Evaluation of the chorda tympani' s variations of origin from the facial nerve on high resolution CT

Chorda tympani is the largest intratemporal branch of the facial nerve. Separated from the mastoid segment of the facial nerve and move to the superior and anterolateral. It leaves the skull after passing the tympanic cavity and then anterior canalicul. Chorda timpani carries the taste sensation from the anterior two-thirds of tongue and provides the secretomotor stimulation of the salivary glands in the floor of the mouth. Today, helical CT is the gold standard imaging of the temporal bone due to its high resolution quality of bony structures. HRCT is a method that can provide quite thin sections and can be displayed chorda tympani accurately and reliably. Chorda tympani is a structure that may get injured in surgery such as posterior tympanotomy, otosclerosis surgery, cholesteatoma surgery and myringoplasty. After middle ear surgery, postoperative complications associated with the taste sensation develops in 15% of patients. Preoperative evaluation of chorda tympani on HRCT will help reduce the nerve damage that may occur. In our study, we searched retrospectively temporal bone HCRTs, in January 2013-December 2015 in Duzce University, Department of Radiology. Individuals with normal temporal bone structure at least on one side, were included in the study. Multi-planar reconstruction images were created then chorda tympani was imaged and measurements were performed. The distance between chorda tympani and stylomastoid foramen is 3,7±1,6 mm. The furthest distance between the mastoid segment of the facial nerve and chorda tympani is 2,3±0,6 mm. The angle of branching chorda tympani from facial nerve is 28,2±10,7º. In the axial plane, chorda tympani branching localization was found in 4 different ways; %11,7 anteriorly, %52,1 anterolaterally, %33,7 laterally, %2,5 posterolaterally. 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 branching 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.