Venous Porencephaly
Types of Porencephaly
Diverging descriptions of ‘porencephaly’ exist. Literally one would want to observe a cavity in brain substance with a connection (porus) linking it to the lateral ventricle and/or the brain surface. Cavities without pore should be referred to as (pseudo)cysts. Three major entities are present, depending on timing of the insult: (i) schizencephaly, a transmantle defect lined by heterotopic neurons because of onset before the end of neuronal migration; (ii) fetal porencephaly (<24 weeks of gestation): soft-walled, punched out defects, with (arterial) or without (deep venous) involvement of cortex but with ventricular connection; large artery infarcts of onset before 25 weeks of gestation may be bordered by polymicrogyria, when one enters a semantic discussion whether they are arterial porencephaly or schizencephaly (Takada et al. 1989); (iii) perinatal (clastic) porencephaly (> 24 w of gestation): clastic lesions, often vascular but sometimes infectious, generate multiple or isolated cavities, generally with irregular walls on account of the more mature character of tissue reaction against necrosis; examples can be seen after leukomalacia and following parenchymal extension of germinal matrix haemorrhage. Extensive destruction leads to multicystic encephalopathy (polyporencephaly). Other porencephalies (not lateral ventricle-related):- dorsal porencephaly (upward extension of the third ventricle) is discussed with callosal agenesis;
- ventral porencephaly, a peculiar anomaly described with cerebral hemiatrophy. In our experience most porencephalies of antenatal onset seem to correspond with a venous mechanism. They follow prenatal periventricular venous white matter haemorrhagic infarction and leave the cortical mantle intact, although extensive venous infarction may also provoke ipsilateral arterial hypoperfusion that secondarily destroys overlying cortex. As in the neonatal period, the vein involved determines the porencephalic end stage. Most often a white matter defect in the area of the terminal vein is the end result. Simple porencephaly is a term one can use for abnormal focal dilatation of the lateral ventricle in the terminal vein area. Larger porencephalic defects are similar to those of postnatal onset that follow venous infarction. Antenatal porencephaly can be seen in the terminal vein area, but also in the longitudinal caudate, inferior ventricle and atrial vein areas.
Venous (Haemorrhagic) Porencephaly
Brain haemorrhage may occur in utero for various reasons. The three most commonly occurring mechanisms are haemorrhagic diathesis, fetal trauma and an ischaemic event.Antenatal Intracranial Haemorrhage
Acute prenatal asphyxia may be caused by maternal disease, fetoplacental disruption, intrinsic fetal conditions or an unknown event. Maternal conditions leading to fetal asphyxia can be: shock or severe hypotension (as due to anaphylaxis or following a traffic accident with major injury), hypoxia (as in gas poisoning, e.g. with CO or butane), severe psychological stress (as with failed abortion, failed suicide attempt, accident or physical abuse), cocaine use, acidosis (as during a diabetic ketoacidotic crisis), pancreatitis, hypoglycaemia or seizures. Fetal mechanical trauma may be penetrant (shot wound, stab wound as in uncareful amniocentesis, Squier et al. 2000) or blunt (Gunn et al. 1988, 1989, 1991, Kawabata et al. 1993, Strigini et al. 2001, Karimi et al. 2004). In the latter case we have to consider physical abuse of pregnant women, a fall with abdominal trauma, a traffic accident, cranial bone displacement from external version (for medical or religious reasons) or minimal fetal trauma with an aggravating factor such as a haemostatic defect. Both cerebral and cerebellar haemorrhage may occur in utero (Hille et al. 2003, Glenn et al. 2007, Hayashi et al. 2015). Haemorrhage in relation to germinal matrix is most common (Ghi et al. 2003), and presumably with a mechanistic context that does not differ from postnatal onset matrix haemorrhage (Ballabh et al. 2014). Most antenatal lesions are suspected with fetal ultrasound during the third trimester, and documented by additional MR imaging in utero (Achiron et al. 1993, Sanapo et al 2017, Adiego et al 2017). Focal cerebellar clastic lesions (e.g. unilateral cerebellar hypoplasia or cerebellar clefts) on postnatal MRI are considered sequelae of prenatal disruption, the haemorrhagic