Incidence of multiple intracranial aneurysms. Influence of arterial hypertension and gender.

Theoretically, if arterial hypertension plays a role in aneurysm formation, it might also be associated with a higher incidence of multiple aneurysms as compared to their occurrence in normotensive patients. In an unselected series of 737 aneurysm patients, the structure of dependence between 1) number of aneurysms, 2) patients' sex, 3) patients' age, and 4) the presence or absence of hypertension was analyzed using contingency-table analysis. Evidence of arterial hypertension was determined by means of three complementary criteria of hypertension. A significant mutual state of dependence was demonstrated between the presence or absence of hypertension and the number of aneurysms, and between number of aneurysms and sex of the patient. In addition, for patients with a given number of aneurysms, the action of gender was independent of the blood pressure level. No interaction between the age of the patient and the number of aneurysms could be demonstrated. In order to quantify the relative contribution of the patients' sex, the patients' age, and the presence of hypertension to multiplicity of aneurysms, a probability model for multiplicity of aneurysms was estimated by logistic-regression analysis. It was demonstrated that the most important factor explaining multiplicity was the presence of hypertension, whereas the age of the patient had no influence. A "pure" effect of gender was revealed, indicating that females are significantly more susceptible to aneurysm formation, even in cases without arterial hypertension.