Vascular Cerebral Anomalies

Definition

Aneurysm of the vein of Galen is a complex arteriovenous malformation (AVM) characterized by multiple communications between the system of the vein of Galen and the cerebral arteries. Fig. 42.1 is a diagrammatic representation of the cerebral venous system. This anomaly consists of dilatation of the median prosencephalic vein in association with AV fistulas within the wall of the vein, or multiple shunts communicating with the anterior part of the vein.

Prevalence and Epidemiology

Aneurysm of the vein of Galen is a rare vascular malformation; it represents less than 1% of all intracranial AVMs.

Etiology and Pathophysiology

Aneurysm of the vein of Galen is thought to be a developmental abnormality. However, several previous publications reported normal cranial US scans in the early second trimester, but a vein of Galen malformation was detected later on in the pregnancy.

Consequences of a vein of Galen malformation include the following :

• 1.

  Cardiac failure: high-velocity left-to-right shunt through the AV communication causes cardiac failure. Left-to-right shunt leads to an increase in the workload of the heart, of the cardiothoracic ratio, and often of the heart rate. Postnatally, infants often have pulmonary hypertension.

• 2.

  Vascular steal: AV shunt in the brain can result in a vascular steal from other arteries in the brain. The result is progressive cerebral atrophy.

• 3.

  Venous hypertension: Increase in the venous pressure can lead to a reduction in the absorption of cerebrospinal fluid and progressive ventriculomegaly.

Manifestations of Disease

Imaging Technique and Findings

Ultrasound.

Prenatal diagnosis of the vein of Galen malformation has been made on several occasions. A classic finding is an echo-poor structure in the posterior region of the midline superior to the tentorium cerebelli and superior to the thalamus ( Fig. 42.2 ).

The sagittal sinus is dilated in most cases. US with color flow mapping and Doppler interrogation reveals the presence of the turbulent flow typical of an AV malformation ( Fig. 42.3 ). However, the flow may be absent if the lesion has undergone thrombosis. Three-dimensional (3D) power angiography has been used to define the structure of the malformation.

Magnetic Resonance Imaging.

Prenatal magnetic resonance imaging (MRI) has been used to assess vascular connections and explore cerebral damage. Many associated anomalies have been described with the vein of Galen malformation. Table 42.1 lists commonly associated abnormalities. Fig. 42.4 shows cardiomegaly in a case of an aneurysm of the vein of Galen.

TABLE 42.1

ASSOCIATED ANOMALIES IN VEIN OF GALEN MALFORMATION ( N = 25)

Data from Sepulveda W, Platt C, Fisk N: Prenatal diagnosis of cerebral arteriovenous malformation using color Doppler ultrasonography: case report and review of the literature. Ultrasound Obstet Gynecol 6:282–286, 1995.

Ultrasound Finding	n (%)
Cardiomegaly	16 (64)
Enlarged neck veins	8 (32)
Ventriculomegaly	6 (24)
Polyhydramnios	4 (16)
No associated findings	6 (24)

Postnatal

Most affected newborns show features of cardiac failure. Control of cardiac failure is the most immediate postnatal intervention. Definitive postnatal treatment consists of total excision of the lesion, surgical ligation, or embolization. Lasjaunias et al. reported their experience of 317 cases with vein of Galen aneurysms. Initial management involved control of heart failure with diuretics and digitalis. Endovascular embolization was successfully employed as the first-line definitive treatment in 233 of 317 infants. Despite treatment, 23 (10.6%) newborns died. Severe mental retardation was reported in 20 infants, and moderate mental retardation was reported in 30 infants. Normal neurologic development was reported in 74% of survivors.

Spontaneous thrombosis of the malformation in the postnatal period has been reported. In these cases, the thrombosed lesion was seen as a mass of high density or intensity values on computed tomography (CT) or MRI. However, in most cases, the lesion does not resolve spontaneously, and definitive postnatal treatment is required.

Definition

DSM is a rare disorder, and reported prognosis is poor, with a mortality rate of 38%. These malformations are rarer than vein of Galen aneurysms. DSM often manifests in the prenatal period.

Prevalence and Epidemiology

No robust data are available on the prevalence of DSM.