Extracranial-intracranial bypass to reduce the risk of ischemic stroke in intracranial aneurysms of the anterior cerebral circulation: a systematic review.

BACKGROUND AND PURPOSE

If clip application or coil placement for treatment of intracranial (IC) aneurysms is not feasible, the parent vessel can be occluded to induce thrombosis of the aneurysm. In the case that such an occlusion cannot be tolerated without subsequent sequel, the additional construction of an extracranial (EC)-IC bypass is needed for sufficient ipsilateral revascularization. Hitherto, the effectiveness of this combined treatment option was not investigated in a controlled randomized trial or in a review. The aim of the current report was to analyze clinical effectiveness of EC-IC bypass for cerebral revascularization in patients with Hunterian ligation in case of otherwise untreatable aneurysm of the anterior cerebral circulation. Special reference was given to different hemodynamic subgroups.

METHODS

A computerized database search was conducted from November 1985 to November 2002 using MEDLINE, relevant Internet sources, and full-text journal articles using appropriate indexed terms. Journal of Neurosurgery, Neurosurgery, Acta Neurochirurgica, and Stroke were manually searched for the period November 1985 to November 2002 and checked reference lists of all relevant articles for additional eligible studies. Language restriction was done for English, French, and German. Reports dealing with EC-IC bypass surgery for cerebral revascularization in case of aneurysm of the anterior cerebral circulation were reviewed when appropriate. Studies were included that contained evaluable data on clinical state, preoperative and postoperative hemodynamic state, surgical outcome, and follow-up. A statistical analysis was performed for different outcome parameters and clinical effectiveness in the included studies.

RESULTS

Overall, 20 studies were included, each with a study quality of 0-1. The postoperative outcome related to death or stroke depended mainly on preoperative hemodynamic subgroups (cerebral blood flow [CBF]/cerebral blood volume [CBV]; oxygen extraction fraction [OEF]). The final functional status was worse the more CBF/CBV ratio and OEF increased. Perioperative risk for death (0.8%) or stroke (1.5%) during the first month after operation was similar to the death or stroke rate during the following 2 to 12 months after operation. Neurologic function was improved over the preoperative state in 74% of the patients and was unchanged in 9%. The modified Rankin scale score was postoperatively 0 to 1 in 81% and 2 in 6% of the patients. Long-term patency was excellent, with 2.3% failure rate per year after the first year after surgery. There was no de novo aneurysm formation in the follow-up.

CONCLUSION

Neurologic function and subsequent stroke attributable to hemodynamic insufficiency in patients with otherwise untreatable IC aneurysm improves significantly by EC-IC bypass surgery if the brain area corresponding to the impaired neurologic function remains viable. The hemodynamic parameters observed for patients who experience improved neurologic function or diminished stroke risk profile after EC-IC bypass surgery contain both significantly elevated OEF and CBF/CBV. Therefore, hemodynamic state represents an important indicator for EC-IC bypass surgery. The large amount of data leads to narrow stroke with no significant heterogeneity, and the overall results are, therefore, likely to be statistically robust.