Schizencephaly is a rare cortical malformation that manifests as a grey matter-lined cleft extending from the ependyma to the pia matter

The cleft extends across the entire cerebral hemisphere, from the ventricular surface (ependyma) to the periphery (pial surface) of the brain

Cause: segmental developmental failure of cell migration to form cerebral cortex / vascular ischemia of portion of germinal matrix

Time of injury: 30 to 60 days of gestation

Schizencephaly is rare with an estimated incidence of ~ 1.5 : 100,000 live births.

It is almost always sporadic.

There is no known gender predilection.

Most often the cleft involves the posterior frontal or parietal lobes (70%).

Presentation and outcome are variable◦ Seizures◦ Hemiparesis ◦ Developmental deficits

Usually, the severity of symptoms is related to the amount of brain affected by the abnormality

The clefts may be unilateral or bilateral

-CLOSED LIP (Schizencephaly type I) the cleft walls are in apposition most common form in unilateral cases

-OPEN LIP (Schizencephaly type II) the cleft walls are separated and filled with CSF most common form in bilateral cases

Schizencephaly is frequently (50-90%) associated with :

o Polymicrogyria(66%)o Grey matter heterotopiao Absence/Focal thinning of corpus callosumo Absent septum pellucidum

Focal cortical dysplasia Heterotopic grey matter Porencephaly Arachnoid cyst Cystic tumor

Focal cortical dysplasia◦ sometimes may have a cleft on the cortical surface that

does not extend completely to the ventricular surface Heterotopic grey matter ◦ closed lip schizencephaly can mimic a band of grey

matter heterotopia.

◦ Assessing the ventricular outline will often demonstrate a slight cleft whereas periventricular grey matter will usually bulge into the ventricle.

Porencephaly◦ A zone of encephalomalacia that extends from the

cortical surface to the ventricular surface but is lined by gliotic white matter, not grey matter

Arachnoid cystoCSF containing intra arachnoid cyst without ventricular

communication

MRI is the imaging modality of choice, and enables identification of the pial-ependymal cleft visualization of cortical dysplasia and heterotopic gray matter.

Closed lip (type I) : seen as nipple-like out-pouching at the ependymal surface

Open lip (type II) : heterotopic gray matter lined CSF cleft seen extending from ventricular to cortical surface

Using computed tomography (CT) scanning, the diagnosis of schizencephaly is sometimes difficult, particularly type I, or closed lip schizencephaly.

On CT scan Closed lip (type I) may show only a slight outpouching at the ependymal surface of the cleft, and a full-thickness cleft may be difficult to identify on CT scan

The degree of confidence is high when the extent of the cleft and the gray matter lining its walls can be identified.

may show a unilateral or bilateral defect extending from the pial surface to the ventricular wall

there may be other features such as ◦ absent cavum septum pellucidum ◦ occasional fetal hydrocephalus

In schizencephaly type I, a hyperechoic line extends from the parasylvian region to the anterior portion of the lateral ventricle.

The hyperechoic line represents the cortex lining the fused cleft.

In schizencephaly type II, an anechoic band or cavity, representing the fluid-filled cleft, extends from the cortical surface to the lateral ventricle.

The meeting of the closed-lip portion, or apex of the cleft, with the margin of the ventricle may be identified as a ventricular diverticulum or dimple.

Holoprosencephaly denotes an incomplete or absent division of the embryonic forebrain (prosencephalon) into distinct lateral cerebral hemispheres

Although rare in absolute terms, holoprosencephaly is the most common forebrain abnormality and is seen in1per 10,000 - 16,000 live births.

The early embryonic occurrence may be even higher but may not be detected due to most fetuses aborting in early gestation.

Alobar holoprosencephaly

Semilobar holoprosencephaly

Lobar holoprosencephaly

Alobar holoprosencephaly: there is a complete absence of midline forebrain division, resulting in a monoventricle and fused cerebral hemispheres.

Alobar holoprosencephaly is visible on all modalities, but in general is identified on antenatal ultrasound and best characterized by MRI. 

The basic structure of the cerebral hemispheres is lost, with variable amounts of residual cortex.

single midline monoventricle (or holosphere) ◦ lateral and third ventricles are absent

absent midline structures ◦ absent septum pellucidum ◦ agenesis or hypoplasia of the corpus callosum◦ absent interhemispheric fissure and falx cerebri

dorsal cyst of holoprosencephaly thalami fused

Associated craniofacial features may also be present which include

o probosciso mono-orbit / cyclopiao mono-nostril o hypotelorismo cebocephaly

The fused cortex can take on three basic shapes :o pancake : cerebral tissue is confined to the

anterior basicranium o cup : cerebral tissue lines variable amounts of the

anterior cranium with a dorsal cyst present posteriorly

o ball : a complete rim of tissue surrounds the monoventricle without dorsal cyst

Death within 1st year of life / stillborn

Semilobar holoprosencephaly Hydranencephaly Severe hydrocephalus

Semilobar holoprosencephaly: is characterized by an incomplete forebrain division, resulting in partial separation of the cerebral hemispheres, typically posteriorly.

The basic structure of the cerebral lobes are present, but are fused most commonly anteriorly and at the thalami and there is partial diverticulation of brain (dorsal cyst).

absence of septum pellucidum

monoventricle with partially developed occipital and temporal horns

rudimentary falx cerebri : absent anteriorly

incompletely formed interhemispheric fissure

partial or complete fusion of the thalami absent olfactory tracts and bulbs

agenesis or hypoplasia of the corpus callosum

incomplete hippocampal formation

Associated craniofacial abnormalities:

o mild facial anomalies: midline cleft lip + palate

o Hypotelorism

o mental retardation

infants survive frequently into adulthood

lobar holoprosencephaly 

alobar holoprosencephaly

porencephalic cyst

arachnoid cyst

colpocephaly

Lobar holoprosencephaly: there is complete ventricular separation, with focal areas of incomplete cortical division or anterior falcine hypoplasia present

mildest form with two cerebral hemispheres and two distinct lateral ventricles

fusion of the frontal horns of the lateral ventricles wide communication of this fused segment with

the third ventricle fusion of the fornices absence of septum pellucidum agenesis or hypoplasia of the corpus callosum

Unlike semilobar holoprosencephaly, the falx is present, the interhemispheric fissure is fully formed and the thalami are not fused.

survival into adulthood

semilobar holoprosencephaly

septooptic dysplasia

Focal cavity as a result of localized brain destruction

Congenital

Acquired

The congenital form is due to localized agenesis of the cortical mantle resulting in the formation of a cavity or a lateral slit through which the lateral ventricle communicates with the convexity of the brain.

The cavity is lined by ependyma and laterally by a thin pia-ependymal layer which may rupture into the subarachnoid space.

In less severe forms the cavity may be reduced to a lateral slit lined by ependyma and partially fused.

The acquired type is secondary to any type of cerebral destructive process, ranging from trauma to infarction.

Sometimes called false porencephaly, such cases are better labeled by their etiological cause if this is known, e.g. post-traumatic or post infarction cerebral cavities

Porencephalic cavities or clefts can be identified or suspected by ultrasound in the neonate or infant.

In children or adults they are demonstrated by CT or MRI