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Anterior circulation aneurysms: surgical perspectives
Anterior circulation aneurysms: surgical perspectives Fernando G. Diaz MD PhD Richard D. FesslerMD Bernard Velardo MD* Christine Kennedy BSN Harvey Wilner hmD* Neurological Surgery Department Anesthesia Department* Neuroradiology Division? Wayne State University,School of Medicine Detroit, Michigan, USA.
Aneurysms arising from the internal carotid circulation represent 85% of all intracranial aneurysms. The intimate relationship of the internal carotid artery and its branches with the brain and cranial nerves, and the distribution of the internal carotid artery flow, make these aneurysms challenging, and potentially complicated in their surgical management. Great attention to detail, and clear understanding of the operative anatomy of the carotid system, facilitate the safe and successful treatment of these aneurysms. The surgical experience with 475 anterior circulation aneurysms treated from 1980 to 1992 is presented. The aneurysms arose from the internal carotid artery: 230(40%), middle cerebral artery: 152(32%), and anterior cerebral artery: 133(28%). Of aneurysms arising from the internal carotid artery, there were 142(30%) from the posterior communicating artery; internal carotid bifurcation: 29(6%), and anterior choroidal artery: 19(4%). There were 62( 13%) giant aneurysms evenly distributed among the middle cerebral, internal carotid bifurcation and anterior cerebral artery. Serious neurological morbidity was observed in 13(3%) patients, who presented a combination of different neurological symptoms including: hemiplegia 3, hemiparesis 6, dysphasia 7, and loss of vision 4. Wo
patients developed a myocardial infarct and survived. Mortality occurred in 16(3%); these patients
died from: a hemispheric infarction 7, severe vasospasm 6, myocardial infarction 2, and pulmonary emboli 1. All aneurysms appeared angiographically obliterated. Vasospasm was observed in 75(16%) patients of which nine were symptomatic, and six of them died. Six major arterial trunks were occluded in the post-operative angiogram, and three patients had occlusion of the internal carotid artery, not identified during surgery. Three of these patients with unexpected occlusions died from a major cerebral infarction, and three had lasting hemipareses and dysphasia. Surgical correction of internal carotid aneurysms can be conducted safely when the anatomical characteristics of the intracranial vessels is preserved, and when these patients are treated with appropriate medical support. Journal of Clinical Neuroscience Keywords:
0 Longman Group UK Ltd
1994, 1(4):222-230
Cerebral aneurysm, Internal carotid artery
Clinical material
Introduction Aneurysms
arising
represent
from
the internal
85% of all intracranial
relationship
of the internal
with the brain and cranial the internal
carotid
challenging,
and potentially
to detail,
artery
ful treatment
circulation
From
The intimate
carotid artery and its branches nerves,
and the distribution
flow, make complicated.
and clear understanding
tomy of the carotid
carotid
aneurysms.
aneurysms
Great attention
of the operative
system, facilitates
of these aneurysms.
these
of
ana-
the safe and success-
The surgical approaches
can be divided into: extracranial internal carotid ligation; pterional; convexity; interhemispheric; and endovascular. The pertinent surgical anatomy, pre-operative preparation, intra-operative procedures, operative approaches, and potential complications will be reviewed.
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were carotid
1980 to 1992, 47’5 anterior treated.
The
artery:
aneurysms
230(40%),
circulation
arose
from
middle
cerebral
152(32%), and anterior cerebral artery: those aneurysms arising from the internal there
were
142(30%)
communicating bifurcation, artery. evenly
There from
arising
artery, 29(6%) and
19(4%)
aneurysms the internal
from
artery:
133(28%). Of carotid artery, the
posterior
from the internal
from
the anterior
were 62(13%) giant the middle cerebral,
aneurysms internal
carotid
choroidal arising carotid
bifurcation and anterior cerebral artery area. Patients who had a subarachnoid hemorrhage were admitted to an intensive care unit for evaluation, in preparation for surgery.’ A complete
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pre-operative
medical evaluation
was
Review articles
Anterior circulation aneurysms obtained in elderly patients to prevent intra-operative cardiac, respiratory or renal complications that may develop from the use of mannitol, hypertension, hypotension, blood loss, or the use of cardiac suppressants such as barbiturates or lidocaine.’ A Swan-Ganz catheter, an intra-arterial recording catheter, and a Foley catheter were inserted in preparation for surgery. All patients received dexamethasone 10 mg i.v. on admission and 4 mg every six hours, and nimodipine 1 mg per kg orally until surgery. Salt poor albumin was infused until a cardiac output of at least 5-7 litres per minute was obtained. Anaesthesia was induced with thiopental and maintained with nitrous oxide-oxygen and ethrane. During induction the patients received intravenous diphenylhydantoin 15 mg per kg, vancomycin 1000 mg, dexamethasone 10 mg, gentamicin 80 mg, furosemide 20-40 mg, and mannito10.5 gm per kg. Spinal fluid drains were not used, since drainage of spinal fluid from the cisterns and the lamina terminales was effective in achieving cerebral relaxation. Arterial blood gases, end expiratory CO, recordings and pulse oximetry were monitored throughout the operation. Arterial pC0, was maintained at about 30-35 mmHg, p0, at about 95 mmHg, and oxygen saturation at about l-00%. The patients were maintained normothermic and normotensive throughout the operation. Intra-operative hypotension was only used when proximal arterial control could not be accomplished with a temporary clip. Direct clipping was accomplished in 85% (n=404) of the patients. An intracranial to extracranial anastomosis was required in 11% (n=52) of patients, in addition to a clip to obliterate the aneurysm. A reconstructive procedure was performed in the remaining 4% (n=19) of the patients, including a direct end to end anastomosis in 5 patients, an end to side anastomosis of one branch to another branch in 10 patients, an end to side anastomoses of a branch to a main arterial trunk in 2, and an endoaneurysmorrhaphy in 2 patients. The aneurysm had to be opened and decompressed in 57 of 62 giant aneurysms, with removal of formed thrombus in all 57. and removal of wall atheroma in 37 patients. Serious neurological morbidity was observed in 13 patients (2.7%), who presented a combination of different neurological symptoms including hemiplegia 3, hemiparesis 6, dysphasia 7, and loss of vision 4. Two patients developed a myocardial infarct and survived. Mortality was found in 16(3.3%); these patients died from a hemispheric infarction 7, severe vasospasm 6, myocardial infarction 2, and pulmonary emboli 1. All aneurysms were angiographically proven to be obliterated. Vasospasm was observed in 75(16%) patients of which 9 were symptomatic, and 6 of these died. Six major arterial trunks were found occluded in the post-operative angiogram, and 3 patients had occlusion of the internal carotid artery, not identified during surgery. Three of these patients with unexpected occlusions died from a major cerebral infarction, and 3 had lasting hemipareses and dysphasia.
Discussion Anatomical
considerations
The internal carotid artery enters the skull through the foramen lacerum, and becomes intracranial as it passes through the petrous canal into the cavernous sinus. Several small branches arise from the cavernous portion of the internal carotid, including the inferior hypophysial artery, the meningohypophysial trunk, and the artery to the clivus. As the internal carotid artery leaves the cavernous sinus it traverses the subarachnoid space giving rise to the ophthalmic artery, the posterior communicating artery, the anterior choroidal artery, and terminates dividing into the anterior and middle cerebral arteries. For the purpose of this discussion, emphasis will be placed on the most proximal portion of the circle of Willis. The internal carotid artery from the cavernous sinus to the bifurcation is variable in length, and in the number of branches it gives rise to. Besides the ophthalmic artery, the posterior communicating and anterior choroidal arteries, there are branches directed to the anterior perforated substance, and in some cases, a proximal branch to the temporal pole or to the inferior frontal area.‘” The perforating branches generally arise from the posterior wall of the internal carotid, either before or after the bifurcation, not from the bifurcation itself. The perforating branches from the anterior cerebral artery may arise from a common trunk, or they may arise as several small branches directed to the medial portion of the anterior perforated substance.J,J The anterior perforating arteries originating from the middle cerebral artery arise from a single common trunk or from several small perforating branches.“,’ These middle cerebra1 perforators may originate from the most medial portion of the artery, close to its origin (37%). or they may originate from the middle one-third of the M-l segment (47%). The remaining (16%) perforating vessels arise from the most lateral portion of M-l. The pattern of arterial supply to the anterior perforated substance is one of dominance by either the anterior cerebral or the middle cerebral; the branches arising from the other artery will be smaller and fewer in number.“,“,’ In a few cases,” a large vessel may arise from the distal portion of the A-l segment and go to the anterior perforated substance retrogradely, substituting for the recurrent artery of Huebner. When the territories of the anterior and middle cerebral perforators overlap, permanent occlusion of one perforator may not be of great importance, and may go unnoticed clinically. However, when the perforating vessel is dominant, permanent occlusion of this artery may be followed by a severe and lasting neurological deficit. As the anterior cerebral passes from the carotid bifurcation to the interhemispheric fissure, it gives rise to branches to the anterior perforated substance, the inferior frontal area, the fronto-polar artery, the recurrent artery of Heubner, the septal perforating arteries and the anterior communicating artery. The anterior cerebral then continues in the interhemispheric fissure towards the .~.
