J Neurosurg 73:165-173, 1990
Surgical treatment of unruptured aneurysms of the posterior circulation BEVERLY J. RICE, M.D., SYDNEY J. PEERLESS, M.D., F.R.C.S.(C), AND CHARLES G. DRAKE, M.D., F.R.C.S.(C) Division of Neurosurgery, The University of Western Ontario, University Hospital, London, Ontario, Canada With the ever-increasing number of intact aneurysms revealed by modern imaging, the options for their management are assuming great importance. While some knowledge has emerged as to their natural history and the results of surgical treatment of those in the anterior circulation, little information has been published concerning unruptured aneurysms arising from the posterior circulation. The authors report their experience since 1971 with 167 patients operated on for 179 unruptured vertebrobasilar aneurysms up to 25 mm in diameter. Overall, 160 aneurysms were treated by direct clip obliteration, while 19 were managed by alternative methods. Fifty-three patients (32%) had solitary aneurysms and the other 114 patients (68%) had multiple aneurysms or an associated arteriovenous malformation, which were commonly treated concurrently. Many of these coexisting vascular anomalies had ruptured in the recent or remote past, adding to the complexity of management and interpretation of specific surgical results related to the intact posterior circulation aneurysm. There were 78 documented postoperative complications including 23 systemic complications, seven postoperative hematomas, six brain injuries from retraction, five cases of aseptic meningitis, three instances of seizures, three wound infections, and three patients with hydrocephalus. Multiple complications occurred in 23 patients. Seventy-one of the patients with these untoward events recovered, without disability, with time or treatment. There were only six poor results and one death in the series, resulting in a 4.2% combined morbidity/ mortality rate. However, since two of these poor outcomes and the single death were attributable to a coexisting aneurysm, the actual surgical morbidity related specifically to the posterior circulation aneurysm was only 2.4%. This experience suggests that non-giant, intact vertebrobasilar aneurysms can be obliterated surgically at a very low risk, and this treatment should eliminate the greater lifetime risk related to an unsecured aneurysm. KEY WORDS vertebrobasilar aneurysm unruptured aneurysm 9 aneurysm ~
p
OSTERIOR circulation aneurysms have long been associated with a high morbidity rate and often with a fatal outcome. As the majority of reported lesions were managed after aneurysmal rupture, subarachnoid hemorrhage (SAH) further complicated the surgery and clinical outcome. The early operative mortality rate was in excess of 50%, 3-5'15'16'31 not dissimilar to that associated with the natural history of these deadly lesions. 2,7'14'31'32 Remarkable advances in the treatment of ruptured vertebrobasilar aneurysms have occurred over the past three decades. 2~176 At our institution, with a cumulative 31-year experience of over 1500 such cases, overall 5% mortality and 10% morbidity rates have been achieved. With the ever-increasing number of intact aneurysms revealed by modern imaging, the options for managing J. Neurosurg. / Volume 73/August, 1990
9 posterior circulation
9
these lesions are assuming great importance. We have treated 179 intact vertebrobasilar aneurysms with a very low morbidity rate and rare mortality. Natural history data, for comparison, are derived from published subgroups of untreated intact aneurysms (largely in the anterior circulation). In 1966, Locksley 19found a yearly rupture rate of 6.25 % (all fatal) for solitary symptomatic intact aneurysms, as calculated for that group by Jane, et al., ~7 based upon an average follow-up period of 4 years. Wiebers, et al., 33 indicated a 1.5% risk of rupture per year after studying a group with multiple incidental aneurysms. Both studies showed higher rupture rates when aneurysms of less than critical size were excluded. Specifically, a rupture rate of 3.4% per year is suggested by Weiber's series when aneurysms less than I0 mm were excluded, and a rate of 10% per year is suggested 165
B. J. R i c e , S. J. P e e r l e s s , a n d C. G . D r a k e TABLE 1 Location of179 aneurysms in this series Location basilar artery bifurcation superior cerebellarartery basilar trunk vertebrobasilarjunction vertebral artery posteriorcerebralartery
No. of Aneurysms 150 99 43 7 1 11 18
by Locksley's review if only aneurysms greater than 7 mm are considered. The importance of critical aneurysm size was also reflected by the autopsy study of McCormick and Acosta-Rua, 2j revealing that 60% of intracranial aneurysms greater than 6 mm had ruptured whereas smaller aneurysms appeared to confer little risk. Thus, we advise operating on intact aneurysms only when they have reached a critical size of approximately 6 mm. Several studies have addressed the natural morbidity for patients with multiple aneurysms specifically discovered after S A H . 6'j0'12'23'24 Heiskanen 1~ found a rupture rate of 1% per year in his group of patients followed for 10 years. Jane, et aL,17 after an extensive review, proposed that intact aneurysms generate the same 3% rates of rebleeding shown for untreated ruptured aneurysms after 6 months. They contended that intact aneurysms behave like healed aneurysms. Nevertheless, although the natural history remains uncertain, it confers a considerable lifetime risk of potentially catastrophic rupture. Summary of Cases Patient Population A total of 167 patients with 179 unruptured posterior circulation aneurysms were operated on between 1971 and 1988 at University Hospital in London, Ontario, Canada. There were 59 males and 108 females, with a mean age of 49 years (range 16 to 75 years). The distribution of the aneurysms was: 150 arising from the basilar artery, 18 from the posterior cerebral artery (PCA), and 11 from the vertebral artery (Table 1). One hundred seventy aneurysms were saccular and nine were fusiform; 128 aneurysms were small (< 12 m m in diameter) and 51 were large (12 to 25 mm). Giant aneurysms were not included in this review because of their unique technical problems. Twelve tiny aneurrysms (< 5 mm), which were too small for clipping, were treated by coagulation and/or gauze wrapping, mostly because they were coincident with another significant aneurysm or arteriovenous malformation (AVM). Since this treatment poses little risk, they were not included in this series or statistics. Fifty-three patients (32%) had solitary unruptured aneurysms and the remaining 114 patients (68%) had
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multiple intracranial aneurysms or AVM's. This latter group harbored an additional 209 aneurysms (97% in the anterior circulation) and 15 AVM's (l 1 supratentorial and four infratentorial). Eleven of the AVM's were supplied by parent arteries of posterior circulation aneurysms. Seventy patients (61% of the group with multiple cerebral vascular anomalies) had a known history of SAH ranging from l week to 9 years (mean 9.4 months) before presentation. They comprised 42% of the entire population. Four of these patients with recent SAH had a poor preoperative grade with confusion and fixed neurological deficit. Seven patients had significant stable neurological dysfunction on admission, six had moderate or severe hemiparesis related to previous stroke or aneurysm treatment, and one patient had parietal lobe deficits related to AVM rupture. In each case, the informed patient and family desired treatment of the intact posterior circulation aneurysm. Clinical Presentation The aneurysms were asymptomatic in 89% of the patients and were discovered incidentally when unrelated conditions led to an angiogram (Fig. 1). Sixty-four cases (38%) were discovered after rupture of a coexisting aneurysm or AVM. Idiopathic headache accounted for the investigation in 37 patients (22%). Cerebrovascular events led to the diagnosis of the intact aneurysm in 18 patients (11%). The remaining patients with incidental aneurysms had diverse presentations including seizures, endocrine disorders, vestibular or cognitive impairment, unrelated cranial nerve dysfunction, or otolaryngological disorders. Eighteen patients (11%) had presentations attributed to mass effect or emboli from an unruptured posterior circulation aneurysm (Fig. 1). Cranial nerve dysfunction was seen in eight patients. Six third nerve palsies (one mild Weber's syndrome) were associated with superior cerebral artery (SCA) aneurysms and one with a PCA aneurysm. One patient with a fusiform basilar aneurysm near the anterior inferior cerebellar artery (AICA) had a sixth nerve paresis and episodic ipsilateral facial paresis. Thromboembolism likely occurred in the remaining patients. Vertebrobasilar transient ischemic attacks seemed related to two fusiform aneurysms of the proximal basilar artery. Minor ischemic brain-stem strokes were evident in two individuals with large thrombosed basilar trunk aneurysms. Six patients with a saccular lesion at the distal basilar artery had events suggesting PCA ischemia. Three of these had transient homonymous visual scotomata. Episodes of transient global amnesia or disorientation occurred in two patients. A small posterior temporal lobe infarction occurred in a young patient with a small PCA aneurysm without risk factors for stroke. Surgical Approach
Exposure of 138 bifurcation region aneurysms was via the subtemporal approach. 26 A transsylvian apJ. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms
FIG. 1. Pie chart summarizing the presentation of 179 aneurysms. VB = vertebrobasilar location; CN = cranial nerve; SAH = subarachnoid hemorrhage; HA = headache, n = number of patients; percentages are of the total 167 patients.
proach was used in six cases to facilitate treatment of multiple aneurysms. Subtemporal-transtentorial exposure allowed access to seven basilar trunk aneurysms and one low bifurcation lesion. One AICA and l0 vertebral aneurysms were approached suboccipitally. Three distal PCA lesions required occipital craniotomy. A subtemporal-transmastoid-suboccipital approach provided access to the single vertebral junction aneurysm of the series. Another combined procedure was required for treatment of multiple aneurysms.
