Effectiveness of anatomic criteria for predicting parotid tumour location

Objective We evaluated the accuracy, positive predictive value ( PPV ), negative predictive value ( NPV ), specificity and sensitivity of eight anatomic landmarks to differentiate parotid deep lobe tumours from superficial lobe tumours: the lateral margin of the retromandibular vein ( RMV ), a straight line from the facial nerve trunk ( FN trunk) to the mandibular ramus ( FN line), a straight line from the FN trunk to the RMV ( tRMV ), a straight line from the FN trunk to the lateral margin of the masseter ( tM asseter), a straight line from the ipsilateral vertebral posterior end to the RMV (U‐line), an arc with a radius of 8.5 mm centred on the mandibular ramus (Conn's arc), a straight line from the lateral surface of the masseter muscle to the lateral margin of the RMV ( rM asseter) and an angle from the FN line, tumour and the lateral margin of the masseter muscle ( FTM angle). Methods A total of 181 patients with a parotid gland tumour who underwent parotidectomy at a tertiary hospital were identified retrospectively from May 2005 to May 2013. Pre‐operative computed tomography and intraoperative findings were compared to evaluate each landmark. Results rM asseter (accuracy: 85.5%, PPV : 90.0%, NPV : 85.12%, specificity: 98.1%, sensitivity: 22.2%) and tM asseter (accuracy: 86.3%, PPV : 80.0%, NPV : 87.1%, specificity: 97.1%, sensitivity: 44.4%) showed superior results as diagnostic criteria. Conclusion rM asseter and tM asseter were useful as anatomic landmarks to differentiate a parotid deep lobe tumour from a superficial lobe tumour.