The review, led by Emily Gallmetzer and Kejal Kantarci, followed PRISMA guidelines and screened 461 records from PubMed, ultimately including 18 peer-reviewed studies assessed with the Newcastle-Ottawa Scale. Fourteen were rated good quality, two fair, and two poor. The imaging modalities spanned the full modern neuroimaging toolkit: 16 studies used in vivo structural magnetic resonance imaging, four used diffusion tensor imaging, two used functional MRI, and three used positron emission tomography. Study designs ranged from massive population cohorts such as the UK Biobank, with more than 13,000 imaged participants, to small case-control studies of women recruited from familial cancer clinics.

Definitions matter enormously in this literature, and the review highlights how inconsistent they have been. Premature menopause is defined as onset before age 40, and early menopause as onset between ages 40 and 44. Both can arise spontaneously or be induced by chemotherapy, pelvic radiation, or premenopausal bilateral oophorectomy, the surgical removal of both ovaries before natural menopause. By contrast, hysterectomy with ovarian conservation stops menstruation but preserves endocrine function and is not a cause of ovarian hormone loss. The hallmark consequence of spontaneous menopause is the gradual decline of estradiol, the predominant and most biologically active ovarian estrogen during reproductive life, whereas oophorectomy causes abrupt and complete loss of estradiol and all other ovarian hormones.

Estrogen is far more than a reproductive hormone. In the brain it has important antioxidative effects, contributes to the suppression of immune activation led by astrocytes and microglia, and supports cerebral energy metabolism by upregulating glucose transporters. Early estrogen loss has been associated in experimental studies with increased oxidative stress, accelerated neuroinflammatory processes, and dysregulated iron homeostasis within the central nervous system. Loss of estrogenic support may increase vulnerability to neuronal injury, gliosis, and accumulation of pathological proteins. Because ovarian hormones act on multiple organ systems, their early loss has systemic consequences that extend well beyond reproductive health, and this accelerated somatic aging may itself exacerbate brain aging.

Across the structural MRI studies, the review found regionally specific rather than global patterns of brain differences. Women with premature or early menopause showed lower gray-matter volume or cortical thickness in medial temporal, frontal, and basal forebrain regions. In population-based cohorts, women who underwent oophorectomy before age 50 showed smaller amygdala volume and thinner parahippocampal-entorhinal cortex compared with age-matched controls. A more recent Mayo Clinic study found that oophorectomy before age 46 was associated with thinner entorhinal cortex independent of age at imaging, whereas lower temporal-lobe cortical thickness emerged only at older ages. In women with idiopathic premature ovarian insufficiency, voxel-based analysis revealed regional reductions in the bilateral olfactory cortex and right parahippocampal gyrus, together with reduced cortical thickness in parietal and insular regions and smaller hippocampal subfield and thalamic volumes. Notably, no significant global gray-matter difference was observed in the full sample, and younger participants showed exploratory global differences that were uncorrected for multiple comparisons.

Diffusion tensor imaging added a complementary microstructural picture. This technique quantifies axonal architecture through metrics such as fractional anisotropy, which measures the directionality of water diffusion, and mean diffusivity, which serves as an inverse index of membrane density and tissue integrity. Reduced fractional anisotropy, often accompanied by increased mean diffusivity, indicates loss of axonal integrity and myelination. Women who underwent oophorectomy before age 40 showed lower fractional anisotropy and higher mean diffusivity in the anterior corona radiata, the genu of the corpus callosum, and the inferior fronto-occipital fasciculus. Strikingly, women whose oophorectomy occurred between ages 40 and 44 showed no such differences, a pattern consistent with a threshold or dose-response effect of earlier hormone deprivation. In spontaneous premature menopause, altered structural connectivity involved the olfactory cortex, amygdala, hippocampus, and thalamus, while global network topology remained relatively preserved.

