Evaluating Depth of Invasion in Tongue Carcinoma: Correlation of Intraoral Ultrasound and Magnetic Resonance Imaging and With Histopathological Findings.

BACKGROUND: Tongue carcinoma requires accurate preoperative assessment of depth of invasion (DOI) for optimal management and prognostication. The 8th AJCC/UICC TNM staging system recognizes DOI as a key determinant of T-stage, risk of nodal metastases, and survival. Magnetic Resonance imaging (MRI) offers excellent soft-tissue contrast, whereas intraoral ultrasound (IOUS) provides a rapid, high-resolution, and cost-effective alternative. This study correlates DOI measured on IOUS and MRI with histopathological DOI and evaluates their association with cervical nodal metastasis in early tongue carcinoma. METHODS: This prospective cross-sectional study was conducted over 2 years and included 30 adult patients with histopathologically confirmed tongue carcinoma planned for surgical resection. IOUS was performed with an hockey-stick probe on GE LOGIQ machine and MRI was acquired on a 3 T system using T1W, T2W, and post-contrast 3D VIBE sequences. Post-surgical specimens and neck nodes were sent for histopathological assessment. RESULTS: Both IOUS and MRI showed strong correlation with histopathological DOI (p < 0.01), with IOUS demonstrating slightly higher accuracy (Spearman's ρ = 0.89) than MRI (ρ = 0.86). MRI showed excellent interobserver agreement (ρ = 0.97). T-staging on imaging closely matched histopathology. Bland-Altman analysis showed a mean difference of 0.7 mm (95% LOA: -4.2 to 5.7 mm) for IOUS-DOI relative to histopathological DOI, whereas MRI exhibited a mean difference of 0.2 mm (95% LOA: -5.4 to 5.9 mm). Cervical lymph node metastasis occurred in 8 patients and correlated significantly with higher T-stage (p = 0.029). A DOI > 10 mm predicted increased risk of nodal metastasis. CONCLUSIONS: IOUS and MRI are reliable modalities for preoperative DOI assessment in tongue carcinoma, with IOUS offering marginally superior accuracy in early tongue carcinoma. DOI strongly correlates with nodal metastasis, highlighting its prognostic and surgical importance.