Ruptured internal carotid artery aneurysm presenting as retrobulbar neuritis: A case report

Giant intracranial aneurysms (GIAs) are rare but devastating vascular lesions with a high mortality risk upon rupture. While 80–90% of aneurysms occur at the circle of Willis bifurcations, GIAs—traditionally defined as ≥25 mm—may present uniquely when compressing the anterior visual pathway. Isolated acute visual loss is uncommon and frequently misdiagnosed. A 60-year-old hypertensive female presented with sudden profound vision loss in the left eye over 48 hours, associated with headache and vomiting. Examination revealed no perception of light with a relative afferent pupillary defect. Fundus examination was normal in both eyes. Computed tomography (CT) and CT angiography revealed a ruptured, partially thrombosed supraclinoid internal carotid artery aneurysm (17 × 16 × 18 mm) with subarachnoid and intraventricular hemorrhage. This case illustrates the normal fundus, wherein functional deficits precede structural optic nerve changes by 4–6 weeks due to retrograde degeneration. The presentation mimicked retrobulbar neuritis. Large aneurysm size (>15 mm) and wide neck were associated with poor prognosis. A contralateral temporal hemifield defect indicated chiasmal involvement. To conclude, unexplained visual loss with a normal fundus in elderly patients warrants urgent neuroimaging to exclude vascular causes. Early diagnosis can be life-saving.