Functional MRI, though available in only two studies from the same Canadian research group, provided convergent functional correlates. Women who underwent bilateral salpingo-oophorectomy without hormone therapy showed lower right posterior lateral hippocampal activation during novel face-name encoding compared with those who received hormone therapy. A later study from the same group found lower posterior hippocampal activation in both treated and untreated groups compared with age-matched controls, though it did not fully replicate the earlier group-specific pattern, and anterior hippocampal activation and raw task accuracy did not differ across groups. The convergence with structural findings is only partial, and independent replication in separate cohorts is needed before firm conclusions can be drawn.

The PET evidence, though limited to three studies, offers the most provocative molecular findings. In cognitively unimpaired women with elevated amyloid-beta, earlier age at menopause was associated with higher regional tau burden, with effects clustering in medial temporal, lateral temporal, parietal, and occipito-temporal regions, a distribution consistent with Braak staging of early-to-intermediate Alzheimer’s tau pathology. In the Mayo Clinic cohort, women who underwent oophorectomy before age 46 showed higher amyloid-beta load when imaged at older ages, and tau was elevated only at higher amyloid-beta levels. Women whose oophorectomy occurred between ages 46 and 49 showed no comparable biomarker differences. These findings suggest that a woman’s age at the time of menopause, rather than menopause type alone, may be the most sensitive determinant of later molecular vulnerability.

Mechanistically, the review proposes that early loss of ovarian hormones may weaken the brain’s compensatory reserves and converge on interconnected deleterious molecular pathways. Reduced estrogen levels may diminish neurotrophic support, leading to loss of synaptic density within the medial temporal lobe and reduced neuronal resilience to age-related stressors. Estrogen normally supports cerebral energy metabolism, and its loss may contribute to mitochondrial dysfunction and impaired cellular bioenergetics, resulting in a hypometabolic state where the brain metabolizes its own myelin-derived lipids for energy. This metabolic shift may increase production of reactive oxygen species, including superoxide and hydrogen peroxide, which can damage neuronal membranes and further destabilize mitochondrial function. Estrogen also regulates enzymes involved in amyloid-beta degradation, such as the insulin-degrading enzyme, supports autophagic flux, and helps maintain microglia in a homeostatic state, so its depletion may shift the brain toward chronic neuroinflammation and failed protein clearance.

The authors are careful to emphasize that the evidence remains heterogeneous and largely cross-sectional, limiting causal inference about the temporal sequence between ovarian hormone loss and neurobiological change. Sixteen of the 18 included studies used age cutoffs that reached into the usual-age menopause range of 45 to 54 years, meaning many reported associations cannot be tied specifically to premature or early menopause. Large volunteer cohorts such as the UK Biobank tend to recruit healthier participants than the general population, and almost all studies imaged women only once. The review’s conclusions are therefore best seen as a rationale for prevention-oriented research rather than established clinical guidance. Still, the convergent pattern across imaging modalities, spanning gray-matter atrophy, white-matter microstructural deficits, reduced hippocampal activation, and preliminary evidence of altered amyloid and tau burden, suggests that women’s reproductive history deserves consideration as an integral part of dementia risk profiles. Large-scale longitudinal studies tracking the same women with serial neuroimaging over years, and evaluating interactions with genetic predisposition such as the apolipoprotein E epsilon 4 genotype, are now needed to determine when brain alterations begin in relation to the drop in estrogen levels and whether specific critical windows exist during which hormonal interventions could decelerate degeneration in networks vulnerable to Alzheimer’s disease.

Subject of Research: Neuroscience

Article Title: Premature and early menopause and neuroimaging biomarkers of neurodegenerative diseases: a systematic review

Article References: Gallmetzer, E., Mak, E., Kara, F., Zeydan, B., Kapoor, E., Shufelt, C. L., Rocca, W. A., & Kantarci, K. (2026). Premature and early menopause and neuroimaging biomarkers of neurodegenerative diseases: a systematic review. Frontiers in Dementia, 5, Article 1912295. https://doi.org/10.3389/frdem.2026.1912295

Image Credits: AI Generated

DOI: 10.3389/frdem.2026.1912295

Keywords: menopause, Alzheimer's disease, neuroimaging, estrogen, dementia, women's health, MRI, PET, Premature, early, biomarkers, neurodegenerative