Fetal Vein of Galen Malformation

Vein of Galen Aneurysmal Malformation (VGAM) is a rare intracranial arteriovenous malformation that develops during embryonic life between the sixth and 11th weeks of gestation. During the fetal period, the low-resistance placental circulation typically balances the low-resistance systemic shunt of the malformation, which often protects the fetus from developing overt heart failure while in utero. However, the presence of the malformation still causes significant hemodynamic alterations that can be detected via prenatal imaging, making fetal echocardiography a crucial tool for diagnosing and prognosticating the severity of the condition before birth. When performing a fetal echocardiography scan for a suspected VGAM, clinicians primarily look for markers of cardiac overload and altered blood flow distribution. Hallmark findings include right-sided heart dilation, characterized by an enlarged right atrium and right ventricle, which frequently results in tricuspid regurgitation. Additionally, the superior vena cava (SVC) is often significantly dilated due to the massive increase in venous return from the brain. Doppler ultrasound is used to identify retrograde diastolic flow across the aortic isthmus, indicating that blood is being "stolen" from the systemic circulation and redirected toward the low-resistance intracranial shunt. Specific indicators on a fetal echo can help predict the clinical course after delivery.

An enlarged cardiothoracic ratio (exceeding 0.50) is a significant prognostic marker, as it is strongly associated with the development of severe high-output heart failure at birth and an increased risk of mortality. Furthermore, the high pulmonary blood flow experienced in utero—which can be three to four times higher than normal—may cause pulmonary vascular remodelling, potentially complicating the infant's transition to postnatal life. The redirection of cardiac output away from the lower body can also lead to isthmal hypoplasia, which may be misdiagnosed as coarctation of the aorta during prenatal scans. Other findings, such as higher oxygen saturation in the right heart and pulmonary arteries, occur because the high-velocity shunt bypasses normal oxygen extraction in the brain.

The middle cerebral artery (MCA) is frequently involved in the vascular tangle of the malformation as a feeding vessel. A critical marker to look for is the presence of arterial "pseudofeeders." These are dilated branches of the middle cerebral artery visible in the sylvian valley that are not actually part of the choroidal system. Their appearance is interpreted as a sign of severe arterial steal, venous hypertension, and overall cerebral blood flow impairment. In fetal assessments, the presence of pseudofeeders is significantly associated with severe high-output heart failure (HOHF) at birth and can be an indicator for early delivery for emergency embolization.

Doppler ultrasound specifically monitors the ductus venosus and umbilical venous velocities to evaluate fetal cardiac overload.

In fetal VGAM, ductus venosus (DV) and umbilical venous (UV) Doppler become important markers once the circulation is decompensating, reflecting rising right atrial pressure and impaired diastolic filling. The high‑output state with progressive right‑sided volume overload and ventricular dysfunction leads to increasing central venous pressure, which is transmitted back to the DV and umbilical vein. Abnormal venous Doppler almost always coexists with other markers of advanced disease.
The presence of reversal of flow in the ductus venosus is a sign of increased right heart pressure and overload. On Ductus Venosus Doppler, the classic sign of haemodynamic compromise is attenuation, zero flow, or reversal of the a‑wave during atrial contraction. In a healthy fetus, the a‑wave remains forward because right atrial pressure stays lower than DV pressure in late diastole; in VGAM with elevated right atrial and ventricular end‑diastolic pressures, atrial contraction causes pressure to exceed DV pressure, producing blunting or retrograde flow in the a‑wave. This pattern indicates significantly raised central venous pressure and impaired ventricular compliance, and in published VGAM series is associated with high rates of fetal heart failure, hydrops, and perinatal death (reference).
Pulsatile umbilical venous flow in VGAM context reflects transmission of elevated, often phasic right atrial pressure back into the UV. Normally, the umbilical vein shows continuous, non‑pulsatile forward flow; in VGAM, as right atrial pressure rises and venous compliance decreases, UV flow becomes increasingly pulsatile and may even show brief flow cessation or reversal with atrial systole. The coexistence of DV a‑wave reversal and pronounced UV pulsatility is therefore a strong marker of advanced decompensation and is frequently used, alongside cardiac and arterial Doppler, to identify fetuses at very high risk and to guide discussions about surveillance, timing of delivery, and realistic prognosis.

