64.1 Introduction

The facial nerve (FN) is one of the most important structures in the skull base and its tortuous transtemporal course poses a formidable challenge to a lateral skull base surgeon. Saving or salvaging the FN is often as important as tumor clearance itself, if not more, because of the social, emotional, and psychological consequences of a damaged nerve, especially in young patients. The FN is intimately involved with the vestibular schwannoma (VS) capsule and in most cases is found adherent to the tumor. There is a small but significant number of patients in whom the goals of total tumor removal and FN preservation are not compatible. In some situations, the surgeon may decide in favor of total tumor removal, as the possibility and consequences of an aggressive growing residual tumor are more hazardous than a compromised FN. In other circumstances, the FN may be accidentally sectioned during tumor removal. Once the nerve is interrupted, reconstruction must be performed immediately to obtain the best results, either by means of a primary end-to-end anastomosis or by a cable nerve graft interposition.s. Literatur The results of immediately establishing continuity of the FN have been found to be superior to alternatives such as facial–hypoglossal anastomosis, with a significant number achieving House–Brackmann (HB) grade III function in the long term, not to mention the obvious benefit of avoiding a subsequent additional procedure.s. Literatur ^,​ s. Literatur In 2009, we reported our experience with intracranial cable nerve grafting for VS in 33 cases and found that approximately 75% of patients achieve HB grade III function at 1 year (Table 64‑1 ).s. Literatur We recently updated our series and found similar results in a larger cohort of patients with VS and other pathologies.s. Literatur It is generally unacceptable that in the event of FN interruption during VS surgery, no intraoperative attempt is made to reestablish continuity of the FN.s. Literatur ^,​ s. Literatur In this chapter, we will discuss the techniques and results of FN grafting after VS excision.

64.2 Preoperative Protocols

Pre- and postoperative FN function should be recorded according to the HB grading system.s. Literatur To precisely evaluate FN function, color photographs are taken of the face in a minimum of four positions (facial muscles at rest, tight closure of eyes, raised eyebrows, and smiling and pouting lips) during the preoperative workup and postoperatively, when FN paresis is apparent.s. Literatur All cases are evaluated with thin slice magnetic resonance imaging with contrast enhancement.

64.3 Indications for Cable Nerve Graft Interposition of the Facial Nerve

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  Grafting is considered when there is a definite and complete interruption of the FN during tumor removal and when a proximal stump of the FN is available at the brainstem that is long enough for the anastomosis.

  
  
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  If there is no tension and retraction of the two nerve ends (proximal and distal) and the apposition can be self-maintained without the help of any instrument, an end-to-end anastomosis is indicated.

  
  
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  If the proximal stump of the FN is unavailable, too short, or severely injured, FN reinnervation using a donor nerve, such as the hypoglossal or masseteric branch of V3, should be considered.

  
  
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  When anatomical continuity of the nerve is confirmed but the nerve shows no response during electrical stimulation, it is advisable to leave the nerve undisturbed and consider reinnervation procedures at a later stage if satisfactory spontaneous recovery does not occur. In most cases, postoperative total paralysis of the anatomically intact nerve recovers considerably over 12 months.s. Literatur The rate of recovery may provide the surgeon with important information regarding ultimate prognosis as discussed further in Chapter 66.

64.4 Preferred Cable Nerve Grafts

The two nerves most commonly used for FN grafting are the great auricular nerve and the sural nerve (SN). Both nerves are suitable for use because of their comparable size to the FN and because their loss produces minimal sensory loss that is generally acceptable to patients. In our practice, we prefer the use of the SN (Fig. 64‑1 ) because a longer graft can be harvested if needed and because the harvest of the nerve can be done by an assistant while the surgeon continues working on the tumor. Over the years, the SN cable graft interposition has developed as a standard procedure for FN repair. In 1885, Albert Einige performed the first two cases of SN reconstruction for a 3-cm median and a 10-cm ulnar nerve defect, respectively.s. Literatur Seventy years later, in 1955, John Conley performed the first case of great auricular nerve interposition of the FN after total parotidectomy.s. Literatur Recent studies have shown that cable nerve graft interpositioning has the potential to provide as good a result as a primary end-to-end anastomosis.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur However, the best possible postoperative outcome is HB grade III regardless of the graft material used or the technique employed, because frontal muscle function rarely recovers and a certain degree of synkinesis is unavoidable after grafting.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur

64.5 Types of Cable Nerve Graft Interposition Anastomosis

The site of anastomosis is based on the proximal and distal sites where the nerve is involved. According to this, three groups can be described: (1) intradural anastomosis, wherein the proximal anastomosis is at the brainstem and the distal site is in the internal auditory canal (IAC; Fig. 64‑2 a); (2) transdural anastomosis, wherein the proximal site is in the cerebellopontine angle (CPA) or the IAC and the distal site is in the part of the temporal bone that remained after excision of the lesion (Fig. 64‑2 b); and (3) extradural anastomosis, wherein both the proximal and distal sites of anastomosis are in the temporal bone or extratemporally (pre-parotid and parotid parts of the FN; Fig. 64‑2 c,d). In case of FN reconstruction after VS resection, the anastomoses are usually intradural.