Treatment Methods Intraoperative 20% mannitol, lumbar drainage of cerebrospinal fluid at the time of dural opening, and maintenance of normocapnia were routine adjuncts. Hypotension (range 35 to 65 m m Hg) was induced in 67 patients (40%) for an average of 30 minutes (range 5 to 90 minutes). The parent vessel was temporally clipped in 30 cases (18%), with an average of two clip applications (range 1 to 6) separated by periods of reperfusion. Average time for temporary clipping of basilar aneurysms was over 4 minutes (range 1 to l0 minutes). Temporary clipping has been used more routinely only in recent years; this explains the infrequency of its use in this series. A total of 260 aneurysms were treated in 168 operations, with an average operating time of 4 hours (range 22 to 8 hours). Seventy-eight cases involved the treatment of multiple vascular lesions, including the excision of four AVM's and the ligation or embolization of major feeding vessels of four other malformations. Of the 64 cases discovered after SAH, 28 had concurrent treatment of the ruptured aneurysm (mean interval 2.5 J. Neurosurg. / Volume 73/August, 1990
weeks, range 1 to 8 weeks). The intact aneurysms were treated at the same time only if obliteration of the ruptured sac had been uneventful. Of the 179 unruptured aneurysms, 160 (89%) were clipped; tandem or multiple clipping was used in 25 of these cases. Hunterian ligation was required in six cases (3%); however, poorly defined aneurysmal neck or perforating vessels of the neck required basilar artery clipping in five of these. A fusiform, atherosclerotic vertebral artery aneurysm was treated by proximal vertebral artery occlusion. Treatment was confined to gauze wrapping or acrylic coating in five complex aneurysms (2.8%) in order to avoid injury to the parent or perforator vessels. Patients with six (3.4%) of the aneurysms underwent surgical exploration only. Two lesions were inaccessible due to dense adhesions from previous surgery or an overlying giant aneurysm. One completely calcified basilar aneurysm required no further treatment. Three other unclippable atherosclerotic aneurysms were not treated indirectly due to inadequate collateral circulation. Proximal PCA ligation facilitated excision of two distal PCA aneurysms and their associated occipital AVM's.
Operative Findings In 14 cases there was evidence suggesting previous hemorrhage from the aneurysm but without a compatible clinical history. Staining of regional arachnoid with hemosiderin, small organizing hematomas adjacent to cranial nerves, or yellow adhesions associated with the fundus of the sac were seen. Compression of the third 167
B. J. Rice, S. J. Peerless, and C. G. Drake TABLE 2
TABLE 3
Surgical results in 167 patients with intact basitar aneurysms*
Causes of permanent morbidity or death*
Location of Aneurysm
No. of Cases Excellent Good Poor Dead
small aneurysms (< 12 ram) basilar bifurcation 71 63 5 3 0 basilar: SCA 20 19 1 0 0 basilar: trunk 4 4 0 0 0 vertebrobasilar 1 1 0 0 0 vertebral 9 8 1 0 0 P~,P2 11 8 2 0 1 total cases 116 103 9 3 1 percent 89 8 2.6 0.9 large aneurysms (12-25 ram) basilar bifurcation 28 21 4 3 0 basilar: SCA 16 13 3 0 0 basilar: trunk 3 2 1 0 0 vertebrobasilar 0 0 0 0 0 vertebral 2 2 0 0 0 P, P2 2 2 0 0 0 total cases 51 40 8 3 0 percent 78 16 5.9 all cases 167 143 17 6 1 percent of total 86 10 3.6 0.6 * Excellent: normal or unchanged from preoperative status; good: minor new neurological deficit; poor: major new neurologicaldeficit.
and sixth cranial nerves was confirmed in seven cases of symptomatic aneurysms. In one case, there was recent hemorrhage in the oculomotor nerve; this patient (with a Weber's syndrome) had an SCA aneurysm deforming the third nerve and buried in the adjacent peduncle. Ventral pontine compression by a large basilar aneurysm was confirmed in one o f the patients with fixed brain-stem dysfunction.
Surgical Results Surgical o u t c o m e was recorded at the time of discharge or follow-up (Table 2) and later modified if further functional capacity or disability was realized. Analysis of outcome was complex because o f the various associated anomalies, preexisting morbidity, and c o m m o n treatment o f coexisting intracranial lesions. Results from the entire population, stratified for aneurysm location and size (Table 2), indicate 2.6% morbidity (poor results) and 0.9% mortality rates for small aneurysms and a 5.9% morbidity rate without mortality for large aneurysms. A n overall management o u t c o m e o f 3.6% morbidity and 0.6% mortality was achieved. The causes of permanent morbidity or death are summarized in Table 3. Although the overall m a n a g e m e n t morbidity/mortality rate was 4.2%, morbidity specifically related to the surgical obliteration of the posterior circulation aneurysm occurred in only four cases (2.4%). The other three cases (1.8%) had morbidity due to vasospasm (in two) or an infarction from operation on a middle cerebral aneurysm (in one). Subgroup analysis o f solitary aneurysms and those complicated by multiplicity or rupture o f a coexisting aneurysm or A V M is shown in Fig. 2. Results for 168
Related Relatedto to PC Coexisting Aneurysm Aneurysm aneurysm rupture 1 0 perforator vessel infarction 2 0 major hemispheric infarction 1 1 vasospasm 0 2 total cases 4 3 * Combined surgical morbidity and mortality rate was 2.4% compared with an overall management morbidity and mortality rate of 4.2%. PC = posterior circulation. Cause
patients who had concurrent treatment o f multiple lesions, including recently ruptured aneurysms, are also shown. Such figures are too small for statistical analysis, although they m a y suggest higher combined morbidity and mortality rates for cases involving treatment of multiple intact aneurysms. Results according to treatment m e t h o d indicated a combined morbidity/mortality rate o f 3.8 % for the 160 aneurysms treated by direct clipping. However, only in the two patients (1.3 %) with disabling perforator vessel ischemia was clipping responsible for a poor outcome. An operative morbidity rate o f 20% was noted for the five patients whose aneurysms were treated by wrapping; this single poor result resulted from early postoperative aneurysm rupture. There were no poor results or deaths a m o n g the patients whose aneurysms were treated indirectly, excised, or explored (Table 4). Details regarding the various complications follow.
Complications A s u m m a r y o f postoperative complications in patients with solitary and multiple aneurysms is given in Table 5. The complications are described below.
Postoperative Aneurysmal Rupture. Postoperative rupture o f one basilar aneurysm treated by gauze wrapping occurred 10 days after surgery. This patient required prolonged nursing-home convalescence and had a poor functional recovery. Postoperative rupture of an untreated posterior c o m m u n i c a t i n g artery (PCoA) aneurysm complicated another patient's o u t c o m e within hours after treatment o f her SCA aneurysm. Left hemispheric injury with hemiparesis and aphasia dramatically improved over the ensuing four months, with an eventual good outcome. Persistence o f Preoperative Cranial Nerve Dysfunction. Persistent third nerve palsies were seen in three patients after 15 months, 3 years, and 7 years, respectively. Four other patients showed almost complete resolution o f their severe oculomotor palsies after several months.
Cranial Nerve Injuries. Some degree o f third nerve dysfunction resulted in most patients with subtemporal surgery. The majority improved during hospitalization J. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms TABLE 4 Results in 179 aneurysms according to treatment method No. of Major Mortality Combined - Aneurysms Morbidity No. % direct clipping 160 5 1 6* 3.8 Hunterian ligation 6 0 0 0 0 wrapping 5 1 0 1 20 exploration only 6 0 0 0 0 excision 2 0 0 0 0 totals 179 6 1 7 4.2 * Clip technique alone accounted for only two bad outcomes (1.3%). Treatment Method
FIG. 2. Summary of findings and treatment of aneurysms in 167 patients in this series. AVM = arteriovenous malformation; SAH = subarachnoid hemorrhage, n = number of patients; percentages are of the total 167 patients.
TABLE 5 Summary of complications among 167 patients*
Complication a n d returned to n o r m a l within 12 weeks. O n e patient with a large A I C A a n e u r y s m developed an ipsilateral sensorineural hearing loss a n d vestibular nerve i m p a i r m e n t as a result o f treatment.
