Final answer:
The correct medical diagnosis for an adolescent with fluid in the tunica vaginalis of his testes is hydrocele. It is essential to distinguish this condition from other disorders such as cryptorchidism and orchitis, and a biopsy may be performed if testicular cancer is suspected.
Step-by-step explanation:
An adolescent with a collection of fluid in the tunica vaginalis of his testes would receive the medical diagnosis of hydrocele. Hydrocele is a condition where there is an accumulation of serous fluid in the space between the layers of the tunica vaginalis, the serous membrane that covers the testes. This is different from cryptorchidism, where the testes fail to descend into the scrotum; orchitis, an inflammation of the testicle; and prostatism, which pertains to issues with the prostate gland. If the healthcare provider suspects underlying issues like testicular cancer, a biopsy may be important for accurate diagnosis. Disorders such as epididymitis and prostate cancer can also affect the male reproductive system, but they have distinctive symptoms and causes that differentiate them from hydrocele.