Schizencephaly or Porencephaly

Both terms denote a defect (cavity) in the cerebral wall, but according to one concept they differ regarding the underlying mechanisms. Schizencephaly specifically refers to a failure of development due to a defect in the germinal matrix or a failure in the migration of neuro-blasts. Mutation in homeobox gene EMX2 has been reported in familial cases.

Conversely, porencephaly specifically refers to a destructive-encephaloclastic cause, probably a vascular insult early during the first half of gestation. Current concept favors a vascular origin for cerebral mantle defects, and the term porencephaly is commonly used.

Pathology: In schizencephaly the defects vary greatly in extent (Fig. 13.11). They may be narrow clefts along the Sylvian fissure or may involve a greater portion of the lateral wall of one or both hemispheres. Large cavities connect the ventricle with the subarachnoid space. In an extreme form, the defects symmetrically involve the lateral and medial walls of both hemispheres (doughnut brain). The leptomeninges over the defects are usually torn, so the ventricles communicate with the subdural space. The convolutions in the walls of the defects are oriented radially and display a polymicrogy-ric pattern.

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