Surgical treatment and prognosis of posteriorly invading oral cancer: Potential clinical significance of pterygomandibular raphe

BACKGROUND/PURPOSE: The prognosis of oral squamous cell carcinoma (OSCC) with posterior invasion is poor. We examined whether the pterygomandibular raphe (PMR) is useful for the diagnosis of invasion and determination of surgical methods. MATERIALS AND METHODS: Of 390 patients with OSCC treated surgically at our hospital between June 2009 and June 2020, 80 patients with posterior invasion were included in the study. Preoperative magnetic resonance imaging was used to classify the lesions into three types: non-contact with PMR (non-contact type), contact with PMR (contact type), and invasion beyond PMR (invasion type). We compared the local control, recurrence, and survival rates of each of the three types. RESULTS: The invasion type showed a significantly higher recurrence rate than the non-contact type (P < 0.001) and contact type (P = 0.018). Overall survival rate comparisons showed that the invasion type had significantly worse prognosis than the non-contact (P = 0.004) and contact types (P = 0.041). CONCLUSION: OSCCs with posterior invasion beyond the PMR showed a poor treatment outcome and, therefore, should be treated with caution. The initial surgery is especially important and must ensure local control. This study indicates that the PMR is an important criterion for surgical method determination and that invasion beyond the PMR is a predictor of local recurrence and poor prognosis.