Porencephaly (Gr.Poros a passage, ford, pore) was originally defined as a defect that creates a communication between the cerebral ventricles and the subarachnoid space but now, it it used to describe any fluid-filled cavity in the fetal or neonatal brain. A thin membrane may separate the cavity from the lateral ventricle or the subarachnoid space. Such membranes rupture in life or during the autopsy. The pathology has its origin in fetal life. Most cases begin as ischemic infarcts that subsequently cavitate, and are usually located in the middle cerebral artery territory. Similar lesions may result from brain necrosis occurring in prenatal infections. The pathogenesis is no different from necrotic lesions that arise in late gestation or in the neonatal period. The main difference is that lesions arising early in gestation heal without gliosis, and the defect is frequently bordered by dysplastic cortex. On the other hand, lesions arising later are associated with gliosis, macrophage reaction, and calcification.