Two cases of cytomegaly of the central nervous system of infants, disclosing typical viral inclusions in the brain tissues, associated with agenesia of the corpus callosum and cystic symmetrical post-infarction encephalopathy are reported. It is suggested that the callosal defect was caused by cystic degeneration occuring within the lamina reuniens and the prematurely fused sulcus medianus, in early intrauterine life. The possibility of cytomegalic etiology of the malformation is discussed. However the occurrence of viral disease in a previous abnormal brain cannot be discarded. The cystic symmetrical encephalopathy is explained through a redistribution (shunting) of the cerebral blood flow, brought about by the existence of a peculiar mechanism which he calls — priority blood supplying system. This proposed system probably acts independently of the cerebral blood flow autoregulatory mechanisms in emergency states, shunting the blood to the vitaly more important homeostatic neurovegetative centers. This mechanism, in spite of its actual effectiveness, if prolonged, may be deleterious to the excluded territories and produce irreversible damages. The morphologic expression of these damages are the multiple symmetrical brain infarctions. Following occasional survival, the tissue debris of the destroyed structures in the involved areas, are slowly and progressively removed by reabsorption and replaced by unusual symmetrical cavitations.