WK 4 L 2 Serous cystadenoma in a 34-year-old woman with a cyst. A, Transabdominal scan at 19 weeks shows a 10-cm left adnexal cyst (calipers), anechoic, with a thin wall. B, At 31 weeks, the cyst (calipers) increased in size to 13 cm. After delivery (not shown), the cyst was 15 cm. It was removed and found to be a benign serous cystadenoma.