Collagen type III deficiency in patients with rupture of intracranial saccular aneurysms

Hormonal influences on cerebral aneurysms: unraveling the complex connections

INTRODUCTION

Intracranial aneurysms (IAs) occur in 3-5% of the general population and are characterized by localized structural deterioration of the arterial wall with loss of internal elastic lamina and disruption of the media. The risk of incidence and rupture of aneurysms depends on age, sex, ethnicity, and other different factors, indicating the influence of genetic and environmental factors. When an aneurysm ruptures, there is an estimated 20% mortality rate, along with an added 30-40% morbidity in survivors. The alterations in hormonal levels can influence IAs, while the rupture of an aneurysm can have various impacts on endocrine pathways and affect their outcome.

AREA COVERED

This review explores the reciprocal relationship between endocrinological changes (estrogen, growth hormone, and thyroid hormones) and IAs, as well as the effects of aneurysm ruptures on endocrine fluctuations.

EXPERT OPINION

Based on the data presented in this paper, we recommend further exploration into the influence of hormones on aneurysm formation and rupture. Additionally, we propose conducting endocrine assessments for patients who have experienced a rupture of IAs. Monitoring hormonal changes in patients with IAs could serve as a potential risk factor for rupture, leading to interventions in the approach to managing IAs.

Alport's syndrome and intracranial aneurysm: mere coincidence or undiscovered causal relationship

A 44-year-old Caucasian man with a history of deceased donor renal transplant for end-stage renal disease from Alport’s syndrome (AS), presented with a spontaneous subarachnoid haemorrhage and hydrocephalus. Following an external ventricular drain for the hydrocephalus, a CT angiography revealed a dissection of the left vertebral artery extending into vertebro-basilar junction necessitating a bypass between left occipital artery to left posterior inferior cerebellar artery. He had a posterior fossa Craniectomy, C1 laminectomy and coiling off, of the left vertebral artery. Postprocedure course was prolonged but uneventful with complete recovery and normal renal function 18 months postpresentation. AS, a disease caused by abnormalities in the synthesis of type IV collagen, can cause aneurysms with severe and permanent neurological sequalae. We present a case of AS with intracranial arterial dissection with potential life-threatening consequences and discuss the genetic and molecular basis of AS along with review of the relevant literature.

Association of vascular endothelial growth factor B (VEGFВ) gene polymorphisms with intracranial aneurysms

Intracranial aneurysm (IA) is a complex disease resulting in subarachnoid hemorrhage (SAH) due to a rupture. The average worldwide prevalence of this disease is about 2–5 %, with 50 % of them ending in death or neurological disorders of varying severity, with a high probability of recurrence of hemorrhage during the frst half of the year after rupture. Subarachnoid hemorrhage is annually registered in at least 18 thousand people in Russia. Associations of polymorphic variantsrs594942andrs11603042of theVEGFBgene in intracranial aneurysm development in the Volga-Ural region of the Russian Federation with the presence of the symptom complex of undifferentiated connective tissue dysplasia (uDST) and arterial hypertension (AH) were investigated. TheC* allelers594942andrs11603042of theVEGFBgene is a marker of an increased risk of IA as a whole (p= 0.025; χ2 = 5.052; OR = 1.32) in women as a whole (p= 0.001; χ2 = 10.124; OR = 1.70) and in comorbid state with uDCT (p= 0.002; χ2 = 9.501; OR = 2.34) and AG (p= 0.006; χ2 = 7.385; OR = 2.109). We found that the genotype *C*Cof locusrs594942of theVEGFBgene is a marker of an increased risk of intracranial aneurysm in general (p= 0.017; χ2 = 5.702; OR = 1.49) and among women in general (p= 0.0005; χ2 = 12.078; OR = 2.25) and with the symptomatic complex uCTD (p= 0.007; χ2 = 7.173; OR = 2.67) and AH (p= 0.010; χ2 = 6.471; OR = 2.51). We have obtained new results on the role of polymorphic variants of theVEGFBgene in the formation of intracranial aneurysm, taking into account the presence of the symptom complex uDCT and AH among the residents of the Volga-Ural region of Russia. A burdened comorbid background and the presence of undifferentiated connective tissue dysplasia and arterial hypertension can contribute to an increased risk of intracranial aneurysm, as evidenced by the results of our study.

Modeling of Saccular Aneurysm Growth in a Human Middle Cerebral Artery

Saccular aneurysm growth in a human middle cerebral artery is modeled. The aneurysm growth model was presented in a companion paper by Kroon and Holzapfel (“A Model for Saccular Cerebral Aneurysm Growth by Collagen Fibre Remodelling,” J. Theor. Biol., in press) and was assessed there for axisymmetric growth. The aneurysm growth model is now evaluated for a more realistic setting. The middle cerebral artery is modeled as a two-layered cylinder, where the layers correspond to the media and the adventitia. An instant loss of the media in a region of the artery wall initiates the growth of the saccular aneurysm. The aneurysm wall is assumed to be a development of the adventitia of the original healthy artery, and collagen is assumed to be the only load-bearing constituent in the adventitia and in the aneurysm wall. The collagen is organized in a number of distinct layers where fibers in a specific layer are perfectly aligned in a certain fiber direction. The production of new collagen is taken to depend on the stretching of the aneurysm wall, and the continuous remodeling of the collagen fibers is responsible for the aneurysm growth. The general behavior of the growth model is investigated and also the influence of the structural organization of the collagen fabric. The analysis underlines the fact that the material behavior of aneurysmal tissue cannot be expected to be isotropic. The model predictions agree well with clinical and experimental results, for example, in terms of aneurysm size and shape, wall stress levels, and wall thickness.

A novel arterial pouch model of saccular aneurysm by concomitant elastase and collagenase digestion

BACKGROUND

An ideal aneurysm model of cerebral aneurysm is of great importance for studying the pathogenesis of the lesion and testing new techniques for diagnosis and treatment. Several models have been created in rabbits and are now widely used in experimental studies; however, every model has certain intrinsic limitations. Here we report the development of a novel saccular aneurysm model in rabbits using an arterial pouch that is subject to in vitro pre-digestion with combined elastase and collagenase.

METHODS

A segment of right common carotid artery (CCA) was dissected out and treated with elastase (60 U/ml, 20 min) followed by type I collagenase (1 mg/ml, 15 min) in vitro. The graft was anastomosed to an arterial arch built with the left CCA and the remaining right CCA, while the other end of the graft was ligated. The dimension and tissue structure of the pouch were analysed immediately, 2 or 8 weeks after operation.

