Intracranial aneurysms in sickle cell disease: Aneurysms characteristics and modalities of endovascular approach to treat these patients

IntroductionThe neurological complications of Sickle Cell Disease (SCD) include cerebral infarction and haemorrhage with rarely subarachnoid haemorrhage due to cerebral aneurysms.Materials and methodsIn our interventional department, working with SCD referral department, we reported our experience concerning management of adult's patients with cerebral aneurysms. We identified 26 adults with 48 intracranial aneurysms documented by imaging.Results18 patients, with 26 cerebral aneurysms were treated by endovascular approach for their aneurysms. No patient was treated by surgical way in our institution. 50% of patients had multiple aneurysms. Locations of aneurysms treated were typical with 70% of cerebral anterior artery and 30% of posterior artery. Three patients suffered from subarachnoid haemorrhage. Two procedure-related complications occurred during the treatment: one thrombo-embolic event with good recovery after medical treatment and one aneurismal perforation leading to the death of patient. Hypercoagulability is a major specific risk in SCD and use of permanent device as stent of flow diverter should be discussed to prevent complications.ConclusionEndovascular management of these aneurysms seems to be a good alternative to treat these patients, with stability of occlusion at follow-up.     

Subarachnoid haemorrhage with "Ecstasy" abuse in a young adult

Abuse of the drugs like amphetamine, cocaine and “Ecstasy” may be complicated by intracerebral, subdural or subarachnoid haemorrhage. Contrary to historical opinion, drug-related intracranial haemorrhage (ICH) is frequently related to an underlying vascular malformation. We report the case of an 18-year-old man with a history of Ecstasy abuse preceding the onset of severe occipital headache. Cerebral computed tomography revealed right-sided subarachnoid haemorrhage and cerebral angiography showed right-sided middle cerebral artery aneurysm of 1 cm diameter. The patient was treated surgically with aneurysm clipping. Three weeks after onset of intracranial haemorrhage, neurological examination demonstrated normal findings. A history of severe headache immediately after using amphetamine, Ecstasy, or cocaine should alert doctors to the possibility of intracerebral haemorrhage. Arteriography should be part of the evaluation of most young patients with stroke or non-traumatic ICH. Received: 26 March 2002 / Accepted in revised form: 11 July 2002 Correspondence to J. Auer     

Endovascular management of unruptured intracranial aneurysms: does outcome justify treatment?

OBJECTIVE: The appropriate management of unruptured intracranial aneurysms depends on a complete understanding of their natural history and on the risks and efficacy of treatment options. There is little current data on the risks of endovascular therapy for these aneurysms. The aim of this study was to assess outcome of endovascular treatment of unruptured intracranial aneurysms. METHOD: A retrospective analysis was performed on all unruptured aneurysms treated by Guglielmi detachable (GD) coils at this institution from 1994 to 2000. RESULTS: Seventy three unruptured aneurysms were treated in 62 patients. There were 52 female and 10 male patients, with a median age of 55.7 years. Clinical background was: subarachnoid haemorrhage due to rupture of an additional aneurysm (40), headache (4), third nerve palsy (four), familial (four), and incidental (10). There were 14 technical failures with no clinical sequelae. Four procedural complications occurred (5.5%, 95% confidence interval (95% CI) 0.3% to 10.9%). One patient had temporary clinical sequelae (1.4%, 95% CI 0% to 2.7%); 79% of treated aneurysms had stable occlusions at follow up, 10.5% showed improved occlusion grade, 10.5% showed some recurrence, and three patients have required retreatment. Follow up modified Glasgow outcome scores were grade 1, 71%; grade 2, 18%; grade 3, 3%; grade 4, 3%. There were no deaths or haemorrhages during the follow up period. Two patients died as a result of complications from subarachnoid haemorrhage. CONCLUSION: The endovascular treatment of patients with unruptured aneurysms is safe with few clinical or procedural complications. Poor outcomes were only seen in those patients who presented with subarachnoid haemorrhage due to rupture of an aneurysm at another site.     

Surgical Results of Unruptured Intracranial Aneurysms in the Elderly : Single Center Experience in the Past Ten Years

Objective

As medical advances have increased life expectancy, it has become imperative to develop specific treatment strategies for intracranial aneurysms in the elderly. We therefore analyzed the clinical characteristics and outcomes of the treatment of unruptured intracranial aneurysms in patients older than 70 years.

