So a pregnant patient with multi-cystic mass present in the uterine cavity (no gestation identified).

Answer: Complete hydatidiform mole (aka complete molar pregnancy)

There are two types of moles , complete (no fetus) or incomplete (normal or abnormal fetus present). But don’t forget this is part of a larger spectrum of gestational trophoblastic disease which also includes invasive moles and choriocarcinoma (yes there are very rare placental site trophoblastic tumors and epitheloid trophoblastic tumors but if you maybe better off forgetting those). ALWAYS look for myometrial invasion!

reference: https://radiopaedia.org/articles/gestational-trophoblastic-disease