In this affection there is a cyst having in many cases much the external appearance of hydrocele, but containing a fluid in which spermatozoa are abundantly present. In other respects also the condition differs from that in hydrocele, for we have here not merely an accumulation in an existing sac, but a proper new-formed cyst. Hence the name Encysted Hydrocele is often used as equivalent to spermatocele. The cyst is most frequently single, but there may be several or many.

The cyst arises in connection with the epididymis for the most part, and probably takes origin in one or more aberrant tubules which have formed blind diverticula from the seminal tubules. It usually arises near the upper end of the epididymis, but it may be at the lower end or from the rete testis. The cysts grow often to a large size, and they sometimes push themselves into the sac of the tunica vaginalis, inverting one layer of the wall against the other. As a rule, the tunica vaginalis is found below and in front of the cyst, this position being connected with the origin of the cyst in the neighbourhood of the epididymis.

The fluid from these cysts has a peculiar opalescent appearance, which is due to the presence of multitudes of lively spermatozoa. The existence of these shows that the cyst has retained its connection with the seminal tubules. The cyst is usually lined with a ciliated epithelium, but in large ones the pressure of the fluid may cause these cells to assume the pavemented form.

It will be observed that the spermatic cysts are comparable in their origin to the parovarian cysts.

Other forms of hydrocele have been described, but they require only a passing notice. There may be an encysted hydrocele without spermatozoa in the fluid. Then there is encysted hydrocele of the cord, sometimes arising by a portion of the communication between the tunica vaginalis and the peritoneum remaining unobliterated and becoming the seat of an accumulation of fluid. There is also diffused hydrocele of the cord, in which there is an oedematous condition of the connective tissue around the spermatic cord. There may even be a hydrocele from a hernial sac, which has got emptied of its contents and shut off from the peritoneum by adhesion of the neck.