Methods

We retrospectively reviewed the medical records and results of neuroimaging modalities on 54 aneurysms of 48 consecutive patients with unruptured intracranial aneurysms. (mean±SD age, 72.11±1.96 years; range, 70-78 years) who underwent surgical clipping over 10 years (May 1999 to June 2010).

Results

Of the 54 aneurysms, 22 were located in the internal carotid artery, 19 in the middle cerebral artery, 12 in the anterior cerebral artery, and 1 in the superior cerebellar artery. Six patients had multiple aneurysms. Aneurysm size ranged from 3 mm to 17 mm (mean±SD, 6.82±3.07 mm). Fifty of the 54 aneurysms (92.6%) were completely clipped. Three-month outcomes were excellent in 50 (92.6%) aneurysms and good and poor in 2 each (3.7%), with 1 death (2.0%). Procedure-related complications occurred in 7 aneurysms (13.0%), with 2 (3.7%) resulting in permanent neurological deficits, including death. No postoperative subarachnoid hemorrhage occurred during follow-up. The cumulative rates of stroke- or death-free survival at 5 and 10 years were 100% and 78%, respectively.

Conclusion

Surgical clipping of unruptured intracranial aneurysms in elderly group could get it as a favorable outcome in well selected cases.     

Rebleeding of intracranial dissecting aneurysm in the vertebral artery following proximal clipping

Abstract

We describe a case of rebleeding from an intracranial vertebral dissecting aneurysm following proximal clipping. This case suggests that proximal clipping alone may not be an adequate surgical procedure to prevent rebleeding. Surgical treatment of intracranial dissecting aneurysms in the vertebral artery presenting as subarachnoid haemorrhage (SAH) is discussed. [Neurol Res 1994; 16: 141-144]     

Arterial fenestrations and their association with cerebral aneurysms

Fenestrations of intracranial arteries and associated aneurysms are rare. The significance of these fenestrations in relation to aneurysms remains unclear. We present four patients with fenestration-associated aneurysms and a comprehensive review of associations with aneurysms and other vascular lesions. A PubMed search of the literature was conducted from 1970–2012 reporting cases of intracranial aneurysms associated with arterial fenestration or duplications. Data were collected on patient presentation, sex, age, aneurysm and fenestration location, aneurysm treatment, and presence of other vascular lesions. We performed a retrospective review of four patients with intracranial fenestrations associated with aneurysms at our institution from 2012–2013. There were 59 cases of fenestrations and associated aneurysms in the literature. Aneurysms were reported as either arising from (n = 50) or adjacent to but distinct from (n = 13) fenestrations. The most common single fenestration location was at the basilar artery (n = 23, 36.5%); however the majority of fenestrations were in the carotid circulation (n = 34, 54.0%). The majority of patients with aneurysms and fenestrations at all locations except those at the anterior communicating artery (70.5%) presented with subarachnoid hemorrhage. Patients with aneurysms arising from a fenestration or adjacent to a fenestration presented with an additional intracranial vascular lesion in 38% and 31% of cases, respectively. The majority of all aneurysms were treated with microsurgical clipping. Aneurysms associated with cerebral arterial fenestrations are most commonly discovered after subarachnoid hemorrhage and are most often located in the carotid circulation. A high index of suspicion must be maintained for an associated vascular lesion if an intracranial fenestration is discovered.     

Detection of intracranial aneurysms with unenhanced and echo contrast enhanced transcranial power Doppler