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convexity. The recurrent artery of Huebner has a variable origin.2ss In most cases (65%)) it arises from the proximal A-2 segment, immediately after the origin of the anterior communicating artery. In 25% of cases, the recurrent artery arises from the A-l segment, proximal to the anterior communicating artery. In the remaining lo%, the recurrent artery originates at the level of the anterior communicating artery. The recurrent artery of Huebner and the septal perforators are the most important branches of the proximal portion of the anterior cerebral artery, supplying the anterior limb of the internal capsule, the anterior commissure, the septal region, the anterior portion of the fornix and hypothalamus, and the most anterior portion of the thalamus.2*3s The middle cerebral artery continues in the sylvian fissure and divides in two or three primary trunks, from which will originate the branches to the cerebral cortex.6p7 Particularly important are the branches to the rolandic area, the angular gyrus, and the opercular area. Damage to one of these branches is poorly tolerated. Every branch of the middle cerebral artery should be identified prior to permanent clip placement9 Veins from the frontal and temporal portions of the cerebral convexity drain into the sylvian or middle cerebral veins, in the sylvian fissure. The sylvian vein is composed of several tributary veins which originate from the anterior frontal lobe, including the frontal pole, the orbital surface, the anterior opercular area, and the anterior and inferior portion of the insular lobe. Venous tributaries from the temporal lobe are variable and include branches from the temporal pole, the most anterior portion of the superior and mid temporal gyri, and the sylvian portion of the temporal lobe. The frontal and temporal venous afferents join to form one or two primary middle cerebral or sylvian venous trunks, but there can be as many as four or as few as one. The primary venous trunks drain directly into the sphenopetrosal sinus. The sylvian veins are predominantly located on the temporal side of the sylvian fissure and can be easily identified and spared. In most patients, the temporal tip veins may be coagulated and transected, but in some cases damage to these veins may result in venous congestion, cerebral edema, or venous infarction.” Venous drainage from the cerebral convexity returns to the systemic circulation by several convexity veins, the two largest are the posterior temporal or vein of Labbe which drains into the transverse sinus, and the mid parietal or vein of Trolard, draining into the superior sagittal sinus. Removing more than one vein in the mid and posterior portion of the superior sagittal sinus, or transecting the veins of Trolard or Labbe can result in significant venous stasis, and a venous infarction. Yasargil” described the subarachnoid cisterns at the base of the brain as small envelopes which encircle all structures contained in the subarachnoid space. In the supraclinoid carotid area, there are cisterns about the internal carotid artery, the carotid bifurcation, the middle cerebral, the anterior cerebral, the optic nerve, the chiasm, the prechiasmatic cistern, the cistern of the lamina terminalis, and the confluence of the sylvian fissure to the middle cerebral cistern. Wide opening and sharp
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dissection of these cisterns is required to expose internal carotid artery aneurysms safely.”
Diagnostic evaluation Computerized tomography and magnetic resonance imaging are necessary to exclude intra or extraparenchymal haematomas, the extent of the subarachnoid haemorrhage, the presence of hydrocephalus, and the possibility of intra-aneurysmal clot formation.‘“~1s,‘4 A false sense of security may be gained from an angiogram which reveals an apparently small aneurysm, when in reality the aneurysm is large, and filled with clot.12,1”.16,17Magnetic resonance imaging facilitates the localization of the haemorrhage within the parenchyma of the brain, and may suggest the presence of a vascular abnormality. A selective four vessel cerebral angiogram must be completed in all patients suspected of having an aneurysm to determine its location, to exclude the presence of multiple aneurysms which occur in 20% of cases, and to rule out the presence of cerebral vasospasm~12.13.14.15
Pre-operative preparation Careful monitoring of the arterial blood pressure with an intra-arterial line will facilitate the management of the blood pressure, and prevent undesirable fluctuations. Fluid balance and cardiac function are best managed with a Swan-Ganz catheter. An optimum intravascular blood volume may be established pre-operatively by the administration of intravenous albumin, and the careful monitoring of the cardiac output and cardiac index. Patients with chronic obstructive pulmonary disease, or with previous pulmonary problems may require securing arterial blood gases or pulmonary function tests, in addition to a chest X-ray.’ Brain protective drugs such as diphenylhydantoin, dexamethasone, and calcium channel blockers may be administered in preparation for surgery.g~1’~16~1g~20~z1 Susukig observed that diphenylhydantoin has a brain protective effect during temporary clipping, exerted by stabilizing the neuronal membrane, and reducing membrane excitability. Dexamethasone has been studied extensively as a possible cerebral protective agent, and found effective only when given prior to the occlusion the effect of of a cerebral artery. 11,20*s1 Since diphenylhydantoin and dexamethasone can be maximized by early administration and tissue saturation, they are ideal for pre-operative administration. Calcium channel blockers reduce the incidence of cerebral ischaemic complications associated with arterial vasospasm, when administered in the immediate posthaemorrhagic period. l4 Their effect results from a direct vasodilatory action on the smooth muscle cell of the cerebral vessels. In addition, calcium channel blockers may have a direct protective effect at a molecular level in the ischaemic neurone, by preventing the sudden influx of calcium, and blocking the onset of the ischaemic cascade triggered by the intracellular accumulation of calcium. Calcium channel blockers are given from the time of
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Anterior circulation aneurysms admission until after surgery. Aminocaproic acid has fallen in disfavor and is no longer recommended, because of the numerous ischaemic complications, and the increased incidence of hydrocephalus observed with its use.20 The decision to proceed with surgery should be based on the clinical condition of the patient, including the neurological evaluation and the general medical status. Patients with poor medical condition but with good neurological status, should not be operated on any sooner than the patient with poor neurological condition but a favorable medical state.’ A poor condition in either case would likely lead to a poor outcome. In general, most would agree that patients with a Hunt-Hess grade of 3 or lower may be operated on almost any time.g~1’,2”.22In the presence of vasospasm, most would tend to wait until vasospasm has lapsed, although patients with a good neurological condition but with angiographic arterial narrowing, may do well with surgery.‘g,2”
Trans-operative
management
Patients with anterior circulation aneurysms require a mild state of hyperventilation to keep the pC0, at about 30 to 35 mmHg. Lowering the PCO, below 30 mmHg will not aid further in reducing cerebral volume, and may in fact induce cerebral ischaemia, by promoting vasoconstriction. Hyperventilation induced vasoconstriction is particularly a problem for patients with residual vasospasm, who will already be in a partial ischaemic state.’ Mannitol is used to decrease brain volume during surgery, and to facilitate brain retraction. Suzuki9 reported a beneficial effect in brain tolerance to cerebral ischaemia, when mannitol was given during surgery. The benefit of mannitol may result from its action as an anti-aggregant, enhancing microcirculatory flow, permitting greater corpuscular deformation, and allowing greater release of oxygen at tissue levels. More recent evidence indicates that mannitol also has a free radical quenching ability. Thiopental acts as a cerebral protective agent producing a functional reduction of oxygen consumption at the synaptic junction, estimated at 80% of the metabolic activitv of the brain.‘,9,“,“12’ This protective effect is demol;strable when the thiopental levels are sufficient to produce an isoelectrical tracing on electroencephalography. The metabolic action of thiopental may be enhanced by the administration of lidocaine, since lidocaine blocks directly the sodium-potassium pump.’ The intra-operative administration of barbiturates and lidocaine in preparation for temporary clipping may produce immediate hypotension and lead to myocardial ischaemia.
Surgical
approaches
Multiple surgical approaches have been reported to manage internal carotid aneurysms, since Dandyz4 treated the first patient with a correctly diagnosed intracranial aneurysm. Proximal ICA occlusion in the neck was followed by numerous direct approaches. Various surgical clips have permitted the obliteration of small and giant aneurysms, facilitated by intracranial vascular re-
constructive and endovascular techniques. The surgical approaches can be divided into: extracranial ICA ligation; and pterional region; convexity; interhemispheric; endovascular. Extracranial internal carotid artery ligation Proximal ligation of the internal carotid in the neck had many advocates and was practised extensively to manage intracranial aneurysms prior to the development of Proximal modern microsurgical techniques. 19.“4,‘15.“1;.27 . ligation of the internal carotid artery in the neck led to a 45% incidence of cerebral ischaemic complications and was soon replaced by the gradual ligation of the common carotid artery, coupled with the ligation of the external carotid artery distal to the origin of the superior thyroid artery. Flow through the superior thyroid artery prevented the development of the dreaded ischaemic complications. However, maintaining permeability in the internal carotid artery allowed the aneurysm to remain patent as well, and in some cases to grow and later rebleed. This once very useful technique has been largely abandoned. Pterional approach Approximately 80% of all anterior circulation aneurysms may be treated successfully via the pterional route.“’ A detailed description of the patient’s position, the craniotomy and dissection of the anterior portion of the circle of Willis, and the clipping techniques will be reviewed. A description of the principles of temporary clipping, aneurysmal opening, debulking, resection, and reconstruction techniques will complete this section. The patient’s position is critical in the success of the procedure. The patient is placed supine, in a reclining position, supported by skeletal fixation, with the head rotated 15” to the opposite side, and with 15” of extension. In this position, the sphenoid wing is perpendicular to the floor. Yasargil”’ recommended the head placed with the nose turned 30” towards the opposite side, and the malar eminence uppermost on the head. When the head is in this position, the temporal lobe is difficult to dissect and the axis of the sylvian fissure rotates away from the surgeon. An incision is made along the hairline from the zygoma to the ipsilateral mid pupillary line. The skin and muscle are reflected in one single flap, exposing the entire squamosal portion of the temporal bone. the frontalis process of the lateral orbital wall, and the vertical portion of the frontal zygomatic area. Yazargil’” recommended a complex muscle incision disinserting the temporalis muscle from its anterior attachment, and retracting it posteriorly, after separating the fatty tissue which contains the frontalis branch of the facial nerve. This dissection lengthens the operation, and does not protect the nerve any more than elevation of a single flap. A free bone flap is elevated, ten tering the craniotomy on the pterion (Fig. 1). The pterion is drilled down until the meningo-orbital branch of the middle meningeal artery is exposed. The dura is sutured to the skull, opened in a semicircular manner based on the pterion, and sutured to the temporalis muscle. The sylvian fissure is
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Fig. 1 Rerional craniotomy: a linear incision is placed along the hairline from the zygoma to the mid pupillary line. The skin and muscle are elevated on a single flap and retracted. A free fronto-temporal flap is elevated, centered on the pterion. A kidney bean shaped exposure reveals the frontal and temporal lobes approximately equidistant. The dura is opened in a semicircular incision along the superior border of the craniotomy and reflected on the temporalis muscle.
