Spermatocele: Retention cyst of rete testis or epididymis containing nonviable spermatozoa

Epididymal head cyst: Collection of simple fluid

Spermatoceles may contain linear septations and internal debris; low-level echoes due to spermatozoa

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  Falling snow sign: Mechanically moving particulate material within cyst due to acoustic radiation force from color Doppler

Epididymal head cysts are anechoic, thin walled, and avascular

Etiology: Unknown, may reflect scarring secondary to either epididymitis, trauma, or vasectomy

Associated abnormalities: Dilation of rete testis within mediastinum of testis

Most common signs/symptoms: Painless scrotal mass

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  Rare hypofertility or torsion

Treatment: Most can be observed if asymptomatic

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  Surgery (spermatocelectomy) only if sufficiently large to cause discomfort

Cystic extratesticular lesions almost always benign; if no vascularized soft tissue elements, not neoplasm

Look for acoustic streaming of nonviable spermatazoa in spermatoceles with both grayscale and color or power Doppler to elicit falling snow sign