OBJECTIVE: To assess transcranial power Doppler and the effect of an intravenous ultrasonic contrast agent for detecting intracranial aneurysms in patients admitted with a subarachnoid haemorrhage METHODS: 203 patients with subarachnoid haemorrhage were examined with the operator blind to the results of the admission CT and subsequent digital subtraction angiogram (DSA). In 98 cases patients were imaged using unenhanced transcranial power Doppler, and in 105 cases, patients were imaged both using unenhanced and echo contrast enhanced (Levovist, Schering AG) transcranial power Doppler. RESULTS: DSA detected 168 intracranial aneurysms in 128 patients (24 patients had multiple lesions) and 75 patients had an aneurysm negative DSA. There was agreement between DSA and transcranial power Doppler in 87 intracranial aneurysms of which 20 were only detected after infusion of contrast agent. Without contrast infusion, transcranial power Doppler showed a sensitivity of 40% and specificity of 91%. A significant increase in detection was noted when using a contrast agent (chi(2) = 9.49, p<0.001). With a contrast study the sensitivity increase to 55% with a specificity of 83%. Intracranial aneurysm detection by transcranial power Doppler was significantly dependent on position using a contrast infusion (chi(2) = 15.87, p<0.05). A positive correlation was also found between the size of intracranial aneurysms measured by transcranial power Doppler and DSA (r = 0.55, p<0.05). The transcranial power Doppler sensitivity and specificity increased with larger aneurysms and reached 100% for intracranial aneurysms greater than 12 mm diameter. Detection by transcranial power Doppler was also dependent on morphology (chi(2) = 14.46, p<0.001). CONCLUSIONS: The detection of intracranial aneurysm by transcranial power Doppler is dependent on aneurysm location, size, and morphology and is enhanced with the use of an intravenous contrast agent.     

Risk factors for multiple intracranial aneurysms

BACKGROUND AND PURPOSE: The presence of multiple intracranial aneurysms may be a sign of significant risk factors for aneurysm formation that differ from those factors that increase risk for aneurysm rupture. Only 2 studies concern independent risk factors for multiple aneurysms, and the results are in part controversial. This study was designed to identify independent risk factors for multiple intracranial aneurysms in patients with subarachnoid hemorrhage. METHODS: Of 266 patients with aneurysmal subarachnoid hemorrhage (139 men and 127 women, aged 15 to 60 years), 80 (30%) had multiple intracranial aneurysms. The prevalence of several health-related habits, previous diseases, and medications of these patients were compared by multiple logistic regression between those with single and those with multiple aneurysms. RESULTS: On the basis of multivariate statistics, only regular cigarette smoking at any time was a significant risk factor for the presence of multiple aneurysms. The odds ratio (OR) of smoking for multiple aneurysms was 2.10 (95% CI, 1.06 to 4.13) after adjustment for age and sex. After additional adjustment for hypertension, the risk was 2.06 (95% CI, 1. 04 to 4.07). Of other variables, only age (OR, 1.02 per year; 95% CI, 1.00 to 1.05; P=0.09) and female sex (OR, 1.60; 95% CI, 0.90 to 2. 85; P=0.11) showed a tendency to increase the risk for multiple aneurysms after adjustment for smoking. On the other hand, patients with hypertension had significantly (P=0.029) more aneurysms (1. 61+/-1.04) than did those without (1.37+/-0.68), although they did not more frequently have multiple aneurysms. CONCLUSIONS: Cigarette smoking and possibly also age and female sex seem to be risk factors for multiple intracranial aneurysms in patients of working age who have suffered a subarachnoid hemorrhage. Patients with hypertension seem to have more aneurysms than those without.     

Clinical experience of 153 patients with posterior circulation aneurysms.

OBJECTIVE: To study the morbidity and mortality of patients with aneurysms of the posterior circulation (basilar-vertebral system) and investigate the natural history of these aneurysms without surgical intervention. METHODS: Of 1232 patients with intracranial aneurysms admitted to Tiantan Hospital from January 1990 to October 2001, 153 (12.4%) had aneurysms of the posterior circulation. Their clinical and angiographic data were reviewed retrospectively. Additionally, to June 2002, 38 of the cases managed without surgery have been followed by telephone and correspondence. For these patients, the annual aneurysm rupture rate was estimated in "person-years". RESULTS: Patients were aged 4-69 years (mean 40.8). The peak incidence was in the 5th decade. There were 88 males and 65 females. One hundred and two patients (66.7%) were treated surgically, and of these, 60 (58.8%) had an excellent outcome, 10 (9.8%) a good outcome, 29 (28.4%) a fair outcome and 3 (2.9%) died. The other 51 (33.3%) patients were treated conservatively for various reasons. Of these, 13 died of ruptured aneurysm in hospital. Ten of these patients had had a previous subarachnoid haemorrhage and 3 had not. The other 38 surviving, conservatively managed patients were followed for 5-95 months (mean 23). Of them, 3 (17.6%) died of aneurysmal rupture, giving an annual rupture rate of 9.2%, or 3/32.47 patient years. CONCLUSIONS: To prevent death and disability due to aneurysmal rupture, posterior circulation aneurysms should be treated aggressively.     

