types III and IV present with microcephaly. In type III lissencephaly
the cortex is thin. Lissencephaly type IV is also called radial microbrain.
The cortex is thick. Lissencephaly type IV occurs in neonates with cytomegalovirus
is a disorder of neuronal organization. The neurons reach the cortex but
do not organize well, leading to the formation of multiple small gyri.
Polymicrogyria is diagnosed by MRI. Polymicrogyria may be an isolated
finding or may be associated with other brain abnormalities. Polymicrogyria
may be associated with degenerative central nervous system disorders (Zellweger
disease or neonatal adrenoleukodystrophy), central nervous system infections
(cytomegalovirus infection), or developmental disorders (Aicardi syndrome).
Neonates with polymicrogyria and clinical suspicion of cytomegalovirus
infection or periventricular cysts, calcifications (often periventricular),
or cerebellar hypoplasia should have their cerebrospinal fluid studied
for the possibility of cytomegalovirus infection. Treatment of cytomegalovirus
infection with Ganciclovir stops the excretion of virus in the urine.
The possibility that treatment with ganciclovir may arrest further progression
of brain damage has been raised. Seizures in patients with polymicrogyria
are treated with antiepileptic drugs. Surgical treatment should be considered.
refers to enlargement of one cerebral hemisphere (Figure 49.1). Magnetic
resonance imaging of the brain is the study of choice to establish the
diagnosis. Unilateral hemimegalencephaly occurs because of hamartomatous
overgrowth of one hemisphere. The cortex is dysplastic and the white matter
is abnormal. The lateral ventricle in the enlarged hemisphere is enlarged
in proportion to the lateral ventricle of the smaller hemisphere. The
anterior aspect of the lateral ventricle on the larger hemisphere points
superiorly and anteriorly.
Hemimegalencephaly. CT of the brain with contrast demonstrates enlarged
left lateral ventricle and pachygyric left posterior cerebral cortex.