opened under the microscope from the surface down. Proximal control is achieved dissecting the internal carotid as it arises from the supraclinoid area, next to the optic nerve. Once proximal control is accomplished, the rest of the sylvian fissure may be opened widely. All arachnoidal bands are released with sharp dissection, to expose the entire course of the internal carotid and its bifurcation, the optic nerve and optic chiasm, the proximal portion of the anterior cerebral, the trunk and bifurcation of the middle cerebral to the level of the limen insulae. The sylvian fissure is then relaxed, and the frontal and temporal lobes fall apart without traction like the petals of a lotus flower. The temporal lobe is supported by the sphenoid
wing and the sylvian veins, and generally it is only necessary to use a single retractor on the frontal lobe, with minimal pressure. Trauma to the brain and draining veins is thus minimized.28 Spinal fluid is drained gradually from the cisterns to obtain maximum brain relaxation with minimal brain retraction. Opening the sylvian fissure is facilitated by not using a lumbar drain, since the subarachnoid space is full, the sylvian fissure is readily apparent, and the dissection can be done without difficulty. When it is necessary to remove additional spinal fluid, it may be obtained opening the lamina terminalis above the chiasm. Opening the lamina terminalis is easy to do once all cisterns are open, and does not carry any of the complications of ventricular puncture.** Incomplete opening of the arachnoid cisterns leads to tension on the frontal and temporal lobes, requires increased pressure on the retractor blades and provides less exposure of the area. Incomplete dissection of the cisterns may also lead to premature rupture of the aneurysm, from traction on the brain. Preservation of the veins is much easier when the cisterns have been dissected widely. Since there is less retractor pressure on the brain, the possibility of venous tears, venous stasis, or venous infarcts is reduced. The actual placement of the clip on the aneurysm neck is much easier when the area of exposure is wide. Direct surgical clipping of the neck of the aneurysm remains the only truly curative approach in the treatment of intracranial aneurysms (Fig. 2). Direct clipping requires complete dissection of the neck of the aneurysm, identification of all afferent and efferent vessels, dissection and isolation of important perforating arteries, and application of the clip on the neck of the aneurysm, flush with the parent vessel. Care must be taken not to cause kinks, or stenoses of the parent vessel. Positioning the clip across the axis of the vessel sometimes leaves small areas
Fig. 2 A 62-year-old woman was evaluated for progressive headaches and visual loss in the left eye. A) A pre-operative left internal carotid angiogram revealed a large aneurysm arising from the origin of the ophthalmic artery. Through a pterional craniotomy, the origin of the aneurysm was exposed after removing the anterior clinoid process, and opening the most distal portion of the cavernous sinus. The aneurysm was isolated between temporary clips, and intraluminal thrombus removed. The wall of the vessel was atheromatous, and the atheroma could not be resected. The atheroma was compressed with a clamp and the permanent clips placed. B) Tram-operative internal carotid angiogram reveals the internal carotid artery to be occluded at the level of the permanent clip. C) Trans-operative internal carotid angiogram revealed the lumen of the internal carotid artery was re-established after the permanent clips were repositioned away from the internal carotid artery lumen. The patient had an uneventful post-operative recovery.
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of the neck outside the clip. For patients with a recent haemorrhage or patients with a large or giant aneurysm, it is safer to apply temporary clips while dissecting the aneurysm neck free from the perforators. Temporary clips may be applied to any intracranial vessel for short periods of time, which vary with the administration of brain protective substances.” When the aneurysm is large or giant, it will be necessary to use temporary clips, and deflate the aneurysm before applying the permanent clip. The aneurysm may be deflated by needle aspiration or puncturing the dome. Once the sac is collapsed, all important arterial branches and perforators may be identified and dissected, and the permanent clip may be placed safely across the neck of the aneurysm. Care must be taken not to encroach on the parent vessel, since the actual diameter of the parent vessel is also decreased by the absence of blood. In some giant aneurysms, it is not possible to clip the neck because the aneurysm is filled with thrombus or is arteriosclerotic. In aneurysms full of thrombus, it is generally safe to isolate the aneurysm complex as described, apply temporary clips, and then open the aneurysmal dome with a knife. An ultrasonic aspirator is then introduced to remove the thrombus, leaving only the supple aneurysm sac behind. The perforators can then be separated away from the aneurysm neck, and a clip applied flush with the parent vessel. It is generally not recommended to remove the aneurysmal sac, since this can be followed by unnecessary injury to the perforators, and other adjacent structures. When the aneurysmal wall is infiltrated with atheroma, it is sometimes possible to perform an endarterectomy of the aneurysmal wall, preserving the aneurysmal wall itself with a small amount of atheroma. In some cases this may be done with ease, but it requires extreme patience. When the atheroma cannot be completely resected, a haemostatic clamp may be used to crush the atheroma and develop a smooth surface over which the clip may then be applied (Fig. 2). When neither of these manoeuvres are successful, it becomes necessary to either resect the aneurysm at the neck and perform an aneurysmorrhaphy, or to clip the aneurysm neck to include a major branch, and then perform an extracranial to intracranial (EC-IC) anastomosis, distal to the clip. An alternative to temporary clipping and complete obliteration of the aneurysmal neck was the use of aneurysm glues with or without wrapping.2g Wrapping and gluing techniques failed because they required that the entire aneurysm complex be included in the encasement. In most cases, the inability to expose the entire complex is what motivated the use of these techniques as substitutes. In addition, none of the glues adhere to the vessel wall, leaving a virtual space between the glue and the aneurysm wall, where the aneurysms would then expand and rebleed. Cotton is the only substance that has in fact produced a strong enough reaction to reinforce the aneurysm. Gluing and wrapping have largely been abandoned. Giant aneurysms of the internal carotid and middle cerebral bifurcations represent a serious problem when one of the arterial trunks arises directly from the waist of
the aneurysm. Clipping the aneurysm neck to include the origin of an arterial branch may be tolerated in a few individuals when the collateral arteries are large. However, when a major arterial trunk is included in the clip, it may be necessary to first perform an EC-IC anastomosis distal to the vessel.“~‘6,3” One could rely on collateral circulation to take over the territory of the occluded vessel but, in most, the collateral circulation is insufficient when it has to come over the cerebral convexity. The EC-IC anastomosis may be performed on the surface of the haemisphere, but it is preferable to perform the bypass as close as possible to the area of occlusion” (Fig. 3). Some giant aneurysms may not be clipped because of extensive atheroma within their wall, or because the branches which arise from the aneurysm dome are too numerous. In some patients, it is possible to resect the entire aneurysm and reconstruct the various branches.‘“,‘” The principles involved in reconstruction of the anterior circulation branches include a wide dissection of the cisterns, careful isolation and identification of the afferent
Fig. 3 A ZQyear-old critical care nurse was admitted with bitemporal haemianopsia, and chronic frontal headaches. A) A pre-operative MRI revealed a large mass in the suprasellar region, with a large signal void, suggestive of a giant aneurysm. 6) Pre-operative left internal carotid angiogram demonstrated a giant aneurysm arising from the supraclinoid internal carotid artery. Through a pterional approach, the aneurysm was found to arise from the distal portion of the supraclinoid left internal carotid artery, just proximal to the bifurcation. No aneurysmal neck existed. An extracranial to intracranial anastomosis was completed with the superficial temporal artery, to the temporal trunk of the MCA; the ICA was ligated in the neck, and the aneurysm was trapped intracranially. C) Post-operative left carotid angiogram shows the entire MCA tree filled by the EC-K anastomosis. D) Post-operative right internal carotid angiogram reveals cross filling of the anterior cerebral arteries. The aneurysm was angiographically not visualized. The patient resumed his duties in our head injury unit without any deficits.
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Review articles and efferent branches to the aneurysm, isolation and preservation of the perforators, and the use of temporary clipping with cerebral protective agents. Having isolated all branches, one must consider initially performing an EC-IC anastomosis to the largest branch arising from the aneurysm in preparation for the period of prolonged cerebral ischaemia. In some patients, it is then possible to resect the branch or branches arising from the aneurysm, and to perform an end to side anastomosis to the artery with the EC-IC anastomosis or to the branch that will remain attached to the parent vessel. It may be necessary to resect the entire aneurysm, and then perform an end to end anastomosis of the parent vessel to the principal branch distal to the aneurysm. SilverbergP3 recommended cardiac arrest in combination with deep hypothermia when dealing with giant aneurysms. Achieving 24°C of core cooling, the brain will be protected for one hour of complete circulatory arrest. Draining the cerebral circulation allows the aneurysm to collapse, and permits the surgeon to dissect the perforators and branches away from the aneurysm, and allows placement of the clip on a supple aneurysm sac. Draining the blood from the cerebral circulation also empties blood from the smaller vessels, and makes their identification difficult. In addition, one must deal with the problems of full heparinization and immediate bleeding once the cardiac bypass is restarted and the circulation begins. Convexity
approaches
Few aneurysms present on the cerebral convexity. Most aneurysms arising in the periphery of the cerebral circulation result from mycotic infections or from trauma. These aneurysms generally require a craniotomy on the area of the middle cerebral distribution. The localization of the aneurysms may be difficult, and may require stereotaxic angiographic techniques for the final approach to the lesion. The aneurysms may sometimes be clipped in a conventional manner, but in cases where there is no defined neck, it will be necessary to resect the aneurysm, and perform an EC-IC anastomosis distal to the vessel occlusion. Some patients may tolerate the complete occlusion of the parent vessel, when the distal branch serves a silent area of the brain.
