Acute Scrotal Syndrome in Children: Ultrasound Signs of Torsion

Clinical Task of Ultrasound in Acute Scrotal Syndrome

Acute scrotal syndrome in children is a situation where ultrasound must quickly answer one main question: are there signs of testicular or spermatic cord torsion? According to the AIUM Practice Parameter for the Performance of Scrotal Ultrasound Examinations, 2021, acute scrotal pain is an indication for ultrasound examination, and the protocol should include grayscale imaging and Doppler assessment of blood flow.

In practical conclusions, it is important not to limit to the phrase "blood flow is detected." In torsion, there can be variations: complete absence of flow, sharp asymmetry, preserved peripheral or reactive flow in incomplete torsion, and signs of spontaneous detorsion. Therefore, interpretation is always based on the comparison of B-mode, Doppler, testicular position, epididymis, and spermatic cord condition.

Minimal Scanning Protocol by AIUM

The examination is performed with a high-frequency linear transducer at the highest possible frequency that provides adequate penetration. Images of both testes in longitudinal and transverse planes, evaluation of the epididymis, tunics, and, if necessary, the spermatic cord are mandatory. Comparison with the contralateral side is a critical element of the protocol when torsion is suspected.

Doppler modes should be set to detect low-velocity blood flow: color or power Doppler is used, as well as spectral Doppler to document arterial and venous components if they are visualized. Incorrect settings are a common cause of false conclusions about the absence or presence of blood flow.

Key Ultrasound Signs of Torsion

The most significant sign is the absence of intratesticular blood flow in the symptomatic testis when blood flow is present in the opposite one. In incomplete torsion, blood flow may be reduced, asymmetric, or partially preserved. In intermittent torsion, the examination may occur during a detorsion phase when blood flow has already been restored or even appears enhanced.

In B-mode, attention is paid to testicular enlargement, changes in echogenicity, reactive hydrocele, thickening of the tunics, epididymal enlargement, and abnormal testicular position. These signs do not replace Doppler but increase diagnostic confidence, especially if the Doppler pattern is atypical.

Spermatic Cord and "Whirlpool Sign"

Evaluation of the spermatic cord is especially important when intratesticular flow is partially preserved. A twisted cord may appear as a spiral structure proximal to the testis; in clinical practice, this sign is described as the "whirlpool sign." Its presence is a strong argument in favor of torsion, even if individual vascular signals are still registered in the testis.

Scanning of the cord begins at the upper pole of the testis and continues along the inguinal canal as far as access allows. Comparison with the opposite side helps distinguish true twisting from tissue folds, edema, and technical artifacts.

Doppler Patterns: How to Formulate Torsion Risk

B-Mode: Ischemia Signs and Associated Findings

In the early stages, the grayscale picture may be poor: the testis appears homogeneous, and the size does not significantly differ from the opposite side. As ischemia progresses, enlargement, decreased or heterogeneous echogenicity, tunic thickening, and reactive fluid around the testis appear. These changes reflect edema and perfusion disturbance but do not reliably date the process.

The epididymis in torsion may be enlarged and altered, creating a diagnostic trap with epididymitis. Therefore, the key is not the fact of epididymal enlargement but its combination with blood flow asymmetry, testicular position, and cord condition.

Technical Pitfalls in Children

In children, intratesticular blood flow may be low amplitude, so Doppler requires careful adjustment. It is necessary to lower the threshold for displaying low velocities, adjust gain without excessive noise, minimize probe pressure, and compare identical zones of both testes. Power Doppler often helps with weak signals but is also dependent on movement and artifacts.

Only tunic or peripheral signals should not be compared: when torsion is suspected, intratesticular perfusion assessment is required. If an arterial signal is detected but venous is absent or the pattern is asymmetric, this should raise suspicion of early or incomplete torsion.

Differential Diagnosis

Main alternatives in acute pain are epididymitis, orchiepididymitis, torsion of the appendix testis, trauma, incarcerated inguinoscrotal hernia, acute complications of a mass. In inflammation, increased blood flow in the epididymis and/or testis is usually expected, whereas in complete torsion, there is an absence or sharp reduction of intratesticular flow. However, intermittent torsion after detorsion may mimic inflammatory hyperemia.

Torsion of the appendix testis is often accompanied by a localized painful structure at the upper pole of the testis and preserved perfusion of the testis itself. In trauma, the AIUM protocol also suggests evaluating the parenchyma, tunics, and blood flow, as hematoma or rupture may change management.

How to Write a Conclusion

The conclusion should be short and operationally useful. Mandatory elements: side, position, and size of the testis if necessary, echostructure, presence or absence of intratesticular blood flow, comparison with the other side, condition of the epididymis, tunics, and spermatic cord. If volume is measured, AIUM specifies the formula: length × width × height × 0.71.

In cases of high probability of torsion, the formulation should not be vague. It is optimal to state: "Ultrasound signs of right/left testicular torsion" or "picture suspicious for incomplete torsion." If there is no data at the time of examination, but the clinic is typical or the pain is paroxysmal, it should be clearly noted that preserved blood flow does not exclude intermittent torsion.

Key Takeaways for Practice

• The main Doppler finding in complete torsion is the absence of intratesticular blood flow compared to the contralateral side.
• Preserved blood flow does not exclude incomplete or intermittent torsion.
• The spermatic cord must be purposefully evaluated; spiral twisting of the cord strengthens the diagnosis.
• The protocol should include B-mode, color/power, and spectral Doppler set for low-velocity flow.
• The conclusion should immediately answer the clinical question: is there torsion, suspicion of torsion, or no ultrasound signs of torsion at the time of examination.