Frozen section detected perineural spread in a grossly normal nerve away from tumor changes the surgical plan in parotid cancer.

Perineural spread (PNS) through the facial nerve is a well-recognized pathway of spread in parotid cancers. Negative margins in the facial nerve are important in the total extirpation of cancer. We report a case of mucoepidermoid carcinoma of the parotid which was involving only the upper temporofacial division of the facial nerve at the periphery clinically and per-operatively. The upper trunk was divided at about 3cm away from the tumor at its junction with the lower trunk and the nerve was grossly normal. To our surprise disease was extending at this distance as a PNS in the frozen section analysis. This unexpected finding made the resection margin positive and we had to sacrifice the main trunk of the facial nerve as back as possible in the parotidectomy field for a negative margin in the nerve which was confirmed with frozen section again. The case emphasizes the importance of microscopic margin assessment of facial nerve in parotid cancers with the involvement of nerve at branches, even if imaging is negative or gross disease is not seen at the cut end or distant from the tumor-involved area.