Description and Causes
Malformations involving the vein of Galen are rare congenital connections occurring between intracranial arteries (usually thalamoperforator, choroidal, and anterior cerebral arteries) and the vein of Galen or other primitive midline vein (37
). These connections can be large direct fistulas, numerous small connections, or a combination thereof. The cause of these connections is unknown. Some investigators have noted a strong association with venous anomalies (absent straight sinus, persistent falcine and occipital sinuses) and suggested that intrauterine straight sinus thrombosis with recanalization is responsible (69
). Raybaud et al. demonstrated that the dilated primitive venous structure represents persistence of the embryonic median prosencephalic vein of Markowski (89
). They suggested that early obstruction of the straight sinus might result in persistence of the primitive veins based upon the need for venous drainage pathways. Moreover, in our experience, vein of Galen malformations are associated with certain cardiovascular anomalies, most commonly aortic coarctation and secundum atrial septal defects (90
FIG. 12-2. A solitary arteriovenous connection (fistula). A. Axial noncontrast CT scan shows a large mass in the right sylvian area (solid arrows) that is hyperdense compared with brain parenchyma. A small focus of calcification (open arrow) is present within the mass. B. After infusion of iodinated contrast, the mass uniformly enhances. C. Coronal T1-weighted image shows a large amount of signal misregistration (arrows) from the mass in the phase-encoding direction. This phase misregistration artifact is essentially pathognomonic for a vascular lesion. D. Arterial phase image from a right internal carotid arteriogram, lateral projection, shows an enlarged Rolandic branch of the middle cerebral artery emptying into a large venous varix at the site of the solitary A-V connection.
Over 90% of the vein of Galen varices falls into the group called “choroidal” malformations (91
). Choroidal malformations are arteriovenous connections from a plethora of vessels, usually numerous choroidal, pericallosal, and thalamoperforator vessels, to the anterior wall of the prosencephalic vein, resulting in a great deal of arteriovenous shunting (92
); the consequence of the shunting is presentation as neonates with CHF. Choroidal malformations have the poorest prognosis, and are usually fatal without treatment. The second, less common, category of vein of Galen malformation is the so-called “mural” malformation (91
). Mural malformations are characterized by fewer (usually one to four) but larger caliber connections with the prosencephalic vein; the posterior choroidal or collicular arteries are most commonly involved. Patients with mural malformations usually present in infancy with developmental delay, hydrocephalus, and seizures but mild or no signs of CHF. The treatment approach to these malformations varies although endovascular therapy has become the method of choice for both and offers a high rate of cure with low morbidity (94
Clinical Presentation and Imaging Findings
The clinical presentation of vein of Galen malformations can be categorized into three groups: (i) the neonate presenting with intractable CHF and loud intracranial bruit, (ii) the infant presenting with hydrocephalus and/or seizures, and (iii) the older child or young adult presenting with hemorrhage (97
). As mentioned in the preceding section, patients in group 1 typically have choroidal malformations, whereas patients in groups 2 and 3 have mural malformations.
FIG. 12-2. (Continued)
With improvements in quality and availability of prenatal imaging, many vein of Galen malformations are now diagnosed antenatally (98
). Prenatal sonograms show a large hypoechogenic to mildly echogenic midline mass that is seen to have rapid flow on Doppler studies. MRI identifies the varix best (Fig. 12-4
) and feeding vessels, and can be used to identify any associated structural abnormalities such as malformation or ischemic injury. If such a patient is identified, the interventional neuroradiology service must be alerted and available to provide assistance at the time of delivery and in the perinatal period. If the patient is found to have neonatal heart failure that is refractory to medical therapy, the neurointerventionalist may need to treat these patients (100
FIG. 12-3. A fourteen-year-old girl with severe unilateral headaches. A. Left internal carotid angiogram, lateral projection, shows a solitary fistula arising from the posterior temporal branch of the posterior cerebral artery. B. Same injection and projection, status post coil embolization, confirms complete closure of the fistula.
