Impact of Aneurysm Size and Flow Diverter Use on Outcomes After Endovascular Therapy of Unruptured Paraclinoid Aneurysms

BACKGROUND: Flow diverters (FDs) are increasingly used for unruptured paraclinoid aneurysms, especially large or giant ones. However, their benefit over conventional endovascular therapy remains unclear. This study evaluated outcomes after endovascular therapy of unruptured paraclinoid aneurysms, with aneurysm size as the primary exposure, and further examined the modifying effect of FD use. METHODS: We analyzed data of patients with unruptured paraclinoid aneurysms from the Japanese Registry of Neuroendovascular Therapy 4, a nationwide, multicenter registry enrolling patients who underwent endovascular therapy in 166 Japanese institutions from 2015 to 2019. The primary outcome was worsening in the modified Rankin Scale score ≥1 at 30 days. Secondary outcomes included ischemic and hemorrhagic complications. Outcomes were compared by aneurysm size (<10 mm versus ≥10 mm) and further stratified by FD use. RESULTS: Of 3860 patients (3326 women, median age 59 years), 3048 had aneurysms <10 mm and 776 had aneurysms ≥10 mm. FD use was more common in aneurysms ≥10 mm (64.2% versus 3.0%). Worsening in modified Rankin Scale score occurred in 5.3% with aneurysms ≥10 mm versus 2.0% with <10 mm (adjusted odds ratio, 2.28 [95% CI, 1.48–3.49]). Ischemic complications were more frequent with larger aneurysms (5.7% versus 4.0%, P =0.035), though not significant after multivariable adjustment (adjusted odds ratio, 1.26 [95% CI, 0.87–1.84]). Hemorrhagic complication rates were similarly low across groups. There was no significant difference in modified Rankin Scale score worsening by FD use, regardless of aneurysm size. FD use was associated with significantly fewer ischemic complications in aneurysms ≥10 mm (3.2% versus 10.1%, P <0.001), but not in aneurysms <10 mm (4.3% versus 3.9%, P =0.88; P for interaction=0.03). CONCLUSIONS: Endovascular embolization of unruptured paraclinoid aneurysms ≥10 mm was associated with a higher morbidity compared with aneurysms <10 mm. FD use may reduce ischemic complications in larger aneurysms; however, this benefit was not clearly reflected in 30-day functional outcomes.