Schizencephaly Imaging 

Schizencephaly is an uncommon disorder of neuronal migration characterized by a cerebrospinal fluid–filled cleft, which is lined by gray matter. The cleft extends across the entire cerebral hemisphere, from the ventricular surface (ependyma) to the periphery (pial surface) of the brain.^{[1, 2]}

The clefts may be unilateral or bilateral and may be closed (fused lips), as in schizencephaly type I, or separated (open lips), as in schizencephaly type II. (See the images below.)

Presentation and outcome are variable, but patients typically present with seizures, hemiparesis, and developmental deficits. Usually, the severity of symptoms is related to the amount of brain affected by the abnormality.^[3]

Preferred examination

Magnetic resonance imaging (MRI) is the imaging modality of choice because of its superior differentiation of gray matter and white matter and its ability to image in more than 1 plane.^[4]

Identification of gray matter lining the cleft is the pathognomonic finding in differentiating schizencephaly from porencephaly; this is best demonstrated on MRIs.

The more complete information obtained by MRI enables a more accurate prediction of neurologic outcome.

Limitations of techniques

MRIs are degraded by patient motion, and sedation may be required for children. MRI is relatively expensive. The examination cannot be done portably in an ill neonate. The study is relatively lengthy.

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

CT scans of closed-lip schizencephaly 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 cleft is partially or totally lined by gray matter and extends from the lateral ventricle to the pial surface of the cerebral hemisphere.

Secondary findings that can be identified on CT scan include hydrocephalus, heterotopia, polymicrogyria, subdural hygromas, and arachnoid cysts.

Degree of confidence

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

As mentioned above, MRI is the modality of choice for evaluating patients with schizencephaly. MRI better delineates the gray matter lining the cleft, which is the pathognomonic finding in schizencephaly. MRI also provides superb cortical anatomy detail and multiplanar capability. Primary findings related to the cleft and secondary findings associated with schizencephaly are identified using MRI. (See the images below.)^[4]

The ability of MRI pulse sequences to differentiate gray matter and white matter permits demonstration of gray-matter heterotopias in the subcortical white matter beneath the cleft, abnormalities involving the cortex (eg, pachygyria or polymicrogyria), and other secondary findings also identified by using CT scans.

Homolateral absence of the sylvian vasculature, small medullary pyramids, a low position of the fornix, and thinning of the corpus callosum are findings related to absent cerebral cortex and are better demonstrated by MRI than with other studies.

Degree of confidence

The degree of confidence is high. A closed-lipped schizencephaly may be difficult to visualize on MRI; however, a dimple at the junction of the cleft and ventricle should alert one to a possible schizencephaly.

Ultrasonography can be used in the neonatal period in patients in whom schizencephaly is suspected.

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. This type of anomaly is difficult to detect with ultrasonography, and requires a high index of suspicion and a highly skilled operator.

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. (See the image below.)

The size of the thalamus, caudate, and lenticular nuclei (subcortical gray matter structures) is decreased. Other associated anomalies, such as ventricular enlargement, may also be identified.