By Jason Naylor PA-C
Doppler ultrasound (DUS) is the study of choice for evaluating testicular torsion. Various studies demonstrated a range of sensitivity from 80 – 98%, while specificity consistently remained between 97 – 100%1-3. DUS findings specific for testicular torsion are twisting of the spermatic cord, no central arterial flow of the affected testis, and diminished central arterial flow relative to the unaffected testis. Demonstrating flow about the periphery of the testis is not useful.
Twisting of the spermatic cord is visualized on US as a coiling of tubal structures4. This finding is elicited with the linear transducer scanning from the superior pole of the testis up to the inguinal canal. A coiled spermatic cord is diagnostic of testicular torsion even in the setting of normal DUS blood flow. Many institutions, however, do not routinely scan the spermatic cord in their evaluation of potential testicular torsion and rely solely on the evaluation of testicular flow.
Central arterial flow of the affected testis can be evaluated in several modes on DUS. The least sensitive is color DUS, which shows red and/or blue color within the center of the testis if flow is present. In infants, testicular arterial flow can be of very low pressures and go undetected by color DUS. In this case, the next best mode is power Doppler which is designed to detect low flow states1. If both color and power DUS fail to demonstrate central flow of the affected testis then testicular torsion is present.
Spectral Waveform Analysis
If, however, color or power DUS reveal central flow then the next step in evaluation is spectral analysis of the Doppler waveform. Spectral waveform analysis cannot be performed unless there are points of color in the testis to analyze. The operator moves the cross-hairs over multiple points of color and the US device will generate a waveform for each point of flow. Both central arterial and venous waveforms comparable to the unaffected testis must be demonstrated to confidently eliminate testicular torsion at the time of the exam5.
Arterial and venous waveforms on spectral analysis have distinctive patterns. Arterial waveforms have steep upstrokes and larger amplitudes. Venous waveforms are either flat or have gradual, rolling upstrokes along with smaller amplitudes. It makes no difference if the waveform is above or below the reference line since this simply indicates whether the flow is moving towards or away from the transducer. Both waveforms (arterial and venous) must be demonstrated because the lack of either is indicative of testicular torsion.
Careful use of spectral waveform analysis can detect early torsions
Early in testicular torsion, venous flow is occluded. Color or power DUS will show central flow and spectral waveform analysis will demonstrate arterial flow is present, but venous flow is absent. As testicular torsion progresses, venous congestion results in increased venous pressures that resist arterial flow. Color or power DUS will show central flow and spectral waveform analysis will demonstrate “venous” flow, but no arterial flow is present. The “venous” flow is actually dampened arterial flow. Finally, the mounting pressures within the venous system will result in complete resistance of arterial flow. Color and power DUS will fail to demonstrate central flow in the testis. Consequently, there are variable findings during the course of testicular torsion. Hence, both venous and arterial waveforms must be demonstrated if color or power DUS show central flow. Additionally, arterial flow of the affected testis must be compared to the unaffected testis since diminished arterial flow is specific for testicular torsion.
To summarize, testicular torsion should be suspected with any of the following findings:
- Color and power DUS fail to demonstrate central flow of the affected testis
- Spectral waveform analysis fails to demonstrate both central arterial and venous flow patterns
- Spectral waveform analysis demonstrates diminished central arterial flow of the affected testis in comparison to the asymptomatic testis
- A twisted spermatic cord is visualized.
Thus Testicular torsion can be confidently excluded at the time of the exam if DUS shows bilateral, equivalent, central arterial and venous flow and that the spermatic cord is free of coiling. However, this does not eliminate the possibility of intermittent testicular torsion, which is generally diagnosed by a history of recurrent, acute scrotal pain that spontaneously resolves6.
Bear in the mind that several other US findings may be appreciated in testicular torsion. Pure gray-scale US may show an enlarged, heteroechogenic testis with hypoechoic areas centrally. Additionally, there may be a hydrocele and thickening of the scrotal tissue. Epididymo-orchitis can mimic testicular torsion with all of the findings previously described, with one important exception: the testis will be hyperemic (increased color DUS signal) when compared to the unaffected testis7. However, a hyperemic testis can be seen after a torsed testis detorses, as in intermittent torsion. Consequently, intermittent testicular torsion is most commonly misdiagnosed as epididymo-orchitis/ epididymitis. Therefore, it is best to consult urology in the emergency department for males less than 25 years old—and especially those less than 16 years old—before making a diagnosis of epididymo-orchitis and discharging the patient with antibiotics and analgesics.
1. Prando D. Torsion of the spermatic cord: the main gray-scale and Doppler sonographic signs. Abdominal Imaging. 2009;34:649-661.
2. Baker LA, Sigman D, Mathews RI, Benson J, Docimo SG. An analysis of clinical outcomes using color doppler testicular ultrasound for testicular torsion. Pediatrics. March 2000;105(3):604-607.
3. Kurlan R, Bruyn R. Ultrasound of the pediatric scrotum: a pictorial review. Ultrasound. November 2006;14(4):216-222.
4. Karmazyn B, Steinberg R, Kornreich L, Freud E, Grozovski S, et al. Clinical and sonographic criteria of acute scrotum in children: a retrospective study of 172 boys. Pediatric Radiology. 2005;35:302-310
5. Adhikari SR. Small parts—testicular ultrasound. Ultrasound Guide for Emergency Physicians: An Introduction. Accessed from http://sonoguide.com/smparts_testicular.html on 11 Nov 2014.
6. Johnston BI, Wiener JS. Intermittent testicular torsion. British Journal of Urology International. 2005;933-934.
7. Weerakkody Y, Gaillard F. Testicular torsion. Radiopea. Accessed from http://radiopaedia.org/articles/testicular-torsion on 22 Nov 2014.