Dobyns et al classified the brains of patients with Type I Lissencephaly based on the gross neuropathologic appearance.
Lissencephaly = "smooth brain"
In lissencephaly type I gyri range from absent (agyria) to reduced from normal (pachygyria).
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Outer Surface of the Brain
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Grade
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no gyri (0) = complete agyria, with no Sylvian fissure
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1
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primarily agyria with 1 to 4 sulci
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2
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mixed agyria and pachygyria (4 to 6), with or without some formation of a Sylvian fissure
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3
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fewer than normal (7 to 10) = pachygyria
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4
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Other findings:
(1) Corpus callosum hypoplasia is variable, most often seen with Grade 1 or 2.
(2) In pachygyria the sulci are few and broad.
(3) The grey matter is relatively enlarged and colpocephaly is present.
