Object. The authors evaluated the efficacy of a new flow reduction strategy for giant partially thrombosed upper basilar artery (BA) aneurysms, for which proximal parent artery occlusion is not always effective. Methods. Eight consecutive patients with severely symptomatic, partially thrombosed, giant upper BA aneurysms were treated with a tailored flow reduction strategy, or received conservative therapies. The flow reduction strategy comprised isolation of several branches from the upper BA at their origins with bypasses in addition to parent artery occlusion. Results. The median follow-up period of all 8 patients was 15.0 months (range 4-31 months). In 6 patients treated with flow reduction, the mean decrease in residual blood lumen was -10.7 mm (95% CI -19.7 to -1.7 mm; p = 0.029) and the mean decrease in diameter of the aneurysms was -11.5 mm (95% CI -25.1 to 2.1 mm; p = 0.082). Complete or virtually complete thrombosis was achieved in all but 1 aneurysm (83%) and shrinkage was observed in 4 (67%). In those in whom complete or virtually complete thrombosis was achieved, significant shrinkage of the aneurysm was observed (mean decrease in diameter -14.8 mm; 95% CI -28.8 to -0.8 mm; p = 0.043). Improvement or stabilization of symptoms occurred in 67% of the patients who received flow reduction treatment. Both patients who received conservative treatment had unfavorable outcomes. Conclusions. The flow reduction strategy is effective at promoting complete thrombosis of the aneurysm. This strategy can also induce shrinkage of the aneurysm if successful thrombosis is achieved. Although the neurological outcome of the treatment appears favorable considering its intractable nature, further study of the treatment is necessary to confirm its clinical efficacy and safety.
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