Schizencephaly: correlation between the lobar topography of the cleft(s) and absence of the septum pellucidum

Abstract

The bipolar defects observed in schizencephalies-clefts in the hemispheric mantle on the one hand, absent septum pellucidum on the other--without any anatomic or functional continuity suggest that there is some sort of common specific vulnerability of both structures. A study of the correlation between lobar location of the clefts and involvement of the septum pellucidum was undertaken, considering the hypothesis that the septum pellucidum is the portion of a "medial medullary velum" that corresponds to the frontal lobe, while the psalterium would correspond to the parieto-occipital lobe and the fimbria corresponds to the temporal lobe. This retrospective study of 16 cases of schizencephaly properly investigated by MR discloses a perfect correlation, all cases with absent septum pellucidum having clefts into the frontal lobe, all cases with present septum pellucidum having clefts in the parietal, temporal, and occipital lobes, and only the few instances (3 cases) of overlapping findings being characterized by clefts in the central area, where the distinction between posterior frontal and anterior parietal lobes is uncertain because of the cortical dysplasia related to the clefts. Partial defects of the septum also proved to correlate closely, topographically, with the location of the clefts. Therefore, the facts confirm a segmental organization of the mantle and septal defects, suggesting a developmental rather than a destructive mechanism, which could at least be related to a segmental pattern of selective vulnerability.

Correlation of Prenatal and Postnatal MRI Findings in Schizencephaly

“…Most of our subjects demonstrated bilateral defects; this finding is higher than that reported in previous publications. 9,10,15,16 In previous studies of postnatal imaging of schizencephaly, open defects were the predominant pattern in some, 10,15 while closed defects were more common in another report. 9 None of these larger case series studies had serial imaging or had documented open defects converting to closed defects as we have shown in this study.…”

“…9,10,15,16 In previous studies of postnatal imaging of schizencephaly, open defects were the predominant pattern in some, 10,15 while closed defects were more common in another report. 9 None of these larger case series studies had serial imaging or had documented open defects converting to closed defects as we have shown in this study. Open defects were consistently the predominant pattern in prenatal imaging of schizencephaly in previous series, 3,17 which is consistent with our results.…”

“…Numerous associated anomalies have been reported with schizencephaly, including polymicrogyria (both adjacent to and remote from the defect) 15 ; partial or complete absence of the septum pellucidum 3,9,12,18 ; a thinned or absent corpus callosum; and gray matter heterotopia. 15 Fetal MR imaging did not detect a grossly dysmorphic appearance of the gray matter lining and polymicrogyria along the cleft in most patients.…”

“…6 The common pathophysiology of injury is frequently ascribed to a vascular disruption, hypoxia-ischemia, and/or prenatal infection at critical time points during neuronal development, [1][2][3] though there are some reports favoring schizencephaly as a developmental disorder. [7][8][9] Classically, schizencephaly has been divided into "closed" or "closed-lip" defects, in which the walls appose one another within the defect, and "open" or "open-lip" defects, in which CSF fills the defect all the way from the lateral ventricle to the overlying subarachnoid space. 10 Open lesions have been further subclassified as small or large according to size of the defect.…”

“…2,10,11 Associated anomalies, such as optic nerve hypoplasia, absence of the septum pellucidum, and other migrational abnormalities, will also adversely affect the prognosis. 2,9,12,13 MR imaging was reported to prenatally diagnose schizencephaly as early as 1989. 14 On the basis of the current literature, the imaging appearance of schizencephaly on fetal MR imaging is considered identical to that in postnatal MR imaging.…”