Perforator Vessel Injuries. M i d b r a i n a n d t h a l a m i c infarction has been a m a j o r cause o f m o r b i d i t y in u p p e r basilar a n e u r y s m surgery. Thirteen patients in this series suffered intraoperative injuries to t e r m i n a l basilar artery or PCA perforator vessels during direct t r e a t m e n t o f aneurysms o f the bifurcation region. Ischemia o f the mesencephalic t e g m e n t u m resulted in eye m o v e m e n t disorders in nine patients. Since m a n i p u l a t i v e ipsilateral third nerve paresis was usually present, this was evid e n c e d by i m p a i r m e n t o f u p w a r d gaze a n d ptosis or a medial rectus palsy on the opposite side; two patients suffered initial c o m p l e t e internuclear ophthalmoplegia. Seven patients showed corticospinal tract or cerebellar dysfunction. T h a l a m i c ischemia was suggested in four patients with confusion a n d i m p a i r m e n t o f short-term m e m o r y . The m a j o r i t y o f these patients i m p r o v e d ; the results were classified as excellent in six patients a n d good in five. O f the two patients with p o o r outcomes, one has been left with disabling ataxia, dysarthria, a n d m i l d d e m e n t i a (Fig. 3), a n d one has severe m e m o r y impairment. Vasospasm. Clinically significant vasospasm c o m plicated four cases, a c c o u n t i n g for one death, one p o o r outcome, a n d two g o o d results. Three o f these patients had suffered recent S A H between 1 a n d 8 weeks before surgical intervention. M i n o r intraoperative bleeding from the P C o A c o m p l i c a t e d the t r e a t m e n t o f intact left PCA a n d P C o A a n e u r y s m s in one case. This patient b e c a m e hemiplegic 1 week later as a result o f left P C A territory infarction a n d eventual b i h e m i s p h e r i c infarction from vasospasm (Fig. 4). D e a t h ensued 3 days later; autopsy c o n f i r m e d a d e q u a t e clipping o f the a n e u r y s m s a n d patency o f the PCA. J. Neurosurg. / Volume 73/August, 1990
total cases rupture persistent CN palsy new injury perforator vessel injury vasospasm major hemispheric infarction retraction injury hematoma related to rupture or Rx of other intracranial lesion aseptic meningitis wound infection seizure hydrocephalus systemic complications
Solitary Aneurysms 53 1 (1) 1 0 3 0 1 (1) 2 0 0 0 0 1 0 7
Multiple Aneurysms Intact + SAH 50 64 0 0 1 1 1 0 8 (2) 3 1 (1) 3 (1) 0 0 1 3 4 3 1 (1) 3 Intact
0 0 0 0 7
5 3 2 3 9
* Numbers in parentheses indicate patients with long-term morbidity or death. SAH = subarachnoid hemorrhage; CN = cranial nerve; Rx = treatment.
FIG. 3. Left." Angiogram showing a large intact basilar bifurcation aneurysm. Right: Postoperative computerized tomography scan revealing central midbrain infarction resulting from perforator vessel occlusion.
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B. J. Rice, S. J. Peerless, and C. G. Drake TABLE 6 Systemic complications in 23 patients
FIG. 4. Computerized tomography scan following operation on intact aneurysms in a patient who subsequently suffered fatal bihemispheric infarction resulting from vasospasm.
The patient with a poor outcome had undergone direct clipping of intact basilar bifurcation and ruptured PCA aneurysms 2 weeks after the latter ruptured. Despite subsiding preoperative vasospasm with the patient in poor clinical grade, surgery was uneventful. Four days postoperatively, the vasospasm increased with mesencephalic and hemispheric infarcts resulting in fixed left hemiparesis, ataxia, and confusional state. Major Hemispheric Infarction. Major fight-hemispheric infarction occurred in a 35-year-old woman with bilateral occlusive carotid disease from severe fibromuscular dysplasia, with a moyamoya-like vascular pattern and extensive dural leptomeningeal collateral supply. Previous stroke had resulted in dense fight hemiplegia, dysphasia, and pseudobulbar palsy which were unaltered by a left extracranial-intracranial (ECIC) anastomosis. Direct treatment of an incidental basilar bifurcation aneurysm resulted in a new left hemiplegia and initial stupor. The infarction was believed to be due to the interruption of numerous dural collateral vessels during exposure and mobilization of the tight temporal lobes. Angiography showed aneurysm obliteration with patent bypass. A fight EC-IC anastomosis was performed the following day. The patient entered a nursing home where she has regained only minor mobility in her left extremities. Retrospective evaluation indicates that this aneurysm should have been approached from the left, even though this would have necessitated some manipulation of the bypass. Another patient suffered a middle cerebral artery (MCA) branch occlusion after treatment of left MCA and basilar aneurysms. Postoperative hemiparesis improved; however, residual dysphasia accounted for a poor outcome. Retraction Injury. Six cases were complicated by probable retraction injury. Temporal and frontal lobe 170
Systemic Complication
No. of Cases
urinary tract infection pneumonia pulmonary congestion hyponatremia gastrointestinal bleeding cardiac arrhythmia pneumothorax
9 5 2 5 1 1 1
contusions caused moderate memory impairment and aphasia in two patients who had recently undergone bilateral craniotomies for aneurysm treatment. Transient left homonymous hemianopsia from retractionrelated occipital contusion occurred after treatment of a distal PCA aneurysm. Two patients developed transient dysphasia after left subtemporal exposures; one of these was attributable to a documented seizure focus. Right hemiparesis resulted from insular infarction in another patient, likely related to retraction pressure. There was no long-term morbidity within this group.
Postoperative Hematoma. Seven cases, complicated by hematomas, had no long-term morbidity. One epidural hematoma (EDH) requiting emergency evacuation, resulted in a minor hemiparesis which resolved after 2 months. Another EDH was evacuated in a patient who later developed local extradural empyema requiting drainage. Three patients had small subdural hematomas which were not treated. A small unexplained frontal intracerebral hematoma caused expressive aphasia in another patient; this had resolved by the time of discharge. Aseptic Meningitis. Aseptic meningitis was reported in five cases with variable expression and confirmation. Three of these patients had suffered SAH within 5 months of surgery; the other two had experienced remote hemorrhages. Other Complications. Three patients developed local wound infection, three had seizures, and three developed early hydrocephalus. Systemic complications were seen in 23 patients (Table 6). Two patients incurred deficits related to the treatment of coexisting posterior fossa AVM's. One showed moderate cerebellar dysfunction postoperatively and the other required early decompression for cerebellar swelling. Both patients eventually had good outcomes. Aneurysm Obliteration Postoperative angiography was performed in 139 (83%) of the 167 patients; most other saccular aneurysms were needled and collapsed at operation. Postoperative angiograms showed complete aneurysm obliteration in 113 (81%) of the 139 patients so studied; minor residual necks (1 to 2 mm) were revealed in 28 patients (20%). Two large basilar aneurysms treated by J. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms basilar occlusion had significant filling of the aneurysm base. In one of these, prominent PCoA collateral inflow caused recanalization of the sac after 6 months; fatal rupture of the aneurysm occurred 1 month later. The other aneurysm showed almost complete thrombosis at 7 months. One basilar aneurysm ruptured 3 years after direct treatment despite only minor residual filling of its neck; aneurysm regrowth was documented at that time. One small aneurysm treated by wrapping showed significant growth when evaluated 12 years later. Discussion
It is the intent of this review to determine any advantage of surgery over the natural risk of intact posterior circulation aneurysms. As these lesions are relatively rare and their nonoperative management has not been studied, natural history was inferred from previous studies involving mostly anterior circulation aneurysms. It is likely that aneurysms of the two circulations share similar factors influencing their growth and ultimate rupture. Morbidity and Mortality Rates
Our results indicate overall 3.6 % morbidity and 0.6 % mortality rates (all locations and sizes). Although the morbidity rate was somewhat higher in patients with large aneurysms, this subgroup was small. These data compare favorably with published surgical series of intact anterior circulation aneurysms. Wirth, et al., 35 reported an overall 6.5% morbidity rate including a 14% rate with larger aneurysms. Freger, et al.,S recorded no morbidity and a 1% mortality rate in their large group of patients with asymptomatic aneurysms. Other series have achieved similar results. ~'~~'j3.22.28,29,36 The medical literature suggests that a minimum risk of rupture for intact aneurysms of all sizes is 1% per year, but that it ranges from 3% to 10% when aneurysms of less than 7 mm are excluded. In patients with multiple aneurysms the risks are compounded. The surgical risk as defined by our heterogeneous population is low and appears to be less than the lifetime risk of an unsecured aneurysm. Our population had several interesting features, including the frequency of multiple vascular lesions (59%), of which over one-half presented with SAH. The major morbidity/mortality rate seen overall for cases complicated by multiplicity was not unlike that for the less complex cases with solitary aneurysms. Furthermore, patients with recent SAH also showed low morbidity, suggesting that hemorrhage was not a major factor influencing outcome in our series. Wirth, et al., 35 noted a similar low morbidity rate (2.3%) in their subgroup of patients who survived SAH and they questioned whether these patients had a selection bias for treatment success. There was evidence, however, that complications in general such as vasospasm, aseptic meningitis, hydrocephalus, and systemic injuries were J. Neurosurg. / Volume 73/August, 1990
more frequent in our group with SAH. The small group with concurrent treatment of the intact and ruptured aneurysms showed similarly good results. In this latter group, the single case with long-term morbidity resulted from vasospasm secondary to recent SAH. These results suggest that an intact posterior circulation aneurysm can be treated safely after recent SAH or concurrently with ruptured aneurysms. 27 Surgical T r e a t m e n t Treatment method is an important factor in analyzing our results. As previously stated, cases with clip occlusion of the aneurysm showed a 3.8% combined morbidity/mortality rate, which was comparable to the overall group including the alternative treatment methods. Within the subgroup of patients whose aneurysms were treated by wrapping, there was one case of early aneurysmal rupture (described earlier); this case is interesting and suggests that the craniotomy or surgical manipulation (for wrapping) may have influenced subsequent aneurysmal rupture. Nevertheless, although aneurysmal wrapping or Hunterian ligation is required for some cases of complex aneurysms, these treatment modalities may be coupled with persistent risk of aneurysmal rupture. Aneurysms at the basilar bifurcation have been the most difficult to manage technically because of the narrow confines involved in access, and particularly due to the risk of perforator vessel injury. It is notable that all major morbidity seen in this series was associated with treatment of aneurysms in this region. However, these complications included vasospasm in two cases and major hemispheric infarction in two others, related to treatment of a coexisting aneurysm or technical difficulties due to moyamoya disease. The two permanent perforator vessel injuries and the 11 minor perforator vessel ischemic injuries highlight the specific risk inherent in treating aneurysms at this location. The incidence of perforator vessel injury has declined dramatically with the use of temporary basilar artery clipping. Patients with preexisting morbidity related to previous brain injury may have lowered thresholds for complications that can be tolerated without causing further functional disability. Surgical risk may be too high to warrant intact aneurysm surgery. The patient with moyamoya disease failed to tolerate interruption of small collateral vessels, resulting in catastrophic infarction. Patients who suffered complications from the treatment of multiple intracranial lesions, on the other hand, had potentially greater surgical risks coupled with heightened natural risks that would justify surgical intervention. The combined morbidity rate of 12% for cases involving treatment of multiple aneurysms or AVM's seems high, but this includes the two patients with disabling perforator vessel infarctions that occurred after treatment of large basilar bifurcation aneurysms. The other two poor outcomes were related to treatment 171
B. J. Rice, S. J. Peerless, and C. G. Drake of a concurrent MCA aneurysm and vasospasm secondary to treatment of a coexisting intact aneurysm.
