Developmental differences of the major forebrain commissures in lissencephalies

Changes of the major forebrain commissures in lissencephaly have not been systematically studied. We investigated the developmental differences of the commissures in patients with varying types of lissencephaly to determine whether specific commissural features may help in distinguishing lissencephaly phenotypes.

MR imaging of 124 patients was retrospectively reviewed. Patients were classified as having cLIS, vLIS, and CBSC, according to cortical phenotype; few patients had genetic diagnoses. Abnormalities of the CC, AC, and HC were recorded, and the overall shape was regarded as hypogenetic, hypoplastic, dysmorphic, a thin flat callosal body with a vertical splenium, and a convex upward callosal body, compared with age-matched controls. Correlations between commissural characteristics and cortical patterns were analyzed by using the Monte Carlo simulation of χ(2), extension to m × n table, and Fisher exact tests as appropriate (P < .05).

Patients were classified as having cLIS (57.4%), vLIS (38.4%), or CBSC (4.2%). The most common callosal developmental anomaly was hypogenesis with an absent rostrum, a small inferior genu, and a small splenium. An angled (90°) splenium was found to be significantly associated with cLIS, as was an excessively convex upward callosal body with VLDLR. ACC with an enlarged AC was found in all cases of ARX.

Specific patterns of the commissure anomalies were associated with certain types of lissencephaly. Callosal anomalies were more common than those of the AC or HC. Developmental variations of commissures may be useful as an imaging criterion in differentiating the groups of lissencephalies and may give insight into the processes causing these malformations.