Role of Magnetic Resonance Imaging in the Evaluation of Ovarian Morphology in Adolescents with Polycystic Ovary Syndrome: A Comparative Study with Transabdominal Ultrasonography

Technical Summary: Role of MRI vs. TAUSG in Adolescent PCOS Evaluation

Problem Statement
Polycystic Ovary Syndrome (PCOS) is a prevalent endocrine disorder in adolescents, characterized by ovulatory dysfunction, hyperandrogenism, and polycystic ovarian morphology (PCOM). While imaging is critical for assessing ovarian morphology, the current standard of care presents a diagnostic dilemma in the adolescent population. Transvaginal ultrasonography (TVUS), the gold standard for adults, is generally avoided in adolescents due to ethical and practical constraints. Consequently, Transabdominal Ultrasonography (TAUSG) is the primary modality used. However, TAUSG suffers from inherent limitations, including reduced spatial resolution, poor visualization of small follicles, and interference from bowel gas or increased body habitus, which can compromise diagnostic accuracy. Magnetic Resonance Imaging (MRI) offers superior soft tissue contrast and multiplanar capabilities, yet its specific role in the routine evaluation of adolescent PCOS remains underexplored and lacks standardized diagnostic criteria.

Methodology
This cross-sectional comparative study was conducted at SRM Medical College Hospital and Research Centre involving 80 adolescent females aged 12–18 years. The cohort consisted of 40 clinically diagnosed PCOS cases and 40 age-matched healthy controls.

• Data Collection: All participants underwent clinical evaluation (menstrual history, hirsutism assessment, BMI) and biochemical screening.
• Imaging Protocol: Participants underwent TAUSG followed by pelvic MRI using a 1.5-Tesla Siemens Magnetom Essenza scanner.
• Parameters: Both modalities assessed ovarian volume (calculated via prolate ellipsoid formula), Follicle Number per Ovary (FNPO), and Follicle Number per Section (FNPS).
• Statistical Analysis: Continuous variables were compared using independent sample t-tests. Diagnostic performance (sensitivity, specificity, PPV, NPV, and accuracy) was calculated for both modalities. ROC analysis was performed to determine optimal cut-off values.

Key Contributions and Results
The study provides a direct comparative analysis of TAUSG and MRI in the adolescent PCOS population, yielding the following findings:

1. Demographics and Anthropometry: The mean age was comparable between groups (PCOS: 14.7 ± 1.58 years; Controls: 15.22 ± 1.62 years; p=0.15). However, the PCOS group exhibited a significantly higher Body Mass Index (26.17 ± 2.38 kg/m²) compared to controls (22.48 ± 2.30 kg/m²; p < 0.05).
2. Ovarian Volume Discrepancies: Both modalities detected significantly larger ovarian volumes in the PCOS group compared to controls. However, MRI consistently measured higher volumes than TAUSG.
   • TAUSG: Right ovary 10.68 mL (PCOS) vs. 6.31 mL (Control).
   • MRI: Right ovary 15.28 mL (PCOS) vs. 8.40 mL (Control).
   • The authors attribute this difference to MRI's superior soft tissue contrast and multiplanar imaging, allowing for more accurate delineation of ovarian margins.
3. Follicular Quantification: MRI demonstrated significantly higher follicle counts.
   • FNPO: PCOS group showed a mean of 15.3 follicles (right) and 14.7 (left), compared to 12.0 and 11.2 in controls, respectively.
   • FNPS: Similarly, follicle counts per section were significantly higher in the PCOS group on MRI.
4. Diagnostic Accuracy:
   • TAUSG: Sensitivity 65%, Specificity 72.5%, Overall Accuracy 68.75%. It identified 26 of 40 PCOS cases.
   • MRI: Sensitivity 82.5%, Specificity 75%, Overall Accuracy 78.75%. It identified 33 of 40 PCOS cases.
   • ROC Analysis: An FNPO cut-off of ≥15 follicles yielded an Area Under the Curve (AUC) of 0.99, with 95% sensitivity and 92.5% specificity for identifying PCOM.
5. Phenotypic Variations:
   • Imaging-Negative PCOS: 35% (14/40) of clinically diagnosed PCOS cases lacked classical imaging features on TAUSG. MRI improved detection but still missed 7 cases (17.5%), suggesting phenotypic variations where hormonal abnormalities precede structural changes.
   • PCOM in Controls: 25% (10/40) of healthy controls exhibited PCOM on MRI without clinical or biochemical evidence of PCOS, reinforcing that morphology alone is insufficient for diagnosis.

Significance and Claims
The paper claims that MRI demonstrates superior visualization and assessment of ovarian morphology compared to TAUSG in adolescents with PCOS. Specifically, it offers better delineation of ovarian margins and follicular distribution, resulting in higher diagnostic accuracy (78.75% vs. 68.75%).

The authors position MRI not as a replacement for first-line imaging, but as a valuable complementary modality, particularly in cases where TAUSG findings are inconclusive or limited by body habitus and bowel gas. The study emphasizes that while imaging is crucial, it must be interpreted in conjunction with clinical and biochemical parameters, as imaging alone cannot definitively diagnose PCOS due to the presence of PCOM in healthy adolescents and the existence of imaging-negative PCOS phenotypes.

Limitations Acknowledged
The authors note that the study is single-center with a relatively small sample size, limiting generalizability. They also acknowledge that TAUSG was used instead of TVUS due to the adolescent age group, which may have limited the detection of smaller follicles. Furthermore, the high cost and limited availability of MRI prevent its routine use as a first-line screening tool.