What is the differential diagnosis of a complex adnexal mass?

CHEETAH 

Cystadenoma or Cystadenocarcinoma (typically solid vascularized components)
Hemorrhagic cyst (usually fenestrated with no discrete solid components)
Endometrioma (typically diffuse low-level echoes)
Ectopic pregnancy
Teratoma or dermoid cyst (typically echogenic shadowing component - dermoid plug)
Abscess (from nearby intestine, as in diverticulitis or a tubo-ovarian abscess)
Hematoma