What Is the Epididymis?
The epididymis is a tightly coiled tube that sits along the back of each testicle and is where sperm mature and are stored before they enter the vas deferens.
If you uncoiled it, the epididymis would stretch to roughly 6 meters (about 20 feet), folded down into a structure only a few centimeters long. Anatomists divide it into three parts: the head (caput), which connects to the testicle through small ducts; the body (corpus), which runs down the back of the testicle; and the tail (cauda), which curves up and becomes the vas deferens at its lower end.
Sperm leave the testicle immature. They cannot swim and they cannot fertilize an egg. As they travel through the head, body, and tail of the epididymis over roughly 2 to 3 weeks, they gain motility and the surface changes that let them fertilize. The tail of the epididymis is also the main storage reservoir. When you ejaculate, mature sperm move from the tail into the vas deferens, then up to the urethra.
A vasectomy does not touch the epididymis directly. The cut is made on the vas deferens, downstream. But the epididymis is the structure where things back up after the procedure, which is what creates one of the most common post-vasectomy issues.
When this matters
For someone who has had or is considering a vasectomy:
- Congestive epididymitis. After a vasectomy, sperm still pour into the epididymis from the testicle, but they have nowhere to go. They are reabsorbed by the body, but the backup can cause inflammation in the epididymis (often called congestive epididymitis). It usually shows up as a dull ache and tender swelling behind the testicle in the first weeks or months. Most cases resolve with ibuprofen, ice, and support. See congestive epididymitis after vasectomy.
- Sperm granuloma. A small lump can form at the cut end of the vas where sperm leak into surrounding tissue. This is not in the epididymis itself, but it is related to the same backup pressure and is usually harmless.
- Vasoepididymostomy. When a vasectomy reversal cannot be done by reconnecting the vas directly (because of blockage or damage upstream in the epididymis), the surgeon bypasses the blockage by connecting the vas to the epididymis itself. That procedure is called a vasoepididymostomy, and it is technically harder than a standard reversal.
- The epididymis is not the testicle. Pain or swelling “behind the testicle” is usually the epididymis. Pain “in” the testicle is a different conversation and warrants a call to the urologist.
Related terms
Sources
- American Urological Association Vasectomy Guideline
- Cleveland Clinic: Vasectomy
- Mayo Clinic: Vasectomy
Editorial and informational. Not medical advice. Read the full disclaimer.
