Neuroradiology Case of the Week

Case 6

Lawrence Buadu MD, PhD, P-L Westesson MD, PhD, DDS,
Ramon DeGuzman MD, and Yugi Numaguchi MD, PhD

Clinical Presentation: A 1-day-old, full-term, female was born via prolonged forceps/vaginal delivery. Pregnancy was complicated by in utero diagnosis of cranial AV malformation. At birth, the infant was floppy and cyanotic requiring stimulation and PPV.

He has cardiac anomalies including, CPAPUR, ASK, and PDA. He has had several episodes of upper extremity flexing, lower extremity extension and right eye deviation.

Radiographic Findings:

Figure 1: Grayscale ultrasound showing a sonolucent posterior third ventricular mass.

Figure 2: Color Doppler image showing turbulent flow within the mass.

Figure 3A: Sagittal T1 weighted MR imaging showing hypointensity of the varix resulting form a loss of phase coherence of mobile protons.	Figure 3B:Axial T2 weighted image showing the varix with collateral vessels.

Figure 4: MRA depicts arterial feeders to better advantage.

Figure 5: MRV depicts venous collaterals.

Figure 6A	Figure 6B
Figure 6A&B: Diffusion weighted images and ADC maps show ischemic changes from venous steel.

Diagnosis: Vein of Galen Malformation

Discussion:

Classification: Several classifications based on the angioarchitecture and anatomy have been developed the most widely used scheme is from Yasagil’s experience [1]. In his classification there are four subtypes of vein of Galen malformations.

• Type I: Lesions are direct arteriovenous shunts to the medial prosencephalic vein supplied by choroidal, pericallosal, and superior cerebellar arteries.
• Type II: Lesions have similar shunts supplied by transmesencephalic and transdiencephalic perforators.
• Type III: Lesions are combinations of types I and II.
• Type IV: Lesions consists of an arteriovenous shunt distant from the vein of Galen but drains into it, producing dilatation.

   Another useful and practical classification has arisen from the endovascular group at Bicetre Hospital in Paris [2]. They have classified anomalous arteriovenous shunts involving the vein of Galen into two groups: (a) true vein of Galen aneurysmal malformations (VGAMs) and (b) vein of Galen dilatations that occur secondary to high-flow parenchymal AVMs draining into this vessel.

   Two subtypes of VGAMs have been identified on the basis of their angioarchitecture: (a) a mural form and (b) a choroidal form. The so-called choroidal form is the most common type. Choroidal AVMs classically demonstrate an abundance of bilateral arterial supply from the choroidal arteries, pericallosal arteries and subependymal branches of the thalamoperforating vessels. These vascular connections are extracerebral, subarachnoid and communicate with the median pros encephalic vein.

   Mural-type AVMs represent approximately one-third of VGAMs, They receive uni- or bilateral supply from the collicular and posterior choroidal vessels and drain into a persistent median prosencephalic vein, Outlet obstruction is common.

Etiology: Vein of Galen aneurysmal malformations probably represent an arteriovenous fistula (AVF) in the wall of a persistent embryonic vascular channel called the median prosencephalic vein [3, 4]. This dorsal vein lies in the roof of the diencephalons and drains the developing choroids plexus [5]. In turn the median prosencephalic vein drains into a primitive accessory sinus called the falcine sinus.

   By week 10 of fetal development the median prosencephalic vein regresses as the definitive internal cerebral veins appear. A caudal remnant remains as the vein of Galen [6]. If the median prosencephalic vein does not regress, a fistulous connection with the primitive choroidal arteries may persist. A VGAM is the result.

Imaging: On imaging studies these malformations appear as large masses in the posterior incisural region, sometimes extending rostrally and anteriorly displacing the third ventricle.

Ultrasound: Transcranial B-mode ultrasound shows a sonolucent posterior third ventricular mass (Fig. 1) and obstructive hydrocephalus. It is important to demonstrate continuity with the straight sinus or a persistent falcine sinus. Color flow imaging (Fig. 2) often discloses turbulent bi-directional flow within the enlarged vein of Galen [7].

