Vein of Galen Malformations

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. 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. Raybaud et al. demonstrated that the dilated primitive venous structure represents persistence of the embryonic median prosencephalic vein of Markowski. They suggested that early obstruction of the straight sinus may result in persistence of the primitive veins based upon the need for venous drainage pathways. Moreover, vein of Galen malformations are associated with certain cardiovascular anomalies, most commonly aortic coarctation and secundum atrial septal defects in our experience.

Patients with mural malformations usually present in infancy with developmental delay, hydrocephalus and seizures but mild or no signs of congestive heart failure.

Over ninety percent of the vein of Galen varices falls into the group called “choroidal” malformations. Choroidal malformations are arteriovenous connections in the anterior wall of the prosencephalic vein supplied by a plethora of vessels, usually numerous choroidal, pericallosal, and thalamoperforator vessels. They have a great deal of arteriovenous shunting, and affected patients typically present as neonates with congestive heart failure. 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. 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 congestive heart failure. 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.

The clinical presentation of vein of Galen malformations can be categorized into three groups: (1) the neonate presenting with intractable congestive heart failure (CHF) and loud intracranial bruit; (2) the infant presenting with hydrocephalus and/or seizures; and (3) the older child or young adult presenting with hemorrhage. As mentioned in the preceding section, patients in group 1 typically have choroidal malformations, whereas patients in groups 2 and 3 have mural malformations.

With improvements in quality and availability of prenatal ultrasound, many vein of Galen malformations are now diagnosed antenatally. Prenatal sonograms show a large hypoechogenic to mildly echogenic midline mass that is seen to have rapid flow on Doppler studies. If such a patient is identified, the interventional neuroradiology service must be alerted. If the patient is found to have neonatal heart failure that is refractory to medical therapy, the neurointerventionalist should be available to treat these patients immediately after birth or in the first few days of life.

If the vein of Galen malformation is not diagnosed prenatally, a postnatal neuroimaging study become critical to making the proper diagnosis. On imaging studies, vein of Galen malformations appear as large masses in the posterior incisural region, sometimes extending rostrally and anteriorly displacing the third ventricle. On sonography, the varix will appear mildly echogenic; it is important to demonstrate continuity with the straight sinus or a persistent falcine sinus. Doppler studies may be useful to quantitate the rapid flow within the varix. On CT, the varix will be iso- to hyperdense to brain prior to contrast administration. 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 MR, the varix will be hypointense resulting from a loss of phase coherence of the mobile protons. Feeding vessels will be identified as thin, curvilinear hypointensities 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 may be difficult to see on T2 weighted images of neonates, as they merge imperceptibly with the normal surrounding hyperintense white matter. Thin section T1 weighted images are more reliable until the brain begins to myelinate.

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. Surgical ligation of the anomalous connections has been described, but the results have been disappointing. In a review of sixty neonates treated by surgery there were only six survivors; half had neurological deficits. Several series have reported the efficacy of endovascular procedures as a palliative or definitive treatment. In the early 1980's, 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, silk sutures, and liquid adhesives, superselective embolization of the fistula connections alone can be achieved. Mickle et al. have 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, and metal coils are deposited to diminish the arteriovenous shunting. Although useful in the presence of bilateral lateral dural sinus hypoplasia or occlusion, the transtorcular approach is not often necessary, as embolic agents can be placed via transfemoral venous access.

Over the past ten years, thirty-four children with Vein of Galen malformations have been treated at our institution; twenty-six harbored the choroidal variety and presented with congestive heart failure. 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. 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. 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, 50% angiographic cure and 75% symptomatic improvement has been achieved in our recent patients, even in those with the high-flow choroidal malformations. 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.

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 congestive heart failure 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, the endovascular team, 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 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 MR 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.

At our institution, 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, a transvenous embolization is performed. 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 and demonstrate the degree of thrombosis in the fistula site.