1Department of Clinical Laboratory, Koshigaya City Hospital, 2Department of Obstetrics and gynecology, Koshigaya City Hospital, 3Department of Obstetrics and Gynecology, Taketani Hospital, 4Department of Obstetrics and Gynecology, Juntendo University School of Medicine
Ultrasound, Human yolk sac, Pathology, Fetus, Embryology
Eighty four pregnant women between 5 and 14 weeks of gestation were examined with an ultrasonic real time scanner and in 23 caces yolk sacs were examined microscopically, which were acquired at artificial abortion. Macroscopically, the yolk sac was found as a round, translucent cyst in the chorionic cavity. This cavity was outside of the amniotic sac which contained the amniotic fluid and the fetus. The yolk sac was demonstrated as a small circular structure on the ultrasonic picture between 5-12 weeks of gestation and mean diameters of yolk sac were 5.0 mm (6 w), 5.6 mm (7 w), 6.1 mm (8 w), 7.2 mm (9 w), 7.0 mm (10 w) and 7.0 mm (11 w) at each gestational week. At the gestation age less than 5 weeks and greater than 12 weeks, the yolk sac was not visualized. Ultrasonic image of yolk sac tended to be most echogenic at 8-9 weeks of gestation among various weeks of gestation. These ultrasonic findings corresponded to the pathological findings; the wall of yolk sac was consisted of endodermal cell layer, mesenchyme and mesothelial cell layer, became thicker in 8-9 weeks of gestation and became thinner then vanished afterward.