Vasospasm Vasospasm proved to be a rare event for our patients with recent SAH due to the delay between hemorrhage and our intervention. The single case of vasospasm that occurred without prior SAH was likely caused by minor intraoperative bleeding. As previously reported, 25 the occurrence of vasospasm after surgical treatment of intact aneurysm is distinctively rare, and this case remains perplexing.
Symptomatic Aneurysms The association of partially thrombosed aneurysms and vertebrobasilar ischemia is suggestive of thromboembolism. Fukuoka, eta[., 9 described the criteria inherent in this association, including absence of other causes for embolization, presence of aneurysmal thrombus, and cessation of attacks after aneurysm obliteration. We had limited follow-up data for some of these patients. Two patients with minor posterior circulation strokes, however, recovered completely and remain well after 6 months and 6 years, respectively. Recurrent episodic disorientation resolved after the treatment of one patient with a large bifurcation aneurysm.
Aneurysm Growth and Rupture Three patients treated in our series subsequently suffered aneurysm rupture. One was treated by wrapping, another was treated partially by Hunterian ligation, and a third underwent clipping with only minor residual filling of the aneurysmal neck seen postoperatively. These events emphasize the need for fully obliterating the aneurysm if possible to avoid further risk of rupture and injuryY 8 We believe that intact aneurysms of the posterior circulation can be treated with low surgical risk and can eliminate the greater lifetime risk of an unsecured aneurysm; the overall surgical morbidity is little more than that experienced by a patient living with the aneurysm for 2 to 3 years. In experienced hands, the surgical risk is not clearly heightened by SAH or multiplicity of aneurysms. Complete obliteration of these (and of all) aneurysms treated surgically should be achieved if possible.
References 1. Asari S, Yamamoto Y: [Unruptured cerebral aneurysms: clinical analysis of 80 cases and its new classification.] No To Shinkei 38:693-700, 1986 (Jpn) 2. Dimsdale H, Logue V: Ruptured posterior fossa aneurysms and their surgical treatment. J Neurol Neurosurg Psychiatry 22:202-217, 1959 3. Drake CG: Bleeding aneurysms of the hasilar artery. Direct surgical management in four cases. J Neurosurg 18:230-238, 1961 4. Drake CG: Further experience with surgical treatment of aneurysms of the basilar artery. J Neurosurg 29: 372-392, 1968
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5. Drake CG: The surgical treatment of aneurysms of the basilar artery. J Neurosurg 29:436-446, 1968 6. Drake CG, Girvin JP: The surgical treatment of subarachnoid hemorrhage with multiple aneurysms, in Morley TP (ed): Current Controversies in Neurosurgery. Philadelphia: WB Saunders, 1976, pp 274-278 7. Duvoisin RC, Yahr MD: Posterior fossa aneurysms. Neurology 15:231-241, 1965 8. Freger P, De Sousa MM, Sevrain L, et al: Faut-il oprrer les anrvrysmes asymptomatiques? Apropos de 114 an6vrysmes asymptomatiques oprrrs. Neurochirurgie 33: 462-468, 1987 9. Fukuoka S, Suematsu K, Nakamuru J, et al: Transient ischemic attacks caused by unruptured intracranial aneurysm. Surg Neurol 17:464-467, 1982 10. Heiskanen O: Risk of bleeding from unruptured aneurysms in cases with multiple intracranial aneurysms. J Neurosurg 55:524-526, 1981 I 1. Heiskanen O: Risks of surgery for unruptured intracranial aneurysms. J Neurosurg 65:451-453, 1986 12. Heiskanen O, Marttila I: Risk of rupture of a second aneurysm in patients with multiple aneurysms. J Neurosurg 32:295-299, 1970 13. Heiskanen O, Poranen A: Surgery of incidental intracranial aneurysms. Surg Neurol 28:432-436, 1987 14. H66k O, Norlrn G, Guzmfin J: Saccular aneurysms of the vertebral-basilar arterial system. A report of 28 cases. Acta Neurol Scand 39:271-304, 1963 15. Jamieson KG: Aneurysms of the vertebrobasilar system. Further experience with nine cases. J Neurosurg 28: 544-555, 1967 16. Jamieson KG: Aneurysms of the vertebrobasilar system. Surgical intervention in 19 cases. J Neurosurg 21: 781-797, 1964 17. Jane JA, Winn HR, Richardson AE: The natural history of intracranial aneurysms: rebleeding rates during the acute and long-term period and implication for surgical management. Clin Neurosurg 24:176-184, 1977 18. Lin T, Fox AJ, Drake CG: Regrowth of aneurysm sacs from residual neck following aneurysm dipping. J Neurosurg 70:556-560, 1989 19. Locksley HB: Report of the Cooperative Study of lntracranial Aneurysms and Subarachnoid Hemorrhage. Section V, Part II. Natural history of subarachnoid hemorrhage, intracranial aneurysms and arteriovenous malformations. Based on 6368 cases in the Cooperative Study. J Neurosurg 25:321-368, 1966 20. MacFarlane MR, McAllister VL, Whitby DJ, et al: Posterior circulation aneurysms. Results of direct operations. Surg Neurol 20:399-413, 1983 21. McCormick WF, Acosta-Rua GJ: The size of intracranial saccular aneurysms. An autopsy study. J Neurosurg 33: 422-427, 1970 22. Mizoi K, Suzuki J, Yoshimoto T: [Results of the surgical treatment of multiple aneurysms - - review of 372 cases.] No Shinkei Geka 16:133-139, 1988 (Jpn) 23. Mount LA, Brisman R: Treatment of multiple intracranial aneurysms. J Neurosurg 35:728-730, 1971 24. Moyes PD: Surgical treatment of multiple aneurysms and of incidentally-discovered unruptured aneurysms. J Neurosurg 35:291-295, 1971 25. Peerless SJ: Postoperative cerebral vasospasm without subarachnoid hemorrhage, in Wilkins RH (ed): Cerebral Arterial Spasm. Baltimore: Williams & Wilkins, 1980, pp 496-498 26. Peerless SJ, Drake CG: Surgical techniques of posterior cerebral aneurysms, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Meth-
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27. 28. 29. 30. 31. 32.
ods, and Results. New York: Grune & Stratton, Vol 2, 1988, pp 973-989 Peerless SJ, Nemoto S, Drake CG: Acute surgery for ruptured posterior circulation aneurysms. Adv Tech Stand Neurosurg 15:115-129, 1987 Salazar JL: Surgical treatment of asymptomatic and incidental intracranial aneurysms. J Neurosurg 53:20-21, 1980 Samson DS, Hodosh RM, Clark WK: Surgical management of unruptured asymptomatic aneurysms. J Neurosurg 46:731-734, 1977 Sugita K, Kobayashi S, Shintani A, et al: Microneurosurgery for aneurysms of the basilar artery. J Neurosurg 51: 615-620, 1979 Troupp H: The natural history of aneurysms of the basilar bifurcation. Acta Neurol Scand 47:350-356, 1971 Uihlein A, Hughes RA: The surgical treatment of intracranial vestigial aneurysms. Surg Clin North Am 35: 1071-1083, 1955
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33. Wiebers DO, Whisnant JP, O'Fallon WM: The natural history of unruptured intracranial aneurysms. N Engl J Med 304:696-698, 1981 34. Wilson CB, U HS: Surgical treatment for aneurysms of the upper basilar artery. J Neurosnrg 44:537-543, 1976 35. Wirth FP, Laws ER Jr, Piepgras D, et al: Surgical treatment of incidental intracranial aneurysms. Nenrosurgery 12:507-511, 1983 36. Yamamoto Y, Asari S, Sunami N, et al: Screening and treatment of unruptured cerebral aneurysms. Nenrol Res 8:88-92, 1986 Manuscript received September 8, 1989. Accepted in final form December 22, 1989. Address reprint requests to: Sydney J. Peerless, M.D., Division of Neurosurgery, Department of Clinical Neurological Sciences, The University of Western Ontario, London, Ontario N6A 5A5, Canada.
