If it is truly a cyst, then it is likely either a hydrocele or an epididymal cyst (larger ones are called "spermatoceles"). Since it sounds like it is high in the scrotum, it's more likely an epididymal cyst. Hydroceles are fluid collections in a space around the testicle called the tunica vaginalis. Epididymal cysts are located above the testicle and feel separate from the testicle (whereas hydrocoeles will be around or directly adjacent to the testicle). Both of these are benign and treatment is usually conservative if they're not causing symptoms. The other possibility is an inguinal hernia which is an outpouching of the abdominal cavity into the scrotum. These are made larger by bearing down (like you're having a bowel movement) and can be painful. Hope this helps.
Ok, that does change things. So it's behind the scrotum. Does it feel like it's fixed to the skin or to the "tube" or neither? Is it directly in the middle or off to one side? Does it compress or is it more solid?
Have you had any problems with urination? Specifically blood in your urine or dribbling?
It sounds like a urologist is what you need. The fact that it is not attached to the skin makes an epidermal inclusion cyst (or sebaceous cyst) less likely. It sounds like it may be arising from the urethra or the adjacent glands. There are a few possibilities: It could be a syringocele, which is a cyst that forms as a result of blockage of the duct of your Cowper's gland (sometimes called the bulbourethral gland). This is fairly uncommon but seems to fit your description. The other options are downright rare: A urethral diverticulum is possible, though rare in men. That is an outpouching of the urethra that can often get infected or cause bleeding. It could also be a tumor of the Cowper's gland but those are very rare. I'm not sure if this information is helpful, but in the end, it doesn't sound like anything serious.
Sarcomas are malignant tumors of soft tissues (muscle, fat, fibrous tissue, etc). Liposarcomas are malignant tumors of fat cells. Liposarcomas in the skin do very well compared with liposarcomas in other locations. So if you find grim information online, realize that the poor prognosis associated with liposarcomas is limited to deep tissue or intraabdominal locations. If completely excised, the recurrence rate for liposarcs in the skin is very low. The other possibility (which is more likely than a liposarc) is a lipoma, which is the benign equivalent of liposarcoma. I can't quote you any probabilities because liposarcomas are so rare in this location, but your urologist is correct in that excision is usually curative. Hope this helps. You don't need to pay again, just let me know what it turns out to be.