Magnetic Resonance Imaging
Findings
Limited information is available on the potential role of MRI in the diagnosis of acute testicular torsion. Findings from small studies to date suggest a high degree of accuracy with MRI, particularly when it is performed with contrast enhancement. These finding are corroborated by results of controlled animal models. In addition, phosphorus-31 magnetic resonance spectroscopy can demonstrate rapidly decreasing levels of adenosine triphosphate (ATP) associated with ischemia.
Degree of Confidence
To our knowledge, no adequate, controlled clinical trials have been performed to assess the degree of confidence with MRI as a diagnostic tool for testicular torsion. However, if the torsion knot or whirlpool patterns are recognized in conjunction with testicular enlargement and absent vascularity, the diagnosis is virtually certain.
Ultrasonography
Testicular torsion. Transverse color Doppler image of both testes demonstrates enlargement, slightly decreased echogenicity, and absent flow on the left side.
Transverse power Doppler image of both testes again illustrates an enlarged, avascular left testicle.
Testicular torsion. Epididymo-orchitis. Longitudinal color Doppler image of the left testis shows diffuse, markedly increased vascularity.
Testicular torsion. Epididymo-orchitis. Transverse color Doppler image demonstrates increased epididymal flow and a hydrocele.
Testicular torsion. Testicular tumor. Transverse color Doppler image displays a hypervascular mass in the periphery of the testis.
Findings
On normal gray-scale and color Doppler images, the testes are homogeneous and symmetric in echotexture, as shown on straddle views. The testes are relatively symmetric in size, but the normal range varies widely. On color or power Doppler sonogram, flow to the testes and epididymis should be symmetric. However, flow may be difficult to visualize in young patients. In patients with torsion, gray-scale images may show testicular enlargement due to engorgement; uniformly hypoechoic testicle (early); heterogenous, hypoechoic texture, which indicates necrosis and nonviability; echogenic areas inside the infarcted testis, which may represent hemorrhage; twisting of swollen cord, which gives the appearance of a torsion knot (an echogenic or complex extratesticular mass); or in infarcted testis, tunica albuginea and mediastinum, which have increased echogenicity (ie, target sign, which is more common in neonatal torsion).
Color and/or power Doppler imaging should be performed in all cases. Flow to the affected testicle is absent, although normal or increased flow may be seen with spontaneous detorsion. The symptomatic side should be compared with the asymptomatic side by using the straddle view obtained with optimal technical settings.
Epididymitis is visualized as an enlarged, hyperemic epididymis, usually with a diffusely affected area.20,21 Involvement of the testis also produces enlargement and increased vascularity. A scrotal abscess, whether intratesticular or extratesticular, is typically seen as a complex fluid collection, often with a vascular capsule. Torsion of the epididymal appendage is easily recognized as a mass adjacent to the epididymal head without flow; this mass does not affect the testicular vasculature. Finally, an intratesticular hematoma may mimic a necrotic testis, but it typically has normal surrounding blood flow. An extratesticular hematoma appears as a complex, cystic collection clearly separate from but possibly displacing the testis.
Degree of Confidence
An absence of flow in a symptomatic, enlarged testicle, with flow demonstrated in the contralateral testicle, is highly specific. Power Doppler and color Doppler imaging should be used together in prepubertal boys, but it demonstrates flow in only 79-90% of normal cases.22,23,24 Color Doppler and power Doppler sonography both demonstrate flow in almost 100% of postpubertal patients.25 Color Doppler and power Doppler imaging have similar sensitivities for demonstrating flow in small testes, although the combination of the 2 techniques has a sensitivity that exceeds the sensitivity of each alone. Overall, the specificity is 77-100%, and the sensitivity is 86-100%.
False Positives/Negatives
Posttorsion hyperemia may be confused with epididymo-orchitis, producing a false-negative finding. Capsular blood flow must be distinguished from intratesticular arterial flow; these observations may produce false-negative results. Although flow may be visible in one testis and is usually evident in the other, false-positive findings are possible in the young child. Technical factors (eg, erroneous flow settings, motion artifacts on power Doppler images) may produce false-positive or false-negative results.
A scrotal abscess may cause a false-positive diagnosis of torsion because of the depiction of hyperemia surrounding a fluid core. Ultrasonography can be used to distinguish abscess from testicular torsion because of its combination of characteristic imaging and flow dynamics.26
Nuclear Imaging
Findings
Technetium-99m pertechnetate is the agent of choice, with an adult dose of 10-20 mCi and a pediatric dose of at least 5 mCi. Typically, immediate radionuclide angiograms are obtained, with subsequent static images as well. In the healthy patient, images show symmetric flow to the testes, and delayed images show uniformly symmetric activity.
The appearance of testicular torsion on scintigraphy depends upon the chronicity. In acute torsion (usually <7 h), blood flow may range from normal to absent on the involved side, and a nubbin sign may be visible. The nubbin sign is a focal medial projection from the iliac artery representing reactive increased flow in the spermatic cord vessels terminating at the site of torsion. (This sign can also be seen in later stages.) Static images demonstrate a photopenic area in the involved testis. In the subacute and late phases of torsion (missed torsion), there is often increased flow to the affected hemiscrotum via the pudendal artery with a photopenic testis and a rim of surrounding increased activity on static images. This has been called a rim, doughnut, or bull's-eye sign.
Acute epididymitis generally appears as an area of focal or diffuse increased activity in the involved hemiscrotum. Testicular appendix torsion has a variable appearance: it may have a normal scan or a focal area of increased or decreased activity. An abscess, tumor, or hematoma may be indistinguishable from a torsed testicle, demonstrating a hyperemic rim surrounding an area of decreased activity.
Degree of Confidence
Scintigraphy has a sensitivity of 90% and a specificity of 60% in the diagnosis of testicular torsion. Color Doppler ultrasonography has distinct advantages in diagnosing nonvascular causes of acute scrotum. Scintigraphy may be more sensitive in the neonatal period than at other times because of the difficulty in detecting flow by means of Doppler imaging. Scrotal scintigraphy may be more sensitive than color or power Doppler imaging to the presence or absence of flow in the prepubescent testicle.
False Positives/Negatives
An abscess, tumor, or hematoma may produce false-positive findings (rim sign). A hyperemic epididymis may be misinterpreted as a halo, producing false-positive study. Most false-negative studies are due to technical reasons or interpretative errors.
More on Testicular Torsion |
| Overview: Testicular Torsion |
 Imaging: Testicular Torsion |
| Follow-up: Testicular Torsion |
| Multimedia: Testicular Torsion |
| References |
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Further Reading
Keywords
torsion of the spermatic cord, spermatic cord torsion, extravaginal torsion, intravaginal torsion, torsed testis, torsed testes, torsed testicles, retorsion, detorsion
