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Year : 2011  |  Volume : 6  |  Issue : 3  |  Page : 109-117

Pediatric aneurysms and vein of Galen malformations

1 Department of Radiodiagnosis and Imaging, Kasturba Hospital, Manipal, India
2 Department of Neurosurgery, PGIMER, Chandigarh, India

Date of Web Publication10-Oct-2011

Correspondence Address:
S N Mathuriya
Department of Neurosurgery, PGIMER, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1817-1745.85728

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Pediatric aneurysms are different from adult aneurysms - they are more rare, are giant and in the posterior circulation more frequently than in adults and may be associated with congenital disorders. Infectious and traumatic aneursyms are also seen more frequently. Vein of Galen malformations are even rarer entities. They may be of choroidal or mural type. Based on the degree of AV shunting they may present with failure to thrive, with hydrocephalus or in severe cases with heart failure. The only possible treatment is by endovascular techniques - both transarterial and transvenous routes are employed. Rarely transtorcular approach is needed. These cases should be managed by an experienced neurointerventionist.

Keywords: Pediatric aneurysms, Vein of Galen malformations, choroidal malformations, mural malformations, endovascular embolization

How to cite this article:
Rao V, Mathuriya S N. Pediatric aneurysms and vein of Galen malformations. J Pediatr Neurosci 2011;6, Suppl S1:109-17

How to cite this URL:
Rao V, Mathuriya S N. Pediatric aneurysms and vein of Galen malformations. J Pediatr Neurosci [serial online] 2011 [cited 2023 Dec 2];6, Suppl S1:109-17. Available from: https://www.pediatricneurosciences.com/text.asp?2011/6/3/109/85728

   Intracranial Aneurysms Top

Intracranial aneurysms in children are rare. They contribute 0.5-5% of all cerebral aneurysms (2.9% in authors experience). Hence, studies of voluminous cases with long term follow-up experiences of clinicoradiological findings and management are not available. A total of 706 cases of pediatric aneurysms have been reviewed since 1939. [1] Therefore it is not possible to formulate strict guidelines for diagnosis and management of these lesions. [2]

The first account of aneurysm was published in 1765 by Biumi and Milan. Nebel (1834) reported first aneurysm series of 13 cases. Succeeded by a review of 49 cases by Brinton (1852). First pediatric intracranial aneurysm (Ped. Icr. An.) was reported in 1871. In 1887 Eppinger reported a ruptured intracranial saccular aneurysm (Icr. An.) responsible for death in 15-year-old boy. Mc Donald and Korb (1939) published post-mortem description of 61 Ped. Icr. An. First aneurysm in childhood was treated in 1960 by Kimbel et al. Subsequently around 32 series have been published the largest by Jian BJ in 2010 (a report of 103 aneurysms in 77 patients). [3],[4]

Intracranial aneurysms constituted 13% of hemorrhagic stroke (HS) in children. They were responsible for 57% of pure subarachnoid hemorrhage (SAH) and 2% of pure intracerebral hematoma (ICH) and 5% of mixed hemorrhages. [3] These formulate 10% of overall hemorrhagic stroke (HS) in pediatric age group. Annual incidence of HS was 0.18 per 100,000 person-years; this was maximum in late adolescence 0.52/100,000. As per studies published it has been worked out that in some of experiences adults constituted 35 times more aneurysmal SAH than children. [3]

Pediatric age is divided into children of four age groups: 0-4, 5--9, 10--14, and 15-­-19. [3] Late adolescence is 15--19 years. Studies present that most of these lesions are in the group above 10 years (81.8%) (95% in the author's experience); below 10 are 18.2% and still lower below 5 years. Those below 1 year are extremely rare. In neonates there are extremely less only 15 cases reported. Allison et al. [5] described a 1-month old child with middle cerebral artery (MCA) aneurysm with SAH.

Childhood aneurysms are unique in incidence, presentation, locations, diagnostic modalities, therapeutic methodology, complications, and outcome, compared to intracranial aneurysm in adults.

Ped. Icr. An. are categorized into four subgroups - saccular, fusiform, traumatic, and infectious. The frequency of presentation with bleed varies in these various subgroups.

