Which ovarian tumor class often presents on ultrasound as a large unilocular or multilocular cyst?

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

Answer: (A)

When evaluating ovarian masses on ultrasound, a large cystic structure that is mostly unilocular or has thin internal septations with smooth, thin walls and mostly anechoic fluid is most characteristic of a serous cystadenoma. These tumors arise from the ovarian surface epithelium and commonly grow large while remaining predominantly cystic, often without solid components. The fluid is typically simple, giving a dark appearance, and the walls are thin unless the cyst becomes extremely large.

Dermoid cysts (mature cystic teratomas) usually contain fat and sometimes calcifications, leading to echogenic areas, shadows, and a Rokitansky nodule rather than a simple cystic appearance. Endometriomas tend to have a homogeneous “ground-glass” or low-level echogenic texture within the ovary and are not typically large, unilocular simple cysts. Fibromas are solid, appearing hypoechoic with possible posterior shadowing, not cystic.

So the described ultrasound pattern—large cystic structure with unilocular or mildly multilocular configuration and thin walls with simple fluid—fits serous cystadenoma best.