Evaluation of Variations of the Chorda Tympani Nerve Originating from The Facial Nerve on High Resolution CT

Objective: The aim of this study is to define the anatomical variations of the chorda tympani nerve originating from the facial nerve on high resolution CT (HRCT). Method: A retrospective study of 100 patients who underwent temporal bone HRCT imaging in Duzce University, Department of Radiology. Individuals with normal bone structure at least on one side, were included in the study. Multiplanar reconstruction images were created then chorda tympani was imaged and measurements were performed. Results: Thirty-seven bone were excluded. When the originating localizations of the chorda tympani from the facial nerve were examined, 19(11.7%) anterior, 85(52.1%) anterolateral, 55(33.7%) lateral and 4(2.5%) posterolateral origins. The distance from the origin of the chorda tympani to the stylomastoid foramen was measured as 3.7±1.6 mm. The originating angle of the chorda tympani from the facial nerve was measured as 28.2±10.7º. The widest distance between the chorda tympani and the mastoid segment of the facial nerve was measured as 2.3±0.6mm. The furthest distance between the mastoid segment of the facial nerve and chorda tympani is inversely correlated with the distance between chorda tympani and stylomastoid foramen. The angle of originating chorda tympani from facial nerve is directly correlated with the distance between chorda tympani and stylomastoid foramen. The ratio of extratemporal branching of chorda tympani is %2.4. Conclusions: The chorda tympani can be clearly seen on axial and reformat images on HRCT. Preoperative evaluation of the chorda tympani nerve might help to plan the surgical approach and thus prevent iatrogenic injury during middle ear surgery