A critical evaluation of computed tomography-derived depth of invasion in the preoperative assessment of oral cancer staging

Background: Depth of invasion (DOI) has been introduced into the latest TNM classification of oral squamous cell carcinoma (OSCC). Despite its primarily pathological definition (pDOI), a preoperative evaluation of a radiological DOI (rDOI) would be useful but a standard and practical definition is lacking. The primary aim of this study is to measure the rDOI by computed tomography (CT) and compare it to the pDOI in a cohort of OSCC patients. Then, we analyze the utility and reliability of rDOI in the preoperative setting.

Methods: 58 cases of OSCC operated at our Institution from 2016 to 2019 were included. After accounting for plane-specific shrinkage factors and for different oral subsites, we have compared pDOI and rDOI for each spatial plane by paired difference test and correlation coefficient. Radiological accuracy and survival analysis were also determined to identify rDOI's clinical value.

Results: For lateral tongue, pDOI was more strongly related with axial rDOI (P < 0.01); for hard palate, the best plane was the sagittal one (P < 0.01); in floor of mouth (FOM) lesions, the strongest correlation was with coronal rDOI (P < 0.01), as well as for cheek buccal mucosa; sagittal scans seem to be the best to evaluate dorsum of the tongue and retromolar trigone; gingiva (P < 0.01) was most correctly evaluated in the coronal plane. Overall accuracy of rDOI restaging was 75.41%. Disease-free survival seems to be worse as rDOI increases.

Conclusions: We suggest that with a standardized imaging protocol patients could be better classified according to CT-derived DOI.