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  • Updated 05.02.2020
  • Released 04.01.2010
  • Expires For CME 05.02.2023

Malformations of the brain

Introduction

Overview

Neuroembryology is the basis for understanding both normal and abnormal development of the nervous system. Developmental malformations mainly result from an alteration, suppression, or interruption in 1 or more of the several developmental processes that occur more simultaneously than sequentially. Such an alteration often is due to a mutation or deletion of 1 or more genes that program neural development in a precise temporal and spatial sequence. Such genes often are expressed as gradients along 1 or more of the 3 axes of the neural tube. Acquired lesions of the fetal brain also can produce malformations. Induction is the influence of 1 embryonic tissue on another, and the nervous system is intimately related to surrounding tissues to be both induced by them and also influence their development. Correlations must always be considered between morphogenesis and genetic programming. The nervous system also must be seen as a whole, not narrowly focused on 1 part, such as the cerebral cortex or cerebellum, because genetic mutations often affect multiple structures even if the clinical manifestations are predominantly referable to 1 part of the brain.

Key points

• Maturation of developmental process within the nervous system, including differentiation and maturation of individual cells, normally occurs in a genetically-programmed synchronous and predictable temporal pattern.

• Developmental processes in the nervous system are mostly simultaneous and overlapping rather than sequential in a series.

• Development and maturational timing are altered not only in genetic disorders, but also by acquired epigenetic disorders affecting the fetus, such as exposure to teratogenic toxins including alcohol, fetal cerebral infarcts, and congenital infections.

• Function does not necessarily require complete neuroanatomical maturation.

• CNS malformations may exhibit altered timing of developmental processes with maturational delay, arrest, or even precociousness.

• In laminated cortices, such as the cerebral and cerebellar, dysmorphic alteration may be focal, as in focal cortical dysplasias, or generalized as in congenital metabolic encephalopathies.

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