The “falling snow” sign

Excerpt

Spermatoceles and epididymal cysts are the most commonly encountered extratesticular cystic lesions. On ultrasound, they may be difficult to differentiate from one another as they both can present as thin-walled, well-defined anechoic lesions with posterior acoustic enhancement arising from the epididymis. Spermatoceles can be distinguished from epididymal cysts when the lesion demonstrates fine, low-level internal echoes with associated “falling snow” sign [1, 2]. The “falling snow” sign describes the movement of the low-level echoes within the spermatocele away from the transducer during power or color Doppler ultrasound evaluation (Fig. 1a, b), mimicking falling snow as can be seen in a snow globe (Fig. 2). High-intensity ultrasonic waves emitted by Doppler ultrasound mechanically move the particulate material within the lesion, a phenomenon known as acoustic streaming [3]. Acoustic streaming is not only encountered in spermatoceles but has also been described in other cystic lesions that contain low-level internal echoes, including ovarian cystic lesions, breast cysts, hydroceles, and cystic thyroid lesions [4].

…