Total-length invasion of the facial nerve by parotid carcinoma ex pleomorphic adenoma.

A case of parotid carcinoma extending along the facial nerve up to the internal auditory canal is presented. Total parotid resection with neck dissection was performed, as well as resection of the ear canal, eardrum, ossicles, and transmastoid and translabyrinthine facial nerve, and obliteration using the fascia lata and fatty tissue. This was followed by adjuvant radiotherapy. The facial nerve showed continuous swelling along its length with lump formation at the site of the geniculate ganglion and the internal acoustic canal. Pathological examination revealed the salivary duct carcinoma subtype of carcinoma ex pleomorphic adenoma. Within the facial nerve, the epineurium, perineurium and endoneurium were affected throughout its length. Preoperative MRI with a contrast medium revealed the site of lump formation on the facial nerve, though it did not reveal the consecutive spread of the tumor along the nerve trunk. CT of the temporal bone is strongly recommended for detection of swelling of the temporal bone segment of the nerve trunk, which could provide confirming evidence of invasion by a parotid carcinoma.