Schizencephaly is a rare grey matter malformation of the brain. It belongs to the group of malformations of the central nervous system.
Presentation
Schizencephaly is a rare developmental disorder of brain characterized by abnormal continuity of histologic grey matter tissue extending from the ependyma lining of the cerebral ventricles to the pial surface of the cerebral hemisphere surface. Type I Schizencephaly has a cord of grey matter tissue, either with no fluid cleft or with ventricular or cortical lips closing one end of an abnormal fluid cleft through the hemisphere. Type II Schizencephaly shows a cerebrospinal fluid-filled cleft of varying size and shape extending through the hemisphere from the ependyma centrally to the pia peripherally. Schizencephaly can be distinguished from porencephaly by the fact that in schizencephaly the fluid-filled component, if present, is entirely lined by heterotopic grey matter while a porencephalic cyst is lined mostly by white matter. Schizencephaly is probably a disorder in normal neuron migration during the second trimester of intrauterine development, when primitive neuron pre-cursors (germinal matrix) migrate from just beneath the ventricular ependyma to the peripheral hemispheres where they form the cortical grey matter. Grey matter contains neuronal cell bodies and dendrites whereas white matter contains axons, which are coated in myelin (i.e., a fatty tissue that aids in the speed of action potentials down the axon). Individuals with clefts in both hemispheres, or bilateral clefts, are often developmentally delayed and have delayed speech and language skills and corticospinal dysfunction. Individuals with smaller, unilateral clefts (clefts in one hemisphere) may be weak on one side of the body and may have average or near-average intelligence. Patients with schizencephaly may also have varying degrees of microcephaly, mental retardation, hemiparesis (weakness or paralysis affecting one side of the body), or quadriparesis (weakness or paralysis affecting all four extremities), and may have reduced muscle tone (hypotonia). Most patients have seizures and some may have hydrocephalus.
Causes
In schizencephaly, the neurons border the edge of the cleft, implying a very early disruption of the usual grey matter migration during embryogenesis. The cause of the disruption is not known, but likely the cause may be either genetic or a physical insult, such as infection, infarction, hemorrhage, toxin or mutation. There was once thought to be a genetic association with the EMX2 gene, although this theory has recently been disproved.[1] Causes of Schizencephaly may be caused by environmental exposures during pregnancy such as medication taken by the mother, sickness during pregnancy (such as Cytomegalovirus), exposure to toxins, or a vascular insult. Often there are additional associated heterotopias (isolated islands of neurons) which indicate a failure of migration of the neurons to their final position in the brain.
Treatment
Treatment for individuals with schizencephaly generally consists of physical therapy, occupational therapy (with specific emphasis on neuro-developmental therapy techniques), treatment for seizures, and, in cases that are complicated by hydrocephalus, a shunt.
Prognosis
The prognosis for individuals with schizencephaly varies depending on the size of the clefts and the degree of neurological deficit.
Frequency and inheritance
So far there have been only few documented case histories. The majority seem only sporadic, but one case with two brothers has been described. Another instance occurs in identical twins, one was diagnosed at seven months while the other is not affected. The inheritance is autosomal dominant or recessive inheritance, the locus is 10q26.1.[citation needed]
References
- ^ Tietjen, I.; Bodell, A.; Apse, K.; Mendonza, A. M.; Chang, B. S.; Shaw, G. M.; Barkovich, A. J.; Lammer, E. J.; Walsh, C. A. : Comprehensive EMX2 genotyping of a large schizencephaly case series. Am. J. Med. Genet. 143A: 1313-1316, 2007.
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