Graph showing risk of rupture of intracranial aneurysms among patients with and without history of prior subarachnoid hemorrhage

Retrospective analysis of the probability of subarachnoid hemorrhage (SAH) over time in patients with an unruptured intracranial aneurysm: 446 without (top panel) and 438 with (bottom panel) a history of SAH from a different aneurysm. The results are shown according to the size of the aneurysm. The risk is clearly related to the size of the aneurysm in patients with no prior history of SAH, with aneurysms <10 mm in size having a very low incidence of rupture. Such a relationship was not apparent in those with a prior history of SAH; the values are not shown for aneurysms ≥25 mm in this group because of the small number of patients.