The pachygyria-polymicrogyria spectrum of cortical dysplasia in X-linked hydrocephalus

Neural cell adhesion molecules (CAM) play important roles in neural development, neurite outgrowth, axonal guidance, fasciculation and synapse formation. Neuropathological studies of X-linked hydrocephalus (XLH) associated with L1 CAM mutations emphasize marked hypoplasia of the pyramidal tract, agenesis of the corpus callosum and septum pellucidum, and a thin cerebral mantle with hypoplastic white matter, but there are no detailed studies of the cerebral cortex in the literature. We report clinical, neuroimaging, and neuropathological findings in three boys with XLH. All had severe congenital hydrocephalus with marked thinning of the cerebral mantle and severe development disabilities. The brain specimens from the three boys showed both pachygyria and polymicrogyria, hypoplasia of the medullary pyramids, hypoplasia of the corpus callosum, small anterior commissure, hypoplasia and poorly differentiated hippocampi. A small but patent aqueduct was present in all three brains. Despite the extensive cerebral malformations, the cortex in all three brains showed normal-appearing laminar cortical neuronal architecture and absence of gliosis. In XLH, it is likely that the poor developmental outcome of spasticity, contractures and severe mental retardation results from a disturbance of neuronal connectivity, fasciculation, and synapse formation rather than aqueductal stenosis, increased intracranial pressure, or abnormal neuroblast migration.