If the vein of Galen malformation is not diagnosed prenatally, postnatal neuroimaging becomes critical to making the proper diagnosis. On imaging studies, the dominant feature of the vein of Galen malformation is the varix, which appears as a large mass in the incisural region, sometimes extending rostrally and anteriorly displacing the third ventricle (Fig. 12-4
). On sonography, the varix will appear mildly echogenic on two-dimensional (2D) imaging and show turbulent flow on Doppler (Fig. 12-5
); it is important to demonstrate continuity with the straight sinus or a persistent falcine sinus. Doppler studies may be useful to quantify the rate of flow within the varix for future reference. On CT, the varix will be iso- to hyperdense to brain prior to contrast administration (Fig. 12-5
). Mixed attenuation may be seen if the varix is partially thrombosed. Areas of low attenuation (encephalomalacia, usually secondary to ischemia) and high attenuation (hemorrhage or dystrophic calcification) are often present in the brain parenchyma. The extent of brain injury should be carefully analyzed, and the parents informed of likely neurological and developmental sequelae, before therapy is begun. On MRI, the varix will be hypointense (Fig. 12-4
) resulting from a loss of phase coherence of the mobile protons; mismapped signal will often be seen across the image in the plane of the phase-encoding gradient (Figs. 12-4
). Feeding vessels will be identified on axial images as round areas of signal void in the ambient cisterns and on MRA as thin, curvilinear structures demonstrating flow-related enhancement and connecting to the varix. Areas of acute thrombosis will usually be isointense to brain on T1-weighted sequences and hypointense on T2-weighted sequences, whereas subacute thrombus will have a high intensity on both T1- and T2-weighted sequences. Thrombus of varying age usually lines the wall of the varix. Areas of damaged brain will typically appear hyperintense on T1-weighted images and hypointense on T2-weighted images in the neonate (Fig. 12-6
); they may be difficult to see on FLAIR. Diffusionweighted images will show acute injury as regions of reduced diffusivity (Fig. 12-6
). As the brain begins to myelinate, injured brain is better seen on T2-weighted images and then on FLAIR images (see explanations in Chapter 4
). If left untreated, the fistula will continue to grow, recruiting additional blood supply and engendering new fistulas (Fig. 12-7
FIG. 12-4. Fetal and postnatal MRIs of vein of Galen malformations. A-C. Fetus of 29 week gestational age. Sagittal T2-weighted image (A) shows a large varix (black arrow) above the quadrigeminal plate cistern. The straight sinus (black arrowhead) appears normal or enlarged. Coronal T2 (B) and axial T1 (C) images show the large varix (black arrows). It appears hyperintense in (C) because of inflow of unsaturated protons on this spoiled gradient-echo image. E-H. A two-year-old boy with increased head circumference and Parinaud syndrome (paralysis of upward gaze due to compression of the brainstem tectum). D and E. Sagittal T1-weighted and axial T2-weighted images reveal marked enlargement of a central venous structure (the dilated median prosencephalic vein of Markowski, V) with hydrocephalus resulting from compression of the dorsal midbrain and cerebral aqueduct. F. Left vertebral artery injection, frontal projection in the arterial phase, demonstrates a mural-type vein of Galen malformation supplied by the collicular arteries through a single-hole fistula (curved arrow). G. Left vertebral injection, lateral projection in the late venous phase, shows to advantage the dilated prosencephalic vein of Markowski draining into a persistent falcine sinus. In these cases, the straight sinus is often absent, and it has been proposed that intrauterine thrombosis of the straight sinus results in the vein of Galen malformation. H. Left vertebral injection, frontal projection in the arterial phase following occlusion of the right and left collicular arteries, show complete occlusion of the malformation. The patient made an uneventful recovery and is now neurologically normal.
FIG. 12-4. (Continued)
FIG. 12-5. Newborn with severe intractable congestive failure. A. Portable chest radiography demonstrates cardiomegaly and increased pulmonary vascular markings compatible with pulmonary edema due to high-output CHF apparent on physical examination. B. Transfontanelle color Doppler ultrasonography, sagittal plane, shows prominent anterior cerebral arteries in continuity with an enlarged deep central venous structure. C. Nonenhanced CT brain scan confirms the presence of markedly enlarged central venous structures (V), normal brain development, and the absence of hydrocephalus or hemorrhage. D-H. Complete cerebral arteriography in multiple projections demonstrates a choroidal-type vein of Galen aneurysmal malformation supplied by every major vascular distribution. Arteriovenous shunting converges upon a dilated primitive prosencephalic vein of Markowski continuous with a persistent falcine sinus. Presumably, due to the high-flow state, venous drainage includes persistent occipital sinuses (arrows, H).
