Controversy: Clipping of Asymptomatic Intracranial Aneurysm That is <7 mm

Abstract

The second (prospective) International Study of Unruptured Intracranial Aneurysms (ISUIA), published in 2003 in The Lancet ,1 suggested that the risk of hemorrhage from an unruptured intracranial aneurysm <7 mm is extremely low, and that present microsurgical or endovascular treatment for patients harboring these lesions carries a far greater risk of incurring a neurological deficit than the natural history. This has led to a much more conservative approach toward managing such patients. However, considerable controversy remains on whether or not to offer therapy (surgical or endovascular) to these patients. We recall that the first (retrospective) ISUIA study, published in New England Journal of Medicine in 1998,2 demonstrated that asymptomatic intracranial aneurysms ≤10 mm had a very low rupture rate (0.05%/yr for group 1, no previous bleeding from another aneurysm; 0.5%/yr for group 2, previous bleeding from another aneurysm). The authors concluded that 10 mm should be the cutoff for considering treatment of these aneurysms, particularly in group 1 patients. This study also promoted a major change in clinical practice, so that many patients with aneurysms <10 mm were not treated. Was this a reasonable response? Probably not, especially in view of the more recent ISUIA data indicating that aneurysms that are 7 to 12 mm carry a considerable risk of bleeding. Should we significantly alter our practice on the basis of a single nonrandomized study, such as the 2003 ISUIA study? A closer examination of the 2003 ISUIA study reveals that some aneurysms <7 mm have a significant risk of bleeding (Table). Five-year cumulative risks of hemorrhage were 2.5% for posterior communicating artery aneurysms in group 1; 1.5% for anterior communicating (AC), middle cerebral (MC), and internal carotid aneurysms in group 2; and 3.4% for posterior communicating artery aneurysms in group 2. All patients with these asymptomatic aneurysms …