Depth of Invasion in Squamous Cell Carcinoma of Buccal Mucosa: Is Magnetic Resonance Imaging a Good Predictor of Pathological Findings?

This prospective analysis of patients with squamous cell carcinoma of the buccal mucosa, aimed to analyze the correlation between depth of invasion (DOI) observed in pre-operative imaging and the post-operative histopathological findings, and to assess the predictive value of magnetic resonance imaging.All cases of squamous cell carcinoma of buccal mucosa, planned for primary surgery followed by adjuvant treatment, between June 2017 to December 2019 were included in the analysis. All patients were taken up for imaging using 3 Tesla MR imaging system and subsequently had undergone surgery. The imaging parameters and the histopathological data were analyzed statistically.Of the 45 patients analyzed, 86.7% were males. Mean age at presentation was 60.62 years. All had squamous histology, with 62.2% being moderately differentiated. 68.9% were T4, 46.7%, N0 and 31.3%, N3. Six node positive patients showed perinodal invasion on histopathology. The mean DOI observed in MRI was 16.54mm, while that in histopathological evaluation was 20.24mm.A significant correlation was observed between imaging and histopathology values in terms of the DOI, with Spearman's Rho correlation coefficient showing 0.693 (p-<0.001). Nodal positivity observed in the imaging and the histopathological findings showed only a moderate correlation of 0.409, with p values of 0.005 (Pearson, Spearman's rho) and 0.007 (Kendall's tau_b). A significant correlation was not observed between nodal involvement and DOI assessed by imaging nor with histopathological assessment. With a cut-off value of 5mm as imaging DOI, the positive predictive value (PPV) for nodal positivity was only 37.14%, while the negative predictive value (NPV) was 95%. The sensitivity was 96.3%, and specificity 30.16%. When the cutoff was raised to 10mm, the values for PPV, NPV, sensitivity and specificity were, 44.07%, 61.29%, 68.42% and 36.54%.Despite being a histopathological parameter, accurate or near accurate evaluation of DOI can be achieved using MR imaging. Our study convincingly shows that magnetic resonance imaging can be considered the imaging of choice for the evaluation of depth of invasion of the tumour in squamous cell carcinoma of the buccal mucosa, though it fails to show any predictive value for nodal involvement.