Growth potential and response to multimodality treatment of partially thrombosed large or giant aneurysms in the posterior circulation.

Objective: This study examined the growth potential and response to multimodality treatment of partially thrombosed large or giant aneurysms in the posterior circulation.
Methods: The 17 aneurysms arose from nonbranching sites of the vertebral artery (VA) in 6 patients and from branching sites in 11 patients (the VA-posteroinferior cerebellar artery [PICA], 3 cases; basilar artery [BA] fenestration, 1 case; BA-superior cerebellar artery [SCA], 5 cases; and BA tip, 2 cases).
Results: Endovascular trapping was performed in 5 VA aneurysms at nonbranching sites, 2 VA-PICA cases with or without revascularization of the PICA, and 1 BA fenestration case. Endosaccular embolization was performed in 2 BA-SCA aneurysms as the sole treatment or after superficial temporal artery-SCA bypass for a broad-necked lesion. Surgical proximal occlusion (PO) with or without revascularization of the PICA was performed in 2 VA cases. Endovascular treatment failed to prevent growth in 1 VA-PICA case and the broad-necked BA-SCA case. Simple flow alteration by PO of 3 BA aneurysms, with gadolinium enhancement on T1-weighted images, did not prevent growth. Maximum flow reduction by various combinations of bypass (superficial temporal artery-posterior cerebral artery or superficial temporal artery-SCA) and BA PO, aimed at reducing hemodynamic stress on the neck, was tailored to 5 cases, including those refractory to PO; it achieved marked shrinkage in 2 cases and stabilization of the aneurysms in 3 cases. The aneurysms harboring neither gadolinium enhancement nor hyperintensity on fluid-attenuated inversion recovery images showed significantly lower growth potential before treatment and a lesser degree of shrinkage after tailored treatment than the remaining cases (P = 0.03 and P = 0.01, respectively). Overall, marked shrinkage was achieved in 27%, moderate shrinkage in 20%, stabilization in 47%, enlargement in 7%, and favorable outcome in 71%. Maximum flow reduction strategy for BA aneurysms tended to show higher shrinking efficacy than endovascular trapping for VA and BA aneurysms (P = 0.08).
Conclusion: For aneurysms at nonbranching sites, endovascular trapping may be effective, although its shrinking efficacy may be moderate. For the most formidable BA aneurysms at branching sites, maximum flow reduction may cause marked shrinkage, even of aggressive lesions.