Interhemisphericapproach The anterior communicating artery (ACA) region may be approached also via the interhemispheric route.2g Giant aneurysms with no apparent neck, and distal aneurysms are the only anterior cerebral artery aneurysms that we would approach via the interhemispheric route. The patient is positioned in a reclining manner with the head facing directly perpendicular to the horizontal plane, and supported by skeletal fixation. A bicoronal incision may be used, although a linear incision may be placed in a skin fold. A bifrontal flap is elevated, with the inferior edge placed directly over the orbital rim. When the frontal sinus is entered, the mucosa is removed from the flap, and the portion of the sinus remaining on the skull is packed with
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muscle or fat, and covered with a pericranial flap. The dura is opened bilaterally with the flaps based on the sagittal sinus, and the insertion of the superior sagittal sinus on the crista galli is ligated and transected. After the frontal lobes are gently retracted, the olfactory nerves are dissected from the inferior frontal surface and preserved. The area of the suprasellar cisterns and supraclinoid carotid arteries is then dissected, and the anterior communicating artery complex is isolated. Depending on the anatomy of the aneurysm, temporary clips may then be applied on all branches to the anterior communicating artery complex, and the aneurysm clipped, resected or reconstructed depending on the pathology found. For distal anterior cerebral aneurysms arising from the pericallosal artery, the craniotomy is placed two-thirds anterior to the coronal suture, and one-third behind. The craniotomy is placed across the superior sagittal sinus, three-fourths to the right and one-fourth to the left of the sinus. Only the dura on the right side of the sinus is opened, with the flap based on the sinus. If necessary, one cortical vein may be resected in the anterior most portion of the exposure. Occasionally, it is possible to take two cortical veins, but this increases the danger of venous congestion and venous infarction. The right frontal lobe is retracted away from the midline, and the pericallosal artery is found at the level of the rostrum of the corpus callosum. The anterior cerebral may be followed anteriorly and posteriorly to isolate the aneurysm, and the vessels around it. Temporary clips may be applied and the aneurysm dissected and clipped as necessary. It is very important to verify the position of both anterior cerebral arteries before closing, to ensure that both vessels remain patent past the clip.
Endovasculartechniques Mullan’s26~27use of intravascular copper wires to manage complicated intracranial aneurysms, served as the foundation for the modern use of endovascular therapeutic techniques. A promising approach to the management of intracranial vascular lesions is the technique of balloon embolization introduced by Serbinenko.31 Balloons may be used to occlude the internal carotid proximal to the aneurysm, at the level of the aneurysm neck, to occlude the aneurysmal neck itself, or most commonly to fill the space within the aneurysmal sac. 17.31,32Endovascular balloon occlusion has met with limited success because of the difficulty of adapting a balloon configuration to the anatomy of the aneurysm, the necessity to use one or more balloons per procedure, the potential of embolization of the balloon to an undesirable site, or premature dislodgement of the balloon. Some balloons have deflated partially allowing the aneurysm to refill or enlarge, rebleeding has occurred during, or after unsuccessful balloon occlusion, and chemical reactions with vessel damage have occurred after spontaneous rupture of the balloons in the vascular tree.17,18,32Complications as high as 20% in grade I and II aneurysmal subarachnoid haemorrhage patients have been reported.”
October 1994
Review articles
Anterior circulation aneurysms
A new and exciting approach to the endovascular management of intracranial aneurysms is the introduction of endovascular coils by Guglielmi.33 Small metal coils are introduced in the cerebral vessels or into the aneurysm itself, and fed progressively until the aneurysm sac is filled by the coil. The coils are thrombogenic because of their electromagnetic properties, and may eliminate the aneurysm from the circulation. Limited experience is currently available with the electrothrombotic coils, and no long term results have been reported with their use in the treatment of intracranial aneurysms. The coils are most effective when treating aneurysms 5 mm or less in diameter, and with a neck smaller than 5 mm.33 Like the endovascular balloons, it is likely that the coils will serve as a primary therapeutic option in the acute management of the patient with subarachnoid haemorrhage who is otherwise too ill to undertake an operative procedure.
Conclusions The management of aneurysms of the anterior circulation is an exciting and challenging part of neurovascular surgery. Special techniques and years of experience permit the safe, successful ancl permanent exclusion of these aneurysms from the circulation. Although most aneurysms of the anterior circulation do not require any specialized techniques for their successful treatment, some principles must be kept in mind when dealing with these problems. Most aneurysms may be treated safely and fully through a pterional approach. It is necessary to maximize the exposure of the aneurysm and the collateral vessels by optimizing the position of the patient, and dissecting widely the basal cisterns. Minimal brain retraction will be needed when the basal cisterns and the lamina terminalis are opened widely to permit drainage of spinal fluid. Aneurysms are best clipped in a direction parallel to the axis of the vessel to minimize the possibility of leaving a remnant of aneurysm, and to preserve the diameter of the vessel wall. When aneurysms cannot be totally excluded from the circulation, the remaining aneurysm sac will regrow, with a high probability of rebleeding. Those aneurysms that cannot be clipped may be trapped or resected, with reconstruction of the collateral vessels by EC-I(: anastomosis, or intracranial vessel re-anastomoses. Multiple drugs have been used to lengthen cerebral tolerance to ischaemia; probably a combination of several of these give the best potential for brain tolerance to ischaemia. Endovascular approaches may be used to supplement the surgical procedures, but most complicated aneurysms can not be treated successfully by endovascular techniques. Careful planning and execution of surgical procedures are likely to bring the most successful treatment to these very difficult and challenging problems. Received 5 September 1993 Accepted for pubhcation 30 September 1993
Correspondence
and offprint requests:
Dr Fernando G. Diaz. Neurological Surgery Department, Wayne State University, School of Medicine. Detroit. Michigan. USA.
References 1. Varkey GP (ed) . Anesthetic Considerations in the Surgical Repair of Intracranial Aneurysms. International Anesthesiology Clinics. Boston: Little Brown, 1982. 2. Gibo H, Lenkey C, Rhoton AL. Microsurgical anatomy of the supraclinoid portion of the internal carotid artery. J Neurosurg 1981;55:560-74. 3. Gomes F, Dujovny M, Umansky F, AusmanJI, Diaz FG, Ray WJ, Mirchandani GF. Microsurgical anatomy of the recurrent artery of Heubner. J Neurosurg 1984;60: 130-39. 4. Comes FB, Dujovny M, Umansky F, Berman SK, Diaz FG, Ausman JI, Mirchandani HG, Ray WJ. Microanatomy of the anterior cerebral artery. Surg Neurol 1986;26:129-41. 5. Grand W. Microsurgical anatomy of the proximal middle cerebral artery and internal carotid bifurcation. Neurosurgery 1980;7:215-18. 6. Umansky F, Montoya Juarez S, Dujovny M, Ausman JI, Diaz FG, Gomes F, Mirchandani HG, Ray WJ. Microsurgical anatomy of the proximal segments of the middle cerebral artery. J Neurosurg 1984;61:458-67. 7. Umansky F, Gomes FB, Dujovny M, Diaz FG, Ausman JI, Mirchandani HG, Berman SK. The perforating branches of the middle cerebral artery: A microanatomical study. J Neurosurg 1985;62:261-68. 8. Yokoh A, Ausman JI, Dujovny M, Diaz FG, Berman SK, Sanders J, Mirchandani HG. Anterior cerebral artery reconstruction. Neurosurg 1986:19:26-35. 9. Suzuki-J. Cerebral Aneurysms, Experience with 1000 Directly Operated Cases. Tokyo: Neuron Publishing Co, 1979. 10. Yasargil MG, Antic J, Laciga R,Jain KK, Hodosh RM, Smith RD. Microsurgical pterional approach to aneurysms of the basilar bifurcation. Surg Nemo1 1976;6:83-91. 11. Diaz FG, Umansky F, Mehta B, Montoya S. Dujovny M, Ausman JI, Cabezudo J. Cerebral revascularization to a main limb of the middle cerebral artery in the sylvian fissure. An alternative approach to conventional anastomosis. J Neurosurg 1985;63:21-29. 12. Andrews RJ, Spiegel PK. Intracranial aneurysms. Age. sex, blood pressure, and multiplicity in an unselected series of patients. J Neurosurg 1979;51:27-32. 13. Da Pian R. Pasqualin A, Scienza R. Direct microsurgical approach to aneurysms of the internal carotid bifurcation. Surg Nemo1 3980;13:27-37. 14. Kassell NF, Sasaki T, Colohan ART, et al. (Cerebral vasospasm following aneurysmal subarachnoid haemorrhage. Stroke 1985;16:562-72. 15. hllcock JM, Canham PB. Angiographic study of the growth of intracranial aneurysms.,J Nemoslug 1976;45:617-21. 16. Ausman.JI, Diaz FG, Sadasivan B, Gonzales-Portillo M, Malik GM, Deopujari CE. Giant intracranial aneurysm surgery: The role of microvascular reconstruction. Surg Neural 1990;34:8-15. 17. Higashida RT, Halback W, Barnwell SL, Dowd CF, Dormandy B, Bell J, Hieshima GB. Treatment of intracranial aneurysms with preservation of the parent vessel. AJNR 1990;11:633-40. 18. Hodes JE, Aymard A. Gobin P. Rufenacht D, Bien S, Reizine D, Gaston A. Merlandg. Endovascular occlusion of intracranial vessels for curative treatment of unclippable aneurysms: report of 16 cases..J Neurosurg I99 1:75:694-701. 19. Ausman JI, Charbel FT. Diaz FG, Malik GM, Dujovny M. Timing of surgery in Grade IV aneurysmal subarachnoid haemorrhage. Surg Forum 1988;39:499-501. 20. XusmanJI, Diaz FG, Malik GM, Andrews BT, McCormick P, Balakrishnam G. Management of cerebral aneurysms: Further facts and additional myths. Surgical Neurology, 1989:32:21-35.
