That extra lump in your scrotum is almost certainly not a third testicle. In the vast majority of cases, what feels like an additional ball-shaped mass is a fluid-filled cyst, a loop of intestine from a hernia, or a swelling in the tube that sits behind the testicle. Most of these causes are benign and painless, but a few require prompt attention, so understanding the differences matters.
The Most Likely Cause: A Spermatocele
A spermatocele is a fluid-filled sac that develops in the epididymis, the small coiled tube that sits on top of and behind each testicle. Because it forms right next to the testicle and can grow to a noticeable size, it often feels like a separate, round mass, giving the impression of a third testicle. Spermatoceles are benign, typically painless, and extremely common. You might notice a sense of fullness behind and above the testicle, or you might feel a smooth, movable lump that’s clearly separate from the testicle itself.
Most spermatoceles are discovered by accident during a self-exam or a routine physical. They don’t interfere with fertility or hormone production, and they rarely need treatment unless they grow large enough to cause discomfort. If one is bothering you, a urologist can discuss options, but many people live with them indefinitely without any problems.
Inguinal Hernia: A Bulge That Changes Size
An inguinal hernia happens when a loop of intestine or fatty tissue pushes through a weak spot in the abdominal wall and slides down into the groin or scrotum. This can create a soft, bulging mass next to or around the testicle that feels like an extra structure in the scrotum.
The telltale sign of a hernia is that the lump changes. It may get larger when you stand, cough, or strain, and shrink or disappear entirely when you lie down. You might also feel a dragging or aching sensation in the groin, especially after standing for long periods. Hernias don’t resolve on their own and typically require surgical repair, but they’re rarely an emergency unless the tissue becomes trapped (a situation that causes sudden, severe pain and requires immediate care).
Other Benign Lumps and Swellings
Several other harmless conditions can create a mass that mimics a third testicle:
- Epididymal cyst: Very similar to a spermatocele but filled with clear fluid rather than sperm-containing fluid. It feels like a small, smooth, movable lump near the top of the testicle.
- Varicocele: A cluster of enlarged veins inside the scrotum, sometimes described as feeling like a “bag of worms.” Varicoceles are more prominent when standing and tend to occur on the left side.
- Hydrocele: A collection of fluid surrounding the testicle that makes the entire side of the scrotum feel swollen and heavy. Rather than a distinct third lump, a hydrocele usually makes one side noticeably larger than the other.
- Lipoma: A painless, soft fatty lump that can develop in the spermatic cord. These are benign and slow-growing.
Could It Actually Be a Third Testicle?
Technically, yes, but it’s extraordinarily rare. The medical term is polyorchidism, and a 2022 systematic review in the Journal of Clinical Medicine found only about 231 cases documented in the medical literature over a 90-year span. About 76% of supernumerary testicles are located inside the scrotum, which means they can feel like a normal (if unexpected) third testicle. Most cases are discovered incidentally during imaging for something else. Polyorchidism itself isn’t dangerous, though the extra testicle carries a slightly elevated risk of other conditions that warrant monitoring.
When the Lump Needs Urgent Attention
Most scrotal lumps are benign, but a hard, painless mass that feels fixed to the testicle (rather than floating freely next to it) is treated seriously. The American Urological Association’s clinical guidelines state that any solid mass in the testicle identified by exam or imaging should be managed as potentially malignant until proven otherwise. That sounds alarming, but it reflects a “better safe than sorry” approach. Testicular cancer is highly treatable, especially when caught early.
A few characteristics distinguish a worrisome lump from a harmless one. Benign cysts tend to feel smooth, soft, and movable, sitting above or behind the testicle. A concerning mass is more likely to feel hard, irregular, and attached to the testicle itself. That said, you can’t reliably tell the difference through touch alone, which is why imaging is the standard next step.
Sudden, severe pain is a different kind of emergency. Testicular torsion, where the testicle twists on its blood supply, causes abrupt, intense pain and requires surgery within hours to save the testicle. This is distinct from epididymitis (an infection of the epididymis), which tends to develop gradually over days with increasing soreness, swelling, and sometimes fever. If pain comes on suddenly and severely, that warrants an emergency visit.
What Happens When You Get It Checked
A doctor will start with a physical exam, asking you to stand and cough to check for hernias, and feeling the mass to assess its size, texture, and position relative to the testicle. In most cases, the next step is a scrotal ultrasound with Doppler, a painless imaging test that uses sound waves to distinguish between solid and fluid-filled masses and evaluate blood flow. Studies show ultrasound has about 95% sensitivity for detecting testicular tumors, making it a reliable first-line tool.
If the ultrasound shows a simple cyst or spermatocele, you’ll likely need no further workup. If it reveals a solid mass, your doctor will order blood tests to check specific tumor markers before deciding on next steps. For hernias, the diagnosis is often made on physical exam alone, though imaging can confirm it when the findings are unclear.
The bottom line: finding what feels like a third testicle is usually a benign cyst or hernia, and a quick ultrasound can give you a definitive answer. It’s worth getting checked, not because the odds of something serious are high, but because the process is simple and the peace of mind is immediate.