Object: A small percentage of patients will develop a completely new or de novo aneurysm after discovery of an initial aneurysm. The natural history of these lesions is unknown. The authors undertook this statistical evaluation a large cohort of patients with both ruptured and unruptured de novo aneurysms with the aim of analyzing risk factors for rupture and estimating a risk of subarachnoid hemorrhage (SAH).
Methods: A review of a prospectively maintained database of all aneurysm patients treated by the vascular neurosurgery service of Goodman Campbell Brain and Spine from 1976-2010 was performed. Of the 4718 patients, 611 (13%) had long-term follow-up imaging. The authors identified 27 patients (4.4%) with a total of 32 unruptured de novo aneurysms from routine surveillance imaging. They identified another 10 patients who presented with a new SAH from a de novo aneurysm after treatment of their original aneurysm. The total study group was thus 37 patients with a total of 42 de novo aneurysms. The authors then compared the 27 patients with incidentally discovered aneurysms with the 10 patients with SAH. A statistical analysis was performed, comparing the 2 groups with respect to patient and aneurysm characteristics and risk factors.
Results: Thirty-seven patients were identified as having true de novo aneurysms. This group had a female predominance and a high percentage of smokers. These 37 patients had a total of 42 de novo aneurysms. Ten of these 42 aneurysms hemorrhaged. De novo aneurysms in both the SAH and non-SAH group were anatomically small (< 10 mm). The estimated risk of hemorrhage over 5 years was 14.5%, higher than the expected SAH risk of small, unruptured aneurysms reported in the ISUIA (International Study of Unruptured Intracranial Aneurysms) trial. There was no statistically significant correlation between hemorrhage and any of the following risk factors: hypertension, diabetes, tobacco and alcohol use, polycystic kidney disease, or previous SAH. There was a statistically significant between-groups difference with respect to patient age, with the mean patient age being significantly older in the SAH aneurysm group than in the non-SAH group (p = 0.047). This is likely reflective of longer follow-up and discovery time, as the mean length of time between initial treatment and discovery of the de novo aneurysm was longer in the SAH group (p = 0.011).
Conclusions: While rare, de novo aneurysms may have a risk for SAH that is comparatively higher than the risk associated with similarly sized, small, initially discovered unruptured saccular aneurysms. The authors therefore recommend long-term follow-up for all patients with aneurysms, and they consider a more aggressive treatment strategy for de novo aneurysms than for incidentally discovered initial aneurysms.