Rapid presentation of a de novo intracranial aneurysm: illustrative case.

backgroundIntracranial aneurysms are prevalent, particularly with advancing age. De novo aneurysms, occurring independently from the initial lesion, pose a unique challenge because of their unpredictable nature. Although risk factors such as female sex, smoking history, and hypertension have been proposed, the mechanisms underlying de novo aneurysm development remain unclear. OBSERVATIONS: A 79-year-old female developed a de novo saccular aneurysm within a year after management of a ruptured vertebral artery dissecting aneurysm. Her complex clinical course involved subarachnoid hemorrhage with diffuse vasospasm, stent occlusion of a dissecting aneurysm, discovery of a right 7- to 8-mm de novo middle cerebral artery aneurysm at the 1-year magnetic resonance angiography follow-up, and successful coil embolization. LESSONS: This rare occurrence challenges established timelines, as most de novo aneurysms manifest over a longer interval. Studies have attempted to identify risk factors, yet consensus remains elusive, particularly regarding the influence of treatment modality on de novo formation rates. This unique case urges reconsideration of posttreatment surveillance protocols, proposing shorter intervals for imaging and more vigilant follow-up strategies to detect asymptomatic de novo aneurysms. Timelier identification could significantly impact patient outcomes by averting potential ruptures. This emphasizes the need for further research to delineate effective monitoring and preventive measures for these enigmatic lesions.