Cerebral aneurysm - The Causes and Risk factors

Cerebral aneurysm is defined as a cerebrovascular disorder causes of the blood vessel to bulge or balloon out of the wall of a blood vessel as a result of the weaken of blood vessels and veins and occurred mostly at the bifurcations and branches of the large arteries located at the Circle of Willis.
Cause and Risk factors 
A. Causes 
Cerebral aneurysms develop as a result of the weaken of blood vessels and veins of which exhibit the risk of ruptured cerebral aneurysm. Aneurysms often occur mostly at the bifurcations and branches of the large arteries located at the Circle of Willis based of the brain.

B. Risk factors
1. Hypertension (significant risk factor for future SAH)
In the study to reveal and assess risk factors for intraoperative rupture (IOA) of aneurysms, which will reduce the incidence of this complication and improve the outcome of treatment, Dr.Taylor CL, and the research team at Case Western Reserve University indicated that for patients with an unruptured cerebral aneurysm as the primary diagnosis, hypertension was found to be a significant risk factor for future SAH (risk ratio: 1.46, 95% confidence interval (CI): 1.01-2.11), whereas surgical treatment (risk ratio: 0.29, 95% CI: 0.09-0.97) had a significant protective effect. Advancing age had a small but significant protective effect in both groups. Elderly patients identified with unruptured aneurysms are more likely to have coexisting hypertension than the general hospitalized population. In elderly patients hospitalized with an unruptured cerebral aneurysm as their primary diagnosis, hypertension is a risk factor for subsequent SAH, whereas surgical treatment is a protective factor against SAH(5).

2. Family history
In the study of the incidence of asymptomatic, unruptured cerebral aneurysms  among patients with a family history of SAH within the second degree of consanguinity. Forty-one unruptured cerebral aneurysms were found in 34 (13.9%) of 244 patients. This incidence was significantly higher than that found in a control group of healthy volunteers (6%). Furthermore, patients who had a family history of SAH combined with multiple systemic risk factors were found to have the highest incidence of unruptured aneurysms (32%; odds ratio 3.49, 95% confidence interval 1.37-8.9)(6).

3. Old Age and gender
a. Old age is considered as one of risk factor of Cerebral aneurysm. In the study of the complication of Three hundred fifty-five patients underwent 394 endovascular procedures treating 75 aneurysm recurrences and 319 untreated aneurysms. One hundred eight (30%) were elderly(7)
b. Women are at increased risk of Cerebral aneurysm than men,

4.  Smoking
In the study to investigate whether cigarette smoking increased the risk of developing cerebral aneurysms and of SAH. Degree of smoking was investigated in 182 patients with SAH and in 123 patients with an unruptured cerebral aneurysm incidentally detected during investigation of other diseases, showed that Smoking significantly increased the risk of both aneurysm formation and SAH; The odds ratio for SAH was 2.4, and for unruptured cerebral aneurysm 1.7. Smoking especially increased the occurrence of SAH in women and in youngsters. However, smoking did not influence the occurrence of cerebral vasospasm and multiplicity of aneurysms(8).

5. Arteriosclerosis
Disruption of the entire arterial wall may be a critical event in the development of IDA and result in the medial disruption and subadventitial haemorrhage. Non-atheromatous intima might function as a protective factor in arterial wall disruption. On the other hand, atherosclerosis may predispose to intra-atheromatous plaque haemorrhage type of IDA through intramural haemorrhage originating from the newly formed vessels(9).

6. Drug abuse
Dr. Vannemreddy P, and the team at the Louisiana State University Health Sciences Center suggested that Aneurysms were significantly smaller and ruptured at a younger age among cocaine users compared with nonusers. Although the poor clinical grade was not significantly different between the 2 groups, outcome was significantly worse in cocaine users(10).

7. Head injury 
There are a report of three cases of ruptured traumatic aneurysms of the peripheral anterior cerebral artery after closed head injury. These cases were all young men with closed head injury due to traffic accidents(11).