FINDINGS

Ten terminal aneurysms were produced. The gross morphology of the aneurysm resembles the human cerebral terminal aneurysms. We have observed the following pathological changes: (1) growth of the aneurysm (mean diameter increased from (2.0+/-0.1) to (3.2+/-0.3) mm at 2 weeks, P<0.001, n=7-10); (2) thinning of the aneurysmal wall (the mean wall thickness decreased to 44% at 2 weeks), which was accompanied by significant losses of elastic fibres, collagen and the cellular component; and (3) spontaneous rupture (3 out of 9, one aneurysm ruptured 24 h after operation with the other two at 2 and 4 weeks respectively).

CONCLUSION

This rabbit arterial pouch model mimics human cerebral aneurysms in relation to morphology and histology. In particular, this model exhibited an increased tendency of spontaneous rupture.

Genetics Of Intracranial Aneurysms

Despite advances in the treatment of intracranial aneurysms (IA) in recent years, the overall outcome of patients with aneurysmal subarachnoid hemorrhage has shown only modest improvement. Given this poor prognosis, diagnosis of IA before rupture is of paramount importance. Currently, there are no reliable methods other than screening imaging studies of high-risk individuals to diagnose asymptomatic patients. Multiple levels of evidence suggest that environmental factors acting in concert with genetic susceptibilities lead to the formation, growth, and rupture of aneurysms in these patients. Epidemiological studies have already identified aneurysm-specific risk factors such as size and location, as well as patient-specific risk factors, such as age, sex, and presence of medical comorbidities, such as hypertension. In addition, exposure to certain environmental factors such as smoking have been shown to be important in the formation of IA. Furthermore, substantial evidence proves that certain loci contribute genetically to IA pathogenesis. Genome-wide linkage studies using relative pairs or rare families that are affected with the Mendelian forms of IA have already shown genetic heterogeneity of IA, suggesting that multiple genes, alone or in combination, are important in the disease pathophysiology. The linkage results, along with association studies, will ultimately lead to the identification of IA susceptibility genes. Identification of the genes important in IA pathogenesis will not only provide novel insights into the primary determinants of IA, but will also result in new opportunities for early diagnosis in the preclinical setting. Ultimately, novel therapeutic strategies based on biology will be developed, which will target these newly elucidated genetic susceptibilities.

Ruptured Cerebral Artery Aneurysm and Bacterial Meningitis in a Man With Osteogenesis Imperfecta

This report describes a 38-year-old man with osteogenesis imperfecta who died of a ruptured cerebral artery aneurysm and bacterial meningitis. He had multiple long bone fractures in the past, and approximately 4 months before death, he had surgery to relieve symptoms of basilar impression. The surgery was complicated by a postoperative wound infection. For the next 4 months, he had intermittent headaches and vomiting. He was found dead in his bed at home. At autopsy, he had a ruptured anterior communicating artery aneurysm and bacterial meningitis. Cerebrospinal fluid and blood cultures had growth of Staphylococcus aureus. Osteogenesis imperfecta is a disorder of type I collagen. Type I collagen is present in many tissues, including blood vessels. The etiology of cerebral artery aneurysm formation is multifactorial. Some patients with cerebral artery aneurysms have been shown to have abnormalities in type III collagen. There has not been a reported relationship made between abnormalities in type I collagen and aneurysms. Meningitis can also result in cerebral artery aneurysms, but they are usually due to Aspergillus or Mycobacterium species. The case we report is unique; cerebral artery aneurysm formation may have been due to osteogenesis imperfecta and/or bacterial meningitis.

Expression of structural proteins and angiogenic factors in normal arterial and unruptured and ruptured aneurysm walls

OBJECTIVE

To identify differences in the expression of certain structural proteins and angiogenic growth factors in vessel tissues that represent different phases of the process of intracranial aneurysm formation and rupture: normal vessel wall, intact (unruptured) aneurysm wall, and ruptured vessel wall.

METHODS

The novel study design involved 10 pairs of specimens (ruptured and unruptured aneurysm wall) obtained perioperatively during clipping operations in 10 patients with multiple aneurysms. All surgeries were performed within 5 days of subarachnoid hemorrhage. As controls, five circle of Willis specimens were obtained from five cadavers. Sections of each of the 25 specimens were separately immunostained for five structural proteins (collagen Types III and IV, alpha-smooth muscle actin, fibronectin, and laminin) and three angiogenic factors (vascular endothelial growth factor, basic fibroblast growth factor, and transforming growth factor-alpha). Levels of expression for each protein and factor were graded, and the average grades for each tissue group were recorded and compared.

RESULTS

Among the structural proteins studied, fibronectin specifically is densely expressed in ruptured aneurysms, which is graded as 2.0. However, its expression is less prominent both in nonaneurysmal vessel wall (Grade 1.0) and unruptured aneurysm vessel wall (Grade 1.1). Contrary to fibronectin, laminin is more intensely and regularly expressed in normal vessel wall (Grade 2.7) than in ruptured (Grade 1.1) and unruptured (Grade 1.0) aneurysmal specimens. Among the angiogenic growth factors studied, transforming growth factor-alpha shows a peculiar grading of staining, different from the other two angiogenic factors examined, so that it is more highly expressed in normal circle of Willis specimens (Grade 2.1) than in unruptured and ruptured aneurysm walls, graded as 0.5 and 0.6, respectively.

CONCLUSION

Normal vessel wall, unruptured aneurysm wall, and ruptured aneurysm wall exhibit different levels and patterns of expression for the structural proteins and regulator growth factors investigated. If one accepts the premise that immunohistochemical study has its inherent methodological problems, these results suggest that the biological mediators of aneurysm formation in a vessel wall differ from those of the biological mediators of aneurysm rupture. There was a novel finding related to fibronectin and laminin: the results indicated that a rise in the fibronectin-to-laminin ratio in an unruptured aneurysm wall may contribute to rupture. A drop in transforming growth factor-alpha expression in a vessel wall may also contribute to aneurysm formation.