FIG. 12-5. (Continued) I-K. Following curative endovascular occlusion of the malformation, MRI brain scan demonstrates the coil mass (C), normal flow through the mature cerebral venous drainage system, the absence of cerebral infarction, and no hydrocephalus. Maximum intensity projection from 2D time-of-flight MR venogram shows intact superficial venous drainage. Drainage of the deep venous system is obscured by susceptibility artifact from the coils. L-N. Complete cerebral arteriography following both transarterial and transvenous embolization confirms complete absence of arteriovenous shunting and durable occlusion of this malformation. The child is now 4 years old, has a normal neurological exam, and meets all developmental milestones. Endovascular techniques are now the preferred treatment method for these lesions.
FIG. 12-6. Damaged brain in a vein of Galen malformation. This newborn presented with CHF. A. Sagittal T1-weighted image shows the large curvilinear varix (V) that compresses the aqueduct (white arrowheads), resulting in hydrocephalus, and anteriorly displaces the posterior wall of the third ventricle (white arrows). B. Parasagittal T1-weighted image shows abnormal subcortical hyperintensity (white arrows), indicating parenchymal injury. C and D. Axial (C) and coronal (D) T2-weighted images show the varix (V), multiple enlarged tortuous vessels around the midbrain and the varix, and abnormal hypointensity of the periventricular white matter (white arrows), indicating parenchymal injury/ necrosis. In addition, the ventricles are enlarged, likely secondary to a combination of hydrocephalus and loss of periventricular white matter volume. E. Average diffusivity (Dav) image shows reduced diffusivity (low signal intensity, arrows) in the posterior frontal periventricular and deep white matter. F and G. Partition image from time-of-flight MR angiogram (F) and maximum intensity projection from MR venogram (G) show the mural type of vein of Galen varix with enlarged anterior cerebral artery (large white arrowhead) and multiple branches and feeders from the posterior circulation (small white arrowheads) terminating in the varix (V). Note the enlarged emissary veins (white arrows in G) helping to shunt blood from the engorged intracranial venous system into extracranial veins.
FIG. 12-6. (Continued)
Aggressive medical management of the cardiac failure associated with Galenic malformations is an essential adjunct to surgery or endovascular procedures, but medical management alone can rarely control the failure. Johnston’s review of neonates presenting with CHF revealed a mortality of 95%, and none were stabilized without surgical intervention (101
). Surgical ligation of the anomalous connections has been described, but the results have been disappointing. In a review of 60 neonates treated by surgery, there were only six survivors; half of the survivors suffered from neurological deficits (101
). Several series have reported the efficacy of endovascular procedures as a palliative or definitive treatment (102
). In the early 1980s, these procedures consisted of free particle embolization. While the majority of these emboli would lodge in the fistulous connections, the risk of an errant embolus occluding a normal cerebral blood vessel was inversely proportional to the flow in the fistula, and the majority of these procedures were palliative. With the development of newer microcatheter delivery systems and embolic agents such as platinum coils (105
), silk sutures, and liquid adhesives (91
), superselective embolization of the fistula connections alone can be achieved (Figs. 12-5
). Mickle et al. developed a technique where the torcular is surgically exposed, a small catheter is placed transvenously through the straight or falcine sinus into the involved vein of Galen, so metal coils can be deposited to diminish the arteriovenous shunting (104
). Although useful in the presence of bilateral transversesigmoid or occipital sinus hypoplasia or occlusion, the transtorcular approach is not often necessary, as embolic agents can be placed via transfemoral venous access.
