Magnetic resonance imaging findings of styloglossus and hyoglossus muscle invasion: Relationship to depth of invasion and clinical significance as a predictor of advisability of elective neck dissection in node negative oral tongue cancer

Purpose: By comparing styloglossus and hyoglossus muscle invasion (SHMI) of oral tongue squamous cell cancer (OTSCC) on MR imaging to pathological depth of invasion (DOI) and prognosis, we aimed to evaluate the clinical significance of MR imaging findings of SHMI. Method: Forty-five, early stages and clinically NO OTSCCs were retrospectively reviewed. Data included pathological DOI, DOI on MR imagings, two-year potential cervical lymph node positive, locoregional control, disease-free survival, and overall survival. Data were statistically compared between the groups with MR evidence of SHMI (SHMI + ) and without MR evidence of SHMI (SHMI-). Results: There were 17 SHMI + and 28 SHMI-. Elective neck dissections performed on 13 cases revealed five node positive cases, all of which were SHMI + . Pathological DOI in SHMI + was significantly larger than SHMI-(average 9.0 vs 4.6 mm, p < 0.001). All SHMI + revealed pathological DOI larger than 4 mm. The two-year potential cervical lymph node positive rate of SHMI + was significantly higher than SHMI- (p = 0.01). Locoregional control rate and disease-free survival of SHMI + were significantly lower than in SHMI- (p = 0.02). There was no significant difference in overall survival. Interobserver agreement in evaluation of SHMI on MR imaging was good (kappa value = 0.72, p < 0.001). Conclusions: Pathological DOIs of SHMI + were all larger than 4 mm, which is the cut-off point that National Comprehensive Cancer Network recommends for neck dissection, and SHMI + had a worse prognosis than SHMI-. SHMI + can be used as a criterion for elective neck dissection.