Anatomical Validity of MRI-Based Choroid Plexus Segmentation: Regional Boundaries, Age-Related Morphology, and Implications for Neuroimaging Biomarkers

Magnetic resonance imaging (MRI)-derived choroid plexus (ChP) volume is increasingly investigated in studies of brain aging and neurodegeneration, yet its anatomical meaning remains uncertain because segmentation methods differ in ventricular coverage, image contrast, and reference annotations. This narrative review examines the anatomical basis and methodological validity of ChP volumetry by integrating evidence on ventricular anatomy, age-related tissue changes, manual and automated segmentation, and associations with cognitive impairment and Alzheimer’s disease. The lateral ventricular ChP, particularly the atrial glomus, is generally easier to delineate on conventional MRI than its thin extensions and the third and fourth ventricular components. Segmentation performance depends on the anatomical reference and acquisition protocol; agreement with manually drawn masks does not necessarily establish complete anatomical coverage. In addition, age-related vascular remodeling, changes in stromal composition, calcification, and cystic alterations can affect MRI appearance and the interpretation of total volume. Although ChP enlargement has been associated with aging, cognitive impairment, and Alzheimer’s disease, volume alone cannot identify the contributing tissue compartments or establish blood–cerebrospinal fluid barrier dysfunction. We propose an anatomy-centered approach to ChP volumetry based on explicit regional definitions, complementary measures of spatial and volumetric accuracy, assessment of test–retest and multicenter reliability, and independent biological validation when functional interpretations are intended.