Superficial white matter hyperintensities are associated with mild tissue alterations in vascular aging

In the elderly, white matter hyperintensities (WMH) are usually rated as periventricular or deep. However, recent data suggest that superficial WMH may be associated with distinct mechanisms and may be associated with milder underlying tissue alterations. We developed and validated a new grading scale to differentiate superficial WMH from other WMH (either periventricular or deep). We evaluated individuals with high loads of WMH from MEMENTO, a multicenter memory-clinic study, to evaluate the links between superficial WMH and 1) MRI markers of cerebral small vessel disease (number of lacunes and microbleeds and normalized brain volume); 2) cognitive outcomes including global evaluation with Mini Mental State Examination (MMSE). Our analytical sample included 208 participants. Participants with higher grades of superficial WMH had larger normalized brain volumes (82.1±1.3% vs 81.0±1.1%, P<0.001) and were more frequently women (85.0% vs 51.4%, P=0.01). In total contrast but as expected, participants with higher grades of other WMH were older (79.8±8.1 vs 75.5±6.2 years, P<0.001), had more often lacunes (41.7% vs 7.1%, P<0.001) and performed worse at the MMSE (26.8±2.0 vs 28.1±1.7, P=0.01). Our results support the hypothesis that superficial WMH are distinct from other WMH and probably correspond to mild tissue alterations.