Isolated intraventricular haemorrhage caused by de novo posterior communicating artery aneurysm

We report a rare case of a patient with a previously ruptured anterior communicating artery aneurysm, treated with endovascular coil embolisation, who re-presented 8 years later with a ruptured de novo posterior communicating (PCOM) artery aneurysm, manifesting primarily as isolated intraventricular haemorrhage (iIVH). Imaging revealed the de novo PCOM aneurysm, which was successfully managed with balloon-assisted coil embolisation. This case highlights two key learning points: first, de novo aneurysm formation is an uncommon but potentially serious long-term phenomenon following treated aneurysms, particularly in patients with risk factors such as hypertension, smoking and female sex. Second, aneurysmal rupture can present atypically as iIVH, necessitating high clinical suspicion and prompting vascular imaging to avoid diagnostic delays. Lifelong surveillance imaging may be warranted for select high-risk patients. Early recognition and treatment of aneurysmal iIVH are critical for achieving optimal outcomes.