Risk-benefit analysis of the treatment of unruptured intracranial aneurysms

OBJECTIVES: To determine under what circumstances repair of unruptured intracranial aneurysms may be beneficial. METHODS: A life expectancy analysis of patients with unruptured aneurysms with and without repair based on prospective data from the International Study of Unruptured Intracranial Aneurysms (ISUIA). RESULTS: Life years are lost at all ages by repairing anterior circulation aneurysms under 7 mm in diameter in patients with no history of a subarachnoid haemorrhage from another aneurysm (incidental). For all other aneurysms the number of life years saved by repair is dependent on the patient's age at the time when repair is undertaken. Between 2 and 40 years are saved by repairing aneurysms in patients aged 20 years. These benefits fall to 0 when remaining life expectancy falls below 15-35 years, corresponding to the age range of 45-70 years. CONCLUSIONS: Repair of unruptured aneurysms benefits patients harbouring them by improving life expectancy except in certain circumstances. The exceptions are patients with remaining life expectancy less than 15-35 years or aged 45-70 (depending on aneurysm size and location) and patients with aneurysms of the anterior circulation under 7 mm in diameter with no history of a previous subarachnoid haemorrhage. These results are based on the findings of the ISUIA and are dependent on their accuracy.     

Chronic subdural haematoma and arachnoid cyst in autosomal dominant polycystic kidney disease (ADPKD).

We present the unusual association between chronic subdural haematoma (CSDH), intracranial arachnoid cyst and autosomal dominant polycystic kidney disease (ADPKD) in a 27-year-old man. CSDH is a documented complication of intracranial arachnoid cyst, the incidence of which is increased in patients with ADPKD. Awareness of this association may lead to earlier diagnosis of ADPKD and treatment of its systemic complications, including renal insufficiency, systemic hypertension and previously unsuspected intracranial saccular aneurysm. Surgery for CSDH associated with intracranial arachnoid cyst may be complicated by over-drainage of cerebrospinal fluid due to communication between the cyst and the cisternal subarachnoid space, as illustrated in the present case, and the development of epidural haemorrhage.     

Estimate of the maximum time interval between formation of cerebral aneurysm and rupture

The recent publication of the results of the international study on unruptured intracranial aneurysms highlighted a paradox: there do not seem to be enough unruptured aneurysms in the population to account for the observed incidence of subarachnoid haemorrhage. Some authors have suggested that the answer to this paradox is that most aneurysms that bleed do so shortly after formation. This would mean that the bulk of subarachnoid haemorrhages come from recently formed rather than long standing aneurysms. This paradox and proposed answer are examined. The available statistics on the incidence of subarachnoid haemorrhage, the prevalence of unruptured aneurysms, and the risk of bleeding from unruptured aneurysms are used to place a maximum on the time interval between aneurysm formation and rupture. For aneurysms less than 10 mm in diameter in persons with no history of subarachnoid haemorrhage, an estimate of less than 42 weeks was made. The null hypothesis that such aneurysms pose a constant risk with time is rejected with p <10(-9). In larger aneurysms the risk seems to be constant with time.     

Neonatal ruptured intracranial aneurysms: case report and literature review

Introduction  Intracranial aneurysms are exceptional in neonatal patients: There are only 16 cases previously reported. We describe the first case of neonatal posterior inferior cerebellar artery (PICA) aneurysm and review the literature. Case report  A 7-day-old girl presented with irritability, anorexia, fever and abnormally enlarging head circumference. Computed tomography (CT) and magnetic resonance (MR) imaging demonstrated intraventricular haemorrhage, secondary hydrocephalus and a pontine cistern haematoma. A PICA aneurysm was suspected on the CT angiogram (CTA) and the diagnosis was confirmed by conventional cerebral angiography. She was successfully treated by surgical clipping of the parent vessel and excision of the aneurysm. Postoperatively, she experienced transient swallowing difficulties and required a ventriculo-peritoneal shunt for hydrocephalus. Histopathological evaluation demonstrated a calcified arterial wall with thrombosis, signs of prior haemorrhage and the absence of the internal elastic lamina. Conclusion  Neonatal intracranial aneurysms are rare. Clinical presentation of subarachnoid haemorrhage in this age group is often non-specific. First-line investigation should start with transfontanelle cranial ultrasound, followed by MR angiography then CTA if necessary. Posterior circulation aneurysms and large or giant aneurysms are more frequent in neonates and children than in adults. Early diagnosis and treatment are important for improved outcome. Surgery is better tolerated than in adults.     