component of which can best be documented with susceptibility weighted MRI (Hayashi et al. 2015). Collagen 4A and other similar mutations. Antenatal brain haemorrhage (recurrent) due to collagen 4A mutation is extensively documented, including detection in utero but it is often a neonatal sonographic finding (Breedveld et al. 2006, de Vries et al. 2009, Vahedi et al. 2011, Vermeulen et al. 2011, Garel et al. 2013, Yoneda et al. 2013, Meuwissen et al. 2015, Alarcon et al. 2025). Collagen deficiency seems to affect small veins and arteries alike. The tight junction, or zonula occludens, is a specialized cell-cell junction that regulates permeability, and it is an essential component of the blood-brain barrier. Mochida et al. in 2010 identified a homozygous mutation in the tight-junction protein gene JAM3 in a large consanguineous family where some members suffered severe haemorrhagic in utero destruction of the brain, subependymal calcification, and congenital cataracts.Antenatal Intracranial Haemorrhage: Diagnosis and Work-up
The recognition of antenatal brain haemorrhage can be upheld by: (i) a specific maternal event; (ii) an abnormal fetal US or MRI scan: hyperechoic lesion, hydrocephalus, hydranencephaly, non-immune hydrops; (iii) acute heartrate changes in utero (sinusoidal fetal heart rate for instance)(Catanzarite et al. 1995); (iv) an early neonatal brain CUS or MRI dating the lesion before birth. The non-recent and posthaemorrhagic character of a fetal lesion may also become obvious during ventriculoscopic neurosurgery or at postmortem exam. GMH/IVH is most common.Cerebellar haemorrhage in combination with but also in isolation of IVH can occur in utero.
Haemorrhage in choroid plexus or germinal matrix may evolve into a growing hygroma with a capsule: a rounded lesion with a fine dense border and discrete intralesional echoreflections.
Early bleeding may lead to “schizencephaly" (both in utero and in ELBW preterms).
It is impossible to distinguish haemorrhagic conversion of an ischaemic zone from primary haemorrhage, for instance after direct fetal cranial trauma.
It is useful to inspect intracranial veins for thrombosis upon detection of a fetal intracranial haemorrhage (Wetzstein et al. 2006, Tajdar et al. 2017). Patterns of fetal haemorrhagic diathesis.
- thrombocytopenia: iso-immune, auto-immune
- thrombocytopathy: congenital (von Willebrand disease), by salicylates or non-steroidal anti-inflammatory drugs, CAMT (congenital amegakaryocytic thrombocytopenia), TAR (thrombocytopenia absent radius), Wiskot-Aldrich s.
- shortage of coagulation factors: congenital (V, VII, VIII, X), due to cumarins, diffuse intravascular coagulation
- shortage of anticoagulants: protein C deficiency, FV Leiden, FII mutation
- dysfibrinogenemia
- fetal liver failure: on account of acetaminophen, in perinatal hemochromatosis
- glutathion synthetase deficiency
Alloimmune thrombocytopenia
Typical for alloimmune thrombocytopenia is development of superficial haemorrhage in the parenchyma, usually of the temporal lobe. This is a subpial bleeding that, on growing towards the surface, becomes a subarachnoid haematoma (Govaert et al. 1995). Posthaemorrhagic hydrocephalus may occur if bleeding extends deeper and reaches the ventricle. Transmantle destruction from such bleeding may lead to defects that resemble schizencephaly (Kuijpers et al. 1994, Pati and Helmbrecht 1994). The majority of intracranial haemorrhages occurred in the firstborn (Tiller et al. 2013). Most will therefore not be recognised in time for treatment if one does not identify pregnancies at risk before the first child is born. IVIG treatment during the subsequent pregnancy seems protective, reducing fetal intracranial hemorrhage recurrence risk from 79% as previously reported, to 11%. Well documented instances occur in fetuses affected by autoimmune thrombocytopenia (Kutuk et al. 2014).Von Willebrand disease
(Wetzstein et al. 2006)Hereditary porencephaly with hemiplegia (HPH, McKusick 175780)
