Special Report Vein of Galen Aneurysms

Special Report Vein of Galen Aneurysms: A Review and Current Perspective Michael Bruce Horowitz, Charles A. Jungreis, Ronald G. Quisling, and lan Pollack The term vein of Galen aneurysm encom the internal cerebral vein to form the vein of passes a diverse group of vascular anomalies Galen (4). sharing a common feature, dilatation of the vein Differentiation of the venous sinuses occurs of Galen. The name, therefore, is a misnomer. concurrently with development of arterial and Although some investigators speculate that vein venous drainage systems. By week 4, a primi of Galen aneurysms comprise up to 33% of gi tive capillary network is drained by anterior, ant arteriovenous malformations in infancy and middle, and posterior meningeal plexi (3, 4). childhood ( 1), the true incidence of this a nom Each plexus has a stem that drains into one of aly remains uncertain. A review of the literature the paired longitudinal head sinuses, which in reveals fewer than 300 reported cases since turn drain into the jugular veins ( 3, 4). Atresia of Jaeger et al 's clinical description in 1937 (2). the longitudinal sinuses leads to the develop As we will outline below, our understanding of ment of the transverse and sigmoid sinuses by the embryology, anatomy, clinical presentation, week 7 (3, 4). At birth only the superior and and management of these difficult vascular inferior sagittal, straight, transverse, occipital, malformations has progressed significantly and sigmoid sinuses remain, along with a still over the past 50 years. plexiform torcula (3, 4). On occasion, a tran sient falcine sinus extending from the vein of Embryology and Vascular Anatomy of the Galen to the superior sagittal sinus is seen ( 4). Vein of Galen Such sinuses represent persistent intradural channels located within the falx cerebri. The development of the human cerebral vas Under normal circumstances, the mature cular system is complex; a thorough analysis vein of Galen persists as a bridge between the has been conducted by Padget (3) . Cerebral deep parenchymal venous system and the ve vascularization begins during gestational week nous sinuses. As such, it serves as a conduit 4, at the time of neural tube closure. By the end between the internal cerebral veins, basal veins of week 5, the choroidal and quadrigeminal ar of Rosenthal, precentral cerebellar vein, ver teries, the main afferents to the vein of Galen, mian veins, and straight sinus (5). are well developed ( 4). During week 6 the circle Lying within the subarachnoid space in an of Willis is completed. The anterior cerebral ar area known as the great transverse cleft, the tery supplies the choroid plexus of the lateral vein of Galen is bordered superiorly by the free ventricles, and the middle cerebral artery sup margin of the falx, posteriorly by the tentorium plies the striatum (4). Meanwhile, at the roof of cerebelli, anteriorly and inferiorly by the roof of the diencephalon, the median prosencephalic the third ventricle, and laterally by the choroidal vein, or primitive internal cerebral vein, devel fissures of the lateral ventricles ( 4) (Fig 1). ops as the main draining structure for the telen cephalic choroid plexus. By week 10 the me Arterial Supply dian prosencephalic vein is largely replaced by the paired internal cerebral veins, which then In a series of 23 patients with vein of Galen become the predominant means of choroidal aneurysms, Raybaud et al found the posterior drainage (4). Although the median prosen choroidal arteries to be the primary feeders ( 4). cephalic regresses, its most caudal portion joins The anterior cerebral arteries were the second From the Departments of Neurosurgery (M.B.H., C.A.J. ) and Radiology (C.A.J.}, University of Pittsburgh Medical Center; Department of Neurosurgery, Children's Hospital of Pittsburgh (I.P.}; and Department of Radiology, University of Florida , Gainesville (R.G.Q.). Address reprint requests to Michael Bruce Horowitz, MD, University of Texas Southwestern Medical Center, Division of Neuroradiology, Department of Rad iology, 5323 Harry Hines Blvd, Dallas, TX 75235-8896. Index terms: Vein of Galen; Veins, abnormalities and anomalies; Arteriovenous malformations, cerebral; Special reports AJNR 15:1486-1496, Sep 1994 0195-6108/ 94/ 1508-1486 © American Society of Neuroradiology 1486 AJNR: 15, September 1994 VEIN OF GALEN 1487 Fig 1. Midsagittal section of the bra in il lustrating the large thrombosed vein of Galen aneurysm (open arrows) overlying the cerebellum and the collicular plate. The ventricles are distended with recent hem or rhage. Multifocal subarachnoid hem orrhage is also seen. Ye llow streaks represent a postmortem attempt at perfusing the arter ies with yellow silicone. Note the sm all size of the brain and cerebellum. White fibrotic meninges cover the m edial occipital lobe adjacent to the m alformation (curved ar row). (Courtesy of Dr M. A . Barmada, Chil dren's Hospital of Pittsburgh.