Infiltrative fibrous lesion of the facial nerve mimicking a facial nerve tumor

Purpose: To report three cases of facial nerve lesions that were clinically expected to be facial nerve tumors but showed fibrotic infiltration without any apparent signs of a specific tumor on histopathological findings. We also aimed to investigate the clinical characteristics of these cases. Methods: Medical records of patients who underwent surgery for facial nerve lesions were reviewed. Results: All three cases initially had House–Brackmann (HB) grade IV–V facial nerve palsy. On radiological imaging, schwannoma or glomus tumor originating from the facial nerve was suspected. All patients underwent complete surgical removal of the neoplasm followed by facial nerve reconstruction using the sural nerve. The lesions were histologically confirmed as infiltrative fibrous lesions without tumor cells. In two cases, facial nerve palsy improved to HB grade III by nine months post-surgery, and there were no signs of recurrence on follow-up MRI. The other case, after 1 year of follow-up, showed persistence of HB grade V facial nerve palsy without any evidence of recurrence. Conclusion: Fibrotic lesions of the facial nerve could mimic primary facial nerve tumors. Clinicians should consider this condition even when a facial nerve tumor is suspected.