Retrovascular hernia (Narath’s hernia) The hernial sac emerges from the abdomen within the femoral sheath but lies posteriorly to the femoral vein and artery, visible only if the hip is congenitally dislocated. Serafini's hernia The hernial sac emerges behind femoral vessels (E). Velpeau hernia The hernia sac lies in front of the femoral blood vessels in the groin (B).