The term hydrocele refers to a collection of serous fluid in the scrotal sac between the two layers of the tunica vaginalis. The cavity is lined by mesothelium. Congenital hydrocele reflects a patent processus vaginalis testis or its incomplete obliteration. It is the most common cause of scrotal swelling in infants and is often associated with inguinal hernia. Acquired hydrocele in adults is secondary to some other disease affecting the scrotum, such as infection, tumor, or trauma. The diagnosis may be made by ultrasound examination or by transilluminating the fluid in the cavity. Hematocele (choice B) is caused by an accumulation of blood between the layers of tunica vaginalis. It may develop after trauma or hemorrhage into hydrocele. Testicular tumors and infections may also lead to a hematocele. Spermatocele (choice D) contains milky fluid and does not occur in this age group.Diagnosis: Congenital hydrocele