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Surgical treatment of unruptured aneurysms of the posterior circulation BEVERLY J. RICE, M.D., SYDNEY J. PEERLESS, M.D., F.R.C.S.(C), AND CHARLES G. DRAKE, M.D., F.R.C.S.(C) Division of Neurosurgery, The University of Western Ontario, University Hospital, London, Ontario, Canada With the ever-increasing number of intact aneurysms revealed by modern imaging, the options for their management are assuming great importance. While some knowledge has emerged as to their natural history and the results of surgical treatment of those in the anterior circulation, little information has been published concerning unruptured aneurysms arising from the posterior circulation. The authors report their experience since 1971 with 167 patients operated on for 179 unruptured vertebrobasilar aneurysms up to 25 mm in diameter. Overall, 160 aneurysms were treated by direct clip obliteration, while 19 were managed by alternative methods. Fifty-three patients (32%) had solitary aneurysms and the other 114 patients (68%) had multiple aneurysms or an associated arteriovenous malformation, which were commonly treated concurrently. Many of these coexisting vascular anomalies had ruptured in the recent or remote past, adding to the complexity of management and interpretation of specific surgical results related to the intact posterior circulation aneurysm. There were 78 documented postoperative complications including 23 systemic complications, seven postoperative hematomas, six brain injuries from retraction, five cases of aseptic meningitis, three instances of seizures, three wound infections, and three patients with hydrocephalus. Multiple complications occurred in 23 patients. Seventy-one of the patients with these untoward events recovered, without disability, with time or treatment. There were only six poor results and one death in the series, resulting in a 4.2% combined morbidity/ mortality rate. However, since two of these poor outcomes and the single death were attributable to a coexisting aneurysm, the actual surgical morbidity related specifically to the posterior circulation aneurysm was only 2.4%. This experience suggests that non-giant, intact vertebrobasilar aneurysms can be obliterated surgically at a very low risk, and this treatment should eliminate the greater lifetime risk related to an unsecured aneurysm. KEY WORDS vertebrobasilar aneurysm unruptured aneurysm 9 aneurysm ~
p
OSTERIOR circulation aneurysms have long been associated with a high morbidity rate and often with a fatal outcome. As the majority of reported lesions were managed after aneurysmal rupture, subarachnoid hemorrhage (SAH) further complicated the surgery and clinical outcome. The early operative mortality rate was in excess of 50%, 3-5'15'16'31 not dissimilar to that associated with the natural history of these deadly lesions. 2,7'14'31'32 Remarkable advances in the treatment of ruptured vertebrobasilar aneurysms have occurred over the past three decades. 2~176 At our institution, with a cumulative 31-year experience of over 1500 such cases, overall 5% mortality and 10% morbidity rates have been achieved. With the ever-increasing number of intact aneurysms revealed by modern imaging, the options for managing J. Neurosurg. / Volume 73/August, 1990
9 posterior circulation
9
these lesions are assuming great importance. We have treated 179 intact vertebrobasilar aneurysms with a very low morbidity rate and rare mortality. Natural history data, for comparison, are derived from published subgroups of untreated intact aneurysms (largely in the anterior circulation). In 1966, Locksley 19found a yearly rupture rate of 6.25 % (all fatal) for solitary symptomatic intact aneurysms, as calculated for that group by Jane, et al., ~7 based upon an average follow-up period of 4 years. Wiebers, et al., 33 indicated a 1.5% risk of rupture per year after studying a group with multiple incidental aneurysms. Both studies showed higher rupture rates when aneurysms of less than critical size were excluded. Specifically, a rupture rate of 3.4% per year is suggested by Weiber's series when aneurysms less than I0 mm were excluded, and a rate of 10% per year is suggested 165
B. J. R i c e , S. J. P e e r l e s s , a n d C. G . D r a k e TABLE 1 Location of179 aneurysms in this series Location basilar artery bifurcation superior cerebellarartery basilar trunk vertebrobasilarjunction vertebral artery posteriorcerebralartery
No. of Aneurysms 150 99 43 7 1 11 18
by Locksley's review if only aneurysms greater than 7 mm are considered. The importance of critical aneurysm size was also reflected by the autopsy study of McCormick and Acosta-Rua, 2j revealing that 60% of intracranial aneurysms greater than 6 mm had ruptured whereas smaller aneurysms appeared to confer little risk. Thus, we advise operating on intact aneurysms only when they have reached a critical size of approximately 6 mm. Several studies have addressed the natural morbidity for patients with multiple aneurysms specifically discovered after S A H . 6'j0'12'23'24 Heiskanen 1~ found a rupture rate of 1% per year in his group of patients followed for 10 years. Jane, et aL,17 after an extensive review, proposed that intact aneurysms generate the same 3% rates of rebleeding shown for untreated ruptured aneurysms after 6 months. They contended that intact aneurysms behave like healed aneurysms. Nevertheless, although the natural history remains uncertain, it confers a considerable lifetime risk of potentially catastrophic rupture. Summary of Cases Patient Population A total of 167 patients with 179 unruptured posterior circulation aneurysms were operated on between 1971 and 1988 at University Hospital in London, Ontario, Canada. There were 59 males and 108 females, with a mean age of 49 years (range 16 to 75 years). The distribution of the aneurysms was: 150 arising from the basilar artery, 18 from the posterior cerebral artery (PCA), and 11 from the vertebral artery (Table 1). One hundred seventy aneurysms were saccular and nine were fusiform; 128 aneurysms were small (< 12 m m in diameter) and 51 were large (12 to 25 mm). Giant aneurysms were not included in this review because of their unique technical problems. Twelve tiny aneurrysms (< 5 mm), which were too small for clipping, were treated by coagulation and/or gauze wrapping, mostly because they were coincident with another significant aneurysm or arteriovenous malformation (AVM). Since this treatment poses little risk, they were not included in this series or statistics. Fifty-three patients (32%) had solitary unruptured aneurysms and the remaining 114 patients (68%) had
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multiple intracranial aneurysms or AVM's. This latter group harbored an additional 209 aneurysms (97% in the anterior circulation) and 15 AVM's (l 1 supratentorial and four infratentorial). Eleven of the AVM's were supplied by parent arteries of posterior circulation aneurysms. Seventy patients (61% of the group with multiple cerebral vascular anomalies) had a known history of SAH ranging from l week to 9 years (mean 9.4 months) before presentation. They comprised 42% of the entire population. Four of these patients with recent SAH had a poor preoperative grade with confusion and fixed neurological deficit. Seven patients had significant stable neurological dysfunction on admission, six had moderate or severe hemiparesis related to previous stroke or aneurysm treatment, and one patient had parietal lobe deficits related to AVM rupture. In each case, the informed patient and family desired treatment of the intact posterior circulation aneurysm. Clinical Presentation The aneurysms were asymptomatic in 89% of the patients and were discovered incidentally when unrelated conditions led to an angiogram (Fig. 1). Sixty-four cases (38%) were discovered after rupture of a coexisting aneurysm or AVM. Idiopathic headache accounted for the investigation in 37 patients (22%). Cerebrovascular events led to the diagnosis of the intact aneurysm in 18 patients (11%). The remaining patients with incidental aneurysms had diverse presentations including seizures, endocrine disorders, vestibular or cognitive impairment, unrelated cranial nerve dysfunction, or otolaryngological disorders. Eighteen patients (11%) had presentations attributed to mass effect or emboli from an unruptured posterior circulation aneurysm (Fig. 1). Cranial nerve dysfunction was seen in eight patients. Six third nerve palsies (one mild Weber's syndrome) were associated with superior cerebral artery (SCA) aneurysms and one with a PCA aneurysm. One patient with a fusiform basilar aneurysm near the anterior inferior cerebellar artery (AICA) had a sixth nerve paresis and episodic ipsilateral facial paresis. Thromboembolism likely occurred in the remaining patients. Vertebrobasilar transient ischemic attacks seemed related to two fusiform aneurysms of the proximal basilar artery. Minor ischemic brain-stem strokes were evident in two individuals with large thrombosed basilar trunk aneurysms. Six patients with a saccular lesion at the distal basilar artery had events suggesting PCA ischemia. Three of these had transient homonymous visual scotomata. Episodes of transient global amnesia or disorientation occurred in two patients. A small posterior temporal lobe infarction occurred in a young patient with a small PCA aneurysm without risk factors for stroke. Surgical Approach
Exposure of 138 bifurcation region aneurysms was via the subtemporal approach. 26 A transsylvian apJ. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms
FIG. 1. Pie chart summarizing the presentation of 179 aneurysms. VB = vertebrobasilar location; CN = cranial nerve; SAH = subarachnoid hemorrhage; HA = headache, n = number of patients; percentages are of the total 167 patients.
proach was used in six cases to facilitate treatment of multiple aneurysms. Subtemporal-transtentorial exposure allowed access to seven basilar trunk aneurysms and one low bifurcation lesion. One AICA and l0 vertebral aneurysms were approached suboccipitally. Three distal PCA lesions required occipital craniotomy. A subtemporal-transmastoid-suboccipital approach provided access to the single vertebral junction aneurysm of the series. Another combined procedure was required for treatment of multiple aneurysms.
