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1991-11-20-12 Vein of Galen Malformation © Suma www.TheFetus.net
Vein of Galen Malformation

Vincenzo Suma, MD, Alberto Marini, MD, Onofrio S. Saia, MD, Luca Rigobello, MD

Ultrasonic Service, Dept. of Obstetrics & Gynecology, Ospedale Civile, Padua, Italy.

updated 2010-10-13-13 by Eva Leinart*, MD
*  Inner Vision Women's Ultrasound, Nashville, Tennessee, USA.

Synonyms
Vein of Galen aneurysm,
Ectasia or varix of the vein of Galen

Definition
Rare arteriovenous malformation of the central nervous system characterized by a high venous flow.

Types
1) arteriovenous fistula, 2) arteriovenous malformation with ectasia of the vein of Galen and 3) varix of the vein of Galen [1,2]

Prevalence:
Unknown.

Etiology: Unknown.

Pathogenesis
Aneurysmal dilation with arteriovenous fistula. Results from
immaturity of the cerebral vascular system with persistence of fetal vessel. It actually involves median prosencephalic vein of Markowski. Develops between 7 -12 weeks of fetal development when the median prosencephalic vein drains the large choroid plexuses.

Diagnosis
Midline cystic mass in the pineal region of the brain with high velocity flow on Doppler examination. Size depends on volume of shunt.

Associated anomalies: Hydrocephalus, non-immune hydrops and porencephaly.

Differential diagnosis

  • Arachnoid cyst
  • Porencephalic cyst
  • Choroid plexus cyst
  • Choroid papilloma
  • Teratoma
  • Congenital dural arteriovenous fistula


Prognosis:
Poor when cardiac failure and hydrops is present.

Recurrence risk: Not increased.

Management: Ultrasound monitoring, no known in utero treatment. Risk of intrauterine or early neonatal death due to congestive heart failure, requires agressive postnatal care. If possible, method of treatment is emergency embolization or surgery.

Introduction

The aneurysmal enlargement of the vein of Galen is a rare and complex malformation which involves several afferent branches of the vertebrobasilar system and carotid arteries draining into the great cerebral veins. These vessels are located in the brain deeply and posteriorly above the pineal gland, in the subarachnoid space called "cistern of the great cerebral vein of Galen" (fig. 1).

Figure 1: Schematic illustration of the venous drainage of the brain. Left: normal; right: pathologic. 1: right internal cerebral vein, 2: left internal cerebral vein, 3-4: right & left basilar veins; 5-6: right & left medial occipital veins; 7: tentorium; 8: left transverse sinus; 9: torcular Herophilus; 10: inferior sagittal sinus; 11: superior sagittal sinus; 12: falx; 13: vein of Galen aneurysm.

 

Case report

A 32-year-old primigravida patient was referred for routine ultrasound at 33 weeks of pregnancy. Her history was unremarkable. Two previous ultrasounds, done elsewhere during the 16th and 25th weeks, demonstrated a live singleton fetus without apparent structural abnormalities and with normal morphological development. An examination was done with an ATL Ultramark 5, with pulsed Doppler and convex 5 MHz transducer.

Ultrasound revealed, in the axial section of the cranium, the presence of a well-defined fluid-filled oval structure measuring 24 x 19 mm, located posteriorly above the thalamus. Angling the probe slightly behind the oval mass revealed a tubular anechoic prolongation reaching up to 3 mm from the skull at the inion (fig. 2).

Figure 2: 33rd week of pregnancy: a midline supratentorial cystic lesion with draining vessel that extends posteriorly in the direction of the straight sinus is visible.

The lateral, third and fourth ventricles appeared normal and no other intracranial abnormalities were present. Pulsed Doppler of the cystic lesion and its elongation throughout all its extension demonstrated a high velocity venous flow (fig. 3).

Figure 3: Pulsed Doppler in draining vessel documents continuous venous flow.

