Delayed posterior tilting of a giant basilar tip aneurysm following stent-assisted coiling with therapeutic P1 occlusion: A case report

Background: Giant basilar tip aneurysms remain difficult to treat due to their location, bifurcation anatomy, adjacent perforators, and potential for mass effect. Endovascular treatment, including stent-assisted coiling, is a valuable option. Despite angiographic occlusion, mass effect may still be clinically significant. Case Description: A 67-year-old man presented with headache and was diagnosed with a 27 × 17-mm giant unruptured basilar tip aneurysm. Preoperative angiography demonstrated perforators arising predominantly from the left P1 segment and a well-developed right posterior communicating artery (PComA), while the left PComA was hypoplastic. Stent-assisted coiling was performed with stent placement from the basilar artery to the left posterior cerebral artery and occlusion of the non-stented right P1 segment. The early postoperative course was uneventful. Posterior tilting of the coiled aneurysm was first noted 1 week after treatment and subsequently progressed. Approximately 3 months after treatment, mass effect resulted in midbrain compression and obstructive hydrocephalus. Skull radiographs in different body positions demonstrated posture-dependent displacement of the coil mass, suggesting a role of gravity. Levodopa administration and ventriculoperitoneal shunting resulted in partial symptomatic improvement. Angiographic follow-up through 3 years demonstrated stable occlusion without recurrence, with no substantial progression of posterior tilting after the first postoperative year. Conclusion: Stent-assisted coiling with therapeutic P1 occlusion may contribute to durable angiographic occlusion in selected giant basilar tip aneurysms. However, delayed posterior tilting of the coiled aneurysm may occur as a postoperative phenomenon. This potential delayed complication, leading to mass effect, should therefore be considered in treatment strategy and postoperative follow-up.