Utility of Diffusion-weighted MR Imaging for Evaluating the Depth of Invasion in Oral Tongue Squamous Cell Carcinoma

Abstract

Purpose: The 8th edition of the American Joint Committee on Cancer staging system included the depth of invasion (DOI) for the T classification of oral cancer. However, no standardized method has been established to clinically measure the DOI. This study aimed to investigate the accuracy of MRI-based DOI for oral tongue squamous cell carcinoma (OTSCC) in each MRI sequence.

Methods: We enrolled 49 patients with histologically proven OTSCC, treated surgically between April 2017 and February 2021. We divided the DOI into three groups using 5 and 10 mm, the thresholds for determining the T stage, and retrospectively evaluated the agreement between MRI-based DOI and pathological DOI (pDOI) for each MRI sequence, axial T1-weighted imaging (T1WI), T2-weighted imaging with fat suppression (FS-T2WI), contrast-enhanced T1WI with fat suppression (CE-T1WI), diffusion-weighted imaging (DWI), and apparent diffusion coefficient (ADC) maps. We also divided the DOI into two groups using 3 mm, the threshold for considering elective neck dissection, and evaluated the overestimation rate of MRI-based DOI in lesions with pDOI ≤ 3 mm.

Results: With 5-mm and 10-mm divisions, the accuracy of the DOI assessment was highest on DWI (0.82, weighted kappa = 0.85). With a 3-mm division, the accuracy was also highest on DWI (0.87, kappa = 0.73). The overestimation rate of the MRI-based DOI in lesions with pDOI ≤ 3 mm was lowest on DWI (27.8%).

Conclusion: DOI on DWI exhibits a comparatively higher rate of concordance with pDOI. DWI may be more useful than other MRI sequences in evaluating the DOI of OTSCC.

Keywords: depth of invasion; diffusion-weighted imaging; magnetic resonance imaging; oral cancer; squamous cell carcinoma.

Supplementary Fig. 1

An 80-year-old man with OTSCC in the tip of the tongue. The DOIs measured on axial T1WI, FS-T2WI, CE-T1WI, and DWI were 10.2, 10.9, 12.0, and 5.0 mm, respectively. The pDOI was 7 mm.

Fig. 1

(a) Inclusion and exclusion criteria. (b) We measured DOI as the distance from the horizontal line through the normal mucosa to the deepest point of the lesion. In cases in which the straight line through the normal mucosa appeared to be inappropriately labeled as a “horizontal line,” we considered the distance from the estimated mucosal surface (dashed line) to the deepest point of the lesion as the DOI. Double-headed arrows indicate MRI-based DOI. DOI, depth of invasion; pDOI, pathological DOI.

Fig. 2

Correlation between the DOI on each MRI sequence and the pDOI. MRI-based DOI significantly correlated with pDOI in every MRI sequence. ADC, apparent diffusion coefficient; CE-T1WI, contrast-enhanced T1-weighted imaging with fat suppression; DOI, depth of invasion; DWI, diffusion-weighted imaging; FS-T2WI, T2-weighted imaging with fat suppression; pDOI, pathological DOI; T1WI, T1-weighted imaging.

Fig. 3

A 37-year-old man with right OTSCC. The DOIs measured on axial T1WI, FS-T2WI, CE-T1WI, DWI, and ADC map were 8.5, 5.7, 8.1, 4.2, and 4.5 mm, respectively. Measurement of the DOI was difficult on CECT because the entire lesion could not be recognized due to metallic dental artifact (arrows). The pDOI was 4 mm. ADC, apparent diffusion coefficient; CECT, contrast- enhanced CT; CE-T1WI, contrast-enhanced T1-weighted imaging with fat suppression; DOI, depth of invasion; DWI, diffusion-weighted imaging; FS-T2WI, T2-weighted imaging with fat suppression; OTSCC, oral tongue squamous cell carcinoma; pDOI, pathological DOI; T1WI, T1-weighted imaging.

Fig. 4

A 78-year-old man with right OTSCC. The DOIs measured on axial T1WI, FS-T2WI, DWI, and ADC map were 6.1, 7.1, 6.1, and 6.5 mm, respectively. The pDOI was 4 mm. ADC, apparent diffusion coefficient; DOI, depth of invasion; DWI, diffusion-weighted imaging; FS-T2WI, T2-weighted imaging with fat suppression; OTSCC, oral tongue squamous cell carcinoma; pDOI, pathological DOI; T1WI, T1-weighted imaging.