Small cerebral aneurysms presenting with symptoms other than rupture

Background: Recent natural history studies have suggested that unruptured intracranial aneurysms smaller than I cm have a low risk of rupture. Symptomatic aneurysms may be underrepresented in natural history studies because they are preferentially treated. The authors compared the number of patients with symptoms caused by unruptured intracranial aneurysms smaller than I cm treated surgically at their institution with similar patients enrolled in the International Study of Unruptured Intracranial Aneurysms (ISUIA) from their institution over the same time period. Methods: The records of all unruptured aneurysms treated surgically at the Mayo Clinic from 1980 through 1991 were reviewed. There were 97 patients with 117 unruptured aneurysms smaller than 1 cm by angiography. Aneurysms with a history of rupture or larger than 1 cm on cross-sectional imaging were excluded from analysis. The presence and characteristics of symptoms directly attributable to the aneurysm were recorded. Comparison was made with patients from the Mayo Clinic enrolled in the ISUIA retrospective natural history cohort over the same time period. Results: Of the 97 patients studied, 15 presented with symptoms other than rupture (15.5%). The symptoms were third nerve deficit (seven patients), cerebral ischemia owing to emboli originating from within the aneurysm (five patients), and visual acuity loss (three patients). Eleven other aneurysms had possibly but not definitively caused symptoms; these were considered asymptomatic. No patient from the Mayo Clinic enrolled in the retrospective cohort of the ISUIA had a symptomatic aneurysm smaller than 1 cm on both angiography and cross-sectional imaging. Conclusions: Unruptured intracranial aneurysms smaller than 1 cm occasionally present with neurologic symptoms. These symptoms are typically owing to mass effect on the second and third cranial nerves or cerebral ischemia as a result of emboli originating from within the aneurysm. Patients with symptomatic unruptured aneurysms less than I cm at the Mayo Clinic were preferentially treated. Although existing natural history data may be applied to most unruptured aneurysms, small symptomatic aneurysms may be underrepresented in natural history studies.