Deficiencies in estrogen-mediated regulation of cerebrovascular homeostasis may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in menopausal and postmenopausal women

Despite the catastrophic consequence of ruptured intracranial aneurysms, very little is understood regarding their pathogenesis, and there are no reliable predictive markers for identifying at-risk individuals. Few studies have addressed the molecular pathological basis and mechanisms of intracranial aneurysm formation, growth, and rupture. The pathogenesis and rupture of cerebral aneurysms have been associated with inflammatory processes, and these have been implicated in the digestion and breakdown of vascular wall matrix. Epidemiological data indicate that the risk of cerebral aneurysm pathogenesis and rupture in women rises during and after menopause as compared to premenopausal women, and has been attributed to hormonal factors. Moreover, experimental evidence supports a role for estrogen in the modulation of each phase of the inflammatory response implicated in cerebral aneurysm pathogenesis and rupture. While the risk of aneurysm rupture in men also increases with age, this increased risk has been attributed to other recognized risk factors including cigarette smoking, use of alcohol, and history of hypertension, all of which are more common in men than women. We hypothesize, therefore, that decreases in both circulating estrogen levels and cerebrovascular estrogen receptor density may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in women during and after menopause. To test our hypothesis, experiments are needed to identify genes regulated by estrogen and to evaluate gene expression and intracellular mechanisms in cells/tissues exposed to varying concentrations and duration of treatment with estrogen, metabolites of estrogen, and selective estrogen receptor modulators (SERMs). Furthermore, it is not likely that the regulation of cerebrovascular homeostasis is due to the actions of estrogen alone, but rather the interplay of estrogen and other hormones and their associated receptor expression. The potential interactions of these hormones in the maintenance of normal cerebrovascular tone need to be elucidated. Additional studies are needed to define the role that estrogen and other sex hormones may play in the cerebrovascular circulation and the pathogenesis and rupture of cerebral aneurysms. Efforts directed at understanding the basic pathophysiological mechanisms of aneurysm pathogenesis and rupture promise to yield dividends that may have important therapeutic and clinical implications. The development of non-invasive tools such as molecular MRI for the detection of specific cells, molecular markers, and tissues may facilitate early diagnosis of initial pathophysiological changes that are undetectable by clinical examination or other diagnostic tools, and can also be used to evaluate the state of activity of cerebral aneurysm pathogenesis before, during, and after treatment.

Corticosteroid use and risk of aneurysmal subarachnoid haemorrhage

OBJECTIVES

Corticosteroids can induce hypertension and inhibit collagen synthesis in the blood vessel wall. Deficiencies in collagen have been found in intracranial aneurysms. Therefore use of corticosteroids could be a risk factor for intracranial aneurysms and aneurysmal subarachnoid haemorrhage (SAH). We investigated the relationship between the systemic use of corticosteroids in the past and the occurrence of aneurysmal SAH.

METHODS

We compared the systemic use of corticosteroids (oral or intravenous) in the past between a consecutive series of 1158 patients with aneurysmal SAH and a control group consisting of 1019 patients diagnosed with a primary central nervous system (CNS) tumour. We discriminated between definite use of corticosteroids defined as use mentioned in the medical record and possible use defined as note in the medical record of a disease that may be treated with corticosteroids. We calculated odds ratios (OR) with corresponding 95% confidence intervals (CI) and adjusted for age and sex by means of logistic regression analyses.

RESULTS

Twenty (1.7%, 95% CI 1.1-2.7) of the SAH patients and eight (0.8%, 95% CI 0.3-1.5) of the controls had used systemic corticosteroids (OR: 2.22; 95% CI 0.97-5.05; p-value 0.058; adjusted OR 2.23; 95 % CI 0.97-5.15; p-value 0.059). For definite plus possible use the OR was 1.67 (95% CI 1.09-2.54; p-value 0.016) and the adjusted OR 1.52 (95% CI 0.99-2.33; p-value 0.055).

CONCLUSIONS

Patients with aneurysmal SAH more often have used systemic corticosteroids in the past than controls. This may suggest that the use of corticosteroids is a risk factor for aneurysmal SAH.

Matrix metalloproteinases in cerebrovascular diseases

Matrix metalloproteinases are important factors for tissue remodelling and are activated during several physiological and pathological conditions, including cerebrovascular diseases. We give an overview of the structure, production and physiological effects of these widely distributed proteases and describe the genetic background and regulation pathways. In particular, we discuss the role of matrix metalloproteinases in vascular remodelling concerning ischaemic stroke, brain haemorrhage, vascular dementia, carotid artery plaques and cerebral aneurysms.

Association of Polymorphisms and Haplotypes in the Elastin Gene in Dutch Patients With Sporadic Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

A locus containing the elastin gene has been linked to familial intracranial aneurysms in 2 distinct populations. We investigated the association of single-nucleotide polymorphisms (SNPs) and haplotypes of SNPs in the elastin gene with the occurrence of subarachnoid hemorrhage (SAH) from sporadic aneurysms in the Netherlands.

METHODS

We genotyped 167 SAH patients and 167 matching controls for 18 exonic and intronic SNPs in the elastin gene. A Bonferroni correction was applied for multiple comparisons with all novel associations, with a correction factor derived from the number of SNPs tested (P value after Bonferroni correction [P(corr)]).

RESULTS

SAH was statistically significant associated with an SNP in exon 22 of the elastin gene (minor allele frequency was 0.000 in patients and 0.028 in controls; odds ratio [OR], 0.0; 95% CI, 0.0 to 0.7; P=0.004; P(corr)=0.05) and possibly with an SNP in intron 5 (minor allele frequency was 0.062 in patients and 0.128 in controls; OR, 0.5; 95% CI, 0.2 to 0.8; P=0.007; P(corr)=0.08). Haplotypes of intron 5/exon 22 (P(corr)=0.002), intron 4/exon 22 (P(corr)=0.02), and intron 4/intron 5/exon 22 (P=9.0x10(-9)) were also associated with aneurysmal SAH.

CONCLUSIONS

Variants and haplotypes within the elastin gene are associated with the risk of sporadic SAH in Dutch patients. Gradual increase of statistical power with the inclusion of 2 or 3 SNPs in the studied haplotypes supports the validity of our conclusion that the elastin gene is a susceptibility locus for SAH.

Altered Arterial Homeostasis and Cerebral Aneurysms: A Review of the Literature and Justification for a Search of Molecular Biomarkers

DESPITE THE CATASTROPHIC consequence of ruptured intracranial aneurysms, very little is understood regarding their pathogenesis, and there are no reliable predictive markers for identifying at-risk individuals. Given that intracranial aneurysms have a strong but complex genetic component and well-characterized modifiable risk factors, it seems likely that the most valuable approach to developing minimally invasive diagnostic and prognostic tools will involve a multifactorial model that includes both genetic and environmental risk factors. Unfortunately, the genetic basis of intracranial aneurysms is poorly described, and reports describing the association of nonrandom deoxyribonucleic acid sequence variation with intracranial aneurysms have been limited to a handful of ad hoc studies that have focused on a variety of markers in small populations. One reason for this lack of coordinated analysis of the genetic basis of intracranial aneurysms is that the molecular pathogenesis and pathobiological characteristics of the disease are poorly described, so candidate marker selection has been problematic. Few studies have addressed the molecular pathological basis of intracranial aneurysms or the possible mechanisms of intracranial aneurysm formation. In this regard, candidate gene selection strategies have relied almost exclusively on limited knowledge of monogenic disorders such as Ehlers-Danlos syndrome and Marfan's syndrome, in which intracranial aneurysm is a feature of a spectrum of syndromic phenotypes. Without exception, these approaches have not affected the clinical identification and/or management of intracranial aneurysms significantly. Therefore, it is imperative that coordinated large-scale efforts in genetics, molecular biology, and genetic epidemiology are implemented to overcome these obstacles and drive developments in the field. In this review, we summarize the current screening modalities for intracranial aneurysms, review the current state of understanding relating to the genetic basis of intracranial aneurysms, and suggest a broader theory of aneurysm pathogenesis to form the foundation of a coordinated molecular search for biological markers that may be associated with aneurysm formation and rupture.

