Porencephaly

Porencephaly is a collective term for a variety of cystic lesions of the brain. Some of these cavities communicate with the ventricular system, the subarachnoid space or both. These defects have many sinmilarities in etiopathogenesis with schizencephaly and hydranencephaly.1

ICD-10: Q04.6

Porencephalic cyst

Porencephaly is very rare with only isolated case reports of the diagnosis made in utero. 2-4

Vascular accidents leading to hypoxic-ischemic lesions are probably the predominant factor in the determination of porencephaly. From the obstetric point of view, it is of interest that congenital porencephaly has been described following a cranial trauma due to amniocentesis.5, 6. Porencephaly and other cystic brain lesions are frequent in monozygotic twins.1.Familial cases of porencephaly have also been described.7-10

Although different theories exist, most believe that porencephaly hydranencephaly, and schizencephaly are most frequently the consequence of a vascular occlusion leading to infarction and sedondary reabsorption of different etrritories of the fetal brain.1Schizencephaly is postulated to occur at an early stage, prior to 24 weeks. This results in migration of neurons over the open lips of the defect that becomes covered with a cortical plate, albeit abnormally structured.

Porencephaly is characterized by a destruction of brain tissue that is replaced by fluid. The resulting cyst may be embedded into the brain but more frequently is widely open towards the subarachnoid space, the ventricular system or both (the term porencephaly derives from the latin porus, that indicates the communication between the ventricular and extra-cerebral space). The surface of the defct is often irregular and is not covered by a cortical plate, as is usually seen with schizencephaly. When multiple cystic cavities are found within the brain the term multycystic encephalomalacia is employed.

With the exception of ventriculomegaly, associated anomalies are rare. There may be atrophy or basal ganglia or other parts of the brain. Most cases of porencephaly are isolated.

Porencephaly is a lateralizing lesion. The typical ultrasound features are that of a cystic cavity in the brain that communicates with the ipsilateral ventricle or the subarachanoid space. The cleft usually increases in size as it progresses away from the ventricle.Less frequent varieties include cases with cysts embedded into the cortex and separate from the ventricular or subarachnoid space, or multiple cystic lesions replacing most of the cortex (multycystic encephalomalacia) Bilateral destruction of the forebrain presumably due to occlusion of the middle cerebral arteries is referred to as a ‘basket’ brain.1-4

Distinction from unilateral schizencephaly may be difficult, usually in schizencephaly clefts with smooth contours are found, while in porencephaly the cavities tend to be rounder and to have a jagged contour, and may contain blood clots or debris. Fetal MRI could be helpful, at least in the third trimester, by demonstating whether the defect is lined with white matter (porencephaly) or gray matter (schizencephaly). Arachnoid cysts are usually smooth-walled, asymmetrical, do not communicate with the lateral ventricles and contrarily to porencephaly, have a mass effect. Cystic neoplasms are rare. They usually have a mass effect with both solid and cystic components. Hydrocephalus may occasionally be unilateral, but should easily be distinguished from porencephaly by noting the distinguishing features of hydrocephalus.

Porencephaly may be missed by antenatal sonography particularly in early gestation because of two reasons. First, it is usually a unilateral lesion and it may be difficult to demonstrate when this occurs in the hemisphere proximal to the transducer, that is usually obscured by sound reverberation and artifacts.11 Second, it usually occurs only in late gestation.1

Patients with porencephaly may have a variety of symptoms, including seizures, developmental delay, hemiparesis, and intellectual impairment. Occasionally children with porencephaly may have normal neurological development. Unfortunately there are no clear cut figures. Most cases diagnosed in utero tend to have however a poor outcome.

Termination of pregnancy may be offered prior to viability. However, most cases of fetal porencephaly are only seen in the third trimester. As porencephaly may be the consequence of a cerebral hemorrage, a similar diagnostic workup is recommended. Conservative management should be offered, as many cases have a poor outcome. In cases with associated ventriculomegaly and macrocrania, cephalocentesis may be an option to overcome feto-pelvic disproportion. Otherwise there is no reason to modify standard obstetric management.

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