Differentiating tumours of the deep and superficial lobes of the parotid gland by computed tomographic sialography.

Parotid computed tomography (CT) combined with sialography is an established method of determining intrinsic from extrinsic tumours in and around the parotid gland. However, differentiation of deep from superficial lobe tumours lacks reliability. Various anatomical landmarks including Stensen's duct, the retromandibular vein, the styloid process, the posterior belly of the digastric muscle and more recently an arc 8.5 mm from the posterior border of the mandible have been used to predict the course of the facial nerve and hence divide the parotid into its deep and superficial portions. Our recent experience of CT in 17 cases of intrinsic parotid tumours and the results of surgery have been reviewed in an attempt to assess the reliability of these various landmarks. In 14 out of the 17 cases (82%) the relationship of the Stensen's duct to the tumour was well shown, and correct differentiation of deep from superficial lobe tumours could be made. We conclude that the relationship of the tumour to the Stensen's duct is most accurate in differentiating tumours of the deep and superficial lobes of the parotid.