Patterns of facial (Level IX) node metastasis in head and neck cancer: Multicenter data supporting sublevel IXa/IXb delineation

Purpose: Bucco-facial nodes are at risk of harboring metastases from mucosal cancers of the skin, nose, maxillary sinus, and buccal mucosa. The incidence of level IX involvement is not well established but likely below 10%. This multicenter study aims to evaluate the incidence of metastases to level IX and its subgroups and assess its impact on target volume delineation. Materials and methods: A search for eligible patients was conducted using the Aria, Mosaiq, and Redcap databases. We included patients with cancer of buccal mucosa, retromolar trigone, oral gum, nasal cavity, nasal vestibule, and paranasal sinuses. Clinical history, imaging (CT, MRI, [18F]-FDG PET), and pathology reports were reviewed. Facial nodes were classified according to Rouvière's anatomical subgroups. Results: Among 102 patients (66 men, 36 women; median age 74), level IX metastases were identified in 7 cases (6.8%). Two cases were diagnosed histopathologically in patients without preoperative imaging evidence: one retromolar trigone and one buccal mucosa tumor. Five cases were identified clinically: one nasal vestibule tumor, three retromolar trigone tumor, and one buccal mucosa tumor. No cases originating from the nasal cavity or paranasal sinuses were found. The level IX subgroups involved were: supramandibular alone (n = 2), supramandibular + buccinator (n = 3), buccinator alone (n = 1), and infraorbital alone (n = 1). Conclusion: Although rare, facial node metastases are clinically relevant in advanced or recurrent retromolar trigone, buccal mucosa and nasal vestibule cancers. Based on our data, a subclassification of level IX into IXa (supramandibular and buccinator) and IXb (infraorbital) is proposed.