Porencephaly is a rare condition that affects the central nervous system. People with Porencephaly develop fluid-filled cysts or cavities in the brain either before or shortly after birth. The severity of the condition and the associated signs and symptoms vary significantly based on the size, location, and number of cysts. Common features include developmental delay, reduced muscle tone (hypotonia), seizures, macrocephaly (unusually large head size), spastic hemiplegia, speech problems, delayed growth, and intellectual disability. Porencephaly is usually the result of damage from infection or stroke after birth. In these cases, the condition occurs sporadically in people with no family history of the condition. There is an inherited form of the condition called familial Porencephaly, which is caused by changes in the COL4A1 or COL4A2 genes and is inherited in an autosomal dominant manner.