Hering’s Law of the Frontal Facial Branch

Sir: Ocular muscles work together to regulate accurate control of eye movements, which is described as binocular eye movement by Hering’s law.1 In general, Hering’s law is used to describe the following mechanisms associated with ptosis palpebrae: significant ptosis palpebrae with slight impairment on one side may result in extra activity of the levator palpebrae muscle on the other side and by that may camouflage the less severe ptosis on the opposite side. Hering’s law, however, also applies to the frontal branch of the facial nerve, as we clinically experience regularly: damage of the (frontal branch of the) facial nerve causes depression of the ipsilateral eyebrow and acute involuntary elevation of the contralateral eyebrow with concomitant increase in horizontal forehead wrinkles. This is attributable to bilateral innervation of the upper facial muscles by the facial nerve (seventh nerve). The facial nucleus is located in the pons, a part of the brainstem, which consists of two parts: one part for upper facial muscles and the other part for lower facial muscles. Lower facial muscles are contralaterally/unilaterally innervated, whereas the upper facial muscles are bilaterally innervated. In a case illustrating Hering’s law of the frontal branch, a 52-year-old woman with sagged jowls underwent a short-scar face-lift procedure performed under local anesthesia with “jungle juice” solution (local anesthesia). Immediately after the procedure, it struck us that the patient had a decrease of the left eyebrow position, with no ability to lift it actively (Fig. 1, left. This was interpreted as temporary facial palsy of the frontal branch caused by the local anesthesia. In contrast, the contralateral eyebrow was significantly elevated compared with the preoperative situation, with an increase in the number of clearly visible horizontal forehead wrinkles above this eyebrow, indicating excessive activity of the frontalis muscle on this side. Other facial mimics were not disturbed. Our patient had a grade VI facial palsy according to the House-Brackmann classification. Within a few hours after the face-lift procedure, both eyebrow positions recovered to the original position; the affected eyebrow increased to its normal position and could be elevated again (Fig. 1, right. The contralateral eyebrow decreased in height to its preoperative normal position and the extra number of horizontal forehead wrinkles had disappeared.Fig. 1.: Evaluation of the patient immediately postoperatively. Local anesthesia induced temporary facial palsy of the frontal branch. There is a decrease of the left eyebrow position and an involuntary elevation of the contralateral eyebrow with an increase in the number of forehead wrinkles, which indicates excessive activity of the frontalis muscle on this side.Fig. 2.: Postoperative evaluation of the patient. Both eyebrow positions are fully recovered to the original position, and the number of forehead wrinkles is decreased.Some authors have described the eyebrow elevation and increased horizontal forehead wrinkles of the contralateral periorbital region after permanent hemifacial palsy of the frontal branch as being caused by frontalis muscle hypertrophy.2,3 The assumption of muscle hypertrophy, however, has never been confirmed by histopathologic biopsy or diagnostic imaging techniques.4,5 We think this phenomenon is just because of Hering’s law, which, as illustrated by our case just described, can already be observed directly after hemifacial palsy of the frontal branch: hemifacial palsy of the frontal branch results directly in eyebrow depression of the affected side with instant overelevation of the contralateral eyebrow. One-side damage of the frontal branch of the facial nerve causes bilateral activation of both brain parts in an attempt to elevate the depressed eyebrow, thereby resulting in overelevation of the contralateral eyebrow. This bilateral innervation enhances facial asymmetry immediately after peripheral facial nerve damage. DISCLOSURE The authors have no financial interest in relation to the content of this article. There was no financial support. PATIENT CONSENT Patient provided written consent for the use of patient’s images. Haydar A. Gülbitti, M.D.Department of Plastic SurgeryUniversity of GroningenUniversity Medical Centre GroningenGroningen Berend van der Lei, M.D., Ph.D.Department of Plastic SurgeryUniversity of GroningenUniversity Medical Centre GroningenGroningen, and Bergman ClinicsHeerenveen, The Netherlands