Detection of cerebral artery fenestrations by computed tomography angiography

Background and purposeCerebral artery fenestrations (CAF) are rare congenital variations usually diagnosed by digital subtraction angiography (DSA). The aim of this study was to examine the frequency of occurrence of fenestrations in cerebral arteries and their coexistence with cerebral aneurysms in computed tomography angiography (CTA).Material and methodsAll reports of cerebral CTA (1140) performed in one institution from March 2005 to December 2007 were analysed. We found 40 patients with single fenestrations of the intracranial arteries. All 40 examinations were retrospectively reviewed for location of vascular malformations and presence of aneurysms or subarachnoid haemorrhage (SAH). Medical histories of those patients were then analysed for evidence of SAH and referral reasons for CTA.ResultsForty fenestrated arteries were found in CTA: 18 basilar arteries (45%), 16 anterior cerebral arteries (40%), 4 anterior communicating arteries (10%) and one middle cerebral artery (2.5%). Only one vertebral artery fenestration was found due to the technique of the examination. Six patients (15%) with fenestrated arteries had a total of 8 aneurysms, although only one aneurysm was ipsilateral to the fenestration. In 8 cases of SAH, two were with no evidence of vascular malformation. The coexistence of CAF and aneurysms in CTA amounted to 15% (6/40), but the incidence of ipsilateral aneurysm was only 2.5% (1/40) and it affected the anterior cerebral artery.ConclusionsBasilar artery fenestration is the most frequent observed fenestration in CTA, followed by anterior cerebral artery and anterior communicating artery fenestrations. Coexistence of fenestration and aneurysm is uncommon in CTA examination.     

Megadolichobasilar artery and acute cerebrovascular pathology

Sixteen patients with a megadolichobasilar artery and acute cerebrovascular symptoms are reported. All were explored by computerized tomography and vertebral angiography. Nine had transient ischaemic attacks or definitive ischaemic lesions, whereas 7 had subarachnoid or intracerebral haemorrhage. Among the patients with ischaemic troubles, vertebro-basilar insufficiency and pontine infarction were the most common clinico-radiological findings. Among the patients with intracranial haemorrhage, 4 had associated aneurysms or arteriovenous malformations, while 3 had subarachnoid or intracerebral haemorrhage with no vascular malformations on the angiograms. The possible relationships between the megadolichobasilar anomaly and the cerebral ischaemic or haemorrhagic pathologies are discussed also from a review of the pertinent literature.     

Dissecting aneurysms limited to the basilar artery: Report of two cases and review of the literature.

Spontaneous dissecting aneurysms limited to the basilar artery are rare. We describe two patients who presented to our institution with different clinical problems, one with brain stem infarction and the other with subarachnoid hemorrhage. We describe the clinical and imaging features in these patients, their treatment, and outcome. We also reviewed the literature concerning this entity, and we have identified 32 patients (including our two pateints) with angiographically confirmed dissecting aneurysms limited to the basilar artery. Of these, 40.6% presented with brain stem infarction, 50.0% presented with subarachnoid hemorrhage, and 9.4% presented with both infarction and subarachnoid hemorrhage. Patients who presented with basilar artery dissecting aneurysms and brain stem infarction tended to be younger (mean age, 38 +/- 7 years) than those who presented with subarachnoid hemorrhage (48 +/- 12 years) and were more likely to be male. We discuss the natural history of this entity and suggest an approach to clinical management for these patients.     

Megadolichobasilar artery and acute cerebrovascular pathology

Sixteen patients with a megadolichobasilar artery and acute cerebrovascular symptoms are reported. All were explored by computerized tomography and vertebral angiography. Nine had transient ischaemic attacks or definitive ischaemic lesions, whereas 7 had subarachnoid or intracerebral haemorrhage. Among the patients with ischaemic troubles, vertebro-basilar insufficiency and pontine infarction were the most common clinico-radiological findings. Among the patients with intracranial haemorrhage, 4 had associated aneurysms or arteriovenous malformations, while 3 had subarachnoid or intracerebral haemorrhage with no vascular malformations on the angiograms. The possible relationships between the megadolichobasilar anomaly and the cerebral ischaemic or haemorrhagic pathologies are discussed also from a review of the pertinent literature.     

