Giant Basilar Tip Aneurysm with Bilateral Internal Carotid Artery Hypoplasia: A Case Report and Literature Review

Background: The association between basilar tip aneurysms and bilateral internal carotid artery hypoplasia represents an exceptionally rare clinical entity that presents unique diagnostic and therapeutic challenges. Only 5-8 cases have been documented in the global literature. Case Presentation: A 42-year-old woman with a history of subarachnoid hemorrhage developed a subacute, progressive brainstem syndrome manifested by right faciobrachial–crural hemiparesis, dysarthria, dysphagia, and a disabling head tremor consistent with a rubral phenotype. Neurological examination suggested involvement of both long motor pathways and cranial nerve–related brainstem structures. Vascular imaging identified a recurrent giant basilar tip aneurysm (~50 mm) and bilateral internal carotid artery hypoplasia, with complete anterior circulation dependence on enlarged posterior communicating arteries. The aneurysm produced significant pontomesencephalic compression and posterior circulation hemodynamic stress, explaining the patient’s progressive neurological decline. The case was evaluated in a multidisciplinary neurovascular setting to guide management and surveillance. Conclusion: This case represents one of fewer than 10 documented cases worldwide of this rare association. The combination of bilateral ICA hypoplasia and giant basilar aneurysm creates unique hemodynamic challenges that predispose to aneurysm formation and complicate therapeutic management, highlighting the critical importance of long-term surveillance and individualized treatment strategies.