This primigravida woman was referred for a structural ultrasound scan at 27.5 weeks because of an asymmetrical enlargement of the fetal head. The pregnancy was complicated by a hyperemesis gravidarum until the second trimester of pregnancy.

The fetal biometry showed a biparietal diameter of 86mm (32 w), a head circumference of 324mm (34.5 w), cerebellar width 35mm (30w), abdominal circumference 237mm (28 w) and a femur length of 55mm (28.5 w). The following images and a  1 MB video were obttained

The following structural defects were observed:

• asymmetrical appearance of the cerebrum;

• enlarged right side with compression of the left hemisphere

• absence of the parietal and temporal lobe of the right hemisphere

• macrocephalia.

• agenesis of the vermis without cyst formation (Dandy Walker variant).

Fetal blood sampling revealed a normal female karyotype.

Because of the absence of the parietal and temporal lobe of the right hemisphere the diagnosis of unilateral schizencephaly type II was made.

The prenatal MRI showed no evidence of a recent or old hemorrhage, and confirmed the presence of a liquefaction of the parietal and temporal region of the right hemisphere. The images were suggestive for an old infarct. No other central nervous defects were observed. Pictures of the MRI study are included for comparison with the ultrasound images.

An induction of labor was performed resulting in the birth of a girl of 1700 g (large for date) and a head perimeter of 380mm! The infant died within 5 minutes.

Gross pathological examination showed no obvious external nor internal malformations. The neuropathological examination was non-contributive due to poor preservation of the brain tissue. A large amount of CSF was present at the right side of the brain at the level of the parieto-occipital zone, where the brain tissue had disappeared. The agenesis of the corpus callosum, the fusion of the thalami and agenesis of the vermis were confirmed. There is no tentative diagnosis made by the pathologist, so that we only rely on the sonographic findings and those of the MRI study to call this malformation an unilateral schizencephaly

Schizencephaly is a rare congenital malformation in which bilateral and nearly symmetrical clefts are present in the cerebral hemispheres. Its true incidence is not known, and all cases appear to be sporadic and have normal chromosomes[i].

Two types can be distinguished:

• In type I the clefts are small and symmetrical and “fused” in the cerebral mantle.
• Type II clefts extend from the lateral ventricle to the bones of the skull. The defect may be either unilateral or bilateral, and are usually wedge shaped.

Schizencephaly may be caused by unilateral or bilateral occlusion of the middle cerebral artery resulting in an ischemic lesion of part of the brain. However, an other theory suggest that, since other brain disorders have been associated, it may be a primary focal migrational disorder of the neuroblast of the cortical matrix early in the first trimester[ii].

Ischemia, fetal hypotension, toxic events or infectious disease are etiological factors associated with the development of schizencephaly. Several case reports describe the association of congenital CMV infection with schizencephaly.

Several malformations can be associated: ventriculomegaly, polymicrogyria, heterotopies, agenesis of the corpus callosum and absent septum pellucidum, and optic nerve hypoplasia [iii].

The differential diagnosis of unilateral schizencephaly include arachnoid cyst, porencephalic cyst, unilateral hydrocephalus, cystic neoplasm and intracranial hemorrhage[iv].

The most difficult differential diagnosis is that with a porencephalic cyst. Sonographically these two entities are hard to distinguish. In both cases the cavity size increases with the distance from the ventricle. However, porencephalic lesions are surrounded by white matter, which can be demonstrated on MRI. Schizencephaly clefts are lined by gray matter4 .

References:

[i] Fetal neurosonography of congenital brain anomalies. A. Monteagudo, I. Timor-Tritsch. In Ultrasonography of the prenatal and neonatal brain. Eds Appleton & Lange, 1996.

[ii] Les malformations cérébrales. A. Couture, P. Drouille, F. Didier. In Echographie cérébrale du foetus et nouveau né. Eds Sauramps Medical 1994.

[iii] Schizencephaly type II. Byrd, Jeanty, The Fetus 1991

[iv] The fetal head. J. McGahan, A. Thurmond. In Diagnostic obstetric ultrasound. Eds JB Lippincott Company, 1994.