Ovarian Cyst: The most common adnexal mass, ovarian cysts can be simple or complex and are often benign, especially in premenopausal women. They can grow and become complex, presenting as an enlarging complex cystic structure.

Dermoid Cyst (Mature Cystic Teratoma): A type of ovarian neoplasm that can contain various tissue types, including hair, muscle, and bone, which can appear complex on imaging due to the presence of these different elements.
Endometrioma: A cyst filled with old blood, typically associated with endometriosis. These can appear complex due to the presence of blood and may grow over time.
Ovarian Torsion: While not a cyst per se, an ovarian torsion can present with a complex adnexal mass due to the associated edema and possible hemorrhage into a pre-existing cyst.

Ovarian Cancer: Although less common, ovarian cancer can present as a complex adnexal mass. It is crucial to consider this diagnosis, especially in postmenopausal women or those with risk factors.
Ectopic Pregnancy: In women of childbearing age, an ectopic pregnancy can present as an adnexal mass and is a medical emergency.
Tubovarian Abscess: A complication of pelvic inflammatory disease (PID), which can form a complex cystic structure due to the accumulation of pus.

Paraovarian Cyst: A rare type of cyst that arises from the paraovarian tissue, which can appear as a complex adnexal mass.
Adnexal Torsion of a Paratubal Cyst: Similar to ovarian torsion but involving a paratubal cyst, which is a rare condition.
Malignant Transformation of a Dermoid Cyst: Although dermoid cysts are usually benign, there is a rare risk of malignant transformation, which would present as a complex and possibly enlarging mass.