Fetal for Tuesday, April 8th, 2025

History

A 20-year-old primigravida was referred for third-trimester targeted ultrasonography for "fluid in the 4th ventricle." A fetal MRI was performed after reviewing the ultrasound images. 

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Question

A full-term neonate is delivered following the fetal MRI. Cranial ultrasound at 24 hours after birth confirms the prenatal MRI findings. What is the ideal timing for definitive treatment in an infant without heart or other organ failure?

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Correct answer

At 4-6 months of age

Discussion

Vein of Galen aneurysmal malformation (VGAM) is a rare, high-flow arteriovenous fistula linking deep choroidal arteries to the median prosencephalic vein (MPV), It is distinct from a true aneurysm of the vein of Galen, which does not form due to the presence of the fistula. This anomaly emerges between 6 and 11 weeks of gestation as an aberrant connection prevents the MPV’s normal regression.

The prenatal diagnosis of fetal Vein of Galen aneurysmal malformation (VGAM) can be achieved through a variety of imaging techniques, each providing unique insights into the condition. The most commonly used method is 2D real-time ultrasonography, which may be enhanced with color Doppler to visualize blood flow dynamics and identify the characteristic high-flow arteriovenous fistula. This modality is widely accessible, non-invasive, and effective for initial detection, especially in the third trimester when VGAM often becomes apparent. Additionally, magnetic resonance imaging (MRI) can serve as a complementary tool for a more detailed assessment of the extent of intracranial damage. MRI offers superior soft-tissue resolution, allowing clinicians to evaluate brain parenchyma, detect associated anomalies such as ventriculomegaly or volume loss, and better understand the malformation’s impact on fetal neurodevelopment. 

A systematic review of prenatally diagnosed Vein of Galen aneurysmal malformations (VGAM), which compiled data from 31 studies, identified hydrocephalus and cardiomegaly as the most prevalent prenatal features. Imaging is pivotal, serving dual purposes: evaluating brain injury and delineating VGAM architecture for embolization planning. Typical findings include ventriculomegaly from venous hypertension impairing cerebrospinal fluid resorption, chronic brain volume loss due to venous hypertension and arterial steal, and tectal compression causing obstruction. Venous outflow stenosis, such as in the sigmoid or jugular veins, modulates outcomes—mitigating cardiac strain while intensifying cerebral damage.

The Lasjunias classification distinguishes two VGAM subtypes: the choroidal type, with multiple choroidal arteries traversing a nidus into the MPV, and the mural type, marked by direct fistulas within the MPV wall. Clinically, VGAM is the leading extracardiac cause of high-output heart failure in neonates. Optimal management involves transcatheter embolization at 4 to 6 months, targeting arterial-side fistula closure, often in staged procedures. The Bicêtre neonatal evaluation score informs treatment by gauging end-organ compromise. Prognosis depends on intervention timing and efficacy—newborns with high-volume shunts face poorer outcomes, whereas delaying treatment to 4 to 6 months is linked to improved results. 

Differential diagnosis

Key differential diagnoses include secondary dilation of the true vein of Galen, childhood dural arteriovenous fistulas, and giant aneurysms. Other differentials include midline intracranial cystic masses, such as arachnoid cysts, porencephalic cysts, choroid plexus cysts, pineal tumors, choroid papillomas, and intracerebral hematomas 

Additional images

References

• 1. Tawfiq A, Alsabban Z, Baradwan S. Multidisciplinary care of fetal vein of Galen arteriovenous malformation diagnosed via Doppler ultrasound and magnetic resonance imaging: A case report. Case Rep Womens Health. 2024 May 9;42:e00615. doi: 10.1016/j.crwh.2024.e00615. PMID: 38746059; PMCID: PMC11092392. 2. Di Meglio L, Sica G, Toscano P, Orlandi G, Manzo L, Mazzarelli LL, Sica C, Di Meglio A. A systematic review of prenatally diagnosed vein of Galen malformations: prenatal predictive markers and management from fetal life to childhood. Front Pediatr. 2024 Jul 3;12:1401468. doi: 10.3389/fped.2024.1401468. PMID: 39022219; PMCID: PMC11251923. 3. Diagnostic Imaging: Pediatric Neuroradiology https://books.google.com/books?id=jyYKEQAAQBAJ&lpg=PP1&pg=PP1#v=onepage&q&f=false 4. Society for Maternal-Fetal Medicine; Monteagudo A. Vein of Galen Aneurysmal Malformation. Am J Obstet Gynecol. 2020 Dec;223(6):B27-B29. doi: 10.1016/j.ajog.2020.08.181. Epub 2020 Nov 7. PMID: 33168212.