Beyond WMH volume: Coalescence score as a new measure of cerebral small‐vessel disease pattern

Abstract

AbstractBackgroundTotal white matter hyperintensity (WMH) volume is a hallmark of cerebral small vessel disease that is associated with accelerated cognitive decline and dementia onset. The shape of lesions is a key component of existing visual rating scales. While automated methods have been developed to assess WMH volume, evaluation of the lesion shape is still limited. We describe an automatic method to derive an overall coalescence score and investigate its association with Framingham cardiovascular risk score (FRS) and blood pressure (BP) in elderly individuals.Method750 individuals from the Southall And Brent Revisited cohort (age 71.1(6.9) years; 54.7% male) underwent brain MRI including 3D T1‐weighted and FLAIR images. WMH volumes were automatically segmented. Each non‐periventricular lesion (<25% of the border touching the ventricles) was automatically classified into a coalescence category ranging from 0 to 4 describing its level of confluency (0 punctuate – 4 fully confluent) using derived shape features. An overall coalescence score (CS) was generated based on the proportion of lesions residing in each of the five categories with respect to the global WMH volume. Biological relevance of the coalescence score (log‐transformed due to its skewness) was evaluated by assessing its association with FRS and BP using linear regression adjusting for global WMH volume and proportion of excluded periventricular lesions as well as age and sex (BP).ResultFigure 1 presents the CS frequency distribution (a), its relationship with global WMH volume (b) and an example of how CS captures differences in WMH pattern independent of classical volumetric measurements (c) (same load but different CS). After correction for global and periventricular WMH volume and other confounders, there was a positive association between CS and FRS (mean[95% confidence interval] +6.9[3.7;10.2] %CS per 10% increase FRS; p<0.0001), and with diastolic BP (+0.5[0;0.90] % per mmHg; p=0.04). There was no evidence of an association with systolic BP [+0.05[‐0.19;0.30]% per mmHg; p=0.63).ConclusionThe coalescence score provides an automated tool to quantify varying degrees of WMH confluency, which may lead to better understanding of the pathophysiology of WMH in the context of ageing, risk factors and dementia.