Dancing megasperm is defined as the sonographic finding of moving, hyperechoic particles within cystic dilatations of an enlarged epididymis in a patient with spermatic duct obstruction.
The particles most likely represent clusters of agglutinated spermatozoa. Oscillating movement of the particles is attributed to the turbulence within an acoustic medium on ultrasound.
These findings were first described as filarial dance in men affected with lymphatic filariasis.