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).
Outer Surface of the Brain
no gyri (0) = complete agyria, with no Sylvian fissure
primarily agyria with 1 to 4 sulci
mixed agyria and pachygyria (4 to 6), with or without some formation of a Sylvian fissure
fewer than normal (7 to 10) = pachygyria
(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.
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