Identical cerebral aneurysms in siblings: report of two families

Two pairs of sisters with identical cerebral aneurysms are reported. In the first family, a sibship of three, the two female members presented with subarachnoid haemorrhages from identical, left internal carotid artery bifurcation aneurysms. The subarachnoid haemorrhage occurred in one of the sisters at the age of 20 and at the age of 50 in the other. The remaining healthy sibling, a 40-year-old male, underwent elective cerebral angiography, which was normal. The other sibship, two 48-year-old female identical twins, had identical right middle cerebral artery aneurysms. The first twin became symptomatic after subarachnoid haemorrhage. The aneurysm in her identical twin was identified by screening angiography. There were no verified subarachnoid haemorrhages among the parents and grandparents in either family. No systemic anomalies were identified and collagen type 3 deficiencies were excluded. The identical location of these familial aneurysms, particularly in view of the relatively rare location in the first family, suggests that local factors in the developing vascular tree may play a role in the pathogenesis of saccular aneurysms in addition to systemic anomalies affecting the general structure of cerebral vascular walls.

Molecular pathogenesis of subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) results from leakage of blood into the subarachnoid space and carries high morbidity and mortality. However, there is limited understanding to date, of the risk factors, cellular, intermediate biochemical and genetic traits predisposing to SAH. Nevertheless, in conjunction with improved methods of diagnostic imaging and less invasive approaches to preventing aneurysmal rupture, there may be utility in gaining a better understanding of the pathogenesis and in identifying pre-disease markers. Additionally, it is not impossible that drugs of value (e.g. matrix or endothelial modifiers) could become available. Several different clinical subtypes can be recognised, distinguished by arterial or venous involvement, presence of unruptured arterial aneurysms, and apparently "sporadic" and "familial" occurrences. Epidemiological risk factors include alcohol consumption and smoking: hypertension is a risk factor for rupture. About 10% seem to reflect strong family history and this subset may be particularly illuminating with respect to the molecular pathogenesis. Haemodynamic stress and poor vascular structure may be the main mechanisms of pathogenesis. The epidemiological and statistical evidence for familial megaphenic genes and modifier genes is reviewed. This review focuses on the pathogenesis, as opposed to inflammatory response to SAH. It sets in context the roles of specific genes and their protein products, such as polycystin (PKD1), fibrillin (FBN1), collagen III (COL3A1), elastin (ELN), collagen IV, protease inhibitor or alpha1-antitrypsin (PI) and proteases. These considerations illustrate the shortfalls in current knowledge, the needs of future biochemical and cellular research and their potential implications for future prevention of this often fatal condition.

Elastin polymorphism haplotype and intracranial aneurysms are not associated in Central Europe

BACKGROUND AND PURPOSE

The occurrence of intracranial aneurysms and of aneurysmal subarachnoid hemorrhage are influenced by genetic factors. Recent genomic studies in Japan have defined 3 chromosomal loci and 1 haplotype of elastin polymorphisms as important risk factors, both for affected sib pairs and sporadic patients.

METHODS

We have genotyped 2 single nucleotide polymorphisms in the elastin gene and evaluated their allelic association with intracranial aneurysm in a Central European sample of 30 familial and 175 sporadic patients and 235 population controls.

RESULTS

We found no allelic association between this elastin polymorphism haplotype and intracranial aneurysm.

CONCLUSIONS

Our data probably reflect increased genetic heterogeneity of intracranial aneurysm in Europe compared with Japan.

Genetics of intracranial aneurysm

Subarachnoid hemorrhage (SAH) secondary to ruptured saccular intracranial aneurysm (IA) is a complex trait, with both genetic and environmental risk factors playing an important part. The 30-day mortality rate of patients with SAH is 40% to 44%, with many survivors suffering from major disability. Because most of the mortality after SAH is caused by rapid and massive brain injury from the initial bleeding, primary prevention of aneurysm formation and rupture is of paramount importance. This article reviews the evidence supporting a genetic predisposition to SAH from saccular IA, the conditions commonly associated with saccular IA, and the search for genetic risk factors.

Ruptured intracranial aneurysm in an adolescent with Alport's syndrome--a new expression of type IV collagenopathy: case report

BACKGROUND

Aneurysmal subarachnoid hemorrhage is uncommon in the pediatric and adolescent age groups. Collagenopathies, particularly of collagen type III and IV, have been recognized in the pathogenesis of intracranial (i.c.) aneurysms in recent studies of cerebrovascular immunoreactivity and the molecular architecture of the walls of cerebral blood vessels. Alport's syndrome is a genetic disease characterized by imperfect synthesis of type IV collagen leading to sensorineural hearing loss and hematuria. The hematuria results from an abnormal synthesis of the type IV collagen of the glomerular basement membrane.

CASE DESCRIPTION

After a motor vehicle accident, this 14-year-old male driver presented with diffuse subarachnoid hemorrhage confirmed by computerized tomography. Subsequent cerebral angiography revealed a left carotid artery bifurcation aneurysm. A retrospective review of the patient's history disclosed renal biopsy-proven hereditary Alport's syndrome. The patient underwent left pterional craniotomy and clipping of the aneurysm, which had clearly ruptured.

CONCLUSIONS

The authors present the first clinical observation of a ruptured cerebral aneurysm in an adolescent male with Alport's syndrome. In this case the type IV collagenopathy of Alport's syndrome may have contributed to the genesis of this adolescent's aneurysm. Intracranial aneurysms may be more common in the population of collagenopathies than previously suspected and non-invasive screening may be appropriate.

Intracranial aneurysms and arterial hypertension: a review and hypothesis

BACKGROUND

Intracranial aneurysms and systemic arterial hypertension coexist in a high percentage of patients. The relationship between intracranial aneurysms and hypertension is poorly defined.

METHODS

Therefore, we reviewed the role of hypertension in the pathogenesis of saccular aneurysms as previously reported in clinical, experimental, and autopsy studies.

RESULTS

Among 24 relevant clinical and/or autopsy studies, the mean incidence of pre-existing hypertension was 43.5% in aneurysm patients compared to 24.4% in the normal population. Although definitive evidence is lacking, data from multiple types of investigations indicate that systemic arterial hypertension creates a greater risk for the development of intracranial aneurysms than previously believed. The underlying pathophysiological mechanism(s) are also poorly defined.

