White matter hyperintensities (WMH)

White matter hyperintensities (WMH) are regions of abnormally high signal intensity on T2-weighted and FLAIR MRI sequences within the cerebral white matter, reflecting focal demyelination, axonal loss, gliosis and small-vessel ischaemia rather than a single pathological entity. Their prevalence rises steeply with age — present in roughly 10–20% of individuals in their 60s and in the majority of those over 80 — and their volume is strongly associated with hypertension, diabetes, and smoking as modifiable risk drivers. WMH predict cognitive decline (particularly processing speed and executive function), incident dementia, stroke and mortality; large or rapidly progressing confluent WMH carry greater clinical weight than small punctate lesions. They are a key imaging marker in the diagnosis of cerebral small vessel disease and in vascular contributions to cognitive impairment and dementia (VCID).