The differential diagnoses include Corpus luteum cyst, hypereactio luteinalis, and pregnancy luteoma. All these entities related to high level HCG or pregnancy and none of them are true neoplasm. Which one matching to this case depends on the size, solitary or multicystic and clinical manifestations. Regardless, they are often incidental finding, especially during C-section procedure. Morphologically one important differential malignancy in your mind when you see the picture shown above is to rule out granulosa cell tumor, especially the cystic variant of GCT.

 囊状白体。

黄素化得间质细胞。

不有趣啊！