Advancement in microsurgical management of unruptured intracranial vertebral artery fusiform aneurysms: indications, techniques, and outcomes focusing on the integrity of vertebral artery and medullary perforators.

[OBJECTIVE] Medullary infarction (MI) is a known complication following the treatment of vertebral artery fusiform aneurysms (VAFAs), particularly when parent artery occlusion (PAO) is used. This condition can be attributed to delayed occlusion of medullary perforating arteries (Mperfs) due to a delayed thrombosis of the vertebral artery (VA) stump. Nevertheless, there is a limit to data regarding microsurgery, specifically those emphasizing Mperf preservation. Therefore, this study aimed to evaluate the indications, techniques, and outcomes of microsurgical management for unruptured VAFAs, focusing on maintaining the VA and Mperf integrity. The authors also propose a novel risk-stratified surgical algorithm based on Mperf classification to minimize MI complications.

[METHODS] The authors retrospectively reviewed patients with unruptured VAFAs who underwent microsurgical treatment between 2012 and 2024 at their institution. The Mperfs were evaluated intraoperatively and correlated with postoperative MRI findings to assess risk factors for MI. Based on their relation to the aneurysm, Mperfs were categorized as proximal, distal, aneurysm, or posterior inferior cerebellar artery (PICA) type, and further stratified into either "blind-end" or "flow-out" configurations regarding their vascular outflow characteristics following clipping procedures. Surgical strategies included PAO, various bypass techniques, and clip reconstruction. The clinical and radiological outcomes were also analyzed.

[RESULTS] Among the 54 patients with 58 aneurysms treated, favorable outcomes (modified Rankin Scale scores 0-2) were achieved in 96.3% of patients. Symptomatic MI occurred in 4 cases (6.9%), all within the blind-end Mperf group. Of the blind-end group, MI incidence was highest in aneurysm-type Mperfs (80%; 4/5), followed by distal (25%; 1/4) and proximal types (14.3%; 1/7). No MI was observed in the flow-out group. Larger aneurysm size and blind-end Mperf configuration, particularly when arising directly from the aneurysm, were significant risk factors for MI (p = 0.006 and p < 0.001, respectively). Revascularization procedures, including occipital artery (OA)-PICA, VA reconstruction utilizing an interposition graft, and OA-Mperf bypasses, were effectively performed, with no complications in bypass-protected Mperfs.

[CONCLUSIONS] Microsurgical management of unruptured VAFAs, guided by a novel Mperf classification and a tailored surgical algorithm, was found to achieve excellent and durable results. The authors emphasize the importance of a thorough intraoperative Mperf evaluation and keep perforator-preserving techniques in mind, including strategic clipping and perforator bypass, to minimize the risk of MI. This study highlights the essential role of microsurgery in the contemporary management of complex posterior circulation aneurysms.