A spermatocele is a cyst that develops in the spermatic duct (vas deferens), the tube that carries sperm away from the testicle. The most common location for these cysts is within the epididymis, a coiled section of the duct that is attached to the bottom of the testicle. Smaller cysts are often called epididymal cysts, while larger ones are called spermatoceles.

The term spermatocele comes from the fact that these cysts are often filled with sperm. It's not clear what causes these cysts to form, but they are often found in middle-aged men.

While any lump on the testicle should raise concern, spermatoceles and epididymal cysts are always benign (noncancerous). Despite the name, there is no evidence that having sex will cause spermatoceles to enlarge. In fact, it's unusual for these cysts to change over time.

While spermatoceles can occasionally cause discomfort, it's rare that they need treatment or removal.