Treatment Methods Intraoperative 20% mannitol, lumbar drainage of cerebrospinal fluid at the time of dural opening, and maintenance of normocapnia were routine adjuncts. Hypotension (range 35 to 65 m m Hg) was induced in 67 patients (40%) for an average of 30 minutes (range 5 to 90 minutes). The parent vessel was temporally clipped in 30 cases (18%), with an average of two clip applications (range 1 to 6) separated by periods of reperfusion. Average time for temporary clipping of basilar aneurysms was over 4 minutes (range 1 to l0 minutes). Temporary clipping has been used more routinely only in recent years; this explains the infrequency of its use in this series. A total of 260 aneurysms were treated in 168 operations, with an average operating time of 4 hours (range 22 to 8 hours). Seventy-eight cases involved the treatment of multiple vascular lesions, including the excision of four AVM's and the ligation or embolization of major feeding vessels of four other malformations. Of the 64 cases discovered after SAH, 28 had concurrent treatment of the ruptured aneurysm (mean interval 2.5 J. Neurosurg. / Volume 73/August, 1990
weeks, range 1 to 8 weeks). The intact aneurysms were treated at the same time only if obliteration of the ruptured sac had been uneventful. Of the 179 unruptured aneurysms, 160 (89%) were clipped; tandem or multiple clipping was used in 25 of these cases. Hunterian ligation was required in six cases (3%); however, poorly defined aneurysmal neck or perforating vessels of the neck required basilar artery clipping in five of these. A fusiform, atherosclerotic vertebral artery aneurysm was treated by proximal vertebral artery occlusion. Treatment was confined to gauze wrapping or acrylic coating in five complex aneurysms (2.8%) in order to avoid injury to the parent or perforator vessels. Patients with six (3.4%) of the aneurysms underwent surgical exploration only. Two lesions were inaccessible due to dense adhesions from previous surgery or an overlying giant aneurysm. One completely calcified basilar aneurysm required no further treatment. Three other unclippable atherosclerotic aneurysms were not treated indirectly due to inadequate collateral circulation. Proximal PCA ligation facilitated excision of two distal PCA aneurysms and their associated occipital AVM's.
Operative Findings In 14 cases there was evidence suggesting previous hemorrhage from the aneurysm but without a compatible clinical history. Staining of regional arachnoid with hemosiderin, small organizing hematomas adjacent to cranial nerves, or yellow adhesions associated with the fundus of the sac were seen. Compression of the third 167
B. J. Rice, S. J. Peerless, and C. G. Drake TABLE 2
TABLE 3
Surgical results in 167 patients with intact basitar aneurysms*
Causes of permanent morbidity or death*
Location of Aneurysm
No. of Cases Excellent Good Poor Dead
small aneurysms (< 12 ram) basilar bifurcation 71 63 5 3 0 basilar: SCA 20 19 1 0 0 basilar: trunk 4 4 0 0 0 vertebrobasilar 1 1 0 0 0 vertebral 9 8 1 0 0 P~,P2 11 8 2 0 1 total cases 116 103 9 3 1 percent 89 8 2.6 0.9 large aneurysms (12-25 ram) basilar bifurcation 28 21 4 3 0 basilar: SCA 16 13 3 0 0 basilar: trunk 3 2 1 0 0 vertebrobasilar 0 0 0 0 0 vertebral 2 2 0 0 0 P, P2 2 2 0 0 0 total cases 51 40 8 3 0 percent 78 16 5.9 all cases 167 143 17 6 1 percent of total 86 10 3.6 0.6 * Excellent: normal or unchanged from preoperative status; good: minor new neurological deficit; poor: major new neurologicaldeficit.
and sixth cranial nerves was confirmed in seven cases of symptomatic aneurysms. In one case, there was recent hemorrhage in the oculomotor nerve; this patient (with a Weber's syndrome) had an SCA aneurysm deforming the third nerve and buried in the adjacent peduncle. Ventral pontine compression by a large basilar aneurysm was confirmed in one o f the patients with fixed brain-stem dysfunction.
Surgical Results Surgical o u t c o m e was recorded at the time of discharge or follow-up (Table 2) and later modified if further functional capacity or disability was realized. Analysis of outcome was complex because o f the various associated anomalies, preexisting morbidity, and c o m m o n treatment o f coexisting intracranial lesions. Results from the entire population, stratified for aneurysm location and size (Table 2), indicate 2.6% morbidity (poor results) and 0.9% mortality rates for small aneurysms and a 5.9% morbidity rate without mortality for large aneurysms. A n overall management o u t c o m e o f 3.6% morbidity and 0.6% mortality was achieved. The causes of permanent morbidity or death are summarized in Table 3. Although the overall m a n a g e m e n t morbidity/mortality rate was 4.2%, morbidity specifically related to the surgical obliteration of the posterior circulation aneurysm occurred in only four cases (2.4%). The other three cases (1.8%) had morbidity due to vasospasm (in two) or an infarction from operation on a middle cerebral aneurysm (in one). Subgroup analysis o f solitary aneurysms and those complicated by multiplicity or rupture o f a coexisting aneurysm or A V M is shown in Fig. 2. Results for 168
Related Relatedto to PC Coexisting Aneurysm Aneurysm aneurysm rupture 1 0 perforator vessel infarction 2 0 major hemispheric infarction 1 1 vasospasm 0 2 total cases 4 3 * Combined surgical morbidity and mortality rate was 2.4% compared with an overall management morbidity and mortality rate of 4.2%. PC = posterior circulation. Cause
patients who had concurrent treatment o f multiple lesions, including recently ruptured aneurysms, are also shown. Such figures are too small for statistical analysis, although they m a y suggest higher combined morbidity and mortality rates for cases involving treatment of multiple intact aneurysms. Results according to treatment m e t h o d indicated a combined morbidity/mortality rate o f 3.8 % for the 160 aneurysms treated by direct clipping. However, only in the two patients (1.3 %) with disabling perforator vessel ischemia was clipping responsible for a poor outcome. An operative morbidity rate o f 20% was noted for the five patients whose aneurysms were treated by wrapping; this single poor result resulted from early postoperative aneurysm rupture. There were no poor results or deaths a m o n g the patients whose aneurysms were treated indirectly, excised, or explored (Table 4). Details regarding the various complications follow.
Complications A s u m m a r y o f postoperative complications in patients with solitary and multiple aneurysms is given in Table 5. The complications are described below.
Postoperative Aneurysmal Rupture. Postoperative rupture o f one basilar aneurysm treated by gauze wrapping occurred 10 days after surgery. This patient required prolonged nursing-home convalescence and had a poor functional recovery. Postoperative rupture of an untreated posterior c o m m u n i c a t i n g artery (PCoA) aneurysm complicated another patient's o u t c o m e within hours after treatment o f her SCA aneurysm. Left hemispheric injury with hemiparesis and aphasia dramatically improved over the ensuing four months, with an eventual good outcome. Persistence o f Preoperative Cranial Nerve Dysfunction. Persistent third nerve palsies were seen in three patients after 15 months, 3 years, and 7 years, respectively. Four other patients showed almost complete resolution o f their severe oculomotor palsies after several months.
Cranial Nerve Injuries. Some degree o f third nerve dysfunction resulted in most patients with subtemporal surgery. The majority improved during hospitalization J. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms TABLE 4 Results in 179 aneurysms according to treatment method No. of Major Mortality Combined - Aneurysms Morbidity No. % direct clipping 160 5 1 6* 3.8 Hunterian ligation 6 0 0 0 0 wrapping 5 1 0 1 20 exploration only 6 0 0 0 0 excision 2 0 0 0 0 totals 179 6 1 7 4.2 * Clip technique alone accounted for only two bad outcomes (1.3%). Treatment Method
FIG. 2. Summary of findings and treatment of aneurysms in 167 patients in this series. AVM = arteriovenous malformation; SAH = subarachnoid hemorrhage, n = number of patients; percentages are of the total 167 patients.
TABLE 5 Summary of complications among 167 patients*
Complication a n d returned to n o r m a l within 12 weeks. O n e patient with a large A I C A a n e u r y s m developed an ipsilateral sensorineural hearing loss a n d vestibular nerve i m p a i r m e n t as a result o f treatment.
