Porencephaly (ORPHA:2940)
A rare, genetic or acquired, cerebral malformation characterized by an intracerebral fluid-filled cyst or cavity with or without communication between the ventricle and subarachnoid space. Clinical manifestations depend on location and severity and may include hemiparesis, seizures, intellectual disability, and dystonia.
Epidemiology
Point prevalence of acquired and genetic forms is unknown. However, birth prevalence of porencephaly is estimated at 1/19,000 in Japan and 1/28,500 in the USA.
Clinical description
Porencephaly may manifest before or after birth. The cysts or cavities can be located anywhere within the cerebral parenchyma and are typically lined by smooth walls and surrounded by an atrophic cortex. The clinical picture is highly variable, even within affected families, with severe cases presenting major disability to mild cases with only slight, or even undetected, neurological involvement. The main clinical manifestations include hypotonia, microcephaly, spastic hemiparesis or quadriparesis, seizures, and global developmental delay. Intellectual disability is also a common finding and ranges from very mild to severe.
Etiology
Prenatal- and postnatally-acquired cysts (acquired porencephaly) may be due to a number of causes including hemorrhage, local damage from ischemia or traumatic brain injury. Mutations in the COL4A1 (13q34) and COL4A2 (13q34) genes have been identified in familial (Familial porencephaly) and de novo  cases. In these genetic cases, porencephaly results from antenatal or perinatal hemorrhage and is often associated with other brain abnormalities (bilateral white matter changes, calcifications, microbleeds) and ocular involvement (congenital cataract, retinal arterial tortuosity).
Diagnostic methods
The diagnosis is suspected based on the clinical manifestations and is confirmed radiologically by computed tomography (CT), magnetic resonance imaging (MRI), or ultrasonography showing characteristic intracerebral lesions. Cysts or cavities are well demarcated, contain cerebrospinal fluid and do not show contrast enhancement.
Differential diagnosis
Differential diagnoses include arachnoid cyst, schizencephaly, ependymal cyst, encephalomalacia, hydranencephaly, and other COL4A1 or COL4A2 related diseases, including childhood stroke, CADASIL and retinal vasculopathy with cerebral leukodystrophy.
Antenatal diagnosis
Ultrasonography may detect porencephaly prenatally after the 30th week of gestation.
Genetic counseling
The pattern of inheritance for familial porencephaly is autosomal dominant. Genetic counseling should inform parents of the 50% risk of transmission for future offspring. Occasionally, genetic cases arise de novo.
Management and treatment
No specific treatment is available for porencephaly. Treatment is therefore symptomatic and supportive and may include physical therapy, speech therapy, and anticonvulsant medication to treat seizures.
Prognosis
Prognosis is variable and depends on the site and extent of the lesion.

                            Last update: 
                            June 2019


                            - Expert reviewer(s): 
                            Pr Patrick VAN BOGAERT