Localization of parotid lesions to the superficial and/or deep parotid gland is an essential aspect of imaging and vital information which needs to be conveyed to the surgeon.
Measurement
The following lines are proposed for differentiating superficial from deep lobe:
Conn's arc (CA): drawn with a radius of 8.5 mm, centered on the posterior-most point of the mandibular ramus
facial nerve (FN) line: connects the lateral surface of the posterior belly of the digastric muscle to the lateral surface of the cortex of the ascending mandibular ramus
Utrecht (U) line: connects the dorsal most point seen on the ipsilateral half of a vertebra and the most dorsal point of the retromandibular vein (which runs posterolaterally to the mandibular ramus at the level of the parotid gland)
Interpretation
Of the aforementioned lines, good results have been seen with the U line and the FN line, with the FN line being the more reliable and reproducible method of prediction for tumor location on MR imaging.
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