3.0T磁共振MRA在蛛网膜下腔出血颅内动脉瘤筛查中的应用价值

目的探讨3.0T磁共振MRA在蛛网膜下腔出血颅内动脉瘤筛查中的应用价值。方法利用3.0T磁共振对31例因蛛网膜下腔出血而筛查出脑动脉瘤患者进行回顾性分析,31例脑动脉瘤患者均行常规T1WI、T2WI及3D TOF MRA检查,对检查的信息进行MIP、MPR及VR后处理并结合原始薄层图像进行分析诊断。所有病例均由DSA最后确诊后治疗。结果小动脉瘤(<5 mm)11个,中动脉瘤(>5 mm)13个,大动脉瘤(>10 mm)9个。动脉瘤的分布:大脑中动脉瘤8个,大脑前动脉瘤7个,大脑后动脉瘤3个,前交通动脉瘤5个,后交通动脉瘤6个,基底动脉瘤1个,颈内动脉海绵窦段动脉瘤2个,椎动脉瘤1个。结论 3.0T磁共振MRA可成为蛛网膜下腔出血颅内动脉瘤筛查的有效检查方法,值得临床推广。     

Risk analysis of treatment of unruptured aneurysms

OBJECTIVES: To calculate the expected number of life-years saved by surgical treatment of unruptured intracranial aneurysms at ages over 20 years. METHODS: An actuarial risk analysis of the treatment of unruptured intracranial aneurysms based on data from the International Study of Unruptured Intracranial Aneurysms (ISUIA). The benefits of operative treatment are calculated in terms of average life-years saved. RESULTS: Results are presented as graphs of life-years saved or lost against age at the time of operative treatment for three groups of aneurysms: those under 10 mm in diameter with no history of subarachnoid haemorrhage (SAH) from another aneurysm, those under 10 mm in diameter and a history of previous SAH from a different aneurysm, and those over 10 mm in diameter. Life-years are lost at all ages in the group under 10 mm with no history of SAH. For the group under 10 mm with a history of SAH about 4 years are saved at age 20 declining to 0 at around age 50. For aneurysms 10 mm or more in diameter about 8 life-years are saved at age 20 declining to 0 at around 50. CONCLUSIONS: Clipping of unruptured aneurysms under 10 mm in diameter with no history of subarachnoid haemorrhage is not justified on actuarial grounds. Intervention in other unruptured aneurysms produces benefits in life expectancy up to the age of 50. There may be subgroups of aneurysms in which larger benefits exist.     

Analysis of phospholipase C gene in patients with subarachnoid hemorrhage due to ruptured intracranial saccular aneurysm

Abstract

This study is designed to determine whether patients with aneurysmal subarachnoid hemorrhage have mutations in the phospholipase C-dl (PLC-51) gene, which was identified as a gene responsible for hypertension in spontaneously hypertensive rats. Seventy-two cases (31 male and 4 1 female) with intracranial saccular aneurysms were analyzed. The mean age was 60.1 ± 11.5 years (mean± SD) (range 24-85 years). There were 35 patients (48.6%) with hypertension, 5 (6.9%) with diabetes mellitus, 72 (16.7%) with hyperlipidemia, 8 (11.1%) with ischemic heart disease, and 25 (34.7%) who were active smokers. The location of aneurysm was distributed as follows: 33 (33%) were at anterior cerebral artery, 23 (23%) were at middle cerebral artery, 28 (28%) were at internal carotid artery, and 16 (16%) were at vertebro-basilar artery. Six patients (8.3%) had a family history of intracranial aneurysms. There were 20 patients (27.8%) with multiple aneurysms, and 8 patients (11.1 %) with a large or giant aneurysm. The four regions of PLC-51 gene (bases 1099-1271, 1254-1401, 1343-1481, and 1882-2023) where genetic mutations were found in spontaneously hypertensive rats, were screened by PCR-SSCP analysis and their nucleotide sequences of all patients were determined. However, no mutations were detected in all patients. These results suggest that mutations ofPLC-d 1 gene previously implicated in hypertensive factor in rats may not be the case with human patients and therefore may be poorly related with aneurysmal subarachnoid hemorrhage. [Neurol Res 1999; 21: 368-372]