Rapid enlargement of a pre-existing intracranial aneurysm during infective endocarditis: a case report

BACKGROUND: Infectious intracranial aneurysms (IIAs) are generally thought to develop de novo as a consequence of septic embolization during infective endocarditis (IE). Rapid infection-related enlargement of a pre-existing unruptured aneurysm during IE has not been previously documented. We report a case in which a small middle cerebral artery (MCA) aneurysm, previously identified on imaging, enlarged rapidly in the course of IE. CASE DESCRIPTION: A 67-year-old woman with a history of mitral valve repair presented with progressive general malaise and mild left hemiparesis. MRI demonstrated acute infarctions in the right caudate nucleus and putamen, and MRA showed occlusion of the right M2 superior branch. A previously identified 2.2-mm right MCA bifurcation aneurysm was not visualized on admission MRA. Infective endocarditis was subsequently diagnosed, and the aneurysm reappeared on day 9 at 5.5 mm and enlarged further to 9.5 mm by day 15. Endovascular coil embolization was performed on day 16, achieving complete aneurysm occlusion. The patient later underwent mitral valve surgery without complications. CONCLUSION: This case demonstrates infection-related enlargement of a pre-existing intracranial aneurysm during IE, documented chronologically with serial MRA. These findings highlight the need for careful interval imaging in patients with IE and known aneurysms, and rapid morphological change should prompt urgent aneurysm treatment.