Presentation
Hypotonic baby with recurrent attacks of seizures.
Patient Data
Brain surface lacks its normal sulcation, with a smooth outline and overconvoluted internal cortical margin consisting of cobblestone cortical malformation - features in keeping with lissencephaly type II.
Well-defined posterior fossa midline cystic lesion with CSF signal intensity, bulging to the right; does not communicate with the 4th ventricle but compresses it, as well as the cerebral aqueduct and right cerebellar hemisphere, with subsequent supratentorial hydrocephalus and tonsillar herniation.
Atretic occipital cephalocele.
Case Discussion
MRI plays an important role in the assessment of the lissencephalic patient.
Lissencephaly occurs due to neuronal migration abnormalities which are typically divided into type I (or "classical") and type II (or "cobblestone complex"). Classical lissencephaly is distinguished from other forms of lissencephaly by the presence of an abnormally thick 4-layer cortex and, typically, by the absence of other major brain abnormalities.
Lissencephaly type II is clinically, genetically, histologically, and neuroradiologically distinct from classical Lissencephaly. It can appear agyric or pachygyric, and the cortex is typically thinner than in classic lissencephaly. Irregularity in the grey-white boundary may be present, similar to that seen in polymicrogyria. Histopathologically, type II is due to overmigration of neurons, in contrast to the undermigration of classical lissencephaly.
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