Ultrasound of the Acute Scrotum

Phebe Chen, MD, Susan John, MD

Disclosures

Appl Radiol. 2006;35(3):8-17. 

In This Article

Testicular Torsion

Torsion occurs most frequently in adolescent boys with an incidence of 1 in 160 by age 25. Two thirds of cases occur between 12 and 18 years of age.[5] Up to 70% of young boys with acute scrotal symptoms have conditions other than torsion -- most commonly epididymitis. Ultrasound is helpful to differentiate testicular torsion from other causes of acute scrotal pain and to identify testicular torsion promptly, ensuring the highest salvage rate. The severity of torsion of the testis can range from 180˚ to 720˚, but complete occlusion of blood flow does not occur until 450˚ of torsion.[4] Transient or intermittent torsion with spontaneous resolution sometimes occurs. Venous congestion progresses to arterial occlusion, testicular ischemia, and infarction. The collateral blood flow is typically not adequate to provide viability to the testicle if the testicular artery is occluded.[5]

Testicular torsion can be classified as extravaginal or intravaginal. Extravaginal torsion occurs in utero or perinatally before the testis is fixed, so the torsion occurs proximal to attachment of the tunica vaginalis, in the inguinal canal or just below it.[5] This form of torsion is found exclusively in newborn infants. Intravaginal torsion is more common and is due to a bell-and-clapper deformity in which the tunica vaginalis has an abnormally high insertion on the spermatic cord and completely encircles the testis, leaving the testis free to rotate within the tunica vaginalis.[3,5] The deformity is bilateral in most cases.[4] Intravaginal torsion may also occur in testes that are retractile or are not fully descended. Blunt trauma, sudden forceful rotation of the body, or sudden exertion also predispose to testicular torsion.

The sonographic appearance of testicular torsion depends on the duration of the torsion. Within 6 hours, the affected testis may be slightly enlarged, with normal or decreased echogenicity (Figure 4A). After 24 hours (late or missed torsion), echogenicity of the testis becomes heterogeneous, a sign of loss of viability.[3,5] The epididymal head may be enlarged because of involvement of the deferential artery. Hydroceles are common.[4,7] Spiral twisting of the spermatic cord may be seen with color Doppler imaging. Normal testicular echogenicity and lack of scrotal wall thickening or hydrocele are strong predictors of testicular viability.[4] Color Doppler imaging provides both structural and physiologic information about the vascular integrity of the testis. Doppler flow may be difficult to demonstrate in young children, even within the normal testis.[3] Unilateral diminished or absent flow is the most accurate sign of testicular torsion (Figure 4B), but the presence of blood flow does not exclude torsion.[7] False-negative studies may occur when torsion is intermittent or low grade. The torsion may result in hyperemia, mimicking epididymo-orchitis. Late torsion may be accompanied by peripheral blood flow, but central testicular blood flow will be absent. Intravenous microbubble contrast material may improve US sensitivity but is not routinely available. There are a few advocates of manual detorsion of the twisted testis under narcotic analgesia, but it is yet unclear whether this maneuver increases the salvage rate in torsion.

Acute testicular torsion. (A) The affected testicle is more hypoechoic because of the edema and venous and lymphatic obstruction. (B) No flow was identified on color Doppler imaging.

Acute testicular torsion. (A) The affected testicle is more hypoechoic because of the edema and venous and lymphatic obstruction. (B) No flow was identified on color Doppler imaging.

Torsion of the testicular appendages occurs less frequently than does testicular torsion (6:1) but can be as painful. Sonography is important for distinguishing this condition, which is self-limiting and does not threaten testicular viability. Clinically, the cremasteric reflex is preserved and a palpable nodule with bluish discoloration (blue dot) is often detected. Approximately 91% to 95% of cases involve the appendix testis in boys 7 to 14 years of age.Ultrasound shows a hyperechoic mass with central hypoechoic area adjacent to the testis or epididymis. Other associated findings include scrotal wall edema and epididymal enlargement. Blood flow in the peritesticular structures may be increased. Ultrasound is helpful to exclude testicular torsion, because blood flow within the testis is normal in torsion of the appendix testis. Torsed appendages may atrophy and calcify.[4]Occasionally, in infants, calcified meconium from an in utero intestinal perforation can descend into the scrotum, mimicking the hard mass of an infarcted testis. Segmental testicular infarction can occur in the absence of torsion, resulting from trauma, vasculitis (Figure 5), or tumor.

Acute trauma. Note the geographic area of abnormal hypoechogenicity within the testicle due to ischemia following direct trauma to the testicle.

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