Primary anastomosis of extensive facial nerve defects: an anatomic study

Recent evidence suggests that end-to-end repair of the facial nerve with or without rerouting is functionally and cosmetically superior to grafting. Most surgical experts feel that facial nerve defects of greater than 10 mm cannot be successfully managed without grafting. Our clinical experience with mastoid-extratemporal rerouting has shown that neural defects greater than 10 mm are amenable to tension-free primary anastomosis with favorable outcome. To verify this observation, we performed the first human cadaveric study to quantify the maximal length of facial nerve defect that is amenable to a tensionless primary anastomosis. Concentrating on the region of the nerve between the second genu and the pes anserinus, four different hearing preserving rerouting procedures were performed. Our investigation demonstrated that decompression and mobilization of the facial nerve allows tension-free closure of 8.2 +/- 0.7 mm defects. Dissection of the tympanic portion of the temporal bone in addition to decompression and mobilization increases the repairable defect size to 14.0 +/- 1.7 mm. Retroposition of the parotid gland adds roughly 3.5 mm to the length of facial nerve gained with either of the above procedures. The most extensive mastoid-extratemporal rerouting procedure with retroposition of the parotid gland, which we refer to as radical temporofacial rerouting of the facial nerve, allows closure of neural defects of 17.6 +/- 1.7 mm. Our results should encourage surgeons to repair facial nerve defects of between 10 and 17 mm by rerouting with primary anastomosis, rather than by grafting.