Microcephaly with a simplified gyral pattern

Last revised by Rohit Sharma on 20 May 2024

Microcephaly with a simplified gyral pattern (MSG) is a congenital malformation characterized by microcephaly accompanied by a simplified gyral pattern. The term “simplified gyral pattern” often describes a reduced number of gyri and shallow sulci with a normal cortical thickness and architecture.

Congenital microcephaly is divided into two main types:

  • primary (genetic) microcephaly: small but architecturally normal brain; the brain never forms normally

    • could be familial (autosomal dominant or recessive) or syndromic (e.g., Edward or Down)

    • some show an abnormally simplified gyral pattern without thickening of the cerebral cortex; this is known as microcephaly with a simplified gyral pattern (MSG)

  • secondary microcephaly: normal continued brain development is arrested by some defined insult such as a hypoxic-ischemic insult, TORCH infection, or metabolic disease

Patients with microcephaly with a simplified gyral pattern may have variable degrees of intellectual disability and neurodevelopmental delay.

Numerous genes have been found to be associated with simplified gyral pattern, however, the pathophysiology is still not completely understood.

Malformations of cortical development are classified depending on the stage at which the developmental process was disturbed, either at cell proliferation/apoptosis stage, neuronal migration stage, or cortical organization stage. Microcephaly is classified as a disorder of cell proliferation 1.

The grading system for sulcation includes:

  • mildly simplified gyral pattern: width of gyri < depth of sulci

  • moderately simplified: width of gyri = depth of sulci

  • severely simplified: width of gyri > depth of sulci

There is a strong correlation between the degree of microcephaly, the volume of white matter, and the presence of a simplified gyral pattern 1.

  • cortical migrational disorders such as pachygyria and lissencephaly in which the cortex is thickened

  • secondary microcephaly occurring secondary to a brain insult (including hypoxic ischemic injury, TORCH infection, metabolic diseases) in which the brain parenchymal architecture is abnormal

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