Spontaneous thrombosis of vein of Galen malformation.

Vein of Galen malformation (VOGM) is a rare intracranial vascular malformation. Before the advent and advancement of various endovascular techniques, there was dismal prognosis. Rarely, this condition may spontaneously thrombose without the need for surgical or endovascular treatment with good prognosis. We report a case of an 8-month-old infant who had serial imaging, suggestive of VOGM and presented to us for further management, wherein the imaging revealed spontaneous thrombosis.

Introduction

In 1895, Steinheil was the first to describe the entity called galenic malformation, which he called as a “varix aneurysm.”[1] Vein of Galen malformations (VOGM) are rare intracranial vascular anomalies, constituting 30% of all neurovascular abnormalities in children, and 1% of all pediatric congenital anomalies.[2] Raybaud et al. recognized that the ectatic vein is not the vein of Galen but the median prosencephalic vein of Markowski, which is an embryonic precursor of the vein of Galen.[3] This condition is a result of arteriovenous communication between arterial network and the median prosencephalic vein.[4] Rarely, there may be spontaneous thrombosis of which <50 such cases have been reported in literature till date.[56] Clinical significance in identifying this entity lies with the fact that there is a significant change in the management and prognosis.

Case Report

We are presenting a case of an 8-month-old male baby born of consanguineous parentage, brought with a history of the progressive increase in the size of the head, for 3 months of age. He had normal motor, mental, and social milestones for his age. He had serial computed tomography (CT) and magnetic resonance imaging (MRI) done elsewhere which had revealed a patent VOGM obstructing the aqueduct and resulting in hydrocephalus.

During evaluation, an MRI study of the brain was obtained [Figures 1 and 2] which showed a circumscribed round extra-axial lesion measuring 4.6 cm × 4 cm posterior to tectum, indenting the posterior part of third ventricle causing dilatation of third and lateral ventricles. The lesion demonstrated thick T1 hyperintense/T2 hypointense rim with the loss of flow void within in the form of T1 hypointense/T2 hyperintense center. These features were suggestive of aneurysmal dilatation of median prosencephalic vein with thrombus of varying ages. On gradient sequence peripheral blooming was evident. On diffusion-weighted imaging, hyperintensity suggestive of restriction was noted. On magnetic resonance angiography, no hypertrophied vessels or feeders were appreciable. It was decided to initially perform diagnostic cerebral angiography, to demonstrate and obliterate the arteriovenous fistula before treatment of hydrocephalus.

Figure 1

(a) Axial section, T1-weighted sequence showing vein of Galen malformation with hyperintense thrombus in the periphery and hypointense center. (b) Axial section, T2-weighted sequence showing vein of Galen malformation with hypointense thrombus in periphery with loss of flow void in center. (c) Sagittal section, T2 fluid-attenuated inversion recovery sequence showing vein of Galen malformation with similar characteristics as in T2-weighted sequence, i.e., hypointense periphery and hypointense center causing obstruction at the level of posterior part of third ventricle and at aqueduct of sylvius

Figure 2

(a) Axial section, gradient echo sequence showing vein of Galen malformation with hyperintense thrombus in the periphery and hypointense center. (b) Axial section, diffusion weighted sequence showing facilitated diffusion in the periphery and restriction in the center. (c) Three-dimensional time of flight magnetic resonance angiography-no obvious feeders/parenchymal arteriovenous malformation

Digital subtraction angiography (DSA) [Figure 3] was performed under general anesthesia, which showed no contrast opacification within the median prosencephalic vein. There were no hypertrophied feeders or parenchymal arteriovenous malformation. Diagnosis of thrombosis within the vein of Galen was confirmed and further endovascular management was deferred. Over time, with a reduction in size of thrombus, the obstructive hydrocephalus is expected to resolve. However, this is likely to be a slow process. Therefore, a ventriculoperitoneal (VP) shunt was inserted. Following which CT brain plain [Figure 4] was obtained which showed VP shunt tip in situ with mild reduction in ventricular dilatation in addition to the peripherally dense and centrally hypodense thrombosis within VOGM.

Figure 3

(a) Digital subtraction angiography-lateral view, posterior circulation injection in arterial phase shows no abnormal feeders or arteriovenous malformation. (b) Digital subtraction angiography-lateral view, posterior circulation injection shows no abnormal feeders or arteriovenous malformation in venous phase no contrast opacification within the thrombosed vein of Galen

Figure 4

Axial section, computed tomography plain brain showed vein of Galen malformation with hyperdense thrombus in the periphery with relatively hypodense center. Foci of calcification seen in the periphery. Ventriculoperitoneal shunt tip noted in right lateral ventricle with mild reduction in the ventricular dilatation

Discussion

By 11th week of intrauterine period, after the development of the basal ganglia in a normal individual there is formation of paired internal cerebral veins, which annex the venous drainage of the choroid plexuses, leading to regression of the median prosencephalic vein, except for its most caudal part, which joins the internal cerebral veins to form the vein of Galen.[5] VOGM results from the development of an arteriovenous communication between primitive choroidal vessels and the persistent median prosencephalic vein of Markowski.[4] There are several classifications of VOGM. Two commonly accepted classifications are provided by Yasargil and Lasjaunias. According to Yasargil, there are four types.[7] First, three types of lesions involve a direct fistulous communication with the vein of Galen without proximal nidus. The Type IV lesion includes parenchymal arteriovenous malformations draining into the vein of Galen. On the other hand, according to Lasjaunias et al., depending on the location of fistula, there are two types A: Choroidal type of malformation (Yasargil Type II and Type III) B: Mural type of malformation (Yasargil Type I).[8]

Spontaneous thrombosis within VOGM is explained by Nikas et al., as a result of the formation of blood clots within the malformation leading to reduced blood flow, in turn leading to reduced intra-aneurysmal pressure with subsequent vanishing aneurysm.[9] According to Konovalov et al., thrombosis occurs due to low blood flow and insufficient venous drainage.[10] While Brunelle, based on his studies with animals, found that increased pressure and venous flow turbulence result in progressive myointimal proliferation with hypertrophy of the vein of Galen wall, leading to gradual venous thrombosis.[11]

According to literature, oldest clots are found at the periphery, posteriorly and laterally while youngest towards the center, anteriorly and close to the origin of aneurysm.[5] On the pathological ground, this thrombosis is described as vintage layering of clot.[5] Other etiologies of thrombus formation could be mass effect of adjacent or intra aneurysmal clot, posthemorrhagic edema, vascular spasm, and regressive changes in the vessel walls.[9]

Treatment and prognosis

Patients with patent VOGM would either require surgical or endovascular management.

In these patients, ventricular shunting may worsen the cerebral venous hypertension, and should be avoided before elimination of the arteriovenous shunt. Hence, VP shunt is not tolerated by these infants and must be preceded by emergency endovascular embolization.[12]

In a rare clinical setting as in our case, the aneurysm may get spontaneously thrombosed resulting in anatomical and clinical cure without need for further treatment. Spontaneous thrombosis of VOGM is a very rare entity. Thrombosis is more common in mural type, since this category have relatively slow flow.[13] In our case, DSA confirmed thrombosis of VOGM and thereby occlusion of arteriovenous shunting. Spontaneous thrombosis is associated with good outcome in about 70% of the cases.[5]

Conclusion/teaching Point

VOGM is a rare intracranial vascular malformation with the occurrence of spontaneous thrombosis in extremely rare setting. Identification of this rare entity is very important, since the critical decision of management completely differs with good prognosis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.