8. Heavy alcohol consumption 
"Heavy drinking impairs outcome mainly through severe rebleeding and delayed ischaemia and to a lesser extent through a poor initial condition and presence of intracerebral haematoma
". Dr. Juvela S. at the Helsinki University Hospital said(12).

9. Certain blood infections 
Certain blood infections may increased the risk of Cerebral aneurysm, including Streptococcus sanguinis(13), endocarditis(14), Etc.

10. Lower estrogen levels after menopause
Researchers at the Affiliated ZhongShan Hospital, DaLian University, in the study of The role of estrogen in the formation of experimental abdominal aortic aneurysm, showed that in the pathogenesis of abdominal aortic aneurysm (AAA), estrogen may play an inhibitory role by decreasing expression of MMP-2 and MMP-9 synthesis(15).

11. Risk factors present at birth
a. Ehlers-Danlos syndrome type IV is defined as a condition characterized by its clinical manifestations, which are easy bruising, thin skin with visible veins, and rupture of arteries, uterus, etc. There is a report of report a case presented with cervical radiculopathy due to a segmental fusiform aneurysm of the cervical vertebral artery(16).

b. Polycystic kidney disease 
Autosomal dominant polycystic kidney disease(ADPKD) is primarily associated with renal failure, but it also causes systemic diseases, including cysts of other systemic organs and cerebral or visceral aneurysm(17). Other suggested that Polycystic kidney disease has been associated with several aneurysms, most notably cerebral, but not popliteal. The patient's marfanoid habitus also may have played a part. This case emphasises the mixed aetiology of popliteal aneurysms(18).

c. Abnormally narrow aorta (coarctation of the aorta), the large blood vessel that delivers oxygen-rich blood from the heart to the body. There is a report of the frequency of IA among patients with CoA is approximately 5-fold that of the general population. Although no risk factors were identified in this cohort, additional prospective evaluation is warranted. These data suggest that noninvasive cerebral imaging to screen for IA should be considered in patients with CoA(19).

d. Cerebral arteriovenous malformation (brain AVM), 
There are reports of 2 cases of subarachnoid hemorrhage associated with neurofibromatosis type I (von Recklinghausen's disease) are reported. A 30-year-old male patient (case 1) had been diagnosed as having neurofibromatosis type I due to neurofibroma and café-au-lait spot. He suffered from subarachnoid hemorrhage and angiography showed multiple aneurysms in the right and left middle cerebral arteries and left internal carotid artery. He also had arteriovenous malformation in the left temporal lobe(20).

e. Etc.

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Sources
(5) http://www.ncbi.nlm.nih.gov/pubmed/7472548
(6) http://www.ncbi.nlm.nih.gov/pubmed/10470812
(7) http://www.ncbi.nlm.nih.gov/pubmed/22241386
(8) http://www.ncbi.nlm.nih.gov/pubmed/10478344
(9) http://www.ncbi.nlm.nih.gov/pubmed/11318898
(10) http://www.ncbi.nlm.nih.gov/pubmed/18312093
(11) http://www.ncbi.nlm.nih.gov/pubmed/9125717
(12) http://www.ncbi.nlm.nih.gov/pubmed/1633519
(13) http://www.ncbi.nlm.nih.gov/pubmed/22385612
(14) http://www.ncbi.nlm.nih.gov/pubmed/7477721
(15) http://www.ncbi.nlm.nih.gov/pubmed/18585678
(16) http://www.ncbi.nlm.nih.gov/pubmed/21430980
(17) http://www.ncbi.nlm.nih.gov/pubmed/22293308
(18) http://www.ncbi.nlm.nih.gov/pubmed/12954963
(19) http://www.ncbi.nlm.nih.gov/pubmed/14661678
(20) http://www.ncbi.nlm.nih.gov/pubmed/9513196