This type of flow was not detected anywhere else. Ultrasound imaging suggested the possibility of an arteriovenous aneurysm, and the location strongly suggested an aneurysm of the vein of Galen. The diagnostic, prognostic and therapeutic problems were frankly discussed with the parents by a team of obstetricians, echographists, neurosurgeons and pediatricians.

As a precaution, the mother underwent a cesarean section after the 39th week. The male newborn had its umbilical cord around the neck and presented an Apgar index of 7 and 10 at 1 and 5 minutes. The weight was 3,310 grams, cranial circumference 36.2 cm (75th percentile.), thorax diameter 33 cm, and the whole length 50 cm. Transfontanellar ultrasound performed immediately after delivery showed an aneurysmal sac of 25 x 20mm, located behind the splenium of corpus callosum (fig. 4).

Figure 4: Transfontanel lar scan, 3 hours after birth. The aneurysmal sac is shown behind the splenium of the corpus callosum.

A CT scan confirmed a big aneurysm of the vein of Galen, with marked contrast medium enhancement (fig.5). The superior sagittal sinus and the straight sinus together with torcular herophili (confluence of the sinuses) appeared widened.

Figure 5: CT scan with contrast medium. Note the enlarged lateral ventricles and the large well-defined globular mass in the pineal region. Contrast enhancement emphazises the venous drainages and Herophylus torcularis.

Hydrocephalus was not present at birth. Echocardiography showed no heart malformations, with normal Doppler, but the right-sided structures (atrium, ventricle, and main pulmonary artery) were slightly enlarged. The child had no signs of cardiac decompensation, polypnea, or liver enlargement. These findings and the absence of hypertensive hydrocephalus allowed postponing of the surgical treatment.

During the following months, the neuro-anatomical development was monitored with serial transfontanellar echography and CT scans. At 9 months, the baby underwent MRI that permitted further definition of the aneurysm and the whole brain (fig. 6). After his first year, the patient underwent selective angiographies in our hospital and in other centers, with the intent to embolize the aneurysm. The infant is currently alive and well.

Figure 6: MRI; midline sagittal projection. T1-weighted image shows the spheroidal lesion with a signal void that is typical of a high flow arteriovenous malformation. The aneurysm causes a mass-efect on the aqueductus of Silvius, the posterior part of the third ventricle and the splenium of the corpus callosum.

 

Discussion

Aneurysm of the vein of Galen was first described by Jager in 1937 [3]. Less than 200 postnatal cases had been reported in the literature up to 1984. The use of high resolution echography and pulsed Doppler sonography allowed the first prenatal diagnosis [4-13]. There are only 10 prenatal diagnoses of aneurysm of the vein of Galen by ultrasound and/or pulsed Doppler. We have attempted to identify the common features of these situations (Table 1).

Table 1: Review of cases detected prenatally

Author

Presenting symptoms

Age*

Features

Outcome

Vintzileos [4]

"Cyst in the head" at outside examination

37

Normal at 22 weeks, enlarged atria and liver 8x50mm

Apgar 3, 8 (1, 5 min). Alive at 10 months, under medical control

Rizzo [5]

Suspicion of hydrocephalus

37

Normal anatomy, no hydrops 24x29 mm

NSVD, Apgar 9, 10 (1, 5 min), alive at 3 months

Mendelson [6]

Routine

34

Cardiomegaly 25x25 mm

Female, NSVD-surgery, death

Ordorica [7]

Routine

27,35

Ballantyne’s syndrome 

Female, Cesarean Section, cardiovascular collapse, death

Reiter [8]

Routine

34

Hydrocephalus, cardiac failure, hepatomegaly,  ascites, 25 mm

Female NSVD, death

Hirsch [9]

Routine

NA

NA

NA

Mao [10]

Routine

38

IUGR, 25x20 mm

Female, NSVD (forceps), death

Filly [11]

NA

NA

NA, 20 mm

NA

Mizejewsky [12]

Elevated maternal AFP in the third trimester

37

Hydrocephalus
Cardiomegaly
NA

Female, Cesarean Section, death

Jeanty [13]

Suspected hydrocephalus, low AFP

40

Cardiomegaly
NA

Cardiac failure, death

 * age at detection, AFP = a-fetoprotein, NSVD = normal spontaneous vaginal delivery, NA = not available. Grey cells are fatal outcome.