Umbilical Artery and Placental Resistance:

- There is an important role of the placenta acting as a low-resistance circuit that competes with the VGAM, thereby reducing the volume of blood shunted through the malformation while the fetus is in utero. During fetal life, the placental circulation provides a high-volume, low-resistance "reservoir" that prevents the fetal heart from failing under the strain of the intracranial shunt. The danger occurs at birth when this placental circulation is removed, causing a sudden and significant increase in the flow through the VGAM due to high SVR, often leading to rapid cardiac decompensation. In fetal VGAM, umbilical artery Doppler is an important part of the global haemodynamic assessment but is usually second‑line to cardiac and cerebral Doppler parameters. Most reported fetuses with VGAM have normal umbilical artery waveforms, because placental resistance typically remains low and the main “runoff” is through the cerebral AV shunt rather than the placenta. When umbilical artery Doppler becomes abnormal, this usually indicates that the haemodynamic disturbance is no longer compensated and that placental and systemic perfusion are being significantly affected. If you see absent or reversed end‑diastolic flow (EDF) in the umbilical artery in a fetus with VGAM, it should be interpreted as a marker of advanced compromise rather than a primary placental disease in most cases. In this setting, retrograde end‑diastolic flow implies markedly increased downstream resistance and reduced effective perfusion of the placental vascular bed, which may result from:
- Very high combined cardiac output being “stolen” by the low‑resistance intracranial shunt, leaving relatively reduced forward flow to the placenta (systemic steal).
- Rising placental vascular resistance due to chronic hypoxia and growth restriction once the fetal circulation can no longer compensate.
- Clinically, end‑diastolic flow reversal in the umbilical artery in VGAM is usually associated with other markers of decompensation such as severe cardiomegaly, significant tricuspid regurgitation, hydrops, and abnormal venous Dopplers (ductus venosus a‑wave abnormalities, pulsatile umbilical vein). Its presence would generally indicate a poor prognosis, a high risk of intrauterine demise, and the need for very close surveillance and multidisciplinary discussion about timing and mode of delivery, balancing the risks of extreme prematurity against ongoing in utero compromise. (See reference here)

In fetal life, beyond cardiomegaly and overt signs of heart failure, there are several additional echocardiographic markers that can help refine risk assessment in VGAM. These include detailed right‑ and left‑sided functional indices, systemic runoff measures, and cerebrovascular markers that correlate with haemodynamic load and neurovascular “steal.” No single parameter is sufficient on its own, but a cluster of abnormalities—especially when evolving on serial scans—suggests higher risk of decompensation and poorer outcome. Key additional markers to look for on fetal echocardiography include:

Right heart size and function: Progressive dilation of SVC, innominate vein, right atrium, and right ventricle; increasing degree of tricuspid regurgitation; and evidence of RV dysfunction (qualitative function, reduced TAPSE, abnormal myocardial performance/Tei index) are all markers of advanced volume load.
Pulmonary circulation: Signs of increased pulmonary blood flow (dilated main pulmonary artery and branches, increased pulmonary valve VTI) are common and may be a substrate for later pulmonary vascular disease.

Fetal neuroimaging (detailed neurosonography and MRI) is complementary for characterizing the cerebral malformation and brain parenchyma, while serial echocardiograms are used to monitor haemodynamic impact and guide counselling and timing of delivery. Careful two-dimensional and M‑mode imaging helps document right‑sided predominance, interventricular septal position, pericardial effusion, and any associated structural heart disease, which can modify prognosis. Color Doppler is then used to interrogate the atrioventricular valves and semilunar valves for regurgitation, with particular attention to tricuspid regurgitation as an early marker of right‑sided volume overload and impending cardiac failure in the fetus. Grading the severity of cardiac involvement is crucial for risk stratification and parental counselling. Features associated with poor outcome in fetuses with vein of Galen malformation include marked cardiomegaly, moderate or severe tricuspid regurgitation, elevated combined cardiac index, signs of fetal heart failure (ascites, hydrops, significant pericardial effusion), and Doppler evidence of advanced redistribution such as reversed aortic isthmus flow. These cardiac parameters are often integrated with neuroimaging markers such as varix volume (e.g., ≥ 20,000 mm³) (1), presence of “pseudofeeder” arteries, and brain parenchymal injury to derive a global prognosis and to decide on frequency of surveillance and optimal timing and place of delivery. Serial echocardiography—often every 1–2 weeks in more severe cases—is recommended to track evolution of cardiomegaly and cardiac function, anticipate decompensation around the time of birth, and coordinate multidisciplinary perinatal care, including early postnatal haemodynamic evaluation and planning for neuro‑intervention when appropriate.

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