Johannes Operation: I need to go for an operation and dont have the funds to do so. A hydrocele is usually diagnosed by an exam of the scrotum, which may appear enlarged. As part of the exam, your doctor will shine a light behind each testicle (transillumination). This is to check for solid masses that may be caused by other problems, such as cancer of the testicle. Hydroceles are filled with fluid, so light will shine through them (transillumination). Light will not pass through solid masses that may be caused by other problems, such as cancer of the testicle. An ultrasound may be used to confirm the diagnosis of a hydrocele.