Vein of Galen aneurysmal malformations (VGAMs), probably better termed as median prosencephalic arteriovenous fistula, are uncommon intracranial anomalies that tend to present dramatically during early childhood with features of a left-to-right shunt and high-output cardiac failure.
These malformations account for less than 1-2% of all intracranial vascular malformations but are the cause of 30% of cerebral vascular malformations presenting in the paediatric age group 1-3. It is also the most common antenatally diagnosed intracranial vascular malformation. There may be an increased male predilection 7.
Increasingly the diagnosis is being made antenatally with third trimester antenatal ultrasound. Presentation is often with high-output cardiac failure in the neonatal period, although low-flow aneurysms may remain undetected into adulthood. As much as 80% of cardiac output may shunt through the fistula. Presentation does however vary with the type of malformation, and different types present at different ages:
- usually choroidal type
- high output cardiac failure
- cranial bruit
The anomaly is actually due to a cerebral arteriovenous fistula of the median prosencephalic vein (MPV) (a precursor of the vein of Galen) occurring at 6-11 weeks gestation and not a malformation (no nidus present). The MPV fails to regress and becomes aneurysmal. It drains via the straight sinus (present only in 50%) or a persistent falcine sinus and the vein of Galen does not form.
Haemodynamically cerebral arteriovenous fistula involving vein of Galen can be subdivided into two groups:
- true VGAMs
- vein of Galen dilatation secondary to high flow parenchymal AVMs draining into this vessel
Malformations have been classified in a number of ways:
- according to clinical presentation (see above)
- Yasargil classification: types I to IV
- Lasjaunias classification: choroidal and mural types
With increased availability and quality of antenatal ultrasound the diagnosis is increasingly made prior to delivery. Antenatal detection is however mostly reported late in pregnancy (3rd trimester).
The dilated median prosencephalic vein (MPV) appears as an anechoic structure in the midline posteriorly and demonstrates prominent flow on Doppler examination. Shunting may lead to complications such as hydrops fetalis or fetal cardiomegaly.
CT and MRI
Both CT and MRI can be used to delineate the malformation cross-sectionally.
CTA in neonates with high output cardiac failure is technically challenging due to the small volumes of contrast and very rapid passage of contrast through the circulation.
The dilated feeding and draining vessels appear as flow-voids on T2. MRA may also be performed which would better delineate vascular anatomy.
Angiography remains the gold standard in full characterisation of the lesion. It enables to individually catheterise feeding vessels. Venous drainage is via the median prosencephalic vein (MPV) , the straight sinus (if present) and then out via the transverse/sigmoid sinuses. By definition there should be no drainage to other components of the deep venous system 6.
Treatment and prognosis
Prior to endovascular intervention, prognosis was dismal, with 100% mortality without treatment and 90% mortality following surgical attempts 5.
Ideally embolisation is deferred until 6 months of age for choroidal VGM and later for mural types, to allow the cavernous sinus to mature. If cardiac failure is refractory to medical management, embolisation may be performed sooner.
Both venous and arterial embolisation is possible, depending on the the number of feeders, and controversy persists in regards to the optimum approach. Options include 5:
- arterial feeder and fistula occlusion
- transtorcular or transvenous embolisation of the dilated vein
- complete or incomplete occlusion
Both coils and acrylic glue can be used 5.
Radiosurgery has been tried, but is limited to patients who are not candidates for other treatment modalities 5.
Hydrocephalus is typically not shunted, as this may exacerbate cerebral ischaemia by altering cerebral haemodynamics and due to the increased risk of intraventricular haemorrhage.
The prognosis is largely determined by the presence or absence of cardiac failure. Thus choroidal types and those presenting in the neonatal period do poorly.
History and etymology
Vein of Galen malformations are named after Galen of Pergamon (also known as Aelius Galenus or Claudius Galenus) (AD 129-199), a Roman physician and philosopher 4.
Once abnormal vessels are identified, there is usually little diagnostic uncertainty, with the only two entities to be considered being:
- arteriovenous malformation (AVM)
- vascular intracranial tumour
Pineal region masses
The pineal region is anatomically complex and plays host to a number of unique masses and tumours as well as potentially affected by many entities seen more frequently elsewhere in the brain.
- cystic non-neoplastic lesions
- pineal parenchymal tumours
- germ cell tumours
- tumours also encountered in the pineal region
- pineal gland metastases
- vascular lesions
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