A common cause of a swollen, firm testicle is testicular torsion. Testicular torsion happens when the testicle twists obstructing usual blood flow. This occurs from strenuous physical activity or from being hit firmly in the scrotum. It also has a hereditary component. This requires emergency surgery. Seek immediate medical attention.
A thin layer of tissues surrounding the testicle can become swollen and firm once liquid. The liquid can be a response to such things as allergies, infections, tumors, or cancer.
Well, it may be a block from the testicle to the epidittimus. The epidittimus may have been unwrapped (so to speak) somehow and is uncloiled in the testicle. It may be cancer or a tumor. It is always wise to concult your doctor.
Nothing good! If it hurts go the emergency room and go to the doctor if not as soon as you can. It might be something minor but it could something as bad as cancer. Testiclur cancer is extreamly dangerous so please take this seriously. The chances are good that nothing is wrong but you never know.