Fig. 1From: Grading criteria for venous invasion in thoracic esophageal squamous cell carcinomaVI refers to tumor cells permeating into blood vessels. A: Example of VI indicating the maximal size (arrow) of VI. B: Example of VI showing the number of VI (arrow) (1–3); C: Example of VI showing the number of VI (arrow) (≥ 4). D: Example of extramural venous invasion (arrows)Back to article page