Which is the second most common benign ovarian neoplasm and tends to present as a rapidly enlarging pelvic mass with a large unilocular or multilocular anechoic appearance?

• A. Serous cystadenoma
• B. Mucinous cystadenoma
• C. Dermoid cyst
• D. Fibroma

Answer: (A)

Serous cystadenoma is a common benign ovarian neoplasm that often presents as a rapidly enlarging pelvic mass. On ultrasound it appears as a large cystic structure with a thin wall and predominantly anechoic fluid, which can be unilocular or have a few thin septations. This simple, fluid-filled appearance matches the typical imaging pattern for serous cystadenoma and helps distinguish it from other ovarian tumors: dermoid cysts usually have mixed echogenicity with fat and calcifications; fibromas are solid and hypoechoic; mucinous cystadenomas tend to be even larger and more multilocular with varying internal echoes due to mucus.