Corpus Luteum Cyst: This is a common finding in women of reproductive age, especially if the patient is in the luteal phase of her menstrual cycle. The internal vascularity is consistent with the expected blood supply to a corpus luteum cyst.

Hemorrhagic Ovarian Cyst: These cysts can appear hyperechoic due to the presence of blood and may show internal vascularity. They are relatively common and can cause acute pain if they rupture.
Dermoid Cyst (Mature Cystic Teratoma): While dermoids can have a variety of appearances, they can be hyperechoic and may show internal vascularity. They are a type of germ cell tumor and are usually benign.
Ovarian Tumor (Benign or Malignant): Various types of ovarian tumors can present as hyperechoic lesions with internal vascularity. The presence of vascularity increases the concern for a malignant process, but many benign tumors also have a rich blood supply.

Ectopic Pregnancy: Although less likely if a clear intrauterine pregnancy is seen, an ectopic pregnancy can present as a hyperechoic adnexal mass with internal vascularity, especially if it has implanted in the ovary (ovarian ectopic pregnancy). Missing this diagnosis can be catastrophic.
Ovarian Torsion: While not a mass per se, ovarian torsion can cause the ovary to become edematous and hyperechoic with altered blood flow patterns. It's an emergency that requires prompt surgical intervention.

Struma Ovarii: A rare form of dermoid cyst that is composed mostly of thyroid tissue. It can be hyperechoic and show internal vascularity.
Ovarian Metastasis: Metastases to the ovary from other primary sites can appear as hyperechoic lesions with internal vascularity. This would be more likely in patients with a known history of cancer.
Gonadoblastoma: A rare tumor that usually occurs in patients with gonadal dysgenesis. It can present as a hyperechoic mass with internal vascularity.