Hernia sac is a pathologic condition that refers to the prolapsed abdominal wall layer; sheath is a normal physiologic tissue, a membranous structure that encases the testis and spermatic cord. A hernia is a prolapse of abdominal contents and consists of a hernia ring, hernia sac, hernia capsule, and hernia contents; the hernia sac and is the prolapsed abdominal wall layer. The normal abdominal wall is usually not prolapsed, so the hernia sac is a pathological condition. On the surface of the testes, epididymis and spermatic cord, there is a membranous structure called the sheath, which normally contains a small amount of fluid that can be absorbed through the veins or lymphatic vessels. When there is some pathology that causes the fluid to increase, it becomes a pathological condition known as syringomyelia.