Salivary gland malignancy – perineural spread and the skull base

Abstract

Perineural spread (PNS) is a distinct form of tumour spread with special significance in salivary gland tumours. The incidence of PNS in salivary cancer depends on histological subtype. Adenoid cystic carcinoma, salivary duct carcinoma have high incidence of PNS while mucoepidermoid carcinoma and acinic cell carcinoma have lower incidence. The presence of PNS is a significant negative factor for local recurrence and disease free survival but may not affect overall survival. The facial nerve (CNVII), the maxillary branch (CNV2) and mandibular branch (CNV3) of trigeminal nerve are the commonest nerves involved by PNS. Clinical symptoms indicating PNS included nerve palsy, parathesia and pain. MRI is the best imaging option to detect PNS. Gross surgical resection of the primary and the involved nerve should be the primary treatment of salivary cancer with PNS. This may imply facial nerve resection, lateral temporal bone resection or resection of trigeminal ganglion. Adjuvant radiation reduces the incidence of local recurrence and recurrence in the skull base but the impact on overall survival is debatable. The radiation field should include the skull base to prevent recurrence in the skull base. Intensity modulated radiotherapy (IMRT) allowed the delivery of high dose radiation to the targeted volume in the skull base while avoiding critical neural structures. In conclusion, PNS should be taken into consideration in the overall management of salivary cancer. Appropriate imaging to detect PNS; complete resection of the involved nerve with clear margins and post-operative adjuvant radiotherapy should be employed to achieve best possible cure.