Invisible neuronal damage in stroke-free, asymptomatic chronic middle cerebral artery occlusion: evidence from soma...

In the study, we utilized soma and neurite density imaging (SANDI) to investigate stroke-free patients with unilateral middle cerebral artery (MCA) occlusion, with the goal of analyzing gray matter damage in both affected and contralateral hemispheres.

The study involved 59 patients with unilateral MCA occlusion and 35 control subjects. All participants underwent three-dimensional T1-weighted imaging and SANDI examination. Model fitting of SANDI data generated maps of the following parameters: soma signal fraction (f_Soma), neurite signal fraction (f_Neurite), extracellular space signal fraction (f_Extra), and apparent soma size (R_Soma). A comprehensive voxel-based analysis was conducted, employing a voxel-wise general linear model, to compare whole-brain R_Soma, f_Soma, f_Extra and f_Neurite between patients with unilateral MCA occlusion and the controls.

Patients with unilateral MCA occlusion demonstrate significantly reduced f_Soma and f_Neurite, and increased f_Extra in some regions of bilateral hemispheres compared to the controls. Right-sided MCA occlusion was associated with widespread bilateral microstructural damage involving the frontal, parietal, temporal, occipital, and limbic cortices, subcortical regions, as well as the hippocampus and parahippocampal gyrus. In contrast, left-sided MCA occlusion was characterized by left hemisphere-predominant damage, with more focal involvement of frontal, parietal, and contralateral occipital regions.

In unilateral MCA occlusion patients with identified abnormalities, the affected brain regions encompass the sensorimotor integration system, language system, limbic-emotional and memory system, subcortical gray matter, and visual processing system. Importantly, the right-sided MCA occlusion patients often have damage to the hippocampus and parahippocampal gyrus, leading to cognitive deficits.

Question For asymptomatic stroke-free patients with chronic unilateral MCA occlusion, is microstructural neuronal damage present and detectable by soma and neurite density imaging? Findings Soma and neurite density imaging detect reduced f_Soma/f_Neurite and elevated f_Extra in MCA occlusion regions, with worse damage in right-sided cases. Clinical relevance This study enables early detection of invisible neuronal damage, alerts to cognitive risks (especially in right MCA occlusion), and provides a basis for targeted clinical interventions.