They have male preponderance 1.8--2.2:1. [1] This male preponderance may suggest involvement of congenital factors in genesis of intracranial aneurysms in children. [3] First-degree relatives of intracranial aneurysm subjects have more chances to harbor aneurysms so should be screened during late adolescence. Seventy five to 82% of them present as SAH. [3],[5],[6] More number than adults present as seizures (20-36%), diplopia, and mass lesions due to propensity to harbor more large and giant aneurysms. [1],[5],[6],[7],[8] They may present as space-occupying lesions. [9] The presentation is as headache (70%), irritability and syncope (in minority) [7] focal motor deficit, direct compressive effect, or unconsciousness (52%). [3],[10]

Diagnosis is delayed and difficult due to nonrecognition of symptomatology due to age. A larger number of patients present as ICH, IVH (36%) and hydrocephalus. This could also be due to a different aneurysm location in children internal carotid artery bifurcation (ICAB)/middle cerebral artery (MCA). [6],[8] Comparatively more patients (around 70--80%) (86% in the author's experience) present in good grade. Lower incidence of poor grade could be due to their inability of the patients in reporting to the hospital. [1],[2],[3],[10] Rebleed has been observed more in children (29--52%) as compared to adults (16--20%). [6] A delay in diagnosis due to ambiguous sympotmatology could be responsible reason for rebleed in a large number of these patients .

The diagnostic modalities adopted in small children are ultrasound to detect bleed and MRI/MRA (which has unacceptably more false +ves) for diagnosing aneurysm and CTA now, as catheter angiography is a bit difficult in small children. [11],[12] The same repeat diagnostic procedures at follow-up are not strictly practical in children which could be a reason for less detection of aneurysms in young children. A false negative study can be secondary to thrombus in the lesion so the study needs repetition after 3--6 months in the case of strong suspicion. [2]

These aneurysms are located more in anterior circulation (76%) as in adults but compared to adults the exact percentage of these lesions in posterior circulation is much more (26--42%). A similarly number of large and giant aneurysms is comparatively higher in young children (23%--42%) than in adults. [2],[3],[5],[8],[9] Children harbor more complex aneurysms than adults (30--50%). [5] ICAB is the commonest location for intracranial aneurysms (ICr. An. 11%--26%) 38% authors) in children; then the next location is anterior communicating artery (A. com); then MCA and M2 with ICH in up to 40% (three times more than other vessels) (mainly in neonates and infants). [3],[5],[7],[10]

The propensity of distribution of Ped. Icr. An. in posterior circulation and higher incidence of giant aneurysms are controversial but most of the studies experienced as mentioned above. [10]

Multiple aneurysms are less common in children. [5] The incidence of fusi form/dissecting infective and traumatic aneurysm are far more in children compared to those in adults. [3],[5],[13]

The male to female ratio in one study in the Indian literature is (1:07) [6] (1.6:1 authors).

   Pathogenesis Top

Not much is known about pathophysiology of aneurysms in children whereas this is clear in adults. The following congenital disorders have been limited to the pediatric aneurysms. The most common pathologies which are associated with aneurysm are coarctation of aorta, autosomal dominant polycystic kidney disease(ADPKD), fibromuscular dysplasia,  Ehlers-Danlos syndrome More Details, primarily type IV connective tissue disorder and pseudoxanthoma elasticum and Marfans syndrome. [13] This was shown that Icr. An. are more common in subjects with these diseases. Around 10% of intracranial aneurysms have family history in the Finnish population. The abrupt termination of internal elastic lamina (IEL) and muscularis media at saccular aneurysms entrance (characteristic of adult aneurysms) lacks in pediatric aneurysm autopsy cases. Fragmentation of IEL and muscularis is present in the vessel wall adjacent to aneurysms and both these layers lack in aneurysm in pediatric patients.