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21. Charbel ET, Ausman JI, Diaz FG, Malik GM, Dujovny M, Sanders J. Temporary clipping in aneurysm surgery: Technique and results. Surg Neurol 1991;36:83-90. 22. Hunt WE, Hess RM. Surgical risk as related to time of intervention in the repair of intracranial aneurysms. J Neurosurg 1968;28:1420. 23. Silverberg GD, Reitz BA, Ream AK. Hypothermia and cardiac arrest in the treatment of giant aneurysms of the cerebral circulation and haemangioblastoma of the medulla. J Neurosurg 1981;55:337-346. 24. Dandy WE. Intracranial Arterial Aneurysms. Ithica, New York: Comstock Pub Co, 1944. 25. Diaz FG. Surgical treatment of aneurysms in the cavernous sinus. Contemporary Neurosurgery 10, 1989;26:1-6. 26. Mullen S. Experiences with surgical thrombosis of intracranial berry aneurysms and carotid cavernous fistulas. J Neurosurg 1974;41:657-70. 27. Mullen S, Reyes C Dawley J, et al. Stereotactic copper electric thrombosis of intracranial aneurysms. Progr Neurol 1969;3: 193211. 28. Kobayashi S, Sugita K, Nakagawa F. An approach to a basilar aneurysm above the bifurcation of the internal carotid artery. Case Report. J Neurosurg 1983;59: 1082-84.
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29. Pool JL, Potts DG. Aneurysms and Arteriovenous Anomalies of the Brain: Diagnosis and Treatment. New York: Hoeber Medical Division, Harper and Row, 1965. 30. Cabezudo-Artero J, Ausman JI, Dujovny M, OrdonezMora E, Umansky F, Diaz FG, Mirchandani H, Berman SK Middle cerebral artery reconstruction. Surg Neurol 1985;24:5-11. 31. Serbinenko FA. Balloon catheterization and occlusion of major vessels. J Neurosurg 1974;41:125-45. 32. Aymard A, Gobin YP, Hodes JE, Bien S, Rufenacht D, Reizine D, George B, Merlanda. Endovascular occlusion of vertebral arteries in the treatment of unclippable vertebrobasilar aneurysms. J Neurosurg 1991;74:393-98. 33. Guglielmi G, Vinuela F, Duckwiler G, Dion J, Lylik P, Berenstein A, Strother C, Graves V, Halback V, Nichols D, Hopkins N, Ferguson R, Spetka I. Endovascular treatment of posterior circulation aneurysms by electrothrombosis using electrically detachable coils. J Neurosurg 1992;77:512-24. 34. Locksley HB. Report on the cooperative study of intracranial aneurysms and subarachnoid haemorrhage. Section V, Part 1. Natural history of subarachnoid haemorrhage, intracranial aneurysms and arterio venous malformations. Based on 6368 cases in the Cooperative Study. J Neurosurg 1966;25:219-39.
October 1994
Aneurysms arising from the internal carotid circulation represent 85% of all intracranial aneurysms. The intimate relationship of the internal carotid artery and its branches with the brain and cranial nerves, and the distribution of the internal carotid artery flow, make these aneurysms challenging, and potentially complicated in their surgical management. Great attention to detail, and clear understanding of the operative anatomy of the carotid system, facilitate the safe and successful treatment of these aneurysms. The surgical experience with 475 anterior circulation aneurysms treated from 1980 to 1992 is presented. The aneurysms arose from the internal carotid artery: 230(40%), middle cerebral artery: 152(32%), and anterior cerebral artery: 133(28%). Of aneurysms arising from the internal carotid artery, there were 142(30%) from the posterior communicating artery; internal carotid bifurcation: 29(6%), and anterior choroidal artery: 19(4%). There were 62( 13%) giant aneurysms evenly distributed among the middle cerebral, internal carotid bifurcation and anterior cerebral artery. Serious neurological morbidity was observed in 13(3%) patients, who presented a combination of different neurological symptoms including: hemiplegia 3, hemiparesis 6, dysphasia 7, and loss of vision 4. Wo
patients developed a myocardial infarct and survived. Mortality occurred in 16(3%); these patients
died from: a hemispheric infarction 7, severe vasospasm 6, myocardial infarction 2, and pulmonary emboli 1. All aneurysms appeared angiographically obliterated. Vasospasm was observed in 75(16%) patients of which nine were symptomatic, and six of them died. Six major arterial trunks were occluded in the post-operative angiogram, and three patients had occlusion of the internal carotid artery, not identified during surgery. Three of these patients with unexpected occlusions died from a major cerebral infarction, and three had lasting hemipareses and dysphasia. Surgical correction of internal carotid aneurysms can be conducted safely when the anatomical characteristics of the intracranial vessels is preserved, and when these patients are treated with appropriate medical support. Journal of Clinical Neuroscience Keywords:
0 Longman Group UK Ltd
1994, 1(4):222-230
Cerebral aneurysm, Internal carotid artery
Clinical material
Introduction Aneurysms
arising
represent
from
the internal
85% of all intracranial
relationship
of the internal
with the brain and cranial the internal
carotid
challenging,
and potentially
to detail,
artery
ful treatment
circulation
From
The intimate
carotid artery and its branches nerves,
and the distribution
flow, make complicated.
and clear understanding
tomy of the carotid
carotid
aneurysms.
aneurysms
Great attention
of the operative
system, facilitates
of these aneurysms.
these
of
ana-
the safe and success-
The surgical approaches
can be divided into: extracranial internal carotid ligation; pterional; convexity; interhemispheric; and endovascular. The pertinent surgical anatomy, pre-operative preparation, intra-operative procedures, operative approaches, and potential complications will be reviewed.
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Number 4
were carotid
1980 to 1992, 47’5 anterior treated.
The
artery:
aneurysms
230(40%),
circulation
arose
from
middle
cerebral
152(32%), and anterior cerebral artery: those aneurysms arising from the internal there
were
142(30%)
communicating bifurcation, artery. evenly
There from
arising
artery, 29(6%) and
19(4%)
aneurysms the internal
from
artery:
133(28%). Of carotid artery, the
posterior
from the internal
from
the anterior
were 62(13%) giant the middle cerebral,
aneurysms internal
carotid
choroidal arising carotid
bifurcation and anterior cerebral artery area. Patients who had a subarachnoid hemorrhage were admitted to an intensive care unit for evaluation, in preparation for surgery.’ A complete
October 1994
pre-operative
medical evaluation
was
Review articles
Anterior circulation aneurysms obtained in elderly patients to prevent intra-operative cardiac, respiratory or renal complications that may develop from the use of mannitol, hypertension, hypotension, blood loss, or the use of cardiac suppressants such as barbiturates or lidocaine.’ A Swan-Ganz catheter, an intra-arterial recording catheter, and a Foley catheter were inserted in preparation for surgery. All patients received dexamethasone 10 mg i.v. on admission and 4 mg every six hours, and nimodipine 1 mg per kg orally until surgery. Salt poor albumin was infused until a cardiac output of at least 5-7 litres per minute was obtained. Anaesthesia was induced with thiopental and maintained with nitrous oxide-oxygen and ethrane. During induction the patients received intravenous diphenylhydantoin 15 mg per kg, vancomycin 1000 mg, dexamethasone 10 mg, gentamicin 80 mg, furosemide 20-40 mg, and mannito10.5 gm per kg. Spinal fluid drains were not used, since drainage of spinal fluid from the cisterns and the lamina terminales was effective in achieving cerebral relaxation. Arterial blood gases, end expiratory CO, recordings and pulse oximetry were monitored throughout the operation. Arterial pC0, was maintained at about 30-35 mmHg, p0, at about 95 mmHg, and oxygen saturation at about l-00%. The patients were maintained normothermic and normotensive throughout the operation. Intra-operative hypotension was only used when proximal arterial control could not be accomplished with a temporary clip. Direct clipping was accomplished in 85% (n=404) of the patients. An intracranial to extracranial anastomosis was required in 11% (n=52) of patients, in addition to a clip to obliterate the aneurysm. A reconstructive procedure was performed in the remaining 4% (n=19) of the patients, including a direct end to end anastomosis in 5 patients, an end to side anastomosis of one branch to another branch in 10 patients, an end to side anastomoses of a branch to a main arterial trunk in 2, and an endoaneurysmorrhaphy in 2 patients. The aneurysm had to be opened and decompressed in 57 of 62 giant aneurysms, with removal of formed thrombus in all 57. and removal of wall atheroma in 37 patients. Serious neurological morbidity was observed in 13 patients (2.7%), who presented a combination of different neurological symptoms including hemiplegia 3, hemiparesis 6, dysphasia 7, and loss of vision 4. Two patients developed a myocardial infarct and survived. Mortality was found in 16(3.3%); these patients died from a hemispheric infarction 7, severe vasospasm 6, myocardial infarction 2, and pulmonary emboli 1. All aneurysms were angiographically proven to be obliterated. Vasospasm was observed in 75(16%) patients of which 9 were symptomatic, and 6 of these died. Six major arterial trunks were found occluded in the post-operative angiogram, and 3 patients had occlusion of the internal carotid artery, not identified during surgery. Three of these patients with unexpected occlusions died from a major cerebral infarction, and 3 had lasting hemipareses and dysphasia.
Discussion Anatomical
considerations
The internal carotid artery enters the skull through the foramen lacerum, and becomes intracranial as it passes through the petrous canal into the cavernous sinus. Several small branches arise from the cavernous portion of the internal carotid, including the inferior hypophysial artery, the meningohypophysial trunk, and the artery to the clivus. As the internal carotid artery leaves the cavernous sinus it traverses the subarachnoid space giving rise to the ophthalmic artery, the posterior communicating artery, the anterior choroidal artery, and terminates dividing into the anterior and middle cerebral arteries. For the purpose of this discussion, emphasis will be placed on the most proximal portion of the circle of Willis. The internal carotid artery from the cavernous sinus to the bifurcation is variable in length, and in the number of branches it gives rise to. Besides the ophthalmic artery, the posterior communicating and anterior choroidal arteries, there are branches directed to the anterior perforated substance, and in some cases, a proximal branch to the temporal pole or to the inferior frontal area.‘” The perforating branches generally arise from the posterior wall of the internal carotid, either before or after the bifurcation, not from the bifurcation itself. The perforating branches from the anterior cerebral artery may arise from a common trunk, or they may arise as several small branches directed to the medial portion of the anterior perforated substance.J,J The anterior perforating arteries originating from the middle cerebral artery arise from a single common trunk or from several small perforating branches.“,’ These middle cerebra1 perforators may originate from the most medial portion of the artery, close to its origin (37%). or they may originate from the middle one-third of the M-l segment (47%). The remaining (16%) perforating vessels arise from the most lateral portion of M-l. The pattern of arterial supply to the anterior perforated substance is one of dominance by either the anterior cerebral or the middle cerebral; the branches arising from the other artery will be smaller and fewer in number.“,“,’ In a few cases,” a large vessel may arise from the distal portion of the A-l segment and go to the anterior perforated substance retrogradely, substituting for the recurrent artery of Huebner. When the territories of the anterior and middle cerebral perforators overlap, permanent occlusion of one perforator may not be of great importance, and may go unnoticed clinically. However, when the perforating vessel is dominant, permanent occlusion of this artery may be followed by a severe and lasting neurological deficit. As the anterior cerebral passes from the carotid bifurcation to the interhemispheric fissure, it gives rise to branches to the anterior perforated substance, the inferior frontal area, the fronto-polar artery, the recurrent artery of Heubner, the septal perforating arteries and the anterior communicating artery. The anterior cerebral then continues in the interhemispheric fissure towards the .~.
