Best Investigation for Suspected Torsion
For suspected testicular torsion, Duplex Doppler ultrasound of the scrotum is the best initial investigation; for suspected ovarian torsion, combined transvaginal and transabdominal pelvic ultrasound with Doppler is the best initial investigation. 1, 2, 3
Testicular Torsion Investigation
Duplex Doppler ultrasound of the scrotum is the established first-line imaging modality, combining grayscale examination with color and power Doppler assessment of testicular perfusion 2. This approach achieves a sensitivity of 69-96.8% and specificity of 87-100% for diagnosing testicular torsion 2, 4.
Key Ultrasound Findings to Identify:
- Decreased or absent blood flow to the affected testicle compared to the contralateral side (which serves as an internal control) 2, 4
- "Whirlpool sign" of the twisted spermatic cord on grayscale imaging, which has 96% sensitivity 2
- Enlarged heterogeneous testis that may appear hypoechoic 2
- Abnormal or absent venous flow, which has 100% sensitivity and 97% specificity 2
- Ipsilateral hydrocele and scrotal skin thickening 2
Critical Pitfall:
Normal arterial flow does NOT rule out testicular torsion 2, 3. Partial or intermittent torsion can show preserved arterial flow because venous obstruction occurs first due to thinner vessel walls and lower pressure 2. False-negative Doppler evaluations occur in 30% or more of cases, particularly with partial torsion or early presentation 2. When clinical suspicion is high, proceed immediately to surgical exploration regardless of ultrasound findings 2, 4.
Power Doppler Advantage:
Power Doppler is particularly useful for detecting low-flow states and is especially valuable in prepubertal boys who normally have reduced intratesticular blood flow 2.
Ovarian Torsion Investigation
Combined transvaginal and transabdominal pelvic ultrasound with Doppler is the most useful imaging modality for initial assessment when ovarian torsion is suspected 1, 3. This combined approach allows assessment of adnexa situated in high positions that may not be visible by transvaginal approach alone 1.
Key Ultrasound Findings to Identify:
- Unilaterally enlarged ovary (>4 cm maximal dimension or volume >20 cm³) 1, 3
- Peripheral follicles in a "string of pearls" pattern (found in up to 74% of cases) 1, 3
- Abnormal or absent venous flow (100% sensitivity, 97% specificity) 3
- "Whirlpool sign" of the twisted vascular pedicle, with 90% of patients having confirmed adnexal torsion on laparoscopy when this sign is present 1, 3
- Central afollicular stroma with edema 1
Doppler Performance:
A meta-analysis of 7 studies with 845 patients showed Doppler ultrasound has 80% sensitivity and 88% specificity for ovarian torsion 1, 3. Grayscale ultrasound alone has 79% sensitivity and 76% specificity based on 12 studies with 1,187 patients 1.
When Ultrasound is Inconclusive:
MRI provides 80-85% sensitivity for ovarian torsion when ultrasound findings are equivocal but clinical suspicion remains high 3. MRI findings include enlarged ovary with stromal edema, surrounding fluid, and absent/diminished enhancement 3.
CT abdomen and pelvis with IV contrast may be used as a second-line modality, showing asymmetrically enlarged ovary, twisted pedicle, abnormal/absent ovarian enhancement, and deviation of uterus to the affected side 1, 3. CT has 74-95% sensitivity and 80-90% specificity for adnexal torsion 1.
Why NOT "USG Abdomen and Pelvis"
The question asks about "USG abdomen and pelvis," but this is not the optimal approach:
- For testicular torsion: A focused scrotal ultrasound with Doppler is required, not an abdominal study 1, 2
- For ovarian torsion: While pelvic ultrasound is correct, the transvaginal component is essential for optimal visualization and should be combined with transabdominal views 1, 3
Time-Critical Nature
Both testicular and ovarian torsion require intervention within 6-8 hours of symptom onset to prevent permanent ischemic damage and gonadal loss 2, 3. Imaging should never delay surgical exploration when clinical suspicion is high 2, 5. Girls with suspected ovarian torsion historically wait 2.7 times longer to reach the operating room compared to boys with testicular torsion, resulting in significantly worse salvage rates (14.4% vs 30.3%) 5.