Studies suggest that the following factors are responsible for Ped. Icr. An.: (1) a large congenital medial defect could be an initiating factor for aneurysm formation; (2) alteration in parietal connective tissue; (3) some inherited connective tissue disorders; (4) inflammatory process can produce a tear in IEL; (5) birth trauma could be responsible for aneurysms located near tentorial incisura; (6) degenerative hemodynamic lesions also play a role in children; (7) impingement of axial stream at bifurcation apex and dissipation of kinetic energy can result in structural fatigue; (8) IEL trauma can be caused by increased hemodynamic stress at the branching points and these areas are prone for aneurysm genesis; (9) vasculopathy predisposes to aneurysm formation. [6]

A complete/near-complete occlusion of aneurysm, without vessel compromise, least/no morbidity and long lasting cure is the aim of management.

Taking into account anatomy, physiology, pathophysiology, and long-term implications of the therapeutic measures adopted it is a great challenge to manage intra cranial aneurysms in childhood. Children are not small adults as per the above considerations. [14] As already discussed there are not only variations in incidence, in locations, symptomatology, and size but the complexity of aneurysms in this population is different than adults; hence, the management has to be customized as per the age, presentation, and any other associated lesions.

Expectant therapy has no role in present day practice for this disease in most of cases rather a multimodality treatment strategy is an accepted method of treatment. [1] Risks of treatment, long-term follow-up, risks of recurrence, and more chances of de novo aneurysm formation need to be taken into account at treatment planning. [15],[16] Incidental pediatric aneurysms need early treatment due to increased cumulative risk of rupture. A pediatric neurovascular and endovascular team consisting of pediatric neurologist, neurovascular surgeon, and neurointerventionist is the best to comprehensively plan and treat these patients.

In case the clinical profile is of a mass lesion/seizures, due to giant aneurysm or a large ICH, microsurgery is the answer. In saccular aneurysms complete obliteration at surgery is around 94% where as this is 82% by endovascular techniques. The recurrence rate after surgery and endovascular was 0% and 14% respectively. [9] Infarction rate is higher in microsurgery compared to endovascular therapy (14% and 7% respectively). The reason could be that the types of lesions tackled by microsurgery are more complex. The microsurgery techniques can be tailored as per the characteristics of pathology (morphology, location, and postoperative implications). These include direct clipping, clip reconstruction of vessel, aneurysm trapping with or without bypass. The children have poorly developed thermoregulatory mechanism. The surface area is disproportionately more in infants which demands special attention to prevent hypothermia. Extra-cautious dissection is mandatory to avoid intraoperative aneurysm rupture and blood loss considering low blood volume in this age group. [6]

Nowadays due to advances in endovascular therapy, these techniques are quite effective; hence, the treatment modality needs to be individualized. [17]

On a few occasions it may not be possible to offer a curative treatment and we may have to provide an expectant line of (conservative) treatment. These situations are multiple aneurysms scattered throughout the intracranial circulation. We may do screening follow-up by MRA/CTA after occluding the offending aneurysm. Conservative management may have to be contemplated and has been experienced in unavoidable states like long-segment vascular dysplasia involving multiple vascular territories. Close follow-up for aneurysm growth in 18 patients reported that no patient bled under an average follow-up of 41 months (6 months to 10 years). [4]

Delayed ischemic deficits were a major cause of deficit in one study only. [8]

Children are tolerant to symptomatic vasospasm even seen on angiography does not manifest clinically. This is due to enhanced perfusion in distal vascular territories by better collateral circulation and the presence of leptomeningeal collaterals at the affected area.

Favorable outcomes can be obtained in 95% of current series in pediatric patients 1, 5, 8 ((83% in the author's experience). Refinements in techniques including bypass and anastomoses and surgery under hypothermic circulatory arrest have contributed to overall improvement of outcome in these patients. [1]

Fusiform and dissecting aneurysms result primarily at the site of acute, subacute, and chronic recurrent dissection of the vessel wall at the intima. When untreated they may produce mass effect, embolic stroke or sometimes hemorrhage. Redirecting flow from aneurysm is required by clip reconstruction of vessel lumen or trapping + revascularization

Traumatic aneurysms[1],[5],[8],[18] account for 14--39% of all pediatric aneursyms. [1],[18] Children with neurological deterioration after head injury should be suspected to have these lesions and investigated accordingly.

