Use of Computed Tomography to Predict the Possibility of Exposure of the First Genu of the Facial Nerve Via the Transmastoid Approach

HYPOTHESIS: The purpose of this study was to investigate whether computed tomography (CT) could predict the possibility of first genu exposure of the facial nerve via the transmastoid approach in patients with acute facial paralysis. BACKGROUND: Temporal bone CT is the best method for visualizing the intratemporal segment of the facial nerve canal, which is known to have diverse anatomic variations. METHODS: A prospective study was conducted on 11 patients who underwent facial nerve decompression via the transmastoid approach. Two groups of patients underwent surgery to expose the perigeniculate area via the transmastoid approach. One group included patients who had anatomic parameters of the temporal bone that met the CT criteria, including length of the labyrinthine segment, level of the geniculate ganglion, bony thickness of the lateral semicircular canal, and height interval between the tympanic and labyrinthine segments. The other group included patients with facial paralysis who required facial nerve exploration, especially distal to the geniculate ganglion. Facial nerve decompression was performed in all patients as far proximal in the transmastoid view as was possible without causing damage to the semicircular canals. RESULTS: We correlated the temporal bone CT images and surgical findings in 11 patients who underwent facial nerve decompression via the transmastoid approach. The facial nerves of 6 patients who had anatomic structures that met the CT criteria were successfully exposed to the proximal labyrinthine segment without labyrinthine damage. The facial nerves of another 4 patients who did not have anatomic structures that met the CT criteria could be decompressed only to the geniculate ganglion. CONCLUSION: CT scan can predict the possibility of first genu exposure of the facial nerve via the transmastoid approach based on the CT parameters suggested in this study.