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

Porencephaly

Porencephaly is a type of cephalic disorder involving encephalomalacia. This is an extremely rare disorder of the central nervous system involving a cyst or cavity in a cerebral hemisphere. The cysts or cavities are usually the remnants of destructive lesions, but are sometimes the result of...

 by the fact that in schizencephaly the fluid-filled component, if present, is entirely lined by heterotopic grey matter

Grey matter

Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...

 while a porencephalic cyst is lined mostly by white matter

White matter

White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...

. 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

Language

Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...

 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

Microcephaly

Microcephaly is a neurodevelopmental disorder in which the circumference of the head is more than two standard deviations smaller than average for the person's age and sex. Microcephaly may be congenital or it may develop in the first few years of life...

, mental retardation

Mental retardation

Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...

, hemiparesis

Hemiparesis

Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....

 (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

Hydrocephalus

Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...

.

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

EMX2

Homeobox protein EMX2 is a protein that in humans is encoded by the EMX2 gene....

 gene, although this theory has recently been disproved. Causes of Schizencephaly may be caused by environmental exposures during pregnancy such as medication taken by the mother, sickness during pregnancy (such as Cytomegalovirus

Cytomegalovirus

Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...

), exposure to toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s, 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.