These aneurysms can result from direct trauma (gun shot wounds, stab wounds or surgical procedures). Indirect causes are trauma by falcine edge, sphenoid ridge, and sharp edge of fractured bone. The patient can present with devastating hemorrhage in 50%. It could be SAH, subdural hematoma (SDH), ICH or extradural hematoma (EDH). Aneurysm can bleed 5 hours to 10 years after trauma with a mean of 3 weeks. The patient can present with irritability/unconsciousness or focal signs due to enlargement of aneurysm. Infraclinoid aneurysm can present with diabetes insipidus, cranial nerve deficits, unilateral blindness, recurrent massive epistaxis, and features of carotid-cavernous fistula.

Rupture carries mortality of 32--50%. These aneurysms can be true, false, or mixed. In true ones disruption of intima along with variable damage of internal elastic lamina (IEL) and media leading onto aneurysm formation, through the weak vessel wall due to their hemodynamics, the adventitia of vessel is preserved, whereas in false aneurysms there is damage of all the three layers with a contained hematoma outside/around which leads to formation of a false lumen generating a dilatation, i.e., aneurysm. This is usually a result of penetrating injury. A true aneurysm with subsequent contained rupture and pseudo wall is a mixed type. [5] Hence, early diagnosis and treatment (surgery/endovascular) prerupture is recommended. Intraoperative rupture is common due to adhesions around and friable wall. Clipping is the best treatment but is quite difficult due to ill-defined and friable neck, pseudo and fusiform structure. Hence wrapping, trapping, excision plus interposition graft, and endovascular arterial occlusion may be needed. [1]9[,20] A total of 41% of conservatively managed and 18% of actively treated patients succumb to the disease.

Infectious aneurysms [5],[6],[8],[21] are 10% in children 2.6% in adults. [6] This is underestimation as the undiagnosed, asymptomatic, and spontaneously resolved lesions are excluded. These result from complications of subacute bacterial endocarditis, from prosthetic value, dental procedures, tooth abscess, nosocomial bacterial infections, mitral/aortic valve stenosis/insufficiency, intravenous drug use, etc. Extravascular contiguous infection can invade large arteries traversing from middle ear, cavernous sinus thrombophlebitis, meningitis, osteomyelitis, and postoperative infection. These mostly involve distal MCA.

Emboli lodge in vasa vasosum resulting in severe inflammation of media and adventitia resulting in weakening of the vessel wall and aneurysm formation.

The mortality may be 80% from hemorrhage; hence early diagnosis and treatment (appropriate antibiotics) is mandatory. Median time of bleed is 5--35 days. Angiography/CTA every week or two then monthly or quarterly is must to document resolution. In case aneurysm is large, not resolving/enlarging even on appropriate antibiotic therapy mandates surgical/endovascular therapy/bypass.

Aneurysms are seen in 10% of subjects with ADPKD four times more than the general population with SAH being five times. These aneurysms rupture at smaller size and early age. Hence, these candidates with past history of SAH/family history of aneurysms should be screened and investigated. [22]

