Characterizing White Matter Tract Organization in Polymicrogyria and Lissencephaly: A Multifiber Diffusion MRI Modeling and Tractography Study

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The authors retrospectively reviewed 50 patients (mean age, 8.3 years) with different polymicrogyria (n = 42) and lissencephaly (n = 8) subtypes. The fiber direction-encoded color maps and 6 different white matter tracts reconstructed from each patient were visually compared with corresponding images reconstructed from 7 age-matched, healthy control WM templates. The authors demonstrated a range of white matter tract structural abnormalities in patients with polymicrogyria and lissencephaly. The patterns of white matter tract involvement are related to polymicrogyria and lissencephaly subgroups, distribution, and, possibly, their underlying etiologies.

Abstract

BACKGROUND AND PURPOSE

Tractography findings in selected patients with lissencephaly and polymicrogyria. T1WI, direction-encoded color maps, and tractography reconstructions in 2 patients with LIS (A and B) and 2 with PMG (C and D) are shown. For each patient, a comparable tractography reconstruction from the age-matched healthy control template is shown in the last column for comparison. A, An irregular (shorter and smaller) bilateral cingulum (arrows on DEC map) in a patient with pachygyria and thick subcortical band heterotopia. B, A bilateral, irregular (smaller and distorted) superior longitudinal fasciculus (arrows on DEC map) in a patient with posterior-quadrant pachygyria and a thick SBH. C, Bilateral irregular (smaller and thinner) CG (arrows on DEC map) in a patient with generalized PMG. D, An irregular (shorter and distorted) right inferior fronto-occipital fasciculus (IFOF; arrows) in a patient with unilateral right peri-Sylvian PMG. The left IFOF (arrowheads) has a normal appearance. r. indicates right.

Polymicrogyria and lissencephaly may be associated with abnormal organization of the undelying white matter tracts that have been rarely investigated so far. Our aim was to characterize white matter tract organization in polymicrogyria and lissencephaly using constrained spherical deconvolution, a multifiber diffusion MR imaging modeling technique for white matter tractography reconstruction.

MATERIALS AND METHODS

We retrospectively reviewed 50 patients (mean age, 8.3 ± 5.4 years; range, 1.4–21.2 years; 27 males) with different polymicrogyria (n = 42) and lissencephaly (n = 8) subtypes. The fiber direction-encoded color maps and 6 different white matter tracts reconstructed from each patient were visually compared with corresponding images reconstructed from 7 age-matched, healthy control WM templates. Each white matter tract was assessed by 2 experienced pediatric neuroradiologists and scored in consensus on the basis of the severity of the structural abnormality, ranging from the white matter tracts being absent to thickened. The results were summarized by different polymicrogyria and lissencephaly subgroups.

RESULTS

More abnormal-appearing white matter tracts were identified in patients with lissencephaly compared with those with polymicrogyria (79.2% versus 37.3%). In lissencephaly, structural abnormalities were identified in all studied white matter tracts. In polymicrogyria, the more frequently affected white matter tracts were the cingulum, superior longitudinal fasciculus, inferior longitudinal fasciculus, and optic radiation–posterior corona radiata. The severity of superior longitudinal fasciculus and cingulum abnormalities was associated with the polymicrogyria distribution and extent. A thickened superior fronto-occipital fasciculus was demonstrated in 3 patients.

CONCLUSIONS

We demonstrated a range of white matter tract structural abnormalities in patients with polymicrogyria and lissencephaly. The patterns of white matter tract involvement are related to polymicrogyria and lissencephaly subgroups, distribution, and, possibly, their underlying etiologies.

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