There are two main forms of porencephaly: (1) developmental porencephaly and (2) congenital encephaloclastic porencephaly. The first type represents primary failure of neuronal development and migration. The second type is more common and results from cortical destruction due to an external insult in an otherwise normal brain.
Porencephaly can be diagnosed prenatally using sonography when fluid-filled spaces are noted in the fetal brain. MRI is a useful adjunct.
A complete family history should be obtained to look for stroke, thrombosis, thromboembolism, and recurrent porencephaly.
Work-up should include ruling out maternal cocaine and warfarin use, infection, hereditary thrombophilias, and increased bleeding.
Long-term prognosis depends on the size and location of the lesions, and whether there is a hereditary thrombophilia or vasculopathy.
The neonate should be evaluated after birth by a pediatric neurologist. Follow-up brain imaging is recommended.
In most cases, an underlying cause for porencephaly is not identified. Most familial cases are due to underlying autosomal dominant mutations.
Porencephaly is a term that describes a fluid-filled cavity in open communication with the lateral ventricle (van der Knaap et al., 2006). The term porencephaly is often used interchangeably with porencephalic cyst, schizencephaly, cystic brain degeneration, and congenital brain clefts. Porencephaly was first described in 1859 as a cavity or cleft of the cerebral cortex (Heschl, 1859). These lesions may or may not communicate with the ventricular and subarachnoid systems. Two major subgroups are described: developmental porencephaly, which includes schizencephaly and congenital midline porencephaly and congenital encephaloclastic porencephaly (Hall, 2006).
Developmental porencephaly represents a primary failure of neuronal development and migration. Synonyms include true porencephaly, schizencephaly, and congenital porencephaly. Congenital midline porencephaly is a more recently described malformation, consisting of the triad of a midline parietal scalp anomaly (such as alopecia or cephalocele), hydrocephalus, and a midline intracranial cyst (Yokota and Matsukado, 1979; Vintzileos et al., 1987). While this malformation most likely represents a form of porencephaly, some authors consider it a variant of holoprosencephaly (Vintzileos et al., 1987).
In contrast, congenital encephaloclastic (disruptive) porencephaly results from cortical destruction due to an external insult in an otherwise normally developed brain. Synonyms include pseudoporencephaly, false porencephaly, and cystic brain degeneration. This destruction results in an intracerebral cystic cavity containing cerebrospinal fluid, and such a cyst may be single or multiple (Figure 21-1) (Hall, 2006). Congenital encephaloclastic porencephaly may have many different causes; of these, hemorrhagic infarction due to fetal venous congestion or occlusion is considered to be the most common (Dekaban, 1965; Cantu and LeMay, 1967; Nixon et al., 1974).
Axial image demonstrating a large porencephalic cyst with adjacent echogenic area suggestive of prior hemorrhage.