2.3 Images analysis
The laryngoscope images of vocal cord leukoplakia were independently evaluated by two experienced laryngologists who were not informed of the pathological diagnosis or other clinically relevant information. The two laryngologists recorded the characteristics of vocal cord leukoplakia by laryngoscopy, including size, thickness, texture, hyperemia, boundary, and whether anterior commissure and bilateral vocal cords were involved. Their consensus was used as the final diagnosis result. Such characteristics were defined as follows: (1) size (unilateral vocal cord leukoplakia covering more than half of the total area of the vocal cord was defined as large leukoplakia; otherwise, the definition was small leukoplakia); (2) thickness (leukoplakia was considered thick if obviously exceeding the height of the vocal cord surface and the blood vessels beneath the lesion were not visible; otherwise, it was considered thin); (3) texture (leukoplakia with a rough and uneven surface, which may manifest as papillary, verrucous, granular, or scattered nodules was defined as irregular, whereas if the surface of the lesion was flat and smooth, and the thickness of each part was almost equal, it was judged to be regular); (4) hyperemia (mucosal erythema or dilated blood vessels seen on or around the leukoplakia were considered hyperemia); (5) boundary (if the boundary between the lesion and the surrounding normal mucosa was clear, neat, and sharp, the lesion boundary was considered clear, whereas if the boundary was disordered, fuzzy, and rough, the lesion boundary was deemed unclear); (6) whether anterior commissure was involved; (7) whether bilateral vocal cords were involved; (8) the general classification of vocal cord leukoplakia under a laryngoscope as proposed by Zhang et al. 5 The groups in this classification system were as follows: (1) flat and smooth type; (2) bulge and smooth type; and (3) bulge and rough type.