CONCLUSIONS

We propose a unifying hypothesis: Endothelial injury, occlusion of the vasa vasorum, and disruption of the synthesis of collagen and elastin are likely the most important factors in initiating the development of aneurysms. Chronic hypertension potentially affects all of these factors. Consequently, chronic hypertension may cause intimal thickening, necrosis of the tunica media, changes in the compositional matrix, and degeneration of the internal elastic lamina to develop in the arterial wall. These structural changes could cause a focal weakening in the arterial wall with resultant bulging. This theory accounts for the high incidence of intracranial aneurysms in the absence of any known associated hereditary or connective-tissue disease. Nor does it exclude the possibility of other etiological factors. From the perspective of prevention, however, it offers clear opportunities for prophylaxis.

Experimental cerebral aneurysms in the female heterozygous Blotchy mouse

The Blotchy mouse is characterized by an X-linked inherited disorder of connective tissue synthesis. The susceptibility to aneurysm formation in the cerebral arteries of the circle of Willis was compared in female heterozygous 'Blotchy' and control mice subjected to unilateral carotid artery ligation either alone or associated with hypertension. Cerebral aneurysms developed only in hypertensive Blotchy mice (6/31 vs. 0/30 in hypertensive controls). Aneurysms of the aorta and its major branches occurred in normotensive mice only in the Blotchy group in which hypertension increased the incidence of mesenteric and coeliac aneurysms. A light microscopic study of interruptions of the internal elastic lamina (IIEL) showed that they developed in arteries of both Blotchy and control mice but to a greater extent in the Blotchy group where hypertension further increased their incidence. The IIEL incidence in the aortic arch varied in parallel to the occurrence of aneurysms in all the different arterial sites. Thus, in an apparently normally viable animal, the presence of a mutated gene which indirectly leads to defective elastin and collagen fibre synthesis, favours the formation of both peripheral and cerebral aneurysms. However, the development of cerebral aneurysms requires the addition of an increase in haemodynamic stress.

Type III collagen deficiency in saccular intracranial aneurysms. Defect in gene regulation?

BACKGROUND AND PURPOSE

We sought to determine whether there are mutations in the COL3A1 gene in patients with saccular intracranial aneurysms with a type III collagen deficiency and whether there is an association between a marker in the COL3A1 gene and saccular intracranial aneurysms. One of the heritable factors possibly involved in the pathogenesis of saccular intracranial aneurysms is a reduced production of type III collagen, demonstrated earlier by protein studies.

METHODS

We analyzed the type III collagen gene in a group of 41 consecutive patients with an intracranial aneurysm, of whom 6 patients had shown a reduced production of type III collagen in cultured diploid fibroblasts from a skin biopsy.

RESULTS

No mutations could be demonstrated in the COL3A1 gene, especially not in the globular N- and C-terminal regions. A null allele was excluded in 25 patients, including 1 patient with a decreased type III collagen production. No differences were found between 41 patients and 41 controls in allele frequencies of a DNA tandem repeat polymorphism located in the COL3A1 gene.

CONCLUSIONS

It is concluded that the COL3A1 gene is not directly involved in the pathogenesis of most of intracranial aneurysms. The reduced type III collagen production in cultured fibroblasts found in some patients with an intracranial aneurysm is not explained by the present study and needs further exploration.

[Cervical artery dissection: recent data physiopathologic hypotheses]

INTRODUCTION

Cervicocranial arterial dissection is a major cause of cerebral infarction in young subjects. Traumatic and infectious factors are frequently suspected to be at the origin of cervicocranial artery dissection. However, they are usually too minor or too common to explain the vessel wall split-off. Underlying arteriopathy predisposing to dissections is therefore often suspected.

CURRENT KNOWLEDGE AND KEY POINTS

The hypothesis of an underlying arteriopathy is based in certain cases on either the discovery of hereditary connective tissue disorders (or secondary signs of these diseases) or their frequent association with vascular and cardiac morphological abnormalities, thus suggesting extracellular matrix abnormalities. Current histological and biochemical data do not suggest the existence of a unique form of the disease but rather indicate the presence of various matrix abnormalities that could involve one of the fibrillar components or its enzymatic regulation.

FUTURE PROSPECTS AND PROJECTS

Classification of dissections according to the various vascular wall alterations would therefore permit to better define recurrence and familial risks and to improve overall management of the patients.

Vascular extracellular matrix remodeling in cerebral aneurysms

OBJECT

The occurrence of cerebral aneurysms has been linked to alterations in the extracellular matrix and to matrix-degrading proteases. The purpose of the present study was to determine whether active extracellular matrix remodeling occurs within cerebral aneurysms.

METHODS

Aneurysm tissue was collected from 23 patients (two of whom had a ruptured aneurysm and 21 of whom had an unruptured aneurysm) and compared with 11 control basilar arteries harvested at autopsy. Active proteinases capable of gelatin lysis were identified by performing in situ zymography in the presence and absence of a metalloproteinase inhibitor (ethylenediamine tetraacetic acid) and a serine proteinase inhibitor (phenylmethylsulfonyl fluoride). Immunohistochemical analysis was used to localize plasmin, tissue-type (t)-plasminogen activator (PA), urokinase-type (u)-PA, membranetype (MT1)-matrix metalloproteinase (MMP), MMP-2, MMP-9, and tenascin. Focal areas of gelatin lysis occurred in most cerebral aneurysm tissue samples (17 of 21), but rarely in control arteries (two of 11) (p = 0.002). Both serine proteinases and MMPs contributed to gelatin lysis; however, the MMPs were the predominant enzyme family. Plasmin (p = 0.04) and MT1-MMP (p = 0.04) were expressed in the aneurysm tissue but were unusual in control tissue. The MMP-2 was also expressed more commonly in aneurysm than in control tissue (p = 0.07). The MMP-9 and t-PA were expressed in both groups; however, different staining patterns were observed between aneurysm and control tissue. Tenascin staining was commonly present in both groups, whereas u-PA staining was rarely present.

CONCLUSIONS

Aneurysm tissue demonstrates increased proteolytic activity capable of lysing gelatin and increased expression of plasmin, MT1-MMP, and MMP-2 when compared with normal cerebral arteries. This activity may contribute to focal degradation of the vascular extracellular matrix and may be related to aneurysm formation and growth.

