2.1 Selection of images
We retrospectively reviewed all laryngoscopic images from patients with vocal cord leukoplakia at our institution between October 2018 and October 2020. The laryngoscope used during this period was the Olympus BF-H290 (Olympus Medical Systems Corp, Tokyo, Japan). The images were originally taken by senior expert endoscopists and categorized by 2 imaging techniques: WLI and NBI. According to surgical treatment needed, we classified the images of vocal cord leukoplakia into two types based on the pathology[7, 15] (Figure 1 ): 1) a nonsurgical group (NSG) including LG dysplasia, and 2) a surgical group (SG) including HG dysplasia and invasive carcinoma. When multiple pathological types appeared in a lesion, senior type was determined.