Terence M. Myckatyn, M.D.1 and Susan E. Mackinnon, M.D.1
An intimate knowledge of facial nerve anatomy is critical to avoid its inadvertent injury during rhytidectomy, parotidectomy, maxillofacial fracture reduction, and almost any surgery of the head and neck. Injury to the frontal and marginal mandibular branches of the facial nerve in particular can lead to obvious clinical deﬁcits, and areas where these nerves are particularly susceptible to injury have been designated danger zones by previous authors. Assessment of facial nerve function is not limited to its extratemporal anatomy, however, as many clinical deﬁcits originate within its intratemporal and intracranial components. Similarly, the facial nerve cannot be considered an exclusively motor nerve given its contributions to taste, auricular sensation, sympathetic input to the middle meningeal artery, and parasympathetic innervation to the lacrimal, submandibular, and sublingual glands. The constellation of deﬁcits resulting from facial nerve injury is correlated with its complex anatomy to help establish the level of injury, predict recovery, and guide surgical management. KEYWORDS: Extratemporal, intratemporal, facial nerve, frontal nerve, marginal mandibular nerve
he anatomy of the facial nerve is among the most complex of the cranial nerves. In his initial description of the cranial nerves, Galen described the facial nerve as part of a distinct facial-vestibulocochlear nerve complex.1,2 Although the anatomy of the other cranial nerves was accurately described shortly after Galen’s initial descriptions, it was not until the early 1800s that Charles Bell distinguished the motor and sensory components of the facial nerve.3,4 Facial nerve anatomy is categorized in terms of its relationship to the cranium or temporal bone (intracranial, intratemporal, and extratemporal) or its four distinct components (branchial motor, visceral motor, general sensory, and special sensory). The plastic surgeon beneﬁts from a basic knowledge of the intracranial and intratemporal components of the facial nerve to help localize facial nerve pathology and distinguish extratemporal from facial nerve lesions at other anatomic locations. Similarly, a knowledge of the four distinct
components of the facial nerve reminds the surgeon that the facial nerve is composed not exclusively of voluntary motor ﬁbers but also of parasympathetics to the lacrimal, submandibular, and sublingual glands; sensory innervation to part of the external ear; and contributions to taste at the anterior two thirds of the tongue.
INTRACRANIAL ANATOMY OF THE FACIAL NERVE Voluntary control of the branchial branch of the facial nerve is initiated intracranially by supranuclear inputs arising from the cerebral cortex projecting to the facial nucleus. These cortical inputs are arranged with forehead representation most rostral and eyelids, midface, and lips sequentially caudal to this.5 The pyramidal system is composed of corticobulbar tracts that project voluntary, ipsilateral cortical inputs via the genu of the internal capsule to the seventh cranial nerve nuclei of the pontine
Facial Paralysis; Editor in Chief, Saleh M. Shenaq, M.D.; Guest Editor, Susan E. Mackinnon, M.D. Seminars in Plastic Surgery, Volume 18, Number 1, 2004. Address for correspondence and reprint requests: Susan E. Mackinnon, M.D., Suite 17424, East Pavilion, 1 Barnes-Jewish Hospital Plaza, St. Louis, MO 63110. 1Division of Plastic Surgery, Washington University School of Medicine, St. Louis, MO. Copyright # 2004 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001 USA. Tel: +1(212) 584-4662. 1535-2188,p;2004,18,01, 005,012,ftx,en;sps00103x.
SEMINARS IN PLASTIC SURGERY/VOLUME 18, NUMBER 1
tegmentum. Cell bodies of the upper facial motor nerves giving rise to the frontal branch receive bilateral cortical inputs, and neurons to the remainder...