Type I, or encephaloclastic porencephaly, is an acquired and usually unilateral
condition thought to occur in the third trimester. It can result from fetal
vascular occlusion, birth trauma, ventricular puncture, inflammatory
processes, coxsackie virus infection, hemorrhage, or embolism. Type II, or schizencephalic porencephaly, usually
is symmetrical, is thought to occur during the second trimester, and
represents a primary defect in morphogenesis of the neuroectoderm. Later
findings indicate that deficiencies in the protein C anticoagulant pathway
have an important role in the etiology of congenital porencephaly.