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convexity. The recurrent artery of Huebner has a variable origin.2ss In most cases (65%)) it arises from the proximal A-2 segment, immediately after the origin of the anterior communicating artery. In 25% of cases, the recurrent artery arises from the A-l segment, proximal to the anterior communicating artery. In the remaining lo%, the recurrent artery originates at the level of the anterior communicating artery. The recurrent artery of Huebner and the septal perforators are the most important branches of the proximal portion of the anterior cerebral artery, supplying the anterior limb of the internal capsule, the anterior commissure, the septal region, the anterior portion of the fornix and hypothalamus, and the most anterior portion of the thalamus.2*3s The middle cerebral artery continues in the sylvian fissure and divides in two or three primary trunks, from which will originate the branches to the cerebral cortex.6p7 Particularly important are the branches to the rolandic area, the angular gyrus, and the opercular area. Damage to one of these branches is poorly tolerated. Every branch of the middle cerebral artery should be identified prior to permanent clip placement9 Veins from the frontal and temporal portions of the cerebral convexity drain into the sylvian or middle cerebral veins, in the sylvian fissure. The sylvian vein is composed of several tributary veins which originate from the anterior frontal lobe, including the frontal pole, the orbital surface, the anterior opercular area, and the anterior and inferior portion of the insular lobe. Venous tributaries from the temporal lobe are variable and include branches from the temporal pole, the most anterior portion of the superior and mid temporal gyri, and the sylvian portion of the temporal lobe. The frontal and temporal venous afferents join to form one or two primary middle cerebral or sylvian venous trunks, but there can be as many as four or as few as one. The primary venous trunks drain directly into the sphenopetrosal sinus. The sylvian veins are predominantly located on the temporal side of the sylvian fissure and can be easily identified and spared. In most patients, the temporal tip veins may be coagulated and transected, but in some cases damage to these veins may result in venous congestion, cerebral edema, or venous infarction.” Venous drainage from the cerebral convexity returns to the systemic circulation by several convexity veins, the two largest are the posterior temporal or vein of Labbe which drains into the transverse sinus, and the mid parietal or vein of Trolard, draining into the superior sagittal sinus. Removing more than one vein in the mid and posterior portion of the superior sagittal sinus, or transecting the veins of Trolard or Labbe can result in significant venous stasis, and a venous infarction. Yasargil” described the subarachnoid cisterns at the base of the brain as small envelopes which encircle all structures contained in the subarachnoid space. In the supraclinoid carotid area, there are cisterns about the internal carotid artery, the carotid bifurcation, the middle cerebral, the anterior cerebral, the optic nerve, the chiasm, the prechiasmatic cistern, the cistern of the lamina terminalis, and the confluence of the sylvian fissure to the middle cerebral cistern. Wide opening and sharp
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dissection of these cisterns is required to expose internal carotid artery aneurysms safely.”
Diagnostic evaluation Computerized tomography and magnetic resonance imaging are necessary to exclude intra or extraparenchymal haematomas, the extent of the subarachnoid haemorrhage, the presence of hydrocephalus, and the possibility of intra-aneurysmal clot formation.‘“~1s,‘4 A false sense of security may be gained from an angiogram which reveals an apparently small aneurysm, when in reality the aneurysm is large, and filled with clot.12,1”.16,17Magnetic resonance imaging facilitates the localization of the haemorrhage within the parenchyma of the brain, and may suggest the presence of a vascular abnormality. A selective four vessel cerebral angiogram must be completed in all patients suspected of having an aneurysm to determine its location, to exclude the presence of multiple aneurysms which occur in 20% of cases, and to rule out the presence of cerebral vasospasm~12.13.14.15
Pre-operative preparation Careful monitoring of the arterial blood pressure with an intra-arterial line will facilitate the management of the blood pressure, and prevent undesirable fluctuations. Fluid balance and cardiac function are best managed with a Swan-Ganz catheter. An optimum intravascular blood volume may be established pre-operatively by the administration of intravenous albumin, and the careful monitoring of the cardiac output and cardiac index. Patients with chronic obstructive pulmonary disease, or with previous pulmonary problems may require securing arterial blood gases or pulmonary function tests, in addition to a chest X-ray.’ Brain protective drugs such as diphenylhydantoin, dexamethasone, and calcium channel blockers may be administered in preparation for surgery.g~1’~16~1g~20~z1 Susukig observed that diphenylhydantoin has a brain protective effect during temporary clipping, exerted by stabilizing the neuronal membrane, and reducing membrane excitability. Dexamethasone has been studied extensively as a possible cerebral protective agent, and found effective only when given prior to the occlusion the effect of of a cerebral artery. 11,20*s1 Since diphenylhydantoin and dexamethasone can be maximized by early administration and tissue saturation, they are ideal for pre-operative administration. Calcium channel blockers reduce the incidence of cerebral ischaemic complications associated with arterial vasospasm, when administered in the immediate posthaemorrhagic period. l4 Their effect results from a direct vasodilatory action on the smooth muscle cell of the cerebral vessels. In addition, calcium channel blockers may have a direct protective effect at a molecular level in the ischaemic neurone, by preventing the sudden influx of calcium, and blocking the onset of the ischaemic cascade triggered by the intracellular accumulation of calcium. Calcium channel blockers are given from the time of
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Review articles
Anterior circulation aneurysms admission until after surgery. Aminocaproic acid has fallen in disfavor and is no longer recommended, because of the numerous ischaemic complications, and the increased incidence of hydrocephalus observed with its use.20 The decision to proceed with surgery should be based on the clinical condition of the patient, including the neurological evaluation and the general medical status. Patients with poor medical condition but with good neurological status, should not be operated on any sooner than the patient with poor neurological condition but a favorable medical state.’ A poor condition in either case would likely lead to a poor outcome. In general, most would agree that patients with a Hunt-Hess grade of 3 or lower may be operated on almost any time.g~1’,2”.22In the presence of vasospasm, most would tend to wait until vasospasm has lapsed, although patients with a good neurological condition but with angiographic arterial narrowing, may do well with surgery.‘g,2”
Trans-operative
management
Patients with anterior circulation aneurysms require a mild state of hyperventilation to keep the pC0, at about 30 to 35 mmHg. Lowering the PCO, below 30 mmHg will not aid further in reducing cerebral volume, and may in fact induce cerebral ischaemia, by promoting vasoconstriction. Hyperventilation induced vasoconstriction is particularly a problem for patients with residual vasospasm, who will already be in a partial ischaemic state.’ Mannitol is used to decrease brain volume during surgery, and to facilitate brain retraction. Suzuki9 reported a beneficial effect in brain tolerance to cerebral ischaemia, when mannitol was given during surgery. The benefit of mannitol may result from its action as an anti-aggregant, enhancing microcirculatory flow, permitting greater corpuscular deformation, and allowing greater release of oxygen at tissue levels. More recent evidence indicates that mannitol also has a free radical quenching ability. Thiopental acts as a cerebral protective agent producing a functional reduction of oxygen consumption at the synaptic junction, estimated at 80% of the metabolic activitv of the brain.‘,9,“,“12’ This protective effect is demol;strable when the thiopental levels are sufficient to produce an isoelectrical tracing on electroencephalography. The metabolic action of thiopental may be enhanced by the administration of lidocaine, since lidocaine blocks directly the sodium-potassium pump.’ The intra-operative administration of barbiturates and lidocaine in preparation for temporary clipping may produce immediate hypotension and lead to myocardial ischaemia.
