Vein of Galen [VOG] malformations are rare intracranial vascular anomalies, but represent about 30% of all vascular malformations presenting in the pediatric population. VOG malformations are of various types but are characterized by one common feature - presence of an aneursymally dilated, midline, deep venous structure fed by arteriovenous [AV] communications. The VOG malformations may have a direct fistulous connection or may have a parenchymal AV malformation draining into the VOG.
The VOG malformation occurs between the 7th and 12th week of gestation. The normal VOG is formed by the joining of the internal cerebral veins and the caudal portion of the median prosencephalic vein. The rest of the median prosencephalic vein, which drains the choroid plexus, regresses. VOG malformations are due to direct arterio-venous communications between the arterial network and the median prosencephalic vein. It is actually the embryonic median prosencephalic vein that dilates in the vascular malformation and not the Vein of Galen, and hence the term VOG malformation is actually a misnomer. Associated abnormal venous drainage patterns or persistence of fetal drainage patterns may also co-exist.
•Antenatal ultrasound enables in utero detection of many cases of VOG malformations.
•Neonate may present with symptoms of high output cardiac failure, myocardial ischemia and cyanosis.
•Infantile presentation may be with macrocephaly or with symptoms of hydrocephalus.
•Older children or adult presentation may be with headache, seizures and focal neurological deficits. They may have subarachnoid or intracerebral hemorrhage.
Ultrasound features- both antenatal and postnatal ultrasound scans demonstrate
•A midline spherical or lobulated cystic structure posterior to the third ventricle.
•If it is partly thrombosed, areas of increased echogenicity may be visualized within the cystic mass.
•The dilated cystic structure may compress the aqueduct and cause obstructive hydrocephalus, seen as dilated ventricles.
•Antenatal scans may show IUGR, hydrops.
•Advanced cases may show parenchymal brain atrophy or signs of cardiac failure such as hepatomegaly, cardiomegaly or ascites.
•Color Doppler has been shown to demonstrate a high velocity or slow flow. The flow is often turbulent or swirling.
•Spectral Doppler can reliably characterize the flow patterns in the feeding arteries and veins, if they are adequately visualized. The feeding arteries demonstrate a characteristic low resistance arterial waveform.
Role of ultrasound in VOG malformation-
•Establish an antenatal diagnosis, so that its prognosis can be altered with timely intervention.
•Establish a diagnosis postnatally. the advent of 3D-color power Doppler enables three dimensional visualization of the vasculature.
•Identify associated dural venous sinus abnormalities or intracranial fistulae.
•Assess the cardiovascular status of the neonate as they often have cardiac failure.
Based on this information, a diagnostic angiography and intervention such as coil embolization can be planned in the same sitting. Neurosonography also allows for easy and non-invasive follow up, after endovascular treatment. MRI and CT scans are the other non invasive modalities that can be performed to demonstrate the intracranial vascular anomalies.