   Vein of Galen Aneurysm Top

Aneurysm of vein of Galen, an uncommon vascular malformation in the pediatric age, is neither an aneurysm nor a vein of Galen according to understanding of embryogenesis of the malformation. It is not a true aneurysm and does not arise from the vein of Galen. Normal deep veins are absent and venous drainage is routed through embryonic vessels. Persistence of the single median prosencephalic vein of Markowski into fetal life results in a dilated venous sac in the midline, supposedly the Galenic malformation. Developmentally, as early as in the fifth week of embryo (Horizon XVI 32 days, 8--11mm) a midline dorsal vein is differentiated on the roof of the diencephalon accompanied by expansion of the telencephalic choroid plexus, coursing from the paraphysis to the interhemispheric or marginal sinus. Hochstetter and Padget described this vein as median prosencephalic vein of Markowski or primitive internal cerebral vein. [23],[24],[25] This temporary vein drains the choroid plexus from both sides almost till the end of the 10thweek With simultaneous development of basal ganglia, thalamus, and cerebral vascularization, paired internal cerebral veins appear to progressively annex the venous drainage of the midline structures. Both the internal cerebral veins join the posterior end of the median prosenchephalic vein, the future vein of Galen, while the remaining segment of the midline solitary embryonic vein of Markowski progressively attenuates [Figure 1]. The vein of Galen is completely in the subarachnoid space. The basal vein of Rosenthal, precentral cerebellar veins, superior vermian vein, splenial and occipital veins drain to the vein of Galen which drains into the straight sinus. Though the aneurysmally dilated midline sac is the persistent median prosencephalic vein of Markowski, secondary ectasia of the true vein of Galen may be observed in arteriovenous malformations located in one of its tributaries. Anomalies of dural sinuses coexist. Often the straight sinus is hypoplastic or absent. Stenosis at the junction of vein of Galen/median prosencephalic vein with the straight sinus is noted in several patients. A transient accessory sinus connects the anterior end of the straight sinus to the superior sagittal sinus appearing as a duplicated straight sinus, persisting into a falcine sinus. [26],[27] The falcine sinus becomes the normal outlet for the persistent median prosecephalic vein of Markowski. Such persistence of fetal pattern maintains the fetal hemodynamics and as a result some dural sinuses may fail to develop altogether. [28] Occipital sinuses may persist, arising from the mid segments of the transverse sinuses on both sides. Duplicated or hypoplastic dural sinuses or jugular viens are commonly observed. Occlusion of the outlets may occur secondarily in certain high flow conditions or may be regarded as a compensatory mechanism. [9] The complex arterial component of the malformation is reflected by development of numerous quadrigeminal and choroidal arteries embedded in the cellular meninx primitiva. These are connected by a meningeal capillary network soon to disappear as the subarachnoid space develops at about 7-8 weeks of fetal life. Persistence of these vessels is what is observed in the arterial maze of the malformation.
Figure 1: Schematic drawing of the afferent choroidal, collicular arteries, and the efferent venous channels during vascularization of the basal ganglia and thalamus

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The arteriovenous shunt lies in the wall of the persistent median vein of Markowski, the embryological precursor of the vein of Galen, which does not develop. Angiographic identification of the two major types of the abnormality, i.e., aneurysmal malformation and aneurysmal dilatation has therapeutic significance. Aneurysmal malformation does not drain the normal brain tissue nor the normal venous system. Alternate drainage pathways develop by the 12th week of gestation and persist into fetal life. Two types are recognized based on the location and nature of the shunt, choroidal, and mural types.

   Choroidal Type Top

The arteriovenous shunt is extracerebral and subarachnoid located in the tela choroidea along the cisterna velum interpositum. The arterial feeders are generally bilateral from the choroidal arteries, subependymal branches of thalamo perforator arteries and pericallosal artery. Communication is into the anterior segment of the median vein of prosencephalon. The arterial network is complex and large volume of shunt results in cardiac failure in the newborns and infants which can be detected in the prenatal period itself [Figure 2]. The aggressive volume overload results in cerebral ischemia and encephalomalacia. [28] Patent foramen ovale and right to left shunt in the presence of large volume overload may result in cyanosis and heart failure.
Figure 2: Vertebral angiography. (a) and (b) Markedly dilated anerysmal vein of Galen is penetrated by numerous choroidal and perforator branches in a choroidal type of malformation. Right carotid angiography. (c) and (d) Fetal origin of the posterior cerebral artery and its branches feed the dilated Galenic choroidal malformation

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   Mural Type Top

Mural type of vein of Galen aneurysm presents in infancy or early childhood with failure to thrive, macrocephaly due to hydrocephalus or heart failure. Hydrocephalus develops mainly due to impaired absorption because of venous hypertension. [29],[30],[31],[32] The enormously dilated vein of Galen itself may be obstructive to the CSF flow although rare. Mental retardation, intractable seizures, and delayed milestones of development are seen regardless of the type of malformation. [33] The lesion may progress into adulthood and present with asymptomatic cardiomegaly or rarely with parenchymal or intraventricular hemorrhage. A single arteriovenous fistula is situated in the inferolateral wall of the median vein of Markowski. Unilateral or bilateral collicular and or posterior choroidal arteries in the subarachnoid space contribute to the shunt as the arterial feeders.