Perforator Vessel Injuries. M i d b r a i n a n d t h a l a m i c infarction has been a m a j o r cause o f m o r b i d i t y in u p p e r basilar a n e u r y s m surgery. Thirteen patients in this series suffered intraoperative injuries to t e r m i n a l basilar artery or PCA perforator vessels during direct t r e a t m e n t o f aneurysms o f the bifurcation region. Ischemia o f the mesencephalic t e g m e n t u m resulted in eye m o v e m e n t disorders in nine patients. Since m a n i p u l a t i v e ipsilateral third nerve paresis was usually present, this was evid e n c e d by i m p a i r m e n t o f u p w a r d gaze a n d ptosis or a medial rectus palsy on the opposite side; two patients suffered initial c o m p l e t e internuclear ophthalmoplegia. Seven patients showed corticospinal tract or cerebellar dysfunction. T h a l a m i c ischemia was suggested in four patients with confusion a n d i m p a i r m e n t o f short-term m e m o r y . The m a j o r i t y o f these patients i m p r o v e d ; the results were classified as excellent in six patients a n d good in five. O f the two patients with p o o r outcomes, one has been left with disabling ataxia, dysarthria, a n d m i l d d e m e n t i a (Fig. 3), a n d one has severe m e m o r y impairment. Vasospasm. Clinically significant vasospasm c o m plicated four cases, a c c o u n t i n g for one death, one p o o r outcome, a n d two g o o d results. Three o f these patients had suffered recent S A H between 1 a n d 8 weeks before surgical intervention. M i n o r intraoperative bleeding from the P C o A c o m p l i c a t e d the t r e a t m e n t o f intact left PCA a n d P C o A a n e u r y s m s in one case. This patient b e c a m e hemiplegic 1 week later as a result o f left P C A territory infarction a n d eventual b i h e m i s p h e r i c infarction from vasospasm (Fig. 4). D e a t h ensued 3 days later; autopsy c o n f i r m e d a d e q u a t e clipping o f the a n e u r y s m s a n d patency o f the PCA. J. Neurosurg. / Volume 73/August, 1990
total cases rupture persistent CN palsy new injury perforator vessel injury vasospasm major hemispheric infarction retraction injury hematoma related to rupture or Rx of other intracranial lesion aseptic meningitis wound infection seizure hydrocephalus systemic complications
Solitary Aneurysms 53 1 (1) 1 0 3 0 1 (1) 2 0 0 0 0 1 0 7
Multiple Aneurysms Intact + SAH 50 64 0 0 1 1 1 0 8 (2) 3 1 (1) 3 (1) 0 0 1 3 4 3 1 (1) 3 Intact
0 0 0 0 7
5 3 2 3 9
* Numbers in parentheses indicate patients with long-term morbidity or death. SAH = subarachnoid hemorrhage; CN = cranial nerve; Rx = treatment.
FIG. 3. Left." Angiogram showing a large intact basilar bifurcation aneurysm. Right: Postoperative computerized tomography scan revealing central midbrain infarction resulting from perforator vessel occlusion.
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B. J. Rice, S. J. Peerless, and C. G. Drake TABLE 6 Systemic complications in 23 patients
FIG. 4. Computerized tomography scan following operation on intact aneurysms in a patient who subsequently suffered fatal bihemispheric infarction resulting from vasospasm.
The patient with a poor outcome had undergone direct clipping of intact basilar bifurcation and ruptured PCA aneurysms 2 weeks after the latter ruptured. Despite subsiding preoperative vasospasm with the patient in poor clinical grade, surgery was uneventful. Four days postoperatively, the vasospasm increased with mesencephalic and hemispheric infarcts resulting in fixed left hemiparesis, ataxia, and confusional state. Major Hemispheric Infarction. Major fight-hemispheric infarction occurred in a 35-year-old woman with bilateral occlusive carotid disease from severe fibromuscular dysplasia, with a moyamoya-like vascular pattern and extensive dural leptomeningeal collateral supply. Previous stroke had resulted in dense fight hemiplegia, dysphasia, and pseudobulbar palsy which were unaltered by a left extracranial-intracranial (ECIC) anastomosis. Direct treatment of an incidental basilar bifurcation aneurysm resulted in a new left hemiplegia and initial stupor. The infarction was believed to be due to the interruption of numerous dural collateral vessels during exposure and mobilization of the tight temporal lobes. Angiography showed aneurysm obliteration with patent bypass. A fight EC-IC anastomosis was performed the following day. The patient entered a nursing home where she has regained only minor mobility in her left extremities. Retrospective evaluation indicates that this aneurysm should have been approached from the left, even though this would have necessitated some manipulation of the bypass. Another patient suffered a middle cerebral artery (MCA) branch occlusion after treatment of left MCA and basilar aneurysms. Postoperative hemiparesis improved; however, residual dysphasia accounted for a poor outcome. Retraction Injury. Six cases were complicated by probable retraction injury. Temporal and frontal lobe 170
Systemic Complication
No. of Cases
urinary tract infection pneumonia pulmonary congestion hyponatremia gastrointestinal bleeding cardiac arrhythmia pneumothorax
9 5 2 5 1 1 1
contusions caused moderate memory impairment and aphasia in two patients who had recently undergone bilateral craniotomies for aneurysm treatment. Transient left homonymous hemianopsia from retractionrelated occipital contusion occurred after treatment of a distal PCA aneurysm. Two patients developed transient dysphasia after left subtemporal exposures; one of these was attributable to a documented seizure focus. Right hemiparesis resulted from insular infarction in another patient, likely related to retraction pressure. There was no long-term morbidity within this group.
Postoperative Hematoma. Seven cases, complicated by hematomas, had no long-term morbidity. One epidural hematoma (EDH) requiting emergency evacuation, resulted in a minor hemiparesis which resolved after 2 months. Another EDH was evacuated in a patient who later developed local extradural empyema requiting drainage. Three patients had small subdural hematomas which were not treated. A small unexplained frontal intracerebral hematoma caused expressive aphasia in another patient; this had resolved by the time of discharge. Aseptic Meningitis. Aseptic meningitis was reported in five cases with variable expression and confirmation. Three of these patients had suffered SAH within 5 months of surgery; the other two had experienced remote hemorrhages. Other Complications. Three patients developed local wound infection, three had seizures, and three developed early hydrocephalus. Systemic complications were seen in 23 patients (Table 6). Two patients incurred deficits related to the treatment of coexisting posterior fossa AVM's. One showed moderate cerebellar dysfunction postoperatively and the other required early decompression for cerebellar swelling. Both patients eventually had good outcomes. Aneurysm Obliteration Postoperative angiography was performed in 139 (83%) of the 167 patients; most other saccular aneurysms were needled and collapsed at operation. Postoperative angiograms showed complete aneurysm obliteration in 113 (81%) of the 139 patients so studied; minor residual necks (1 to 2 mm) were revealed in 28 patients (20%). Two large basilar aneurysms treated by J. Neurosurg. / Volume 73/August, 1990
Unruptured posterior circulation aneurysms basilar occlusion had significant filling of the aneurysm base. In one of these, prominent PCoA collateral inflow caused recanalization of the sac after 6 months; fatal rupture of the aneurysm occurred 1 month later. The other aneurysm showed almost complete thrombosis at 7 months. One basilar aneurysm ruptured 3 years after direct treatment despite only minor residual filling of its neck; aneurysm regrowth was documented at that time. One small aneurysm treated by wrapping showed significant growth when evaluated 12 years later. Discussion
It is the intent of this review to determine any advantage of surgery over the natural risk of intact posterior circulation aneurysms. As these lesions are relatively rare and their nonoperative management has not been studied, natural history was inferred from previous studies involving mostly anterior circulation aneurysms. It is likely that aneurysms of the two circulations share similar factors influencing their growth and ultimate rupture. Morbidity and Mortality Rates
Our results indicate overall 3.6 % morbidity and 0.6 % mortality rates (all locations and sizes). Although the morbidity rate was somewhat higher in patients with large aneurysms, this subgroup was small. These data compare favorably with published surgical series of intact anterior circulation aneurysms. Wirth, et al., 35 reported an overall 6.5% morbidity rate including a 14% rate with larger aneurysms. Freger, et al.,S recorded no morbidity and a 1% mortality rate in their large group of patients with asymptomatic aneurysms. Other series have achieved similar results. ~'~~'j3.22.28,29,36 The medical literature suggests that a minimum risk of rupture for intact aneurysms of all sizes is 1% per year, but that it ranges from 3% to 10% when aneurysms of less than 7 mm are excluded. In patients with multiple aneurysms the risks are compounded. The surgical risk as defined by our heterogeneous population is low and appears to be less than the lifetime risk of an unsecured aneurysm. Our population had several interesting features, including the frequency of multiple vascular lesions (59%), of which over one-half presented with SAH. The major morbidity/mortality rate seen overall for cases complicated by multiplicity was not unlike that for the less complex cases with solitary aneurysms. Furthermore, patients with recent SAH also showed low morbidity, suggesting that hemorrhage was not a major factor influencing outcome in our series. Wirth, et al., 35 noted a similar low morbidity rate (2.3%) in their subgroup of patients who survived SAH and they questioned whether these patients had a selection bias for treatment success. There was evidence, however, that complications in general such as vasospasm, aseptic meningitis, hydrocephalus, and systemic injuries were J. Neurosurg. / Volume 73/August, 1990
more frequent in our group with SAH. The small group with concurrent treatment of the intact and ruptured aneurysms showed similarly good results. In this latter group, the single case with long-term morbidity resulted from vasospasm secondary to recent SAH. These results suggest that an intact posterior circulation aneurysm can be treated safely after recent SAH or concurrently with ruptured aneurysms. 27 Surgical T r e a t m e n t Treatment method is an important factor in analyzing our results. As previously stated, cases with clip occlusion of the aneurysm showed a 3.8% combined morbidity/mortality rate, which was comparable to the overall group including the alternative treatment methods. Within the subgroup of patients whose aneurysms were treated by wrapping, there was one case of early aneurysmal rupture (described earlier); this case is interesting and suggests that the craniotomy or surgical manipulation (for wrapping) may have influenced subsequent aneurysmal rupture. Nevertheless, although aneurysmal wrapping or Hunterian ligation is required for some cases of complex aneurysms, these treatment modalities may be coupled with persistent risk of aneurysmal rupture. Aneurysms at the basilar bifurcation have been the most difficult to manage technically because of the narrow confines involved in access, and particularly due to the risk of perforator vessel injury. It is notable that all major morbidity seen in this series was associated with treatment of aneurysms in this region. However, these complications included vasospasm in two cases and major hemispheric infarction in two others, related to treatment of a coexisting aneurysm or technical difficulties due to moyamoya disease. The two permanent perforator vessel injuries and the 11 minor perforator vessel ischemic injuries highlight the specific risk inherent in treating aneurysms at this location. The incidence of perforator vessel injury has declined dramatically with the use of temporary basilar artery clipping. Patients with preexisting morbidity related to previous brain injury may have lowered thresholds for complications that can be tolerated without causing further functional disability. Surgical risk may be too high to warrant intact aneurysm surgery. The patient with moyamoya disease failed to tolerate interruption of small collateral vessels, resulting in catastrophic infarction. Patients who suffered complications from the treatment of multiple intracranial lesions, on the other hand, had potentially greater surgical risks coupled with heightened natural risks that would justify surgical intervention. The combined morbidity rate of 12% for cases involving treatment of multiple aneurysms or AVM's seems high, but this includes the two patients with disabling perforator vessel infarctions that occurred after treatment of large basilar bifurcation aneurysms. The other two poor outcomes were related to treatment 171
B. J. Rice, S. J. Peerless, and C. G. Drake of a concurrent MCA aneurysm and vasospasm secondary to treatment of a coexisting intact aneurysm.
