Vein of Galen malformation

Vein of Galen malformations (VoGM's), probably better termed as a median prosencephalic vein malformations, 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.

Epidemiology

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.

Clinical presentation

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.

• neonate
  • usually choroidal type
  • high output cardiac failure 
  • cranial bruit
• infant
  • usually mural type
  • hydrocephalus may occur due to venous hypertension or aqueduct stenosis
• child
  • usually mural type
  • developmental delay 
  • hydrocephalus

Pathology

The malformation is due to an arteriovenous fistula of the median prosencephalic vein (MPV) (a precursor of the vein of Galen) occurring at 6-11 weeks gestation. 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. 

Classification

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

Radiographic features

Antenatal ultrasound

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 (3^rd trimester)

The dilated median prosencephalic vein (MPV) appears as an anechoic structure in the midline posteriorly and demonstrates prominent flow on Doppler examination. If the there complications which regard to shunting, other ancillary sonographic features such development of hydrops fetalis or fetal cardiomegaly may be seen.

CT and MRI

Both CT and MRI can be used to delineate the malformation cross-sectionally. 

CT / CTA

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.

MRI / MRA

The dilated feeders and venous drainage appears as flow-voids on T2. MRA may also be performed which would better delineate vascular anatomy. 

Angiography

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 is 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. Even in the most optimistic and successful series, good outcome was only achieved in 60% of cases at most.

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

Differential diagnosis

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