n. the operation of joining the vas deferens to the epididymis in a side-to-side manner in order to bypass an obstruction to the passage of sperm from the testis. The obstruction, which may be congenital or acquired, is usually present in the mid-portion or tail of the epididymis. Vaso-epididymostomy is therefore usually performed by anastomosing the head of the epididymis to a longitudinal incision in the lumen of the adjacent vas.