Computed Tomography: An iso- or hyperdense midline mass posterior to the third ventricle is seen on nonenhanced studies. Mixed attenuation may be seen if the varix is partially thrombosed. Patent VGAMs enhance strongly following contrast administration. Mass effects with hydrocephalus and secondary encephalomalacic changes are common [8].

Magnetic Resonance Imaging: On MR the varix will be hypointense resulting form a loss of phase coherence of mobile protons (Fig. 3). Areas of acute thrombosis will be isointense to brain on short TR/TE sequences and hypointense on T2 weighted spin echo or gradient echo sequences, whereas subacute thrombus will have a high intensity on both short TR and long TR spin echo sequences. Thrombosis of varying age sometimes lines the wall of the varix. MRA (Fig. 4) and MRV (Fig. 5) can depict the arterial feeders and delineate venous flow patterns. T2 and diffusion weighted sequences (Fig. 6) show ischemic white matter changes secondary to venous steel.

Cerebral Angiography: Arterial supply to VGAMs is usually via enlarged choroidal and thalamoperforating arteries. In the fistula group the posterior choroidal arteries are the dominant supply, followed by anterior choroidal and thalamoperforating and anterior cerebral branches. In the nidus type the thalamoperforating vessels are the common arterial feeders [9].

   Venous drainage patterns include aneurismal dilatation of the vein of Galen (venous varix) with or without stenosis. Drainage into an accessory or inferior falcine sinus is also common [10]. The falcine sinus is a primitive channel that connects the vein of Galen into the superior sagittal sinus coursing posterior superiorly within the falx cerebri.

Complications: Complications of VGAMs include obstructive hydrocephalus, atrophy of adjacent structures due to compression, venous thrombosis and hemorrhage. Periventricular leukomalacia, cortical laminar necrosis and atrophy secondary to ischemia and steal phenomenon or high output congestive heart failure are common [5].

Treatment: The current recommendations for treatment of vein of Galen malformations include transarterial or transvenous embolization techniques. Close coordination among the obstetricians, neurosurgeons, neonatologists and the endovascular team is essential to optimize prenatal planning.

References:

1. Yargasil MG. Microneurosurgery. New York: Thieme 1988.
2. Garcia-Monaco R, Lasjuanias P, Berenstein A. Therapeutic management of vein of Galen aneurysmal malformations. Interventional Neuroradiology: Endovascular Therapy of the Central Nervous System: New York: Raven, 1992:113-127.
3. Lasjuanias P. Vascular Diseases in Neonates, Infants and Children. New York: Springer Verlag 1997.
4. Tomsick TA, Ernst RJ, Twe JM, et al. Adult choroidal vein of Galen malformation. AJNR 1995; 16: 861-865.
5. Brunelle F. Arteriovenous malformation of the vein of Galen in children. Pediatr Radiology 1997; 27:501-513.
6. Horowitz MB, Jungreis CA, Quisling RG, Pollock I. vein of Galen aneurysms: a review and current perspective. AJNR 1994; 15:1486-1496.
7. Westra SJ Curran JG, Duckwiler GR et al: Pediatric intracranial vascular malformations: evaluation of treatment results with color Doppler US. Radiology 1993; 186:775-783.
8. MartelliA, Scott G, Harwood-Nash DC et al: Aneurysm of the vein of Galen in children: CT and angiogaphic correlations, Neuroradiol 1980; 20:123-133.
9. Seidenwurm D, Berensteis A: Vein of Galen malformation: clinical relevance of angiographic classification and utility of MRI in treatment planning, Neuroradiol 1991; 33(suppl):153-155.
10. Lasjuanias P, Garcia-Monaco R, Rodesh G, Terbrugge K: Deep venous drainage in great cerebral veins (vein of Galen) absence and malformations, Neuroradiol 1991; 33:234-238.