Collagen cross-linkage, elastolytic and collagenolytic activities in cerebral aneurysms: a preliminary investigation

The pathogenesis of aneurysms formation and rupture is not clearly understood and is undoubtedly a multifactorial event. It is generally accepted that the aneurysm arises from an interaction between structural weakness of arterial wall and hemodynamic factors. Previous studies suggested the possible role of collagenolytic and elastolytic activities in aneurysm development, leading to extracellular matrix alteration. The content of collagen 3-hydroxypiridinium cross-links and elastase and collagenase activities were measured in 12 samples of intracranial aneurysms and in control specimens obtained from temporal superficial arteries and from autoptic samples of Willis Circle. Collagen content is significantly lower in aneurysm than in autoptic control samples (p < 0.01). The total amount of cross-links is significantly lower in ruptured aneurysms than in unruptured and autoptic controls (p < 0.01). Collagenase and elastase activities are significantly increased in ruptured cerebral aneurysms versus unruptured aneurysms (p < 0.01). Linear regression shows that an inverse relationship exists between cross-links content and both elastolytic (p = 0.0032) and collagenolytic (p < 0.001) activities in aneurysmal samples. Multiple regression shows that collagenase has a more important statistic impact (p = 0.027) than elastase (p = 0.08). The results of the study supports the hypothesis that an imbalance of protease-antiprotease homeostasis with elevated collagenolytic and elastolytic activities may represent the predisposing condition leading to aneurysms rupture through collagen depauperation and reduced cross-linkage of collagen fibres.

Ehlers-Danlos syndrome and type III collagen abnormalities: a variable clinical spectrum

Ehlers Danlos syndrome (EDS) comprises ten types. EDS IV is the most severe type because of its often lethal complications, such as arterial rupture. EDS IV is caused by an abnormality of collagen type III as a result of mutations in the corresponding gene COL3A1. A collagen type III abnormality is also seen in patients with EDS without the classical severe EDS IV phenotype. We report on 11 patients with type III collagen abnormality and normal collagen V in whom clinically EDS II, III, and IV were diagnosed. There is no correlation between the type of collagen III anomaly and the clinical phenotype. It is concluded that type III collagen abnormality may lead to a phenotypic spectrum and that it does not predict the severity and course of the disease.

Detection of type III collagen fragments in specimens of abdominal aortic aneurysms

The purpose of this study was to analyze the collagens in aortic aneurysm walls and to investigate the mechanism of the formation of calcified abdominal aortic aneurysms (AAAs). Collagens were extracted from human aneurysmal aortic walls obtained during surgery, and from human nonaneurysmal aortic walls obtained at autopsy, using pepsin-acetic acid digestion. Electrophoresis and immunoblotting were performed. Type III collagen was found to be reduced in the arteriosclerotic aneurysmal aortic walls. The alpha1 chain of type II collagen/alpha1 chain of type I collagen ratio was 0.35+/-0.11 in the aortic aneurysms and 0.68+/-0.11 in the nonaneurysmal aortic walls (P=0.0111). All the calcified aneurysms were associated with type III collagen fragments having molecular mass of approximately 70 kDa and 30 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Thus, we concluded that AAAs with calcification may be caused by an abnormal degradation of type III collagen.

Genetics of stroke--a review

Evidence from twin and family shows that genetic factors contribute to the risk of stroke and that their role may be at least as important in stroke as in coronary heart disease. Additional support for the significance of genetic factors comes from other findings such as epidemiological data showing phenotypic heterogeneity of stroke, genetic influence on many of the risk factors for stroke, and racial and geographic differences in morbidity and mortality in stroke victims. Yet, apart from the reported associations of a small number of cases with Mendelian cerebrovascular diseases, only a few studies have directly investigated gene markers or molecular genetics of stroke. This review presents the existing evidence on the genetic background of stroke and discusses results from the genetic studies of stroke published to date.

Rapid saccular aneurysm induction by elastase application in vitro

OBJECTIVE

To develop a new saccular aneurysm model in vitro using elastase to study aneurysm initiation, growth, and rupture and to create a new in vivo aneurysm model to test endovascular therapies.

METHODS

Seventeen common carotid arteries excised from freshly killed pigs and sheep were treated with seven different methods of elastase delivery. The arteries were mounted in a saline-filled flow chamber. They received pulsatile flow for 48 hours, or until the resulting aneurysms ruptured. Changes were continuously monitored with video camera recordings and validated with histological sections.

RESULTS

All eight arteries treated topically, either on the intimal or on the adventitial surface, with elastase concentrations greater than 1 U/mm2, developed saccular aneurysms; five of them ruptured within 48 hours. All four arteries treated with surface concentrations of 0.1 U/mm2 via microcatheter infusion into the lumen developed fusiform aneurysms. None of the arteries that received surface concentrations less than 0.1 U/mm2 developed aneurysms. Histological sections revealed a reduced number of cellular element in a stretched collagen matrix at the dome of the saccular aneurysms.

CONCLUSION

After empirically testing several methods of elastase delivery, we were able to induce saccular, bifurcation-type aneurysms in animal arterial specimens. These aneurysms are histologically similar and more authentic than surgical models. The procedure is easy and reproducible. Our results suggest a possible enzymatic role in aneurysm formation and highlight the dramatic effects of selective arterial elastic damage. Also, the rapid growth of our experimental aneurysms may reflect the speed of the natural process.

Genetic susceptibility to experimental cerebral aneurysm formation in the rat

BACKGROUND AND PURPOSE

The susceptibility to experimental cerebral aneurysm formation in arteries of the circle of Willis was studied in four strains of rats presenting different susceptibilities to the spontaneous rupture of the internal elastic lamina in extracerebral arteries: Brown-Norway (BN) > Wistar > Long-Evans (LE) > LOU.

METHODS

Rats (150 g body weight) of the four strains were subjected to hypertension and a change in local cerebral blood flow by ligation of one common carotid artery for about 7 months. Six-month-old BN and LE rats were subjected to carotid ligation only for 11 to 13.5 months and treated or not (from 3 to 7 months of age) with an inhibitor of connective tissue fiber maturation, beta-aminopropionitrile (BAPN).

RESULTS

Aneurysmal structures (AS) occurred mainly in the anterior cerebral/anterior communicating arterial complex and proximal part of the posterior artery. In hypertensive rats, the AS incidence was LE, 56%; Wistar, 33%; BN, 17%; and LOU, 11%. When normotensive and subjected to carotid ligation only, LE rats showed an even greater susceptibility to AS formation (86%) than BN (7%). BAPN treatment did not influence AS formation: LE (60%) versus BN (8%).

CONCLUSIONS

These results suggest that genetic factors are involved in cerebral aneurysm formation in the rat. The susceptibility of the internal elastic lamina of extracerebral arteries to spontaneous rupture does not appear to be a determinant genetic trait in the propensity to develop aneurysms in arteries of the circle of Willis. The comparison of these different rat strains may be very useful for studying factors contributing to cerebral aneurysm pathogenesis.