Surgical
approaches
Multiple surgical approaches have been reported to manage internal carotid aneurysms, since Dandyz4 treated the first patient with a correctly diagnosed intracranial aneurysm. Proximal ICA occlusion in the neck was followed by numerous direct approaches. Various surgical clips have permitted the obliteration of small and giant aneurysms, facilitated by intracranial vascular re-
constructive and endovascular techniques. The surgical approaches can be divided into: extracranial ICA ligation; and pterional region; convexity; interhemispheric; endovascular. Extracranial internal carotid artery ligation Proximal ligation of the internal carotid in the neck had many advocates and was practised extensively to manage intracranial aneurysms prior to the development of Proximal modern microsurgical techniques. 19.“4,‘15.“1;.27 . ligation of the internal carotid artery in the neck led to a 45% incidence of cerebral ischaemic complications and was soon replaced by the gradual ligation of the common carotid artery, coupled with the ligation of the external carotid artery distal to the origin of the superior thyroid artery. Flow through the superior thyroid artery prevented the development of the dreaded ischaemic complications. However, maintaining permeability in the internal carotid artery allowed the aneurysm to remain patent as well, and in some cases to grow and later rebleed. This once very useful technique has been largely abandoned. Pterional approach Approximately 80% of all anterior circulation aneurysms may be treated successfully via the pterional route.“’ A detailed description of the patient’s position, the craniotomy and dissection of the anterior portion of the circle of Willis, and the clipping techniques will be reviewed. A description of the principles of temporary clipping, aneurysmal opening, debulking, resection, and reconstruction techniques will complete this section. The patient’s position is critical in the success of the procedure. The patient is placed supine, in a reclining position, supported by skeletal fixation, with the head rotated 15” to the opposite side, and with 15” of extension. In this position, the sphenoid wing is perpendicular to the floor. Yasargil”’ recommended the head placed with the nose turned 30” towards the opposite side, and the malar eminence uppermost on the head. When the head is in this position, the temporal lobe is difficult to dissect and the axis of the sylvian fissure rotates away from the surgeon. An incision is made along the hairline from the zygoma to the ipsilateral mid pupillary line. The skin and muscle are reflected in one single flap, exposing the entire squamosal portion of the temporal bone. the frontalis process of the lateral orbital wall, and the vertical portion of the frontal zygomatic area. Yazargil’” recommended a complex muscle incision disinserting the temporalis muscle from its anterior attachment, and retracting it posteriorly, after separating the fatty tissue which contains the frontalis branch of the facial nerve. This dissection lengthens the operation, and does not protect the nerve any more than elevation of a single flap. A free bone flap is elevated, ten tering the craniotomy on the pterion (Fig. 1). The pterion is drilled down until the meningo-orbital branch of the middle meningeal artery is exposed. The dura is sutured to the skull, opened in a semicircular manner based on the pterion, and sutured to the temporalis muscle. The sylvian fissure is
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Fig. 1 Rerional craniotomy: a linear incision is placed along the hairline from the zygoma to the mid pupillary line. The skin and muscle are elevated on a single flap and retracted. A free fronto-temporal flap is elevated, centered on the pterion. A kidney bean shaped exposure reveals the frontal and temporal lobes approximately equidistant. The dura is opened in a semicircular incision along the superior border of the craniotomy and reflected on the temporalis muscle.
opened under the microscope from the surface down. Proximal control is achieved dissecting the internal carotid as it arises from the supraclinoid area, next to the optic nerve. Once proximal control is accomplished, the rest of the sylvian fissure may be opened widely. All arachnoidal bands are released with sharp dissection, to expose the entire course of the internal carotid and its bifurcation, the optic nerve and optic chiasm, the proximal portion of the anterior cerebral, the trunk and bifurcation of the middle cerebral to the level of the limen insulae. The sylvian fissure is then relaxed, and the frontal and temporal lobes fall apart without traction like the petals of a lotus flower. The temporal lobe is supported by the sphenoid
wing and the sylvian veins, and generally it is only necessary to use a single retractor on the frontal lobe, with minimal pressure. Trauma to the brain and draining veins is thus minimized.28 Spinal fluid is drained gradually from the cisterns to obtain maximum brain relaxation with minimal brain retraction. Opening the sylvian fissure is facilitated by not using a lumbar drain, since the subarachnoid space is full, the sylvian fissure is readily apparent, and the dissection can be done without difficulty. When it is necessary to remove additional spinal fluid, it may be obtained opening the lamina terminalis above the chiasm. Opening the lamina terminalis is easy to do once all cisterns are open, and does not carry any of the complications of ventricular puncture.** Incomplete opening of the arachnoid cisterns leads to tension on the frontal and temporal lobes, requires increased pressure on the retractor blades and provides less exposure of the area. Incomplete dissection of the cisterns may also lead to premature rupture of the aneurysm, from traction on the brain. Preservation of the veins is much easier when the cisterns have been dissected widely. Since there is less retractor pressure on the brain, the possibility of venous tears, venous stasis, or venous infarcts is reduced. The actual placement of the clip on the aneurysm neck is much easier when the area of exposure is wide. Direct surgical clipping of the neck of the aneurysm remains the only truly curative approach in the treatment of intracranial aneurysms (Fig. 2). Direct clipping requires complete dissection of the neck of the aneurysm, identification of all afferent and efferent vessels, dissection and isolation of important perforating arteries, and application of the clip on the neck of the aneurysm, flush with the parent vessel. Care must be taken not to cause kinks, or stenoses of the parent vessel. Positioning the clip across the axis of the vessel sometimes leaves small areas
Fig. 2 A 62-year-old woman was evaluated for progressive headaches and visual loss in the left eye. A) A pre-operative left internal carotid angiogram revealed a large aneurysm arising from the origin of the ophthalmic artery. Through a pterional craniotomy, the origin of the aneurysm was exposed after removing the anterior clinoid process, and opening the most distal portion of the cavernous sinus. The aneurysm was isolated between temporary clips, and intraluminal thrombus removed. The wall of the vessel was atheromatous, and the atheroma could not be resected. The atheroma was compressed with a clamp and the permanent clips placed. B) Tram-operative internal carotid angiogram reveals the internal carotid artery to be occluded at the level of the permanent clip. C) Trans-operative internal carotid angiogram revealed the lumen of the internal carotid artery was re-established after the permanent clips were repositioned away from the internal carotid artery lumen. The patient had an uneventful post-operative recovery.
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of the neck outside the clip. For patients with a recent haemorrhage or patients with a large or giant aneurysm, it is safer to apply temporary clips while dissecting the aneurysm neck free from the perforators. Temporary clips may be applied to any intracranial vessel for short periods of time, which vary with the administration of brain protective substances.” When the aneurysm is large or giant, it will be necessary to use temporary clips, and deflate the aneurysm before applying the permanent clip. The aneurysm may be deflated by needle aspiration or puncturing the dome. Once the sac is collapsed, all important arterial branches and perforators may be identified and dissected, and the permanent clip may be placed safely across the neck of the aneurysm. Care must be taken not to encroach on the parent vessel, since the actual diameter of the parent vessel is also decreased by the absence of blood. In some giant aneurysms, it is not possible to clip the neck because the aneurysm is filled with thrombus or is arteriosclerotic. In aneurysms full of thrombus, it is generally safe to isolate the aneurysm complex as described, apply temporary clips, and then open the aneurysmal dome with a knife. An ultrasonic aspirator is then introduced to remove the thrombus, leaving only the supple aneurysm sac behind. The perforators can then be separated away from the aneurysm neck, and a clip applied flush with the parent vessel. It is generally not recommended to remove the aneurysmal sac, since this can be followed by unnecessary injury to the perforators, and other adjacent structures. When the aneurysmal wall is infiltrated with atheroma, it is sometimes possible to perform an endarterectomy of the aneurysmal wall, preserving the aneurysmal wall itself with a small amount of atheroma. In some cases this may be done with ease, but it requires extreme patience. When the atheroma cannot be completely resected, a haemostatic clamp may be used to crush the atheroma and develop a smooth surface over which the clip may then be applied (Fig. 2). When neither of these manoeuvres are successful, it becomes necessary to either resect the aneurysm at the neck and perform an aneurysmorrhaphy, or to clip the aneurysm neck to include a major branch, and then perform an extracranial to intracranial (EC-IC) anastomosis, distal to the clip. An alternative to temporary clipping and complete obliteration of the aneurysmal neck was the use of aneurysm glues with or without wrapping.2g Wrapping and gluing techniques failed because they required that the entire aneurysm complex be included in the encasement. In most cases, the inability to expose the entire complex is what motivated the use of these techniques as substitutes. In addition, none of the glues adhere to the vessel wall, leaving a virtual space between the glue and the aneurysm wall, where the aneurysms would then expand and rebleed. Cotton is the only substance that has in fact produced a strong enough reaction to reinforce the aneurysm. Gluing and wrapping have largely been abandoned. Giant aneurysms of the internal carotid and middle cerebral bifurcations represent a serious problem when one of the arterial trunks arises directly from the waist of
the aneurysm. Clipping the aneurysm neck to include the origin of an arterial branch may be tolerated in a few individuals when the collateral arteries are large. However, when a major arterial trunk is included in the clip, it may be necessary to first perform an EC-IC anastomosis distal to the vessel.“~‘6,3” One could rely on collateral circulation to take over the territory of the occluded vessel but, in most, the collateral circulation is insufficient when it has to come over the cerebral convexity. The EC-IC anastomosis may be performed on the surface of the haemisphere, but it is preferable to perform the bypass as close as possible to the area of occlusion” (Fig. 3). Some giant aneurysms may not be clipped because of extensive atheroma within their wall, or because the branches which arise from the aneurysm dome are too numerous. In some patients, it is possible to resect the entire aneurysm and reconstruct the various branches.‘“,‘” The principles involved in reconstruction of the anterior circulation branches include a wide dissection of the cisterns, careful isolation and identification of the afferent
Fig. 3 A ZQyear-old critical care nurse was admitted with bitemporal haemianopsia, and chronic frontal headaches. A) A pre-operative MRI revealed a large mass in the suprasellar region, with a large signal void, suggestive of a giant aneurysm. 6) Pre-operative left internal carotid angiogram demonstrated a giant aneurysm arising from the supraclinoid internal carotid artery. Through a pterional approach, the aneurysm was found to arise from the distal portion of the supraclinoid left internal carotid artery, just proximal to the bifurcation. No aneurysmal neck existed. An extracranial to intracranial anastomosis was completed with the superficial temporal artery, to the temporal trunk of the MCA; the ICA was ligated in the neck, and the aneurysm was trapped intracranially. C) Post-operative left carotid angiogram shows the entire MCA tree filled by the EC-K anastomosis. D) Post-operative right internal carotid angiogram reveals cross filling of the anterior cerebral arteries. The aneurysm was angiographically not visualized. The patient resumed his duties in our head injury unit without any deficits.
