Spiral artery of placenta: development and pathology-immunohistochemical, microscopical, and electron-microscopic study.

The spiral artery (=SA) is an important muscular artery, which controls the blood volume to the placenta. Preeclampsia is thought to be induced by the failure of the placenta by dysfunction of SA. To clarify the function of SA, we examined forty-eight placentae and its morphological and biological characteristics: 36 normal placentae and 12 placentae with preeclampsia. Gestational age of normal placentas was between 19 and 40 weeks and placentae with preeclampsia was between 31-36 weeks. The wall of the placental segment of SA by both light and electron microscope, and the wall width of SA and gestation age were compared each other. The wall of SA, with the invasion of trophoblast, was thin, but SA without trophoblasts was thick in width. At normal placenta, the diameter of SA was dilative constantly, but the width of the wall showed a tendency of getting thinning as advances. Ultrastructually, we found the trophoblast of thin wall of SA with dilated lumen. These ultrastructual alternations were consistence with the light microscopical findings. In preeclampsia, the lumen of SA between normal pregnancy and one with preeclampsia was almost same, but the wall width was thick, compared with normal pregnancy (P<0.05). We concluded that trophoblastic invasion control the functions of SA.