Nasal muscle F-wave for peri- and intraoperative diagnosis of facial nerve function.

A new method for recording F-waves from facial muscles in order to assess the function of the intracranial and intracanalicular portion of the facial nerve peri- and intraoperatively has been developed: Direct (M) and F-responses were obtained from the nasal muscle after stimulation of the zygomatic branch of the facial nerve of healthy volunteers. We examined a number of patients with likely or obvious dysfunction of the facial nerve, mostly suffering from cerebellopontine angle (CPA) tumors. F-wave findings were compared to blink reflex and transcranial magnetoelectric evoked potential recordings, the latter obtained from the nasal muscle. The F-wave turned out to be a sensitive parameter for the diagnosis of facial nerve dysfunction. The feasibility of intraoperative nasal muscle F-wave recording and its prognostic value are demonstrated. The nasal muscle F-wave is considered to be a valid parameter for the diagnosis of clinically imperceptible facial nerve lesions, especially of its intracranial portion.