Vasospasm Vasospasm proved to be a rare event for our patients with recent SAH due to the delay between hemorrhage and our intervention. The single case of vasospasm that occurred without prior SAH was likely caused by minor intraoperative bleeding. As previously reported, 25 the occurrence of vasospasm after surgical treatment of intact aneurysm is distinctively rare, and this case remains perplexing.
Symptomatic Aneurysms The association of partially thrombosed aneurysms and vertebrobasilar ischemia is suggestive of thromboembolism. Fukuoka, eta[., 9 described the criteria inherent in this association, including absence of other causes for embolization, presence of aneurysmal thrombus, and cessation of attacks after aneurysm obliteration. We had limited follow-up data for some of these patients. Two patients with minor posterior circulation strokes, however, recovered completely and remain well after 6 months and 6 years, respectively. Recurrent episodic disorientation resolved after the treatment of one patient with a large bifurcation aneurysm.
Aneurysm Growth and Rupture Three patients treated in our series subsequently suffered aneurysm rupture. One was treated by wrapping, another was treated partially by Hunterian ligation, and a third underwent clipping with only minor residual filling of the aneurysmal neck seen postoperatively. These events emphasize the need for fully obliterating the aneurysm if possible to avoid further risk of rupture and injuryY 8 We believe that intact aneurysms of the posterior circulation can be treated with low surgical risk and can eliminate the greater lifetime risk of an unsecured aneurysm; the overall surgical morbidity is little more than that experienced by a patient living with the aneurysm for 2 to 3 years. In experienced hands, the surgical risk is not clearly heightened by SAH or multiplicity of aneurysms. Complete obliteration of these (and of all) aneurysms treated surgically should be achieved if possible.
References 1. Asari S, Yamamoto Y: [Unruptured cerebral aneurysms: clinical analysis of 80 cases and its new classification.] No To Shinkei 38:693-700, 1986 (Jpn) 2. Dimsdale H, Logue V: Ruptured posterior fossa aneurysms and their surgical treatment. J Neurol Neurosurg Psychiatry 22:202-217, 1959 3. Drake CG: Bleeding aneurysms of the hasilar artery. Direct surgical management in four cases. J Neurosurg 18:230-238, 1961 4. Drake CG: Further experience with surgical treatment of aneurysms of the basilar artery. J Neurosurg 29: 372-392, 1968
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5. Drake CG: The surgical treatment of aneurysms of the basilar artery. J Neurosurg 29:436-446, 1968 6. Drake CG, Girvin JP: The surgical treatment of subarachnoid hemorrhage with multiple aneurysms, in Morley TP (ed): Current Controversies in Neurosurgery. Philadelphia: WB Saunders, 1976, pp 274-278 7. Duvoisin RC, Yahr MD: Posterior fossa aneurysms. Neurology 15:231-241, 1965 8. Freger P, De Sousa MM, Sevrain L, et al: Faut-il oprrer les anrvrysmes asymptomatiques? Apropos de 114 an6vrysmes asymptomatiques oprrrs. Neurochirurgie 33: 462-468, 1987 9. Fukuoka S, Suematsu K, Nakamuru J, et al: Transient ischemic attacks caused by unruptured intracranial aneurysm. Surg Neurol 17:464-467, 1982 10. Heiskanen O: Risk of bleeding from unruptured aneurysms in cases with multiple intracranial aneurysms. J Neurosurg 55:524-526, 1981 I 1. Heiskanen O: Risks of surgery for unruptured intracranial aneurysms. J Neurosurg 65:451-453, 1986 12. Heiskanen O, Marttila I: Risk of rupture of a second aneurysm in patients with multiple aneurysms. J Neurosurg 32:295-299, 1970 13. Heiskanen O, Poranen A: Surgery of incidental intracranial aneurysms. Surg Neurol 28:432-436, 1987 14. H66k O, Norlrn G, Guzmfin J: Saccular aneurysms of the vertebral-basilar arterial system. A report of 28 cases. Acta Neurol Scand 39:271-304, 1963 15. Jamieson KG: Aneurysms of the vertebrobasilar system. Further experience with nine cases. J Neurosurg 28: 544-555, 1967 16. Jamieson KG: Aneurysms of the vertebrobasilar system. Surgical intervention in 19 cases. J Neurosurg 21: 781-797, 1964 17. Jane JA, Winn HR, Richardson AE: The natural history of intracranial aneurysms: rebleeding rates during the acute and long-term period and implication for surgical management. Clin Neurosurg 24:176-184, 1977 18. Lin T, Fox AJ, Drake CG: Regrowth of aneurysm sacs from residual neck following aneurysm dipping. J Neurosurg 70:556-560, 1989 19. Locksley HB: Report of the Cooperative Study of lntracranial Aneurysms and Subarachnoid Hemorrhage. Section V, Part II. Natural history of subarachnoid hemorrhage, intracranial aneurysms and arteriovenous malformations. Based on 6368 cases in the Cooperative Study. J Neurosurg 25:321-368, 1966 20. MacFarlane MR, McAllister VL, Whitby DJ, et al: Posterior circulation aneurysms. Results of direct operations. Surg Neurol 20:399-413, 1983 21. McCormick WF, Acosta-Rua GJ: The size of intracranial saccular aneurysms. An autopsy study. J Neurosurg 33: 422-427, 1970 22. Mizoi K, Suzuki J, Yoshimoto T: [Results of the surgical treatment of multiple aneurysms - - review of 372 cases.] No Shinkei Geka 16:133-139, 1988 (Jpn) 23. Mount LA, Brisman R: Treatment of multiple intracranial aneurysms. J Neurosurg 35:728-730, 1971 24. Moyes PD: Surgical treatment of multiple aneurysms and of incidentally-discovered unruptured aneurysms. J Neurosurg 35:291-295, 1971 25. Peerless SJ: Postoperative cerebral vasospasm without subarachnoid hemorrhage, in Wilkins RH (ed): Cerebral Arterial Spasm. Baltimore: Williams & Wilkins, 1980, pp 496-498 26. Peerless SJ, Drake CG: Surgical techniques of posterior cerebral aneurysms, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Meth-
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Unruptured posterior circulation aneurysms
27. 28. 29. 30. 31. 32.
ods, and Results. New York: Grune & Stratton, Vol 2, 1988, pp 973-989 Peerless SJ, Nemoto S, Drake CG: Acute surgery for ruptured posterior circulation aneurysms. Adv Tech Stand Neurosurg 15:115-129, 1987 Salazar JL: Surgical treatment of asymptomatic and incidental intracranial aneurysms. J Neurosurg 53:20-21, 1980 Samson DS, Hodosh RM, Clark WK: Surgical management of unruptured asymptomatic aneurysms. J Neurosurg 46:731-734, 1977 Sugita K, Kobayashi S, Shintani A, et al: Microneurosurgery for aneurysms of the basilar artery. J Neurosurg 51: 615-620, 1979 Troupp H: The natural history of aneurysms of the basilar bifurcation. Acta Neurol Scand 47:350-356, 1971 Uihlein A, Hughes RA: The surgical treatment of intracranial vestigial aneurysms. Surg Clin North Am 35: 1071-1083, 1955
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33. Wiebers DO, Whisnant JP, O'Fallon WM: The natural history of unruptured intracranial aneurysms. N Engl J Med 304:696-698, 1981 34. Wilson CB, U HS: Surgical treatment for aneurysms of the upper basilar artery. J Neurosnrg 44:537-543, 1976 35. Wirth FP, Laws ER Jr, Piepgras D, et al: Surgical treatment of incidental intracranial aneurysms. Nenrosurgery 12:507-511, 1983 36. Yamamoto Y, Asari S, Sunami N, et al: Screening and treatment of unruptured cerebral aneurysms. Nenrol Res 8:88-92, 1986 Manuscript received September 8, 1989. Accepted in final form December 22, 1989. Address reprint requests to: Sydney J. Peerless, M.D., Division of Neurosurgery, Department of Clinical Neurological Sciences, The University of Western Ontario, London, Ontario N6A 5A5, Canada.
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