Fig. 2.

a Difficulty in accurate horizon estimation due to adjacent uninvolved mucosa present on one side only. The arcuate yellow line represents the most likely natural contour and the most appropriate horizon. b Angulated adjacent mucosa limiting horizon estimation. c Arcuate line of horizon replicates the natural rounded contour of the lateral border of tongue rather than drawing a straight line from the edge of the adjacent uninvolved mucosa. d In a polypoidal non-verrucous/non-papillary tumour, the mucosa is heaped up by the tumour and thickness (calculated from yellow line) is a better measure of tumour bulk than depth of invasion