Gelatinase activity and the occurrence of cerebral aneurysms

BACKGROUND AND PURPOSE

Cerebral aneurysms are associated with decreased arterial collagen content; however, whether this deficiency results from impaired collagen synthesis or enhanced collagen degradation is unknown. This study tested the hypothesis that enhanced collagen degradation, not impaired collagen synthesis, is associated with the occurrence of cerebral aneurysms.

METHODS

Cultured skin fibroblasts and serum samples were studied in patients with angiographic evidence of aneurysm (n = 31) and control subjects (n = 14). Transcription of the type III collagen gene was assessed with the use of Northern blots prepared from RNA harvested from confluent cultured fibroblasts. Translation of type III collagen was assessed by Western blot analysis of proteins produced by cultured skin fibroblasts. Collagen metabolism was assessed by radioimmunoassay for type I (PICP) and type III (PIIINP) procollagen peptides in conditioned tissue culture media and serum. We assessed collagen degradation in serum and conditioned tissue culture media by evaluating gelatinase activity using quantitative zymography.

RESULTS

Type III collagen synthesis was the same in aneurysm and control patients. Neither the molecular weight nor the relative amount of type III collagen mRNA differed between aneurysm and control patient fibroblasts. Western blot analysis revealed no difference in the relative amount or molecular weight of procollagen III synthesized by aneurysm and control cells. Aneurysm patients had a threefold increase in native serum gelatinase activity compared with control subjects (P = .004). This increase occurred along with serum evidence of increased collagen metabolism. Serum levels of PICP (P = .03) and PIIINP (P = .02) were decreased in aneurysm patients. Elevated serum gelatinase activity and altered collagen metabolism could not be explained by enhanced secretion of gelatinase by cultured fibroblasts or altered net collagen synthesis by fibroblasts. High serum gelatinase activity was more common in men than in women (P = .04).

CONCLUSIONS

These findings are consistent with the hypothesis that accelerated enzymatic degradation of collagens and other structural proteins compromises the mechanical integrity of the cerebral vessel wall and leads to conditions that favor aneurysm formation.

Genetics of intracranial aneurysms

The etiology and pathogenesis of intracranial aneurysms are clearly multifactorial, with genetic factors playing an increasingly recognized role. Intracranial aneurysms have been associated with numerous heritable connective tissue disorders, which account for at least 5% of cases. Of these disorders, the most important are Ehlers-Danlos syndrome Type IV, Marfan's syndrome, neurofibromatosis Type 1, and autosomal dominant polycystic kidney disease; the association with intracranial aneurysms, however, has been firmly established only for polycystic kidney disease. Familial intracranial aneurysms are not rare but account for 7 to 20% of patients with aneurysmal subarachnoid hemorrhage and are generally not associated with any of the known heritable connective tissue disorders. First-degree relatives of patients with aneurysmal subarachnoid hemorrhage are at an approximately fourfold increased risk of suffering ruptured intracranial aneurysms, compared to the general population. Various possible modes of inheritance have been identified in families with intracranial aneurysms, suggesting genetic heterogeneity. Although the benefits have never been quantified, screening for asymptomatic intracranial aneurysms should be considered in families with two or more affected members. The yield of such a screening program may approximate 10%. Although it is unlikely that there is a single gene with major effect, much effort is currently being directed at locating intracranial aneurysm genes.

Genotypic variations of type III collagen in patients with cerebral aneurysms

It has been hypothesized that either qualitative or quantitative abnormalities in type III collagen may be involved in the pathogenesis of cerebral aneurysms. The current study investigated allele frequencies for the type III collagen gene in patients with cerebral aneurysms. A diallelic Ava II polymorphism defined the type III collagen gene. The smaller of the two alleles was found in 11 of 19 aneurysm patients (58%) versus two of 15 controls (13%) (p = .006). The overall frequency of this allele was 0.34 in aneurysm patients versus 0.10 in controls (p = .011). This significant difference in allele frequency suggests that genotypic variations in the type III collagen gene may be etiologically related to aneurysm formation.

Immunohistochemical alterations of fibronectin during the formation and proliferative repair of experimental cerebral aneurysms in rats

BACKGROUND AND PURPOSE

To determine whether distributional changes of fibronectin, a factor promoting wound healing, occur during the formation and repair of cerebral saccular aneurysms, we performed immunohistochemical analyses in experimental aneurysms.

METHODS

Cerebral aneurysms were induced in rats by both the ligation of the unilateral common carotid artery and induced hypertension. Intimal proliferation in aneurysmal walls was induced by the ligation of the preserved common carotid artery 3 months after the first operation. The distribution of fibronectin was examined by immunohistochemistry in anterior cerebral artery-olfactory artery bifurcations under the following three conditions: normal bifurcations in control rats, early aneurysmal lesions during the aneurysm induction, and aneurysmal lesions with intimal proliferation. Furthermore, the immunohistochemical distributions of type I and IV collagens were examined to evaluate the specificity of fibronectin immunoreactivity.

RESULTS

In the normal bifurcations, fibronectin was positive in the subintimal space, the surrounding area of the medial smooth muscle cells, and the adventitial fibrous tissue. In early aneurysmal lesions, linear staining of fibronectin and type I and IV collagens in the subendothelial space disappeared with the loss of the internal elastic lamina. In the intimal proliferation of early aneurysmal lesions, fibronectin was strongly immunostained in the subendothelial space and diffusely immunostained in the widened extracellular space surrounding proliferated cells. In contrast, the stainings of type I and IV collagens were sparse or negative.

CONCLUSIONS

Although the present findings regarding dynamic changes of fibronectin distribution do not prove any causality in the process of aneurysm formation and repair, these immunohistochemical changes may constitute the crucial sequela of intimal endothelial damage and its subsequent recovery in cerebral aneurysms.

Elevated levels of lipoprotein (a) in association with cerebrovascular saccular aneurysmal disease

The relationship between cerebrovascular aneurysmal disease and atherosclerosis remains unclear. Elevated serum levels of lipoprotein (a) (Lp[a]), are an independent risk factor for atherosclerosis. We measured serum Lp(a) levels in 50 patients who had angiographically proven saccular aneurysmal disease and who were free of clinically significant atheromatous disease (as judged by their medical histories and the results of physical examination, electrocardiography, and carotid angiography). The Lp(a) serum levels in these patients were compared with the Lp(a) serum levels in a group of 42 normal healthy controls. Serum Lp(a) levels in the patients was 20.1 +/- 0.42 mg/dl (median +/- standard error); however, median serum Lp(a) in the control subjects was 10.8 +/- 0.47 mg/dl (P < 0.01). Among females, the difference in serum Lp(a) levels was significant; the levels were 22.2 +/- 0.6 for female patients (n = 29) and 9.5 +/- 0.53 in female control subjects (n = 26) (P < 0.005). The most significant difference (P < 0.002) was seen in females < 50 years old (14 patients, 10 control subjects). No significant differences were seen in the Lp(a) serum levels between 21 male patients and 16 male control subjects. Lp(a) levels above the threshold level (30 mg/dl) were found in 20 patients and 7 control subjects (chi 2 = 5.99, P < 0.02); 12 female patients and 3 female control subjects (chi 2 = 6.16, P < 0.02; 8 male patients and 4 male control subjects (this difference was not significant). These results indicate either that cerebrovascular aneurysmal disease and subclinical atherosclerosis are related or that Lp(a) is a risk factor for vasculopathies other than atheroma.

