Many malformations result from the failure of normal migration of neurons from the periventricular germinal matrix zone to the cortical surface at 1 to 5 months of gestation. Multiple malformations may exist in the same patient. Neurologic development with these anomalies varies and depends on the type and extent of the malformation.
Schizencephaly is characterized by clefts within the cerebral hemispheres that extend from the cortical surface to the ventricular cavity. Unilateral clefts can cause isolated congenital hemiparesis, whereas bilateral schizencephaly causes spastic quadriparesis and associated intellectual disability. Affected individuals are at high risk for focal epilepsy.
A severe defect in cortical migration, lissencephaly results in a smooth brain without sulcation (agyria). The normal six-layered cortex does not develop. Affected children have difficult-to-control seizures and profound developmental retardation. This anomaly most commonly is part of a genetic disorder, which may be x-linked (DCX mutations) or caused by de novo autosomal dominant gene mutations (Lis-1 mutations). In pachygyria, the gyri are few in number and too
Lissencephaly Schizencephaly Pachygyria Micropolygyria Agenesis of the corpus callosum broad. In polymicrogyria, the gyri are too many and too small. Sometimes pachygyria and polymicrogyria affect an entire hemisphere, producing enlargement of that hemisphere and a clinical syndrome of severe, medically intractable seizures that begin in early infancy. Gray matter heterotopiasare abnormal islands within the central white matter of neurons that have never completed the migratory process.
The authors thank Dr. James Dowling for his generous help in preparing Chapter 182 on weakness and hypotonia.
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Yvonne E. Chiu 25
Approximately one in three Americans of any age has at leastone recognizable skin disorder at any time. The most commoncutaneous diseases encountered in community settings aredermatophytosis, acne vulgaris, seborrheic dermatitis, atopicdermatitis (eczema), verrucae (warts), tumors, psoriasis, vitiligo, and infections such as herpes simplex and impetigo. Inchildren attending pediatric dermatology clinics, atopic dermatitis, impetigo, tinea capitis, acne vulgaris, verrucae vulgaris,and seborrheic dermatitis are the most common diagnoses.