Midline arterio-venous
malformation (AVM) between choroidal and/or quadrigeminal arteries and a single median venous sac.
There are multiple communications between the vein of Galen and systemic
arteries (carotid and vertebrobasilar systems).
Embryological development of these non-proliferative
vascular malformations are unknown. Some authors believe it results from
the persistence of the prosencephalic vein of Markowski (1) and not the vein of Galen per se (2).
Vascular anatomy of the aneurysm has wide variations of arteriovenous
connections. It is usually supplied by choroidal
branches from the posterior cerebral artery and occasionally from the transmesencephalic arteries. Venous drainage is far more
complicated. Normally the vein of Galen drains into the confluence of sinuses
(junction of straight, superior sagittal, and both transverse sinuses), however
the straight sinus is absent or thrombosed in cases
of aneurysm of the vein of Galen. The aneurysm therefore usually drains into a falcine sinus that extends directly into the superior
sagittal sinus, rather than directly into the confluence (3,4).
- Diagnosis usually made in
the third trimester (2/3 of cases diagnosed after 34 weeks gestation and
1/3 of cases diagnosed in second trimester)
- Posterior, midline or
slightly lateral anechoic structure (3).
- Supratentorial,
and runs from the splenium of the corpus callosum above the cerebellum all the way to the bony
cranium posteriorly.
- Posterior to the third
ventricle but does not communicate with it.
- Drains into the straight
sinus, which may be normal or dilated. ("Keyhole appearance")
(4).
- Pulsed and color Doppler,
effectively establishes the vascular nature of the lesion. Blood supply is
variable; the posterior cerebral, superior cerebellar and/or anterior
cerebral arteries may supply arterial blood.
- Turbulent flow is usually
present within the lesion and may have arterial and/or venous flow
depending on the area within the lesion that is sampled.
- Postnatal CT, MRI or angiography
confirms the vascular nature of the lesion as well as the origin of the
feeding
vessels. Visualization of blood flow including arterial feeders and
venous drainage may be improved by employing color power angiography
(3,7).
- Associated anomalies (in
67% of fetuses)(3):
- Ventriculomegaly (?
due to mass effect and compression of the aqueduct or abnormal spinal
fluid dynamics).
Compression of the cerebral cortex by the ventriculomegaly in
combination with the “steal” phenomenon may result in
cerebral infarction and leukomalacia) (4)
- Cardiomegaly
± ventricular wall hypertrophy
(64%), ± cardiac failure.
- Neck vessels enlarged
and distended (33%). This is reported as a pathognomonic
sign (6).
- Vascular steal
syndrome (reverse flow in the aortic arch affecting left subclavian blood flow) (8,9).
- Pulmonary
hypertension may occur due to the large systemic shunt.
Ballantyne Syndrome (10); fetal and maternal
edema and placentomegaly.
- Single umbilical
artery; chorioangioma of the placenta and other
variable anomalies have been reported.
- Other features may include, tricuspid insufficiency, polyhydramnios,
pericardial or pleural effusion, edema and ascites.
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Gray-scale image
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Color flow and pulsed doppler
waveforms
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CT scan
– post-natal scan
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Post-natal angiogram
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These include other cystic lesions of the brain such as arachnoid
cyst, porencephalic cyst as well as pineal tumor, intracerebral hematoma and choroid plexus papilloma. The
classical doppler findings
effectively excludes all the other possibilities.
- Poor when associated with hydrops or hydrocephalus (8,9).
- There are two reports of serial
examinations that have shown that in later stages of pregnancy the vein of
Galen aneurysm expands and cardiac decompensation
develops (10,11).
- The prognosis appears to be
related to the appearance of heart failure and not on the size of the
lesion.
- Raybaud
CA, Strother CM, Hald
JK. Aneurysms of the vein of Galen: embryologic considerations and
anatomical features relating to the pathogenesis of the malformation. Neuroradiology 1989;31:109-128.
- Evans A, Twining P. Case report:
in utero diagnosis of a vein of Galen aneurysm using color flow doppler. Clin
Radiol 1991;44:281-282.
- Lee T –H, Shih J
–C, Peng S –F, Lee C–N, Shyu M –K, Hsieh F –J. Prenatal depiction
of an aneurysm of angioarchitecture of the vein
of Galen with three-dimensional color power angiography. Ultrasound Obstet Gynecol 200;15:337-340.
- Romero R, Pilu G, Jeanty P, Ghidini A, Hobbins JC.
Prenatal diagnosis of Congenital Anomalies: The central nervous system.
Appleton and Lange 1988, pp77-79.
- Sepulveda W, Platt CC, Fisk
NM. Prenatal diagnosis of cerebral arteriovenous
malformation using color Doppler ultrasound: a case report and review of
the literature. Ultrasound Obstet Gynecol 1995;6:282-286.
- Strayss
S, Weinraub Z, Goldberg M. Prenatal diagnosis of
vein of Galen arteriovenous malformation by
duplex sonography. J Perinatol
Med 1991;19:227-230.
- Heling KS,
Chaoui R, Bollman R.
Prenatal diagnosis of an aneurysm of the vein of Galen with
three-dimensional color power angiography. Ultrasound Obstet
Gyencol 2000;15:333-336.
- Ishimatsu
J, Yoshimura O, Tetsuou M, Hamada T. Evaluation
of an aneurysm of the vein of Galen in utero by pulsed and color doppler imaging. Am J Obstet Gynecol 1991;164:743-744.
- Yamashita Y, Abe T, Ohara N et.al. Successful
treatment of neonatal aneurysmal dilatation of
the vein of Galen: the role of prenatal diagnosis and trans-arterial embolization. Neuroradiology
1992;34:457-459.
- Ordorica
SA, Marks F, Frieden FJ et.al.
Aneurysm of the vein of Galen: a new cause for Ballantyne
syndrome. Am J Obstet Gynecol
1990;162:1166-1167.
- Reiter A, Huhta J, Carpenter R et.al.
Prenatal diagnosis of arteriovenous malformation
of the vein of Galen. J Clin Ultrasound 1986;14:623-628.
- Comstock C, Kirk J. Arteriovenous malformations. J Clin
Med 1991;10:361-365.
- Ballester
MJ, Raga F, Serra-Serra V, Bonilla-Musoles F. Early prenatal diagnosis of an ominous
aneurysm of the vein of Galen by color doppler ultrasound. Acta
Obstet Gynecol Scand
1994;73:592-595.
- Worswick
L, Lamont R, Thomas R, Gordon H. Prenatal ultrasonic diagnosis of an
aneurysm of the vein of Galen. Br J Radiol 1992;65:609-610.
- Rodesch
G, Hui F, Alvarez H et.al.
Prognosis of antenatally diagnosed vein of Galen
aneurysmal malformation. Child's Nerv Syst 1994;10:79-83.