Berg et al. (1983) provided the first description of familial porencephaly, with sparing of (sub)cortex, contralateral hemiparesis, accompanied in some by migraine and seizures. Imaging reveals unilateral enlargement of the lateral ventricle, although a few had bilateral involvement. The frontal horn is usually most dilated. Asymptomatic obligate carriers, can have normal imaging, indicating that imaging is unreliable as a detector. Porencephaly or mild ventricular dilatation is obligate in carriers with hemisyndrome. Several mechansims and genes are involved. The clinical spectrum of collagen COL4A1 mutations includes recurrent intracranial hemorrhage in association with diffuse leukoencephalopathy, with or without a family history of infantile hemiparesis or ICH (Vahedi et al. 2007). The Factor V G1691A mutation (FV Leiden) and a combination of prothrombotic factors, including plasminogen activator inhibitor-1 4G6755G, are other genetic causes of childhood porencephaly. ‘Porencephaly’ was also reported with several types of oro-facio-digital syndrome (OFD). The HHHH syndrome of hereditary hemihypotrophy, hemiparesis and hemiathetosis described by Haar and Dyken (1977) consisted of congenital left hemiparesis with development of left hemihypoplasia and athetoid posturing of the left hand.Timing with Imaging
Timing of antepartum intracranial haemorrhage can be done with early neonatal US:- an extensive parenchymal hyperechoic lesion seen within a few hours after birth, is of antepartum origin
- after a few days clot in a ventricle begins to undergo lysis, giving rise to cavitation within; the coagulum starts to retract leaving irregular intraluminal structures with a dense ridge and a hypodense centre
- towards the end of the first week, following a sterile reaction to blood, the ependyma becomes denser and granular in some spots, a phenomenon that is to persist for weeks (Rijpens et al. 1994)
- widening of the ventricle without bulky clot presence is an additional subacute or chronic element
- associated lesions in white matter, if cystic, can point to the subacute character of the event
- haemorrhage in plexus or germinal matrix may evolve into a growing chronic hygromatous mass
- as a rule ischaemic echodensities persist for several (≥ 2) weeks, whereas any haemorrhagic area should be cleared of most echoic foci in two to three weeks
Porencephalies
Simple porencephaly. We usually find a cavity at the frontal or parietal horns, communicating with an often dilated ipsilateral ventricle. A border of cortex and white matter remains between the cavity and the pia mater. Its external wall can be undulating. Bilaterality is not exceptional. They generally seem sporadic incidents but the phenomenon may fit in a syndrome. Possible explanations are in utero distal perforator artery stroke or (more likely) venous medullary infarction. The porus may not always develop at the site of the initially compressed or thrombosed ependymal collector vein. Paraventricular porencephaly. In a rare case a cavity is found in white matter, separated from the lateral ventricle, and towards the leptomeninges it may be bordered by a small arachnoid cyst. Often this cavity is found in the region of the middle cerebral artery, and infarction caused by occlusion of one of its branches may be involved. Parenchymal remnants may for a while remain visible in the cavity. -> Discussed with arterial porencephaly. Expansive porencephaly (pressure porencephaly, porencéphalie soufflante). Focal paraventricular necrosis may develop in utero following GMH/IVH, leukomalacia or arterial infarction. The cyst may expand by itself (-> unilateral hydrocephalus). If developed between the 16th and 20th w of gestation, the lesion is bordered by polymicrogyria. If developed in the third trimester, the cortex overlying such porencephalic cavity may be ulegyric. Pressure in the cavity, with a larger surface area, tends to blow the cavity out towards the cortex (Laplace's law). Any further growth of the cyst calls for shunting (Tardieu et al. 1981). Porencephaly following ventricular puncture. Transfontanelle ventricular punctures are still on occasion needed for preterm infants with acute symptomatic posthaemorrhagic hydrocephalus. Inevitably the lateral ventricle will communicate with the puncture path. Should raised intracranial pressure persist, this path may widen and generate irregular cavitations communicating with the ventricle via a small opening. This type of porencephaly can also be seen after endoscopic neurosurgery and along temporary reservoirs (Ommaya, Rickham).Antenatal Intracranial Haemorrhage: Mechanisms
Haemorrhage: mechanisms- within an arterial infarct
- within a venous infarct (thrombosis or compression)
- direct mechanical trauma
- haemostatic problem
- arterial hypertension
- venous congestion without thrombosis
- vascular anomaly
- tumor
- other
- unknown