   Imaging Top

The anatomical and dynamic characteristics of vein of Galen malformation are studied by transcranial Doppler ultrasonography and cross-sectional imaging including computed tomography and magnetic resonance imaging. Color Doppler imaging demonstrates hemodynamic disturbances of the malformation and 2D imaging shows parenchymal changes such as atrophy and encephalomalacia [Figure 3]. Parenchymal calcifications due to chronic venous hypertension and ventricomegaly may be demonstrated. [33],[32],[33],[34],[35] Plain and contrast enhanced CT scan reveals abnormally "dilated vein of Galen" in the midline and hydrocephalus. Thrombus and calcification in its wall may be seen [Figure 4]. Brain atrophy, parenchymal calcification or hemorrhage, and brain stem compression can be appreciated. [36],[37] Of interest is to note curvilinear peripheral rim calcification in the midline in the region of pineal gland on the plain X rays [Figure 5]. Magnetic resonance imaging supplemented by MR angiography and MR venography reveal the venous anomalies in greater detail [Figure 6]. Hemorrhagic components are better shown by MR evaluation. Digital subtraction angiography including both vertebral and both carotid arterial examinations identifies the precise type of the malformation delineating both the arterial feeders and venous drainage. Angiographically four types are identified. Type I is an enlarged and tortuous midline venous varix having multiple feeding arteries into its wall. Generally the feeding arteries are the branches of anterior and posterior choroidal arteries, pericallosal arteries, and superior cerebellar arteries. Transmesencephalic and transdiencephalic perforators establish fistulous connection within the wall of the midline persistent vein in type II. Type III is a combination of types I and II. Secondary dilatation of the vein of Galen due to hemodynamic overload through the venous outflow by a mesencephalic, diencephalic, or cerebellar arteriovenous malformation is classified as type IV. Collateral venous pathways, reflux into dural sinuses and cortical venous rerouting are best revealed by angiography which have significant strategic implications during endovascular therapy. Stenosis or occlusion of the outflow at the straight sinus, torcula, dural sinuses, or internal jugular vein is well seen in the venous phase of angiograpy. Anomalies of dural sinuses, duplications, fenestrations, falcine sinus, falcine loop, and suboccipital sinuses are apparent on careful examination of the delayed venous images [Figure 7]. These structures may appear very early in the arterial phase itself because of high flow across the arteriovenous communications.
Figure 3: Transcranial duplex sonography demonstrating markedly dilated vein of Galen and high velocity flow

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Figure 4: Plain and contrast enhanced CT scan. (a) Hyperdense midline vein of Galen and enlarged straight sinus noted. (b) Intense enhancement of the malformation is seen on contrast administration

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Figure 5: Plain X rays of skull. (a) and (b) Curvilinear midline calcification in the wall of aneurysm of vein of Galen

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Figure 6: MRI of brain. Sagittal T1 weighted image shows partial agenesis of straight sinus in its proximal segment. Alternate venous drainage is seen from the falcine sinus into the superior sagittal sinus from the vein of Galen

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Figure 7: Lateral view of carotid angiogram. (a) Fenestrated falcine sinus is appreciated draining into the posterior end of superior sagittal sinus. (b) Duplicated falcine sinus is seen in another patient. Vertebral angiogram. (c) and (d) AP and lateral views demonstrate occipital sinuses connecting the torcular to the jugular bulbs on both sides symmetrically forming a falcine loop

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   Endovascular Therapy Top

Surgical treatment and natural history are associated with high morbidity and mortality. [38],[39],[40] Adjuvant ventricular shunting is not necessary unless definitive endovascular treatment is unavailable immediately. Endovascular therapy is the treatment of choice performed in appropriate time by experienced neurointerventional radiologists. Clinical status, angioarchitecture, and intravascular pressure data form good guidelines for therapeutic intervention. [41],[42],[43] Dominant clinical presentation and age of onset determine the modality of treatment. Neonates with compensated cardiac function need not be treated immediately and they may be observed till 6--10 months for more favorable outcome of treatment. Similarly endovascular treatment may be postponed in children who had ventricular shunt surgery because of the risk of ascending herniation of cerebellum following shrinkage of the venous ectasia or subdural hemorrhage. [44] Emergency embolization is indicated in infants with refractory cardiac failure, acute or symptomatic hydrocephalus, rapid neurological deterioration or when parenchymal calcifications appear on follow-up scanning of brain. Neonates or infants having encephalomalacia or severe brain damage or severe parenchymal loss do not need any aggressive treatment because of poor clinical outcome in spite of successful closure of the shunt by embolization.