Over the past 10 years, 34 children with Vein of Galen malformations have been treated at our institution; 26 harbored the choroidal variety and presented with CHF (94
). The first five patients were treated by craniotomy and attempted clipping of the feeding
vessels. All five patients died during or shortly after the surgery. The subsequent eight patients underwent transvascular embolization techniques. Six of the eight survived while two died despite treatment (103
). Of the survivors, one suffered a severe middle cerebral infarct resulting from an errant embolus. Another had a partial visual field deficit, presumably a result of ischemic damage secondary to the underlying disease. The remaining patients are neurologically and developmentally normal with marked reduction of the fistula flow following treatment. At long-term independent follow-up, 61% of patients who survived their initial presentation were neurologically normal or demonstrated only minor developmental delay (96
FIG. 12-7. A thirty-two-year-old woman with vein of Galen malformation and presenile dementia. A and B. Midsagittal T1-weighted and axial T2-weighted images show severe calvarial thickening from chronic anticonvulsant use and extensive flow voids along the posterior falx cerebri and tentorium cerebelli, surrounding the primitive median prosencephalic vein and persistent falcine sinus. The basal ganglia hyperintensity probably represents injured, calcified tissue from chronic venous hypertension. C. 3D Phase-contrast MRA illustrates the dramatic increase in the size of intracranial blood vessels caused by the congenital vein of Galen malformation and subsequent recruitment of additional blood supply from all vascular distributions. D-F. Left internal carotid, external carotid, and vertebral injections, lateral projection in the arterial phase, define the recruitment of blood supply to the fistula from all vascular distributions. Chronic venous hypertension has engendered development of several independent and noncontiguous fistulas of the superior sagittal sinus (black arrow) and falx cerebri (white arrowhead).
FIG. 12-7. (Continued)
FIG. 12-8. A three-month-old infant presents with Parinaud syndrome (paralysis of upward gaze) and an enlarging head circumference. A. Left vertebral artery injection, lateral projection, demonstrates a mural type vein of Galen malformation with two large-caliber connections. B. A microcatheter has been navigated into the fistula site and contrast injected delineating the draining prosencephalic vein (arrows). C-E. Superselective injection following embolization with microcoils demonstrates complete occlusion of the fistula. Note preservation of all normal vessels, including the choroidal vessels, parietooccipital branches, and connection to the distal splenial and pericallosal artery.
Improvements in technique and embolic materials allow vein of Galen malformations to be treated by transarterial or transvenous approaches. These new materials and approaches have resulted in a high rate of successful therapy; indeed, greater than 50% angiographic cure and 75% symptomatic improvement have been achieved in our recent patients, even in those with the high-flow choroidal malformations (106
). Our cure rate is 100% for the less common mural type of vein of Galen malformation that most commonly presents later in infancy with hydrocephalus, seizures, and failure to thrive (94
The following are the current recommendations for treatment of vein of Galen malformations presenting with severe congestive failure.
If the diagnosis is established prenatally, the delivery should be performed at an institution offering endovascular techniques to palliate the patient should intractable CHF develop. Severe heart failure in utero
can result in polyhydramnios and hydrops fetalis, which can be an indication for induced delivery. Close coordination among the obstetricians, neurointerventionalists, neonatologists, and neurosurgeons is essential to optimize planning. Baseline ultrasonography with color flow Doppler should be performed to serve as a baseline for blood flow in evaluating the results of the endovascular techniques. If possible, umbilical arterial and venous catheters should be placed at the time of delivery to allow repeated vascular access for both diagnostic and therapeutic procedures. These indwelling catheters obviate the necessity for repeated femoral punctures in the fragile neonatal femoral artery. A CT or MRI should be performed to assess any parenchymal damage already produced by the congenital fistula, disclose hydrocephalus, which may require ventriculoperitoneal shunting, and serve as a baseline.
FIG. 12-8. (Continued)
If intractable congestive failure persists despite aggressive medical management, angiography is performed to delineate the vascular anatomy. Palliative arterial embolization can be performed at this time, preferably with superselective catheterization of each feeding pedicle to reduce the risk of ischemic damage to normal surrounding brain. The embolization procedure may be repeated if congestive failure persists. If the congestive failure continues and further arterial embolization is considered risky or technically impossible, transvenous embolization may become necessary. An arteriogram is performed to localize the draining venous sinuses. If the draining venous sinuses are patent, the transfemoral or transumbilical routes can be used to access the varix. On rare occasions, when the lateral sinuses are absent or severely hypoplastic, surgical access to the intracranial venous system is necessary. A small burr hole is made over the draining falcine or straight sinus. A needle puncture is made into the sinus, a catheter advanced into the varix, and platinum coils deposited. These techniques can be curative or palliative. When palliative, they alleviate the congestive failure and allow the child to develop normally until a definitive treatment can be performed with further surgical or radiological techniques. MRI scanning is useful in our experience to assess brain development, the degree of thrombosis in the fistula site, and delayed development of hydrocephalus.