Criteria for differentiating superficial from deep lobe tumours of the parotid gland by computed tomography.

A retrospective analysis of the CT images of 36 parotid tumours was undertaken to evaluate the potential value of certain criteria for distinguishing tumours of the superficial lobe from those of deep lobe. The criteria were one of three hypothetical lines indicating the course of the facial nerve, or the course of Stensen's duct. The lines representing the course of the facial nerve are straight lines connecting the main facial nerve trunk with the lateral border of the masseter (line 1), the lateral border of the mandible (line 2) and the retromandibular vein (line 3). Line 1 was significantly more accurate than line 2 or line 3 (P < 0.05); all of superficial (28/28) and 63% of deep lobe tumours (5/8) were correctly diagnosed. On the other hand, when Stensen's duct was used as the criterion, all the superficial (8/8) and deep lobe tumours (3/3) were correctly diagnosed. However, this criterion could be applied only to those cases where both the tumour and Stensen's duct were demonstrated on the same CT-sialogram.