Posterior Transposition of the Facial Nerve Using a Modified Transcochlear Approach
Introduction: The tortuous course of the facial nerve makes it susceptible to iatrogenic injury during resection of skull base lesions or reconstruction following trauma. Familiarity with facial nerve anatomy, including the various vascular contributions along its path allows the surgeon to capitalize on facial nerve re-routing techniques that expand surgical corridors while minimizing the risk of nerve palsy. Within the fallopian segment of the facial nerve epineurium, the lateral aspect is important because it contains a network of fine capillaries and an anastomosis between the proximal blood supply from the petrosal artery and the distal supply from the stylomastoid artery. Posterior re-routing of the facial nerve provides maximum exposure compared with anterior re-routing, but is utilized less frequently given a higher risk of post-operative nerve palsy with standard approaches. We demonstrate a safe technique for posterior re-routing of the facial nerve in the transcochlear approach.
Methods: Initial mastoidectomy, facial nerve dissection and skeletonization of the internal auditory canal were performed as in translabyrinthian approaches on 5 preserved cadaveric heads (10 sides) and in numerous clinical cases of petroclival lesions. To avoid drilling on the vascularized lateral surface of the nerve, bone surrounding the nerve was drilled anteriorly and posteriorly, creating troughs and leaving a bony covering of ∼2 mm. The entire horizontal and descending portions of the nerve were exposed, the remaining bone was gently peeled off and the nerve was elevated inferior-superiorly. The chorda tympani were transected, the tympanic portion of the facial nerve was skeletonized to the geniculate ganglion and the greater superficial petrosal nerve was sectioned at its origin in the ganglion. A dural opening was made over the internal auditory canal, the facial nerve was separated from the vestibulocochlear complex and the eighth nerve was transected.
Results: After arachnoid dissection, the facial nerve was reflected out of its position in the internal auditory and fallopian canals and transposed posteriorly. It was then retracted away from the surgical field for the remainder of the procedure where the cochlea was removed, the genu of the intrapetrous carotid artery was exposed, the petrous apex was removed and a surgical corridor extending between the inferior and superior petrosal sinuses was created. A T-shaped dural incision, made parallel to the sigmoid sinus and parallel to the inferior petrosal sinus in the perpendicular direction, allowed for routine visualization of cranial nerves V, VII, IX, X, and XI as well as the clivus, bilateral vertebral arteries, and the basilar artery. Drilling along the anterior and posterior aspects of the nerve destabilized it while mitigating the risk of vascular and/or thermal injury. No cases of persistent facial nerve palsy were observed.
Conclusions: Given the tortuous route of the facial nerve, this technique for transposition of the facial nerve in the transcochlear approach allows for clear identification of petroclival anatomy and preservation of facial nerve function. Posterior re-routing of the facial nerve is a valuable and safe technique that allows for maximal exposure of the clival and petroclival regions.