A silent stroke is a type of stroke that does not produce any severe symptoms, but may slightly affect memory or thinking abilities. Women who take hormone replacement therapy (HRT) may have a higher risk of experiencing a silent stroke than women who do not use HRT. This study will use magnetic resonance imaging (MRI) to determine the prevalence of silent strokes and other changes in brain tissue in women who participated in the Women's Health Initiative Memory Study (WHIMS), a study in which women received HRT, either as estrogen alone or as estrogen and progesterone combined, or placebo.

A silent stroke is a type of stroke that occurs as a result of blockage in the small blood vessels in the brain. Older adults, in particular, are at risk for silent strokes. This type of stroke does not cause any of the typical stroke symptoms, such as vision problems, facial numbness, or walking difficulties; however, subtle changes in a person's cognitive ability or memory may occur following a silent stroke. It is important to diagnose this type of stroke because several occurrences of silent strokes can increase the risk of having a more serious, and possibly fatal, stroke. As women go through menopause, many choose to take HRT to relieve common menopausal symptoms, including hot flashes and mood swings. Unfortunately, the use of HRT may place women at higher risk of experiencing a silent stroke. This study will assess whether women who take HRT, either as estrogen alone or as estrogen and progesterone combined, have a greater risk of silent stroke than women who do not take HRT. Study researchers will also examine changes in brain tissue and changes in the areas of the brain associated with thinking and memory.

This study will enroll women who are participating in the WHIMS study. Participants will attend one study visit at which time a brain MRI scan will be completed. Study researchers will analyze participants' study data from the WHIMS study and the Women's Health Initiative Study of Cognitive Aging (WHISCA) study, an ancillary WHIMS study that examined the effects of HRT on memory and cognition.

Inclusion Criteria:

• Participated in the WHIMS study
• Receives medical care at 1 of the 13 WHIMS MRI clinics

Exclusion Criteria:

• Currently has a pacemaker (either working or non-functioning), intracranial aneurysm clip, neurostimulator, defibrillator, intra-ocular ferrous foreign body (e.g., metal in the eye), or Harrington rods

• Currently has a magnetically or electrically activated device, including any of the following items: cochlear implant, transcutaneous electrical nerve stimulation (TENS) unit, implanted pump (insulin or infusion), or a McGee Stapes implant

• Potential participants who have the following exclusion criteria may be eligible for participation, based on study staff approval:

  1. Metal fragments around critical soft tissue (i.e., shrapnel near spinal cord)
  2. Prosthetics
  3. Eyelid spring or wire
  4. Metallic stent, filter, or coil
  5. Breast tissue expander
  6. Tattoo or non-removable body piercing
  7. Difficulty lying flat
  8. Difficulty breathing
  9. Claustrophobia

Women who participated in the WHIMS study and receive medical care at clinics participating in this study.