Decreased Frontal White-Matter Diffusion and Improved Cognitive Flexibility After Burr-Hole Surgery In Moyamoya Angiopathy

1. Burr-hole surgery for moyamoya angiopathy may be a process of indirect revascularization harboring potential to improve frontal cerebral perfusion and apparent diffusion coefficient values in normal-appearing white matter while also improving cognitive inflexibility as a component of executive dysfunction.

Evidence Rating Level: 2 (Good)

Moyamoya angiopathy (MMA) is a progressive neurological disease that results in a reduction of apparent diffusion coefficient (ADC) as well as stenosis and occlusion of the intracranial carotid artery in spite of seemingly normal frontal white matter (WM). Hypoperfusion of frontal regions is another pathological sign, with consequent risks of stroke and neurocognitive disorders including executive dysfunction. Studies of revascularization surgeries have generally been limited, specifically as they result to cognitive outcomes. This retrospective study of 14 adults with MMA (mean [SD] age = 38.1 [10.7] years, 64.3% female) within one hospital occurred between March 2008 and November 2015, aiming to determine cognitive changes in relation to ADC and cerebrovascular reserve (CVR) following burr-hole surgery due to its focus on perfusion of frontal areas rather than the lateral hemispheres. Surgery included a median of 7 burr-holes (range 4-9) through the frontal bone, perioperative antiplatelet drugs were limited, and low molecular weight heparin treatment was engaged 24 hours post-surgery until sufficient recovery. An average of four regions of interest (ROI) were utilized to calculate anterior ADC in normal WM, though ROIs were altered to avoid WM hyperintensities and ischemic lesions. Executive functioning and processing speed were evaluated with the Trail Making Test (Parts A and B), Stroop inhibition score, Modified Wisconsin Card Sorting Test (WCST), and verbal fluency. Frontal ADC reduced following surgery in 19 of 26 hemispheres – frontal ADC decreased post-surgery (difference -26 mm²/s, p<0.001) but no significant changes were observed in posterior ADC. Perfusion-weighted imaging could be interpreted in 24 of the 26 hemispheres that were operated on due to artifacts in one patient, though no changes were observed in subcortical or frontal CVR in the sample. Cognitively, the greatest impairments were in cognitive flexibility, conceptualization, and inhibition. Following surgery, 60% of patients demonstrated cognitive improvement in TMT B, defined as an increase of at least one standard deviation (TMT B median z-score change -1.47 to -0.21, p – 0.018), but not on other measures. ADC did not significantly differ between those who showed improvement and those who did not, nor did ADC differ among those whose performance improved. Overall, this study found that burr-hole surgery resulted in reduced ADC values in frontal regions with normal WM. While results normalized, though this was sustained at a higher level than other series (700^10-6mm²/s). ADC values may be a proxy for post-surgery cerebral perfusion and may harbor potential in improving cognitive flexibility. 

Click to read the study in BMC Neurology

Image: PD

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