Serum elastase and alpha-1-antitrypsin levels in patients with ruptured and unruptured cerebral aneurysms

Despite advances in surgical treatment and postoperative care, subarachnoid hemorrhage from ruptured cerebral aneurysms remains a devastating event. Excellent surgical results in treating unruptured aneurysms suggest the utility of screening tests to identify high-risk individuals. Unfortunately, none of the known risk factors for subarachnoid hemorrhage correlates strongly enough with the illness to warrant widespread screening for occult aneurysms. Other disease entities suggest that protease-antiprotease imbalances contribute to somatic vessel wall degradation and aneurysm formation. Detection of similar imbalances in selected patients may identify a predisposition to cerebral aneurysm formation. Serum concentrations of elastase and alpha-1-antitrypsin (AAT), important proteolytic and antiproteolytic enzymes, were measured in a series of 19 patients with unruptured aneurysms, 41 patients with ruptured aneurysms, and 27 age-matched operative and nonoperative controls. The elastase:AAT ratio was nearly twice as high in patients with unruptured aneurysms as in operative controls (0.527 +/- 0.1 versus 0.285 +/- 0.06; P < 0.04). Elastase:AAT ratios in patients with ruptured aneurysms (subarachnoid hemorrhage < 48 h) were roughly twice those of controls (0.582 +/- 0.095; P < 0.01). There was no statistical difference between elastase:AAT ratios for patients with ruptured and unruptured aneurysms. Likewise, elastase-AAT values for operative controls and nonoperative volunteers were not significantly different. Differences in serum elastase:AAT ratios between patients with aneurysms and controls reflected differences in elastase concentration (99 +/- 56 micrograms/ml versus 67 +/- 56 micrograms/ml; P < 0.03), not in AAT levels (147 +/- 56 micrograms/ml versus 141 +/- 56 micrograms/ml; P < 0.72).(ABSTRACT TRUNCATED AT 250 WORDS)

Outcome in familial subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The outcome of subarachnoid hemorrhage in patients with familial occurrence of subarachnoid hemorrhage (familial SAH) is an important but neglected factor in balancing the risks of screening for asymptomatic aneurysms and repairing these in unaffected members of such families.

METHODS

We studied the outcome of familial SAH in a prospective, hospital-based series of patients with at least one first-degree relative with SAH and compared it with the outcome in a prospectively collected hospital series of patients selected for the absence of SAH in first- and second-degree relatives. Outcome was graded in three categories: independence, dependence, or death. Poor outcome was defined as death or dependence.

RESULTS

Of 29 patients with familial SAH, 52% had a poor outcome, whereas only 37% of 125 patients with sporadic SAH had a poor outcome. The crude relative risk for poor outcome in familial SAH was 1.4 (95% confidence interval [CI], 0.9 to 2.1; P = .14); the odds ratio adjusted for age and sex was 2.5 (95% CI, 1.0 to 6.0; P = .04). This risk is probably an underestimation due to our strict patient selection criteria.

CONCLUSIONS

Patients with familial SAH have a greater risk of poor outcome than patients with sporadic SAH. This adds to the factors in favor of screening unaffected first-degree relatives of patients with familial SAH.

Experimental saccular aneurysms. I. Review of surgically-constructed models and their laboratory applications

Experimental models of intracranial saccular aneurysms are a useful contribution to our basic understanding of these lesions. Currently, the commonest in use are those constructed surgically in laboratory animals. We review the numerous surgical techniques available since the 1950s, and the research applications and uses of experimental aneurysms. Further development and use of such models is greatly encouraged in future pathophysiological, hemodynamic, and therapeutic investigations of intracranial saccular aneurysms.

Seasonal fluctuation in the incidence of intracranial aneurysm rupture and its relationship to changing climatic conditions

Seasonal and climatic variations have been linked to the occurrence of some types of cerebrovascular disease; however, the conditions that lead to intracranial aneurysm rupture are not known. The purpose of the present study was to determine whether seasonal and climatic conditions are related to intracranial aneurysm rupture. Data provided by the Connecticut Health Information Management and Exchange were analyzed for all patients with a primary diagnosis of aneurysmal subarachnoid hemorrhage (SAH) for the fiscal years 1981, 1983, 1985, 1987, 1988, and 1989. Patient records were correlated with climatic conditions for the years 1981 to 1989 obtained from the National Climatic Data Center, National Oceanic and Atmospheric Administration, National Environmental Satellite Data, and Information Service. During the time periods studied, 1487 patients with a primary diagnosis of aneurysmal SAH were treated by reporting hospitals. Seasonal variation in the incidence of aneurysmal SAH and admission clustering were observed but differed significantly between men and women. Men showed a single large peak in late fall (Roger's r = 11.5, p < 0.005), whereas women had an annual peak occurring in late spring (Roger's r = 10.3, p < 0.01). Substantial climatic change occurred during the 72 hours prior to 10 of the 14 clusters of men who were admitted (p < 0.01, Yates' corrected chi-square 7.33, df = 1). In contrast, clusters of women admitted were not related to preceding climatic change (p > 0.25, Yates' corrected chi-square 0.06, df = 1). Hospital admissions for aneurysmal SAH display seasonal fluctuation, with women showing a different seasonal pattern from men. Changing climatic conditions precede aneurysm rupture in men but not in women, which suggests that weather is causally related to aneurysm rupture in men, and that factors that lead to aneurysm rupture in women may be different from those in men. These data do not explain why weather fronts or gradients are associated with aneurysm rupture in men.

Pathogenesis of abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm involves many factors acting over time. However, destruction of elastin in the aortic wall is a key event that shifts the load produced by blood pressure on to collagen. This is exacerbated in the presence of hypertension. Smoking and age are further important factors, as is the site; elastic lamellae are relatively less common in the abdominal aorta. Once the shielding effect of elastin is lost, further dilatation and rupture of the aorta depend on the physical properties of the collagen present.