What is the preferred initial diagnostic imaging modality, transvaginal (TV) ultrasound or transabdominal (TA) ultrasound, for a woman of reproductive age suspected of having ovarian torsion, potentially with a history of ovarian cysts or pelvic surgery?

Ovarian Torsion: Combined Transvaginal and Transabdominal Ultrasound

For suspected ovarian torsion, perform both transvaginal and transabdominal ultrasound together as the initial imaging approach—this combined technique is the standard of care and provides complementary diagnostic information that neither approach alone can deliver. 1

Why Both Approaches Are Essential

The 2024 ACR Appropriateness Criteria explicitly states that a combined transabdominal and transvaginal approach should be performed when possible for pelvic ultrasound imaging, and both modalities should be done together. 1, 2

Transvaginal Ultrasound Advantages:

• Superior resolution for detecting subtle ovarian and tubal pathology 2
• Sensitivity of 83.3% specifically for ovarian torsion 1
• Better visualization of ovarian architecture, peripheral follicles, and the whirlpool sign 1, 3
• Optimal Doppler assessment of ovarian venous flow (100% sensitivity when abnormal or absent) 1, 3, 2

Transabdominal Ultrasound Advantages:

• Larger field of view to assess adnexa positioned high in the pelvis that may be distant from the transvaginal probe 1, 2
• Better evaluation of free pelvic fluid and overall pelvic architecture 2
• Essential for large masses that extend beyond the transvaginal probe's field 1

Critical Diagnostic Findings

Key Ultrasound Features of Ovarian Torsion:

• Unilaterally enlarged ovary (>4 cm or volume >20 cm³) found in up to 74% of cases 1, 3
• Peripheral follicles in a "string of pearls" pattern 1, 3
• Whirlpool sign (twisted vascular pedicle)—90% of patients with this finding had confirmed torsion at laparoscopy 1, 3, 2
• Abnormal or absent ovarian venous flow on Doppler—100% sensitivity and 97% specificity 1, 3, 2

Important Pitfall to Avoid:

Normal arterial blood flow does NOT rule out ovarian torsion. In a prospective study of 159 patients, 62% of those with only abnormal venous flow (but normal arterial flow and normal grayscale appearance) had confirmed adnexal torsion or subtorsion. 1, 3 Venous obstruction occurs first in the torsion process, making venous flow assessment more sensitive than arterial flow. 1

When Transabdominal-Only Is Acceptable

A transabdominal-only approach serves as an alternative only when transvaginal ultrasound is not feasible: 1, 2

• Post-treatment vaginal stenosis or fibrosis 1, 2
• Juvenile age or sexually naïve patients 1, 2
• Patient discomfort or inability to tolerate transvaginal approach 1, 2
• Large fibroids or surgical changes limiting transvaginal visualization 1, 2

Diagnostic Performance

The combined ultrasound approach with Doppler has: 1, 3

• Sensitivity of 79-80% and specificity of 76-88% for adnexal torsion
• Overall accuracy of 96% when including Doppler assessment 4
• Meta-analysis of 12 studies (1,187 patients) confirms these performance metrics 1

Next Steps If Ultrasound Is Inconclusive

If the combined ultrasound examination is nondiagnostic or equivocal: 2

• Proceed to MRI (80-85% sensitivity, no radiation) as the preferred second-line modality 1, 3, 5
• Consider CT abdomen/pelvis with IV contrast (74-95% sensitivity) if MRI unavailable or when non-gynecologic pathology is in the differential 1, 2, 6

Clinical Context

Early detection is critical—ovarian torsion can lead to adnexal necrosis and infertility if diagnosis is delayed. 1, 3, 2 The combined ultrasound approach maximizes diagnostic accuracy while avoiding radiation exposure, making it the optimal initial strategy for women of reproductive age with suspected ovarian torsion. 1, 2