Selective atrophy of the connected deepest cortical layers following small subcortical infarct

To explore whether in patients with chronic small subcortical infarct the cortical layers of the connected cortex are differentially affected and whether these differences correlate with clinical symptomatology.

Twenty patients with a history of chronic small subcortical infarct affecting the corticospinal tracts and 15 healthy controls were included. Connected primary motor cortex was identified with tractography starting from infarct. T1-component probability maps were calculated from T1 relaxation 3T MRI, dividing the cortex into 5 laminar gaussian classes.

Focal cortical thinning was observed in the connected cortex and specifically only in its deepest laminar class compared to the nonaffected mirrored cortex (p < 0.001). There was loss of microstructural integrity of the affected corticospinal tract with increased mean diffusivity and decreased fractional anisotropy compared to the contralateral nonaffected tract (p ≤ 0.002). Clinical scores were correlated with microstructural damage of the corticospinal tracts and with thinning of the cortex and specifically only its deepest laminar class (p < 0.001). No differences were found in the laminar thickness pattern of the bilateral primary motor cortices or in the microstructural integrity of the bilateral corticospinal tracts in the healthy controls.

Our results support the concept of secondary neurodegeneration of connected primary motor cortex after a small subcortical infarct affecting the corticospinal tract, with observations that the main cortical thinning occurs in the deepest cortex and that the clinical symptomatology is correlated with this cortical atrophy pattern. Our findings may contribute to a better understanding of structural reorganization and functional outcomes after stroke.