[Microsurgical anatomy of the facial nerve trunk in facial-hypoglossal nerve anastomosis].

OBJECTIVE

To study the microsurgical anatomy of the facial nerve (FN) trunk and provide some important morphometric data about facial-hypoglossal nerve anastomosis (FHA).

METHODS

Bilateral microsurgical dissection was performed on the heads of 9 cadavers fixed with formalin with three different methods. In the first method, the posterior belly of the digastric muscle was used as a mark, and the FN trunk was identified on the medial side of this muscle. In the second method, dissection was initiated at the parotid gland, the FN trunk was identified at its entrance into the parotid gland. In the third method, the styloid process was identified and traced back to the stylomastoid foramen (SMF). The FN trunk was identified on its emergence from the SMF. In every dissection, the whole FN trunk was exposed; its diameter and depth at the the SMF and its length were measured; its relationship, with other structures was studied.

RESULTS

The FN invariably emerged from the cranial base through the SMF. Its diameter upon its emergence from the foramen was 2.57 +/- 0.60 mm. The mean minimal distance of the FN trunk from the skin surface in this area was 22.62 +/- 2.88 mm. The length of the FN trunk was 15.71 +/- 1.97 mm. The distance between the bifurcation and the mastoidale was 18.20 +/- 4.41 mm. The distance between the bifurcation and the mandibular angle was 39.91 +/- 8.38 mm. The distance between the mastoidale and the SMF was 17.91 +/- 2.68 mm. The branches from the FN trunk proximal to its bifurcation were the posterior auricular nerve, the digastric muscle nerve and the stylohyoid muscle nerve.

CONCLUSION

The third method to expose the FN trunk on its emergence from the SMF is safe and reliable. It is feasible to use only part of the hypoglossal nerve fibers for anastomosis with the FN trunk.