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Review articles and efferent branches to the aneurysm, isolation and preservation of the perforators, and the use of temporary clipping with cerebral protective agents. Having isolated all branches, one must consider initially performing an EC-IC anastomosis to the largest branch arising from the aneurysm in preparation for the period of prolonged cerebral ischaemia. In some patients, it is then possible to resect the branch or branches arising from the aneurysm, and to perform an end to side anastomosis to the artery with the EC-IC anastomosis or to the branch that will remain attached to the parent vessel. It may be necessary to resect the entire aneurysm, and then perform an end to end anastomosis of the parent vessel to the principal branch distal to the aneurysm. SilverbergP3 recommended cardiac arrest in combination with deep hypothermia when dealing with giant aneurysms. Achieving 24°C of core cooling, the brain will be protected for one hour of complete circulatory arrest. Draining the cerebral circulation allows the aneurysm to collapse, and permits the surgeon to dissect the perforators and branches away from the aneurysm, and allows placement of the clip on a supple aneurysm sac. Draining the blood from the cerebral circulation also empties blood from the smaller vessels, and makes their identification difficult. In addition, one must deal with the problems of full heparinization and immediate bleeding once the cardiac bypass is restarted and the circulation begins. Convexity
approaches
Few aneurysms present on the cerebral convexity. Most aneurysms arising in the periphery of the cerebral circulation result from mycotic infections or from trauma. These aneurysms generally require a craniotomy on the area of the middle cerebral distribution. The localization of the aneurysms may be difficult, and may require stereotaxic angiographic techniques for the final approach to the lesion. The aneurysms may sometimes be clipped in a conventional manner, but in cases where there is no defined neck, it will be necessary to resect the aneurysm, and perform an EC-IC anastomosis distal to the vessel occlusion. Some patients may tolerate the complete occlusion of the parent vessel, when the distal branch serves a silent area of the brain.
Interhemisphericapproach The anterior communicating artery (ACA) region may be approached also via the interhemispheric route.2g Giant aneurysms with no apparent neck, and distal aneurysms are the only anterior cerebral artery aneurysms that we would approach via the interhemispheric route. The patient is positioned in a reclining manner with the head facing directly perpendicular to the horizontal plane, and supported by skeletal fixation. A bicoronal incision may be used, although a linear incision may be placed in a skin fold. A bifrontal flap is elevated, with the inferior edge placed directly over the orbital rim. When the frontal sinus is entered, the mucosa is removed from the flap, and the portion of the sinus remaining on the skull is packed with
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muscle or fat, and covered with a pericranial flap. The dura is opened bilaterally with the flaps based on the sagittal sinus, and the insertion of the superior sagittal sinus on the crista galli is ligated and transected. After the frontal lobes are gently retracted, the olfactory nerves are dissected from the inferior frontal surface and preserved. The area of the suprasellar cisterns and supraclinoid carotid arteries is then dissected, and the anterior communicating artery complex is isolated. Depending on the anatomy of the aneurysm, temporary clips may then be applied on all branches to the anterior communicating artery complex, and the aneurysm clipped, resected or reconstructed depending on the pathology found. For distal anterior cerebral aneurysms arising from the pericallosal artery, the craniotomy is placed two-thirds anterior to the coronal suture, and one-third behind. The craniotomy is placed across the superior sagittal sinus, three-fourths to the right and one-fourth to the left of the sinus. Only the dura on the right side of the sinus is opened, with the flap based on the sinus. If necessary, one cortical vein may be resected in the anterior most portion of the exposure. Occasionally, it is possible to take two cortical veins, but this increases the danger of venous congestion and venous infarction. The right frontal lobe is retracted away from the midline, and the pericallosal artery is found at the level of the rostrum of the corpus callosum. The anterior cerebral may be followed anteriorly and posteriorly to isolate the aneurysm, and the vessels around it. Temporary clips may be applied and the aneurysm dissected and clipped as necessary. It is very important to verify the position of both anterior cerebral arteries before closing, to ensure that both vessels remain patent past the clip.
Endovasculartechniques Mullan’s26~27use of intravascular copper wires to manage complicated intracranial aneurysms, served as the foundation for the modern use of endovascular therapeutic techniques. A promising approach to the management of intracranial vascular lesions is the technique of balloon embolization introduced by Serbinenko.31 Balloons may be used to occlude the internal carotid proximal to the aneurysm, at the level of the aneurysm neck, to occlude the aneurysmal neck itself, or most commonly to fill the space within the aneurysmal sac. 17.31,32Endovascular balloon occlusion has met with limited success because of the difficulty of adapting a balloon configuration to the anatomy of the aneurysm, the necessity to use one or more balloons per procedure, the potential of embolization of the balloon to an undesirable site, or premature dislodgement of the balloon. Some balloons have deflated partially allowing the aneurysm to refill or enlarge, rebleeding has occurred during, or after unsuccessful balloon occlusion, and chemical reactions with vessel damage have occurred after spontaneous rupture of the balloons in the vascular tree.17,18,32Complications as high as 20% in grade I and II aneurysmal subarachnoid haemorrhage patients have been reported.”
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A new and exciting approach to the endovascular management of intracranial aneurysms is the introduction of endovascular coils by Guglielmi.33 Small metal coils are introduced in the cerebral vessels or into the aneurysm itself, and fed progressively until the aneurysm sac is filled by the coil. The coils are thrombogenic because of their electromagnetic properties, and may eliminate the aneurysm from the circulation. Limited experience is currently available with the electrothrombotic coils, and no long term results have been reported with their use in the treatment of intracranial aneurysms. The coils are most effective when treating aneurysms 5 mm or less in diameter, and with a neck smaller than 5 mm.33 Like the endovascular balloons, it is likely that the coils will serve as a primary therapeutic option in the acute management of the patient with subarachnoid haemorrhage who is otherwise too ill to undertake an operative procedure.
Conclusions The management of aneurysms of the anterior circulation is an exciting and challenging part of neurovascular surgery. Special techniques and years of experience permit the safe, successful ancl permanent exclusion of these aneurysms from the circulation. Although most aneurysms of the anterior circulation do not require any specialized techniques for their successful treatment, some principles must be kept in mind when dealing with these problems. Most aneurysms may be treated safely and fully through a pterional approach. It is necessary to maximize the exposure of the aneurysm and the collateral vessels by optimizing the position of the patient, and dissecting widely the basal cisterns. Minimal brain retraction will be needed when the basal cisterns and the lamina terminalis are opened widely to permit drainage of spinal fluid. Aneurysms are best clipped in a direction parallel to the axis of the vessel to minimize the possibility of leaving a remnant of aneurysm, and to preserve the diameter of the vessel wall. When aneurysms cannot be totally excluded from the circulation, the remaining aneurysm sac will regrow, with a high probability of rebleeding. Those aneurysms that cannot be clipped may be trapped or resected, with reconstruction of the collateral vessels by EC-I(: anastomosis, or intracranial vessel re-anastomoses. Multiple drugs have been used to lengthen cerebral tolerance to ischaemia; probably a combination of several of these give the best potential for brain tolerance to ischaemia. Endovascular approaches may be used to supplement the surgical procedures, but most complicated aneurysms can not be treated successfully by endovascular techniques. Careful planning and execution of surgical procedures are likely to bring the most successful treatment to these very difficult and challenging problems. Received 5 September 1993 Accepted for pubhcation 30 September 1993
Correspondence
and offprint requests:
Dr Fernando G. Diaz. Neurological Surgery Department, Wayne State University, School of Medicine. Detroit. Michigan. USA.
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21. Charbel ET, Ausman JI, Diaz FG, Malik GM, Dujovny M, Sanders J. Temporary clipping in aneurysm surgery: Technique and results. Surg Neurol 1991;36:83-90. 22. Hunt WE, Hess RM. Surgical risk as related to time of intervention in the repair of intracranial aneurysms. J Neurosurg 1968;28:1420. 23. Silverberg GD, Reitz BA, Ream AK. Hypothermia and cardiac arrest in the treatment of giant aneurysms of the cerebral circulation and haemangioblastoma of the medulla. J Neurosurg 1981;55:337-346. 24. Dandy WE. Intracranial Arterial Aneurysms. Ithica, New York: Comstock Pub Co, 1944. 25. Diaz FG. Surgical treatment of aneurysms in the cavernous sinus. Contemporary Neurosurgery 10, 1989;26:1-6. 26. Mullen S. Experiences with surgical thrombosis of intracranial berry aneurysms and carotid cavernous fistulas. J Neurosurg 1974;41:657-70. 27. Mullen S, Reyes C Dawley J, et al. Stereotactic copper electric thrombosis of intracranial aneurysms. Progr Neurol 1969;3: 193211. 28. Kobayashi S, Sugita K, Nakagawa F. An approach to a basilar aneurysm above the bifurcation of the internal carotid artery. Case Report. J Neurosurg 1983;59: 1082-84.
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29. Pool JL, Potts DG. Aneurysms and Arteriovenous Anomalies of the Brain: Diagnosis and Treatment. New York: Hoeber Medical Division, Harper and Row, 1965. 30. Cabezudo-Artero J, Ausman JI, Dujovny M, OrdonezMora E, Umansky F, Diaz FG, Mirchandani H, Berman SK Middle cerebral artery reconstruction. Surg Neurol 1985;24:5-11. 31. Serbinenko FA. Balloon catheterization and occlusion of major vessels. J Neurosurg 1974;41:125-45. 32. Aymard A, Gobin YP, Hodes JE, Bien S, Rufenacht D, Reizine D, George B, Merlanda. Endovascular occlusion of vertebral arteries in the treatment of unclippable vertebrobasilar aneurysms. J Neurosurg 1991;74:393-98. 33. Guglielmi G, Vinuela F, Duckwiler G, Dion J, Lylik P, Berenstein A, Strother C, Graves V, Halback V, Nichols D, Hopkins N, Ferguson R, Spetka I. Endovascular treatment of posterior circulation aneurysms by electrothrombosis using electrically detachable coils. J Neurosurg 1992;77:512-24. 34. Locksley HB. Report on the cooperative study of intracranial aneurysms and subarachnoid haemorrhage. Section V, Part 1. Natural history of subarachnoid haemorrhage, intracranial aneurysms and arterio venous malformations. Based on 6368 cases in the Cooperative Study. J Neurosurg 1966;25:219-39.
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