Reliability of the ‘M-Line’ in the Prediction of the Facial Nerve Position in Patients with Parotid Neoplasms

Abstract

Preoperative radiological assessment of parotid tumours represents a crucial step in the planning of a parotidectomy in order to avoid post-operative facial nerve paralysis. The purpose of this study is to determine the reliability of the novel ‘M-line’ in predicting the facial nerve position and compare it to various radiological methods in the same context. 66 patients whom had underwent parotidectomy for parotid tumours from January 2012 to February 2021 were analyzed. Parotid tumour location were identified using the retromandibular vein, facial nerve line, Conn’s arc, Utrecht line and the ‘M’-line were compared to the intraoperative location of parotid tumours.The ‘M’-line is a novel hypothetical line (drawn between the lateral surface of the mandible to the lateral border of the mastoid process) used to identify the location of the facial nerve radiologically. The ‘M-Line’ and other methods of radiological assessments were associated with statistical significance in predicting if the parotid tumours were superficial or deep to the facial nerve (p-value < 0.05).The ‘M-line’ had demonstrated a sensitivity of 73.6% and 92.3% specificity.It had also yielded the highest accuracy (77.3%) in the prediction of the parotid tumour location in relation to the facial nerve. While the radiological lines represented by the Retromandibular vein,facial nerve line,Utrecht line and Conn’s arc were statistically significant in predicting the location of the parotid tumour in relation to the facial nerve, the M-line was the most accurate and sensitive predictor in our study.The M-Line is a potentially useful tool to predict the location of the facial nerve in relation to a parotid tumour.