Intra-parotid lymph node metastasis in primary parotid gland cancer: a narrative review of its significance, anatomic distribution, and therapeutic implications

Background and Objective: Intra-parotid lymph node metastasis (LNM) has been proven to be an independent predictor of worse prognosis in patients with primary parotid gland cancer (PGC) as well as cervical LNM. However, the anatomic information or distribution of intra-parotid LNM within the parotid glands and its clinical significance remain largely unexplored. In this narrative review summarizing the relevant literature, we sought to answer the sub-site distribution of intra-parotid LNM in PGC, and suggest therapeutic implications. Methods: A comprehensive review of the literature was conducted by searching the PubMed and Web of Science databases. Manuscripts offering objective data on the incidence, subsite distribution, and prognostic significances of intra-parotid LNM were selected for inclusion in this review. Key Content and Findings: Overall, the rate of intra-parotid LNM appears to be greater than 40% in high-grade PGC but not in low-grade PGC. As for the lymph node (LN) distribution in the normal parotid gland, the majority (>80%) of LNs in the parotid glands are located in the superficial lobe, while the deep lobe contains just one LN on average. The European Salivary Gland Society (ESGS) classification system of the parotid gland sub-site is straightforward and can be applied to confirm intra-parotid LNM. Taking into consideration the intra-parotid LNM location, most intra-parotid LNMs from PGC are observed in the superficial parotid LNs, while metastasis to the deep parotid LNs seems to compose less than 10% of cases. Conclusions: The rate of intra-parotid LNM in the parotid deep lobe is not high enough to justify total parotidectomy in all PGC cases. In some PGC cases, a more selective approach preserving a portion of the deep parotid gland with a low risk of intra-parotid LNM might be an alternative to total parotidectomy.