AbstractsMedical & Health Science

Rupture of an intracranial aneurysm causes aneurysmal subarachnoid haemorrhage (aSAH), which is an important subtype of stroke. The risk of aSAH consists of three different components, namely the risk factors for developing an unruptured intracranial aneurysm (UIA), risk factors for aneurysmal rupture and trigger factors, which cause the actual rupture. The aim of the present thesis was to identify risk factors for the different components that make up the risk of aSAH and to develop a prognostic model based on these risk factors. A systematic review and meta-analysis was performed to estimate the prevalence of unruptured intracranial aneurysms (UIAs). The prevalence of UIAs in persons without co-morbidity was estimated to be 3.2% and is higher in women, patients with polycystic kidney disease or family history of aSAH or UIAs. Patients <30 years of age have a significantly lower prevalence. Finland and Japan, countries with a high incidence of aSAH, have a similar prevalence of UIAs compared to other regions, suggesting a higher risk of rupture in these populations. Three case-control studies were performed comparing patients with an aSAH, patients with an UIA, and controls from the general population. In the first case-control study it was found that smoking, hypertension and a family history of stroke increase the risk of harboring an UIA, with smoking and hypertension having an additive effect, whereas hypercholesterolaemia and regular physical exercise decrease this risk. Next, risk factors for aneurysmal rupture we studied in a second case-control study. Migraine and smoking increase the risk of rupture, whereas hypercholesterolaemia decreased that risk. In the last case-control study we identified six prognostic factors for aSAH. A model including only the four strongest predictors (i.e. smoking, a family history of aSAH, hypertension and hypercholesterolaemia) was used to estimate incidence and life-time risks of aSAH. Depending on sex, age and the four predictors, the incidence of aSAH varies from 0.4/100,000 to 298/100,000 person-years and life-time risk between 0.02% and 7.2%. In addition, a case-crossover was done to identify trigger factors for aneurysmal rupture. Eight trigger factors were identified, namely coffee consumption, cola consumption, anger, startling, straining for defecation, sexual intercourse, nose blowing and physical exercise. All triggers we identified potentially induce a sudden and short increase in blood pressure, which seems a possible common cause for triggering the aneurysmal rupture. The highest population-attributable risks (i.e. the proportion of aSAH that can be contributed to a specific trigger factor) were found for coffee consumption and vigorous physical exercise. In conclusion, several risk factors for the different steps that lead to aSAH and trigger factors for aneurysmal rupture were identified. Patients with known aneurysm or a family history of aSAH should be advised to quit smoking and to treat high blood pressure. Physical exercise decreases the risk…