} most commonly involved vessels, generally superior sagittal sinus, blood flowed posteriorly providing bilateral blood supply. The anterior into the torcula and then into one transverse thalamoperforators were common secondary sinus. Some blood, however, flowed anteriorly tributaries, joining primary afferents at the level within the superior sagittal sinus, entered a sec of the choroidal fissure. Perimesencephalic ves ond falcine sinus, which angiographically sels were constantly involved in neonates and seemed to cross the first (in a separate dural frequently involved in older children. Distal sheet), and finally discharged into the torcular branches of the posterior cerebral arteries and or other transverse sinus. In these situations posterior thalamoperforators supplied the mal blood may drain via petrosal and tentorial ve formations in a moderate number of neonates. nous channels into the cavernous sinus. Falcine In approximately 50% of patients, the menin sinuses were generally associated with high geal arteries were significant. flow shunts. Five of Raybaud's cases revealed angiographic absence of straight, falcine, trans Venous Drainage verse, and sigmoid sinuses with stasis of con trast within the sacs and lack of jugular vein In healthy persons the vein of Galen drains opacification. In terms of nonsinus venous the internal cerebral veins, basal vein of drainage, the authors at no time demonstrated Rosenthal, posterior mesencephalic vein, supe dilatation of the internal cerebral veins, al rior vermian vein, precentral cerebellar vein, though they did see retrograde flow in these and superior cerebellar veins (5). Sixty-eight structures. Large choroidal veins and an en percent of Raybaud's patients had major ve gorged subependymal system drained into the nous anomalies including absent or interrupted basal veins, uncal veins, and cavernous si straight sinuses, straight sinuses divided into nuses. Lateral mesencephalic venous drainage two segments, and straight sinuses judged too entered the transverse sinus. small in relationship to the sacs (4) . A small number of patients demonstrated both falcine and patent straight sinuses. An equally small Categorization number presented with falcine loops. This ar rangement consisted of a falcine sinus draining Yasargil divides vein of Galen aneurysms into the sac into the superior sagittal sinus. From the four categories (6). Type 1 contains pure fistu - 1488 HOROWITZ AJNR: 15, September 1994 las between arteries and the vein of Galen with venous aspect of the malformation. In grade 1 the nidus of the lesion being the ampulla of the venous structure, the degree of ectasia of the vein. This entire lesion is extrinsic to the brain straight sinus is proportional to that of the vein parenchyma. Type 2 is composed of thalam of Galen, with both being only minimally en operforators that travel through normal paren larged. Grade 2 structure occurs when the vein chyma and supply both brain tissue and give of Galen is more dilated than the straight sinus, branches to the vein of Galen. These lesions are with both structures moderately increased in both intrinsic and extrinsic to the central ner size. Grade 3 lesions demonstrate marked dila vous system. Type 3 malformations are mixed tation of both structures, and grade 4 have sig lesions with characteristics of both type 1 and nificant enlargement of the veins of Galen with type 2 lesions. Type 4 lesions have malforma normal, stenotic, or absent straight sinuses (7). tions proximal to the vein of Galen aneurysms These angiographic findings correlated well that drain into veins that then empty into the with measurements of venous pressure within veins of Galen. the malformation. Whereas the mean venous A further modification of these classifications pressure within Galenic aneurysms in individu has been provided by Quisling and Mickle, who als with venous restrictions was 40 em of water, categorized Galenic vascular malformations on the pressure in patients without venous restric the basis of several factors: nidus complexity, tions averaged 25 em of water (3). These an afferent supply, and efferent drainage patterns giographic findings and pressure measure (7) . Type 1 consists of "true" Galenic fistulas ments were related in a logical way to a number with direct arteriovenous communication via a of clinical features. For example, no patient with unilateral, choroidal arterial trunk. As it ap obstructed drainage was in cardiac failure at the proaches the vein of Galen aneurysm this trunk time of presentation, thus confirming that some can be divided into as many as five smaller measure of cardiac protection is provided by distal branches. When an angiomatous matrix is restriction of venous outflow from the malfor present it is usually less than 1 em in greatest mation. Conversely, no case in which the effer diameter and is typically in direct continuity ent venous pressure was less than 20 em of with the Galenic aneurysm. Type 2 Galenic fis water had brain calcifications, implicating ele tulas are actually "ordinary" deep arteriovenous vated venous pressure in the development of malformations located within the thalamus the finding. Finally, grade 4 patients with severe and/or hypothalamus.

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