Intracranial aneurysms are treated by either microsurgical clipping or endovascular coiling (i.e. embolization), the latter being a much newer treatment method. Thus, long-term outcome studies after endovascular coiling are still sparse. In addition, imaging modalities are more and more frequently used to study patients for many different reasons, and unruptured intracranial aneurysms are detected incidentally. Treatment of those incidentally found unruptured aneurysms is debated a lot because complication rate after both clipping and coiling is high, risk of bleeding is low and we still do not know which aneurysms will eventually rupture. In spite of highly developed imaging methods, there are still patients with subarachnoid bleeding without any etiological factor. This bleeding of unknown etiology has been studied much less than aneurysmal disease in recent years. The aim of this thesis was to determine the long-term outcome of patients treated with embolization and patients with subarachnoid hemorrhage (SAH) of unknown etiology.

This study is based on 1294 patients treated in Tampere University Hospital during 1989-1999. Surviving patients treated with endovascular coiling (n=185) and patients with SAH of unknown etiology (n=97) were studied with magnetic resonance imaging (MRI) 9-18 years (median 9 yrs, mean 11yrs) after hospitalization and the clinical outcome of all treated patients was assessed.

Patients with previous SAH of unknown etiology have a good clinical outcome with no vascular changes in MR-images and they have no excess mortality compared to matched general population. Patients with unruptured aneurysms, however, have excess long-term mortality, especially if the aneurysm is left untreated. Both ruptured and unruptured intracranial aneurysms are stable in long-term MRI studies but complete occlusion should be the goal of the treatment to prevent rebleedings. Brain infarctions without clinical consequences are common after embolization.