Definition

Vein of Galen malformation includes different arteriovenous fistulae located in the vicinity of the midbrain that vary from a single large aneurysmal dilatation of the vein of Galen to multiple communications between the vein and the carotid and vertebrobasilar systems [14]. There 3 types described: arteriovenous fistula, arteriovenous malformation with ectasia of the vein of Galen and varix of the vein of Galen [1,2]. Both the ectasia and the varix appear to present later in life with bleeding episodes and do not present in the neonate with cardiac failure [2]. Rarely, an aneurysm with a single feeder can exist [15]. Arteriovenous fistulae associated with a varix are not part of the definition when they are located anywhere else in the brain [16].

Embryology

According to Padget [17], the primary cerebral vascular plexus becomes arterial and venous vessels between 7 and 9 weeks of gestation. The primary arteries and veins of the neural tube rise from distinct capillary plexuses and are formed by simple endothelial canal joints forming right angles. It is thought that the Galenic system arises from the choroidal veins and the arteriovenous fistula, that give rise to the aneurysm of the vein of Galen, and should correspond to the dimension and the number of the perpendicular vessels crossings through the primary arteries and veins. The pressure of high flow and turbulent arteriovenous shunt leads to the arterialization of the vein of Galen with concomitant increase of volume and thickness of its walls. Histological studies have shown that the wall of the aneurysm is thickened and may have an irregular muscle coat, suggesting hemodynamic perturbations [14,18]. Recent studies have suggested that since angiography may fail to opacify the straight sinus and part of the transverse sinus, the defect probably occurs in the wall of the vein, instead of within the vein [14,18]. Also, since some of the feeders may belong to arteries of the velum interpositum and of the ambient cistern, this suggests that the vessel cannot represent the vein of Galen or an internal cerebral vein but a persistent fetal vein: the median prosencephalic vein. This important study therefore places the origin of the abnormality at around the 7th to 12th week period, during which the median prosencephalic vein drains the large choroid plexuses.

Ultrasound diagnosis

A cystic or tubular mass on the midline of brain or in the pineal region with a turbulent venous and/or arterial flow with Doppler signal is typical of the diagnosis. However, when a clot has formed, it may be iso - or even hyperechoic [19].

Differential diagnosis

Differential diagnosis with other midline cystic cerebral lesions (table 2) is based on the typical localization of aneurysm of the vein of Galen, the presence of a high blood flow within the lesion and the frequent finding of hydrocephalus and cardiomegaly.

Arachnoid cysts are commonly supratentorial and lack flow on Doppler. They appear as thin-walled, fluid-filled cystic masses that usually displace adjacent brain structure [20-22].

Porencephalic cysts are fluid-filled spaces replacing normal brain parenchyma. They do not create any mass effect and often communicate with the lateral ventricles or subarachnoid space.

Choroid plexus cysts are easily discriminated by their location in the choroid plexus. They are identified in the second trimester and usually resolve by the 24th week [23-25], although occasional cysts may resolve later [26]. They are usually located in the posterior aspect (atria) of the lateral ventricles, and might be uni or bilateral. Rarely, large choroid cysts may expand the ventricular wall. In that case, there seems to be a significantly greater risk of chromosomal abnormality (trisomy 18) [27].

Choroid papilloma are characterized by a large, lobulated, highly echogenic mass in the trigone of the lateral ventricle with uniform dilation of the ventricular system and often with an increase in subarachnoid space suggesting communicating hydrocephalus [28].

