The purpose of this study is to evaluate the efficacy and safety of steroids treatment compared with placebo in preserving facial nerve function after craniotomy in patients with vestibular schwannoma who have not received preoperative treatment and have good intraoperative facial nerve function.

Vestibular schwannoma (VS) is a benign tumor arising from the vestibular nerve. Surgical resection is a common treatment, and intraoperative neurophysiological monitoring (IONM) is widely used to protect facial nerve function. However, postoperative facial nerve paralysis remains a common complication, affecting patients' appearance, confidence, and quality of life.

Steroids are often used to reduce inflammation and edema in idiopathic facial palsy, but their efficacy and safety in post-surgical VS patients remain uncertain. The mechanism of post-surgical facial nerve dysfunction is more complex than idiopathic palsy and may involve physical traction, vascular compromise, or inflammatory injury.

This study (SAF-NRVS) is a multicenter, randomized, double-blind, placebo-controlled, parallel-group trial. Patients aged 18 to 60 years with a clinically confirmed untreated unilateral vestibular schwannoma will be enrolled. Eligible patients must have no preoperative facial paralysis (grade I according to the House-Brackmann grading system), and have good intraoperative facial nerve function as determined by intraoperative neurophysiological monitoring. Participants will be randomly divided into two groups in a 1:1 ratio. Intervention group (Steroids group) will receive 80 mg of methylprednisolone sodium succinate powder dissolved in 100 ml of sodium chloride (NaCl) solution by intravenous infusion once daily from the day of surgery to day 3, followed by 20 mg of prednisone acetate oral intake once daily from day 4 to day 10. Control group (Placebo group) will receive methylprednisolone sodium succinate placebo powder dissolved in 100 ml of NaCl solution by intravenous infusion once daily from the day of surgery to day 3, followed by prednisone acetate placebo oral intake once daily from day 4 to day 10. The primary outcome measure is the proportion of patients with good facial nerve function recovery at 90 days after surgery, defined as grade 1 or 2 according to House-Brackmann grading system.

Inclusion Criteria:

1. Age between 18 and 60 years
2. Diagnosed with untreated unilateral vestibular schwannoma
3. No facial palsy before surgery (House-Brackmann grade I)
4. Intraoperative neurophysiological monitoring confirms good facial nerve function preservation, defined as: a）Post-tumor resection, evoked compound muscle action potential amplitude >420 μV under 0.05 mA stimulation；and b）The amplitude is >60% of baseline value measured before dural opening
5. Signed informed consent

Exclusion Criteria:

1. Contraindications for craniotomy
2. Patients requiring corticosteroids during the perioperative period, or with known corticosteroid contraindications
3. Patients or first-degree relatives with a confirmed diagnosis of neurofibromatosis type 2 (NF2)
4. Karnofsky Performance Status (KPS) score <90 before disease onset
5. Pregnant or planning to become pregnant during the study period
6. Participation in other interventional clinical trials
7. Judged unsuitable by the investigators

This study adopted a double-blind design. Study drugs and placebos are identically packaged. The dosage form, size, color, weight, smell, and taste of the placebo were basically similar to those of the research drug, and there was no risk of blinding. Personnel involved in randomization or potentially exposed to treatment allocation (including pharmacy staff) are not involved in patient care, outcome assessment, or data analysis. Blinded investigators and outcome assessors remain unaware of treatment assignments throughout the study.