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ntroduction: Maximal safe resection is established goal of WHO grade 2 low-grade gliomas (LGG). Asleep motor mapping offers an alternative to awake surgery for tumors near motor areas and has been shown to be safe and effective in expert centers.

Research question: We aimed to identify predictors of postoperative motor deficits, and describe patient selection and intraoperative mapping techniques across Scandinavian centers.

Material and methods: We retrospectively analyzed patients (≥18) with WHO grade 2 gliomas who underwent asleep motor mapping across multiple Scandinavian neurosurgical centers. Clinical, surgical, and imaging data were extracted from medical records. The primary outcome was registered permanent postoperative motor deficits at 3 months. Associations with pre-, intraoperative, and radiological variables - including diffusion-weighted imaging (DWI) changes - were assessed using univariate and multivariate logistic regression.

Results: We included 74 patients from eight institutions. Median age was 48 years, 38 (51.4 %) were female and median preoperative tumor volume was 43.2 ml. 13 (17.6 %) patients achieved gross-total resection and median postoperative volume was 7.8 ml. Permanent postoperative motor deficits occurred in 19 cases (25.7 %), and 5 (6.8 %) were considered major deficits. In univariate analysis, preoperative motor deficits (p = 0.009), postoperative DWI changes (p = 0.022), and age (p = 0.043) were significantly associated with new or worsened permanent deficits. Only DWI changes and age was confirmed in penalized multivariate logistic regression.

Discussion and conclusion: Postoperative motor deficits were common despite use of asleep motor mapping. Preoperative motor deficits and diffusion-weighted imaging changes are predictors of permanent motor deficits in this setting.