Intracranial teratomas are generally large tumors that demonstrate a heterogeneous, bizarre appearance [29]. Deformation of the cranium, hydrocephalus (if the mass obstructs cerebrospinal fluid flow), and a highly disorganized intracranial anatomy suggest the diagnosis of intracranial teratoma.

Congenital dural arteriovenous fistula is characterized by enlargement of the meningeal arteries

Table 2: Differential diagnoses of aneurysm of the vein of Galen

Diagnosis

Differences

Arachnoid cyst [15-16]

Collection of fluid that may exist separately as a loculated accumulation between two membranes or may communicate with the subarachnoid space. Common sites are the cisterns,, around the sella turcica,, posterior third ventricle or posterior fossa.

Porencephalic cyst [17]

A fluid-filled space in the normal brain parenchyma. It often communicates with the ventricular system and subarachnoid space.

Choroid plexus cyst [18]

Small areas of cystic dilatation localized in the choroid plexus of the lateral ventricle. They can be uni- or bilateral and usually disapear by the end of the second trimester.

Choroid papilloma [19]

A brightly echogenic mass located at the level of the atrium of one lateral ventricle. Associated with hydrocephalus.

Teratoma [20]

Mass composed of disorganized solid tissue, cystic and calcified components. May be associated with polyhydramnios.

 

Presentation after birth

Although vein of Galen aneurysms may become symptomatic in the elderly [30-31], they are more typically diagnosed in the neonatal period. In a large recent review [32], 80 patients presented as neonates, 82 between 1 and 12 months, 39 between 1 and 5 years and only 44 were over 6 years. The common clinical features in the neonate are cardiomegaly with congestive heart failure [33-34] and increased intracranial pressure with hydrocephaly or cranial bruit [35]. When the associated intracranial abnormality is not recognized, unnecessary cardiac examinations are performed that delay the diagnosis and treatment [36]. Focal neurological deficit, seizures and hemorrhages are less common findings. In older patients, a variety of symptoms have been reported, that include headache [37], visual defect [38], syncope, subarachnoid hemorrhage, seizure [39], mental retardation [40] and even psychiatric disorders.

Prognosis

In analyzing the clinical aspects of aneurysm of the vein of Galen, Amacher in 1973 identified three groups (neonatal, infantile and juvenile) based on the seriousness of the lesion and the age of the patient at the onset of symptoms [42]. The severity of cardiomegaly and cardiac decompensation depends on the size and complexity of the vein of Galen aneurysm. During intrauterine life, the arteriovenous fistula maintains a low flow rate because of the low resistance of placental vascular bed; at delivery the changes of the blood circulation cause a sudden increase of flux through the fistula [43-45]. Therefore, if the aneurysm is small (less than 1 mm), the child may be asymptomatic at birth and the aneurysm may cause no relevant consequences for a long period. Later on, during infancy, adolescence or juvenile age, symptoms may occur such as headache, seizure, visual disturbances, due to chronic hydrocephalus and/or subarachnoid or cerebral hemorrhages. On the contrary, with a large aneurysm (greater than 20 mm), the great amount of blood circulating in the highflow fistula induces an overload of the venous circulation that can cause cardiomegaly, decompensation and hydrops. Therefore, an assessment of the cardiovascular system should be performed to identify early signs of cardiac insufficiency, to establish the time and the type of delivery, and to prepare an adequate assistance for the newborn. A careful echographic prenatal examination allows the neurosurgeon to plan the best neuroradiological and surgical management according to the type of vein of Galen aneurysm and the status of the patient.

Obstetrical management

No data are available indicating the optimal mode of delivery of fetuses with aneurysm of the vein of Galen. If there are other associated anomalies such as severe porencephaly or cardiomegaly with hydrops, aggressive management is not indicated due to the high neonatal mortality (over 90% of neonate). Hydrocephaly may be an indication for elective cesarean section. In the absence of associated anomalies we think that, to avoid possible damage during labor, an elective cesarean section can be performed.

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