context: They may be rare, but testicular diseases can be life-threatening. Here's how to recognize them. Happily, significant testicular disease is uncommon and usually not serious. But if you have any testicular pain or a change in your testicles -- such as a lump or a firmness -- call your doctor. Even if you're embarrassed, delaying an evaluation is not worth the risk. As you might guess, testicular cancer is the most serious form of testicular disease. It's also the most common cancer in men ages 18 to 35, accounting for 1% of cancer in men in the U. S. It is usually curable. Risk factors for testicular cancer include: previous history of testicular cancer undescended testicle as a child a close relative with testicular cancer More common than testicular cancer is epididymitis, which is inflammation of the epididymis, a tubular structure next to the testicle where sperm mature. About 600,000 men get it each year, most commonly between ages 19 and 35. Unprotected sex or having multiple sex partners increases the risk of infectious epididymitis. As many as one out of every five men has varicocele, which refers to swollen and dilated veins above the testicles (not unlike varicose veins), a condition that is usually benign. Hydroceles, which come from increased fluid around the testicle, also pose little risk. Testicular disease can take a variety of forms: Testicular cancer. Like any cancer, testicular cancer happens when cells in the testicle develop mutations that cause them to "misbehave." The cells may multiply recklessly and invade areas where they don't belong. In testicular cancer, this process usually creates a slow-growing painless lump or firmness in one testicle. In most cases, the man himself discovers it at an early stage. If a man gets medical attention early on, testicular cancer is almost always curable. Testicular torsion. " Torsion" means twisting -- and for a testicle, that's not a good thing. When testicular torsion occurs, the twisting kinks -- like a garden hose -- and blocks the blood vessels to one testicle. Certain men have a developmental problem that makes them susceptible to testicular torsion. Although testicular torsion is rare, it is an emergency. Sudden testicular pain demands an immediate trip to the emergency room. If treatment is delayed, the testicle can die. Torsion is most common during puberty - between ages 10 and 15 -- so it's important to let young teens know that any pain should be reported, even if they are embarrassed to say so. Epididymitis. The epididymis is a long, coiled tube that sits alongside the testicle. Its job is to store sperm while they mature. Epididymitis occurs when the epididymis become inflamed or infected. Sometimes, this is a sexually transmitted infection. More often, epididymitis comes from injury, a buildup of pressure such as after a vasectomy, or from urine backwashing into the tubules during heavy lifting or straining. Epididymitis can cause symptoms ranging from mild irritation to severe testicle pain, swelling, and fever. Varicocele. Varicocele is a dilation of the veins above the testicle and is usually harmless. Occasionally, however, varicoceles can impair fertility or cause mild to moderate pain. If you have a bulge above your testicle, especially when you're standing or "bearing down," you should have a doctor examine you. Hydrocele. Hydrocele refers to a fluid collection surrounding the testicle and is usually benign. But if it is large enough, it can cause pain or pressure. Though men can develop a hydrocele after injury, the majority of men with hydroceles have no obvious trauma or known cause. Orchitis. Orchitis is an inflammation of one or both testicles caused by infection or the mumps. It can also be caused by STDs like gonorrhea and chlamydia. There is no proven way to prevent testicular cancer. This is why early detection is so important. Experts recommend that all young men perform a testicular self-exam monthly. There also is no recommended method to prevent varicoceles, hydroceles, or testicular torsion. Epididymitis can sometimes be prevented by practicing safe sex and avoiding heavy lifting or straining with a full bladder. Testicular cancer is treated according to the type of cancer and how far it has spread. Cancer that has not spread from the testicle can be cured by orchiectomy, a surgery to remove the testicle. If it has spread outside the testicle testicular cancer treatments may include surgery to remove the abdominal lymph nodes, chemotherapy, radiation therapy, or a combination of the three. Testicular cancer is one of the most curable cancers. Even after it has spread, testicular cancer is usually curable. The best chances for cure are when the cancer is detected and treated early. Epididymitis is usually treated successfully with antibiotics and anti-inflammatory drugs. Bed rest, pain medications, using an athletic supporter and ice packs on the scrotum may help more severe cases. The pain can resolve very slowly, sometimes taking weeks or months. Testicular torsion is a true medical emergency. If caught in time, the affected testicle can be saved. Emergency surgery is usually required to "untwist" the testicle and to prevent it from happening again. During the surgery, the other side is usually fixed, as the condition tends to be bilateral. Varicoceles usually don't require treatment. But for men with varicoceles and impaired fertility, microsurgery to tie off the dilated veins of the varicocele is effective. Varicoceles can also be corrected without surgery by injecting a tiny coil into the abnormal veins. If a hydrocele is very large or causing pain, surgery can usually correct it. Injecting a special material through the scrotal wall can sometimes fix hydroceles without surgery. Hernias are sometimes mistaken for testicular disease. When a lower part of the abdominal wall muscles are weak, part of the intestine can bulge through it. When the intestine pushes into the scrotum, it's called an inguinal hernia -- although the scrotum swells, and it can appear to be a testicular problem. The solution is surgery to fix the weak part of the abdominal wall.