Ultrasound Sensitivity for Testicular Torsion
Color Doppler ultrasound has a variable sensitivity for detecting testicular torsion, ranging from 69% to 96.8%, with specificity of 87% to 100%, making it an imperfect but essential first-line imaging modality that should never delay surgical exploration when clinical suspicion is high. 1
Understanding the Diagnostic Limitations
The wide range in reported sensitivity reflects real-world challenges in ultrasound interpretation:
- Complete torsion (>450 degrees) shows straightforward findings with absent arterial and venous flow, making diagnosis easier 1
- Partial or incomplete torsion presents the greatest diagnostic challenge, as arterial flow may persist because venous obstruction occurs first due to thinner vessel walls and lower pressure 1
- False-negative evaluations occur in 30% or more of cases, particularly with partial torsion, spontaneous detorsion, or early presentation within the first few hours when the testis may appear normal 1
Key Sonographic Findings to Maximize Accuracy
The "whirlpool sign" of the twisted spermatic cord is the most specific ultrasound finding for testicular torsion, with 96% sensitivity. 2
Critical ultrasound features include:
- Grayscale findings: Enlarged heterogeneous testis that may be hypoechoic, ipsilateral hydrocele, scrotal skin thickening 1
- Color/Power Doppler: Decreased or absent testicular blood flow compared to the contralateral side (use the asymptomatic testicle as internal control) 1
- Spectral Doppler analysis: Diminished arterial velocity, decreased or absent diastolic flow, increased resistive index, reversed diastolic flow, monophasic waveform, or tardus-parvus morphology 1
- Power Doppler advantage: More sensitive for low-flow states and particularly useful in prepubertal boys who normally have reduced intratesticular blood flow 1, 2
Critical Clinical Pitfalls
False-positive Doppler evaluations occur in infants and young boys who often have normally reduced intratesticular blood flow, potentially leading to unnecessary surgery. 1
False-negative evaluations with preserved flow have been documented in surgical cases, resulting in testicular loss when exploration was delayed. 3, 4, 5
Recent research confirms this limitation:
- A 2020 study found sensitivity of only 69.2% when performed by doctors on duty, even with high-frequency transducers 3
- Multiple case reports document testicular torsion with positive blood flow on color Doppler that was only diagnosed at surgery 4, 5
Practical Algorithm for Clinical Use
For intermediate clinical suspicion (TWIST score 1-5), perform urgent Duplex Doppler ultrasound within 60 minutes, but proceed directly to surgical exploration for high clinical suspicion regardless of ultrasound findings. 2
The ultrasound examination must include:
- Spectral Doppler analysis of the upper, mid, and lower poles of each testicle to detect regional flow variations 1
- Comparison to contralateral testis for relative flow assessment 1
- Careful evaluation for the whirlpool sign on grayscale imaging 1, 2
Impact on Clinical Outcomes
Implementation of ultrasound protocols for intermediate-risk patients significantly reduced negative surgical explorations from 8.4% to 3.0% without increasing missed torsion cases. 6
However, the critical principle remains: surgical exploration should be performed promptly even if testicular blood flow is observed when testicular torsion is suspected from history and physical examination, given the 6-8 hour window before permanent ischemic damage occurs. 2, 3
The 30% false-negative rate means that approximately 1 in 3 cases of testicular torsion may show preserved flow on ultrasound, making clinical judgment paramount over imaging findings when managing this surgical emergency.