Facial synkinesis after experimental compression of the facial nerve comparing intratemporal and extratemporal lesions.

OBJECTIVES/HYPOTHESIS: The anatomical configuration of the facial nerve differs greatly between the intratemporal and extratemporal portions. The purpose of this study was to investigate the incidence of facial synkinesis and misdirection on clamping the facial nerve at the intratemporal or extratemporal portion of the facial nerve in guinea pigs.

STUDY DESIGN

Experimental study.

METHODS

In 16 guinea pigs, the facial nerve was clamped with microsurgical needle forceps at either the extratemporal (group A) or intratemporal (group B) segment. Facial nerve function was evaluated 1 week postoperatively using electroneurography (ENoG), and the incidence of facial synkinesis was evaluated 15 weeks postoperatively using an evoked blink reflex test. Fifteen weeks postoperatively, two retrograde fluorescent tracers (Dil [1-1'-dioctodecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate] and True Blue) were injected into the facial muscles to observe reorganization of the facial nucleus.

RESULTS

No significant difference in the ENoG threshold was observed between groups A and B. In group A, none of the animals developed facial synkinesis and the somatotopic organization of the facial nucleus was not disturbed. In contrast, synkinesis occurred and the somatotopic organization was disturbed in group B.

CONCLUSIONS

A lack of funicular structure within the intratemporal facial nerve increases the possibility of misdirected regenerating axons and synkinesis.