Is there any seasonal influence in spontaneous bleeding of intracranial aneurysm and and/or AVM in Istanbul?

PRINCIPLES Despite many reports investigating the relationship of subarachnoid haemorrhage and seasonal variation in different parts of the world, there is no clear correlation. As far as we know this subject has not been reported from Istanbul yet. The purpose of this study is to determine if there is any correlation between season and spontaneous subarachnoid haemorrhage (SAH) caused by intracranial aneurysms and/or arteriovenous malformations (AVM) in Istanbul. METHODS Data were collected retrospectively from the medical reports of patients having intracranial haemorrhage due to aneurysm and/or arteriovenous malformation. The data were analysed with univariate and chi-square tests for all haemorrhages, for haemorrhages of aneurysms and arteriovenous malformations separately per month and per season respectively for all the patients together and according to gender separately. The ANOVA test was used for testing the monthly distribution of SAH cases with regard to age. RESULTS There were 761 cases (417 female, 344 male) of intracranial haemorrhage cases (683 intracranial aneurysms, 78 arteriovenous malformations) from 1994-2000. In this study, a seasonal peak in winter and a nadir in autumn for all subarachnoid haemorrhages were observed but the findings were not significant statistically. The peak season was winter for bleeding due to both aneurysms and AVM's. While the nadir season for aneurysmal bleeding was autumn and was summer for the AVM's. CONCLUSIONS We did not find any significant statistical relation between seasonal variation and intracranial haemorrhage in the Istanbul province. But the peak of bleeding in winter and the nadir in autumn were noticeable for all intracranial haemorrhages. In Istanbul, beside the individual risk factors such as hypertension, alcohol consumption, lifestyle, and environmental factors like weather, season and other possible factors of which we are not yet aware, the relative increase of population in winter season due to social reasons may have a small contribution to these findings.