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This study aims to determine if hormone replacement therapy, given during perimenopause may prevent the progression of saccular cerebral aneurysms.

This is a prospective, randomized, placebo-control trial to test the effect of estradiol in the prevention of progression of cerebral aneurysms. To evaluate the effect, each subject will be treated with either oral estradiol or placebo for 6 months. Subjects will be randomly assigned to 1 of 2 groups as follows:

Double Blind Treatment Group Open-Label Regimen A1 1 mg Estradiol daily for 180 days B1 Placebo for 180 days

Each group will be given oral Progesterone (3300 mg) for 10 days at the end of 90 days regardless of menstrual pattern. Subjects will be asked to keep a menstrual calendar throughout the trial. Serum markers will be drawn at baseline and every 90 days with the results blinded until the end of the trial. Magnetic resonance angiography (MRA) studies of the brain will be performed at month 6.

Inclusion Criteria:

• Generally healthy women, 40-52 years of age.
• At least one documented saccular intracranial cerebral aneurysm detected via catheter angiography, magnetic resonance angiography or computed tomography angiography.
• Clinical diagnosis of perimenopause, defined as regular or irregular menses with or without vasomotor symptoms.

Exclusion Criteria:

• Known or suspected estrogen-dependent neoplasia.
• Endometrial proliferation, hyperplasia, or malignancy at screening.
• Known hypersensitivity to estrogens, progestins.
• History of myocardial infarction, ischemic heart disease, lipid disorder, or congestive heart failure.
• Known or suspected pregnancy, or recent breast feeding (within 6 months).