Ultrasound with Doppler is the Diagnostic Test to Confirm Testicular Torsion
The answer is C - Ultrasound (US). Specifically, Duplex Doppler ultrasound of the scrotum is the established first-line imaging modality for confirming testicular torsion. 1
Why Ultrasound is the Gold Standard
Duplex Doppler ultrasound combines grayscale imaging with color and spectral Doppler to assess both testicular anatomy and blood flow, achieving sensitivity of 69-96.8% and specificity of 87-100% for detecting testicular torsion. 1
Key Ultrasound Findings in Testicular Torsion
The diagnostic ultrasound examination should include three components:
- Grayscale imaging identifies the pathognomonic "whirlpool sign" - the twisted spermatic cord seen in 96% of torsion cases (sensitivity 96%, specificity 99%) 1
- Color Doppler assessment demonstrates decreased or absent testicular blood flow, with sensitivity ranging from 91.7% to 100% 1, 2
- Power Doppler is more sensitive than color Doppler for detecting slow flow states and is particularly valuable in prepubertal boys with naturally reduced testicular blood flow 1
Additional Ultrasound Features
Beyond blood flow assessment, ultrasound reveals:
- Enlarged heterogeneous testis that may appear hypoechoic 1, 2
- Ipsilateral hydrocele and scrotal skin thickening 1, 2
- In partial torsion: spectral Doppler shows diminished arterial velocity, decreased or reversed diastolic flow, and increased resistive index 1
Why Other Imaging Modalities Are Not Appropriate
CT Scan (Option A)
CT of the pelvis with or without contrast is not routinely used for acute scrotal pain evaluation and has no relevant literature supporting its use for testicular torsion diagnosis. 1 CT exposes patients to unnecessary radiation without providing superior diagnostic information compared to ultrasound.
MRI (Option B)
While MRI can identify testicular torsion with high sensitivity (showing decreased perfusion on dynamic contrast-enhanced sequences), it is not used for initial diagnosis due to limited availability, longer acquisition time, and higher cost. 1 MRI may be reserved for equivocal ultrasound cases or to identify complications like segmental testicular infarction. 1
X-ray (Option D)
Plain radiography has no role in diagnosing testicular torsion and cannot assess testicular blood flow or soft tissue pathology. 1
Critical Clinical Pitfalls
False-Negative Doppler Results
Be aware that false-negative ultrasound evaluations can occur in three scenarios: 1, 2
- Partial torsion (less than 360 degrees) may show preserved arterial flow because venous obstruction precedes complete arterial occlusion
- Spontaneous detorsion can restore blood flow temporarily
- Very early presentation (first few hours) may show normal-appearing testis with preserved flow
In these cases, spectral Doppler analysis of the upper, mid, and lower poles of each testicle should be performed, looking for waveform variations, monophasic patterns, or tardus-parvus morphology that suggest underlying ischemia. 1
False-Positive Results
Infants and young boys normally have reduced intratesticular blood flow, which can mimic torsion. 1 Always use the contralateral asymptomatic testicle as an internal control for comparison. 1, 2
Time-Critical Nature
Surgical exploration must occur within 6-8 hours of symptom onset to prevent testicular loss. 1, 2 While ultrasound is the diagnostic standard, if clinical suspicion is high (TWIST score ≥5), proceed directly to surgical exploration without waiting for imaging. 2 Conversely, ultrasound should be obtained urgently for intermediate clinical suspicion (TWIST score 1-5). 2
The key principle: ultrasound should facilitate rapid diagnosis, not delay definitive surgical treatment when clinical suspicion is high. 1, 2