Retrograde Labeling of the Rat Facial Nerve with Carbocyanine Dyes to Enhance Intraoperative Identification

Abstract

Removal of head and neck neoplasms, especially those of the parotid gland and those of the internal auditory canal and cerebellopontine angle, often requires microdissection of the facial nerve. Displacement or splaying of the nerve can make it difficult to identify facial nerve fibers and/or distinguish them from surrounding tissues. Here we tested a method of labeling the facial nerve with fluorescent lipophilic dyes as a method of providing intraoperative visual confirmation of nerve fibers. The facial nerves of adult rats were retrogradely labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO), or 3,3'-dilinoleyloxacarbocyanine perchlorate (Fast DiO) either by direct application to the nerve sheath or by microinjection into the facial muscles. The nerves were examined 30 days after dye application by means of a dissecting stereomicroscope equipped with epifluorescence filters. Of the dyes tested, Fast DiO proved to be the most effective, providing labeling of the nerve sufficient to be seen with combined fluorescent and bright field stereomicroscopy. Nerve conduction studies indicated that fluorescent labeling did not adversely affect nerve function. These results raise the possibility of using fluorescent lipophilic dyes to label nerves as a method of enhancing identification and distinguishing nerve fibers during surgery.