Table 1 Grading criteria of pulmonary artery invasion^a

Grade 0 (no invasion)

No evidence of vessel invasion, ≥1 mm from the closest pulmonary vessel wall (presence of a fat plane between tumor and vessel wall)

Grade 1 (minimal invasion)

Tumor invasion with 0 mm to the closest pulmonary vessel wall, no fat plane, without presence of narrowing or truncation of vessels, nor signs of vessel wall damage (irregularity, discontinuity or intra-luminal mass formation)

Grade 2 (moderate invasion)

Circumferential involvement with narrowing or truncation

Grade 3 (extensive invasion)

Tumor invading pulmonary vessel extensively with any sign of vessel wall damage: irregularity, discontinuity or intra-luminal mass formation or massive haemorrhage due to the tumor invading pulmonary artery