Internal architecture of the parotid gland at MR imaging: facial nerve or ductal system?

A radiologic-anatomic study was performed to determine the nature of the low-signal-intensity curvilinear structures currently seen in the normal parotid gland on axial T1-weighted magnetic resonance (MR) images. These structures are considered by some to represent the intraparotid facial nerve. After cannulation of the Stensen duct, the authors imaged the parotid gland of two cadavers in situ before and after intraductal injection of gadolinium tetrazacyclododecanetetraacetic acid. Retrograde filling was obtained in one gland. The same sections were used throughout a subsequent anatomic study, allowing correlation of the MR findings with the macroscopic and histologic appearance of the gland. Comparison of MR images and gross and histologic sections established that two intraparotid facial nerve segments, although identified from the histologic study, were not visible on corresponding MR images. Many areas of low signal intensity seen within the gland were found to represent the main duct and some afferent ductal branches.