Progressive expanding congenital porencephalies: a treatable cause of progressive encephalopathy.

In congenital porencephalies, diverticulation of the lateral ventricle is a dynamic process producing compression and stretching of the brain tissue bordering the diverticulum, bulging of the overlying skull, macrocephaly, and occasionally progessive neurologic signs (hemiplegia, raised intracranial pressure), even when the rest of the ventricular system is not dilated and the CSF pressure is normal. Ventriculoperitoneal shunting can result in remarkable improvement of focal motor deficits and may apparently also play a beneficial role on further mental development. Successive computed tomography scans demonstrate that the brain parenchyma, which had been stretched by the porencephalic pouch, is capable of regaining near normal thickness. Congenital porencephalies are initiated by a limited destructive brain lesion, but the gradual expansion of the ventricular herniation may imply a mechanism identical to that which has been postulated in normal pressure hydrocephalus. Nine cases of unilateral "expanding" congenital porencephalies are presented and the treatment of this condition is discussed.