The epididymis is actually a six meter long thin tube that is rolled into a ball and attached to the testicle, and the continuation of the epididymis is the vas deferens. The lumen of the duct is very thin, but the wall of the duct has very thick muscles. It is responsible for transmitting the sperm from the testes to the urethra. Why it is so long, no one knows, but I guess it is to let the fastest running sperm win. The epididymis comes from the mesonephros (middle kidney) during embryonic development. Most of the mesonephros disappear automatically, but some of the tubes that do not disappear can evolve into an epididymal cyst. If this cyst contains sperm by the time you reach puberty, it is called a seminal cyst. The diagnosis can be confirmed by ultrasound. Some cysts are single, and some are multicystic. The latter feels like a bunch of grapes to the touch. If there are no symptoms, it can be observed. If there are symptoms, pain, and it gets bigger, then removal should be considered. The surgery is a same-day procedure and some patients will have temporary edema after surgery. Damage to the vas deferens or the epididymis itself should be avoided as much as possible.