The importance of the optic nerves unlocking during the resection of anterior skull base meningiomas for visual function preservation: surgical nuances and clinical outcome

Anterior skull base meningiomas can determine optic nerves (ONs) impingement leading visual disturbances as presenting symptoms. According to the relationship between tumour origin and ON course, different "vectors of compression" can be identified: lateral-to-medial, medial-to-lateral, inferior-to-superior, and anterior-to-posterior. As visual function preservation represents the main goal of surgery, we designed a procedural algorithm concerning approach, cisterns dissection, falciform ligament section, ON mobilization and tumour debulking aimed to reduce ONs manipulation during surgery. We included 40 patients harbouring meningiomas compressing ONs with mean age 61.7 +/- 12.4 years. Sixteen originated from anterior clinoidal process (40%), 10 from sphenoid-ethmoidal planum (27.5%), 10 from tuberculum sellae (25%), and 4 from sphenoid-orbital region (7.5%). A decline in visual acuity was observed in 34/40 (85%) of patients and in visual field in 28/40 (70%). Mean age appeared significantly lower in patients with intact visual field (p = 0.006). No differences were observed between symptomatic and asymptomatic patients according to tumour origin, whereas a significantly lower rate of visual field impairment was observed among patients with inferior-to-superior compression. On the contrary, tumour determining a superior-to-inferior compression showed a trend of higher risk of visual field cut. Falciform ligament opening was performed in 82.5% of cases, optic canal unroofing in 27%, anterior clinoidectomy in 32% and optic strut removal in 5%. At 6-month follow-up, none among patients treated before of visual acuity onset disturbances showed worsening. Among those showing preoperative alterations, an improvement was observed in 17/34 (50%), 14 (41.2%) had an unchanged deficit, and 3 (8.8%) a worsening. Optic canal unroofing was the only significant predictor of postoperative non-improvement at multivariate analysis (p = 0.03, AUC = 0.796; OR = 0.163; 95%CI:0.027-0.983; p = 0.04). Similarly, none patient developed visual field cut when treated before it clinical appearance, and only 28.6% of those with a pre-operative deficit showed post-operative improvement. Worsening was seen in 5/28 of patients with a preoperative visual field deficit (17.6%), with the remaining 15 (53.6%) with unchanged visual field at 6-month. Comparing patients with post-operative visual field improvement and non-improvement, only a younger age and a better preoperative mRS status showed a significant association with a positive outcome. Age emerged as unique significant risk factor for lack of post-operative improvement at stepwise binomial logistic regression model (OR = 0.855, 95%CI: 0.743-0.983, p = 0.028). The surgical management of anterior cranial fossa meningiomas associated with optic nerve compression should prioritize visual preservation over radical tumor resection and a timely decompression reducing the risk of post-operative visual acuity deterioration. The surgical techniques should be also modified to include all the necessary unlocking strategies limiting the ON stress during the tumor manipulation.