   Techniques Top

Percutaneous transfemoral transarterial embolization

Transarterial embolization is employed when the diagnostic angiogram demonstrates accessible feeding arterial branches from the choroidal and perforator arteries having sufficient caliber to permit navigation of the microcatheters. Through a small pediatric arterial sheath (no. 4-5F) both internal carotid arteries, both external carotid arteries, and vertebral arteries on both sides are catheterized and angiography is performed under systemic heparinization. A bolus injection of 200 U/kg of heparin followed by 100 U achieves optimal systemic heparinization in neonates. In older children the dose of heparin is adjusted by weight. [43],[44],[45] The intracranial feeding arteries supplying the arterio­venous malformation/fistula are catheterized by means of soft microcatheters and microguidewires (1.5 F microcatheter over a 0.010 inch guidewire). Superselective angiography is performed to place the tip of the catheter as distally as possible beyond the origins of any normal branches. A mixture of N-butyl cyanoacrylate or iso-butyl-2-cyanoacrylate, myodil, and tantalum powder is delivered into the diencephalic or mesencephalic perforating arteries [Figure 8]. Throughout the procedure the anesthesiologist and neonatologists monitor the patient. Postembolization angiography is performed to evaluate the extent of reduction of the shunt. [46] Transcranial Doppler ultrasonography is useful to follow up the residual shunt and progression of thrombosis. Transarterial route is effective in the mural type of malformation with fistulas having one or two holes, unlike the choroidal type of malformation [Figure 9]. The latter resembles a water-can shower with multiple arterial feeders draining into the venous sac.
Figure 8: (a) Contrast enhanced CT scan. A daughter sac is attached to the main vein of Galen revealing marked enhancement. (b) Vertebral angiography. Mural type. Early arterial phase shows rapid opacification of the vein of Galen and dural sinuses. (c) Stenosis of the origin of straight sinus. (d) and (e) Post-embolization angiogram. Using isobutyl 2¬ cyanoacrylate the malformation is completely obliterated restoring the normal circulation in the posterior fossa. (f) Plain X ray of skull. Cast of the cyanoacrylate is appreciated in the malformation, following embolization

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Figure 9: Right carotid angiogram. (a) and (b) Globular enlargement of the vein of Galen is supplied by a single hole fistula from posterior cerebral artery (mural type). Right carotid angiogram. (c) and (d) AP and lateral views demonstrate complete obliteration of the malformation by a detachable balloon. Plain X rays of skull. (e) and (f) Partially inflated mini-balloon is detached in the feeding artery by coaxial technique. Shunt tube is noted in place

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Percutaneous transfemoral transvenous embolization

