Introduction: Due to the complex anatomy of the paraclinoid region, surgical treatment of paraclinoid aneurysms is often difficult. Only few reports have been published discussing surgical outcomes using multifarious treatments such as high-flow bypass, and the relationship between factors such as aneurysm morphology, surgical treatment, and outcomes remains unclear.

Methods: We retrospectively analyzed findings from 127 consecutive patients (19 males, mean age at surgery: 56.8 years, range: 19-81 years) at our hospital between April 2012 and August 2014. The size of aneurysms ranged from 2.7 mm to 43.2 mm (mean: 6.9 mm). Extradural anterior clinoidectomy was used to clip small aneurysms. As large or giant aneurysms required a longer temporal occlusion period and often could not undergo simple clipping, high-flow bypass with anterior clinoidectomy or cervical internal carotid ligation was performed to reduce aneurysm blood flow and induce thrombosis. We reviewed a postoperative modified Rankin Scale (mRS), radiographic outcomes by three-dimensional computed tomography angiography (3D CTA), and postoperative morbidity such as cerebral infarction and visual disturbance. In addition, we analyzed factors relating to the outcomes and complications, with focus on the aneurysm size, location, and type of surgical treatment

Results: Good outcomes were achieved in all patients, as follows: mRS0:100, mRS 1:16, mRS2:11, and mRS3-6:0. Among the 127 patients, complete exclusion of aneurysm was achieved in 119 cases (93.7%) and residual neck not suitable for retreatment was observed in 7cases (5.5%).One case with giant aneurysm required retreatment for residual aneurysm. Postoperative morbidity included ischemic lesions in 11(8.6%), visual disturbance in 24,(18.8%), transient third cranial nerve palsy in 9 (7.0%) and transient fourth cranial nerve palsy in one case (0.7%). No significant statistical differences were observed for aneurysm location, surgical treatment and outcome, visual disturbance, or cranial nerve palsy. Significant statistical differences were observed between ischemic complication and aneurysm size and location (p=0.0001) and surgical treatment (p<0.0001).

Conclusions: Surgical treatment of unruptured paraclinoid aneurysm has high efficacy with good outcomes, high rate of complete exclusion, and low recurrence rate. However, the rate of postoperative complications, particularly for visual disturbance, is relatively high. Careful surgical techniques and intraoperative monitoring are therefore required.

Patient Care: Surgical outcome of unruptured paraclinoid aneurysm using multifaruous strategy such as high flow bypass has high efficacy with good outcomes, high rate of complete exclusion, and low recurrence rate. Therefore, surgical outcome of paraclinoid aneurysms improve.

Learning Objectives: 1)Clarify surgical outcome of paraclinoid aneurysms using multifaruous strategy such as high flow bypass 2)Describe the relationship between factors such as aneurysm morphology,surgical treatment and outcome

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