-line imaging modality for clinical evaluation of Polycystic Ovary Syndrome (PCOS). This non-invasive technique provides detailed visualization of ovarian morphology, allowing clinicians to identify the characteristic features of PCOS, including enlarged ovaries with multiple small follicles (typically 20 or more follicles measuring 2-9mm in diameter) arranged in a peripheral pattern, often described as a "string of pearls" 1. The threshold for PCOM should be revised regularly with advancing ultrasound technology, and age-specific cut off values for PCOM should be defined 1.

Key Considerations

• The transvaginal ultrasound approach is preferred in the diagnosis of PCOS, if sexually active and if acceptable to the individual being assessed 1.
• Using endovaginal ultrasound transducers with a frequency bandwidth that includes 8MHz, the threshold for PCOM should be on either ovary, a follicle number per ovary of ≥20 and/or an ovarian volume ≥ 10ml, ensuring no corpora lutea, cysts or dominant follicles are present 1.
• In patients with irregular menstrual cycles and hyperandrogenism, an ovarian ultrasound is not necessary for PCOS diagnosis; however, ultrasound will identify the complete PCOS phenotype 1.
• While magnetic resonance imaging (MRI) can provide detailed images of ovarian morphology, it is generally reserved for cases where ultrasound is technically difficult or inconclusive due to its higher cost and limited availability 1.
• Computed tomography (CT) is not recommended due to radiation exposure and inferior soft tissue contrast for ovarian assessment.

Alternative Imaging Modalities

• Transabdominal ultrasound with a full bladder is an acceptable alternative for adolescents or virginal women where transvaginal ultrasound may not be appropriate, though it provides less detailed images 1.
• MRI pelvis without IV contrast may provide additional information on PCOM in obese adolescents or patients in whom TVUS is unacceptable and transabdominal US limited 1.

Reporting Standards

• Clear protocols are recommended for reporting follicle number per ovary and ovarian volume on ultrasound, including last menstrual period, transducer bandwidth frequency, approach/route assessed, total follicle number per ovary measuring 2-9mm, three dimensions and volume of each ovary, and reporting of endometrial thickness and appearance 1.

From the Research

Clinical Imaging of PCOS

The recommended imaging modality for clinical imaging of Polycystic Ovary Syndrome (PCOS) is ultrasound, particularly transvaginal ultrasonography 2, 3, 4, 5, 6.

Ultrasound Criteria

The ultrasound criteria for diagnosing PCOS include:

• Follicle number per ovary (FNPO) with a threshold of 26 follicles having the best compromise between sensitivity and specificity 2
• Ovarian volume (OV) with a threshold of 10 cm(3) 2, 4
• Follicle counts in a single cross section (FNPS) with a threshold of nine follicles 2

Advantages and Limitations

The advantages of ultrasound in diagnosing PCOS include:

• High diagnostic potential for detecting PCOS 2, 3
• Ability to characterize polycystic ovarian morphology (PCOM) accurately 3 The limitations of ultrasound in diagnosing PCOS include:
• Operator dependency and inter-observer variability 3, 5
• Need for standardized protocols and robust AI training datasets to optimize diagnostic accuracy 3

Future Directions

Future directions for improving the diagnosis of PCOS using ultrasound include:

• Integration of artificial intelligence (AI) to minimize observer bias and validate advanced metrics 3
• Development of age-/BMI-specific cut-offs to optimize the balance between sensitivity and specificity 3
• Use of 3D ultrasound and Doppler techniques to refine PCOS diagnosis 3, 6