Orbicularis oculi reflex and facial muscle electromyography. Pre- and postoperative evaluation of posterior fossa space-occupying lesions.

The electrically evoked orbicularis oculi reflex was analyzed in 26 patients with proven posterior fossa space-occupying lesions (11 cerebellopontine angle and 15 cerebellar hemispheric masses). In the former group, although only six had clinical evidence of trigeminal or facial involvement, the reflex analysis showed both nerves to be involved in all. Electromyography (EMG) of the orbicularis oculi showed profound denervation of this muscle while only minimal abnormalities of the masseter were seen. The sensory component of the trigeminal nerve was always more involved than its motor component and this was a reliable guide as to the upward and medial extension of the tumor, especially in the absence of clinical localizing signs. In the 15 patients with cerebellar masses, six with masses located posteriorly and entirely within the confines of the cerebellum had normal studies. In eight, the mass was located anteriorly, and fifth nerve involvement could be detected in all by EMG, although only two patients had clinical evidence of such involvement. One patient with dysfunction of the central reflex arc had EMG evidence of an intraventricular dermoid tumor abutting the pons, later confirmed at surgery. Thus, an invaluable body of diagnostic and prognostic data can be obtained by this nontraumatic and simple electrodiagnostic procedure.