This technique is particularly employed when the perforating arteries are not of sufficient caliber to permit negotiation of the microcatheters. If the shunt is very large with extremely high flow the venous approach is preferred to avoid migration of the embolic material when delivered by the transarterial route. Occasionally it is necessary to use a combination of both techniques. The femoral vein in the groin is punctured with a micropuncture needle and the right internal jugular vein accessed through the right atrium. A guiding catheter is positioned close to the jugular bulb while a microcatheter is advanced into the dilated midline vein in a retrograde fashion through the sigmoid sinus, transverse sinus, torcular of Herophili, and straight sinus. [40],[47],[48] Occasionally it becomes necessary to puncture the internal jugular vein directly in the neck if the femoral veins are not accessible. Although it is advantageous to place larger delivery systems via the transvenous route there is a potential risk of significant hematoma in the neck due to trauma to the jugular vein. Transvenous approach is complementary to the transarterial approach following occlusion of the dominant feeding arteries which allows a gradual increase in the venous pressure in the varix while decreasing the pressure gradient and flow. In the event of thrombosis of either of the sigmoid sinuses it may be necessary to negotiate through a persistent suboccipital sinus into the straight sinus. With the advent of Gugleimi detachable coils (GDC) it is preferred to release long coils as a basket initially into the midline varix followed by delivery of a mixture of liquid acrylic monomer (NBCA) and lipidol. The coils would prevent inadvertent migration of the embolic agent into the pulmonary circulation [Figure 10]. Even pushable microcoils can be released into the preliminary basket within the varix. With substantial reduction of flow in the malformation, a staged embolization through arterial route may be performed. It is mandatory to make sure that the dilated midline venous varix is not connected to the normal cerebral veins when venous route is approached, to avoid immediate or delayed hemorrhagic complications. The goal of treatment is to obliterate the fistula as much as possible, if needed in stages particularly in infants with cardiac decompensation. It is essential to maintain hypotension during delivery of liquid monomer and also to monitor the ACT values during systemic heparinization. Blood pressure is maintained at normal levels after the procedure while the infant is kept intubated for 24--48 hours after the procedure.
Figure 10: (a) Carotid angiogram. AP view shows a complex choroidal type malformation with early draining vein. (b) and (c) Vertebral angiogram AP and lateral views reveal multiple arterial feeders and sinus anomalies. Embolization (d) Guiding catheter is placed in the aneurysmal dilatation of vein of Galen via the sigmoid sinus, transverse sinus and straight sinus. (e) Basket of coil and a mesh is deposited in the dialted varix. (f) Subsequent arterial catheterisation is performed for glue injection. (g) Pre embolization vertebral angiogram. Large Shunt is shown across the straight sinus from the vein of Galen. (h) Tras venous and trans arterial embolization reduces the shunt remarkably showing residual malformation.

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It may be noted that the venous pressure in the dilated midline varix measured more than the normal value of 5 cm of water, ranging between 9 and 55 cm of water in each case reported by Quisling and Mickle. [49] Parenchymal brain calcification is an indicator of venous pressure exceeding 20 cm of water. The pressures are lower in the choroidal type and higher in the dilated vein of Galen secondary to thalamic and parenchymal arteriovenous malformations. Measurements of venous pressure did not show any clear relation between the level of pressure elevation and extent of ventricular dilatation. It appears that the degree of venous pressure elevation is a reflection of the hemodynamic significance in the light of the clinical status and the angioarchitecture of the shunt. Staged transvenous embolotherapy at prolonged intervals is well tolerated by infants and children with lower venous pressures. These children do not develop either brain calcifications or seizures.

Transtorcular embolization

In high flow choroidal malformations with no accessible femoral approach, occipital bone over the torcular is penetrated with a large bore needle for catheterization of the varix in neonates. However it is necessary to make a burr-hole in older children. The torcular is punctured in the lateral position of the head under fluoroscopy control. A road map of transverse sinus and torcular can be obtained by injection into the internal carotid artery. [49] A variety of embolic agents can be introduced through this access: Gianturco coils, detachable balloons, GDC coils, or liquid monomer agents. A fall in venous pressure of 15­20 mm is a good indicator of reduced shunt.

Staged embolization

The goal of treatment is to reduce the volume load initially and attempt to finally obliterate the shunt completely. In the majority of infants and children, it becomes necessary to stage the embolization ranging from a few weeks to a few months based on the angioarchitecture and clinical status. The follow-up endovascular approach is based on the residual shunt and the architecture of the malformation. Occlusive venopathy is a well-known delayed event causing progressive neurological deterioration. The acquired venopathy may be fatal. It is postulated that too long intervals between the embolization procedures would result in high venous pressures in the dural sinuses and cortical veins. The high flow venopathy is transmitted to the medullary veins and cortical veins which would result in progressive parenchymal calcifications and refractory seizures.

Spontaneous thrombosis may result in anatomical cure in rare situations, more commonly in mural type fistulae. Anatomical and clinical cure is possible with appropriate timing and staging of embolization procedures. The technical and clinical outcomes are excellent in experienced hands. It should be noted that in the absence of cardiac overload and in neurologically intact child, the malformation needs observation and follow-up. It is recommended that the fetus diagnosed prenatally harboring a vein of Galen malformation may be delivered normally with no definite risk of cerebral ischemia during delivery because of the low resistance circulation of the placenta.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]

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