What happened, in summary

A 68-year-old man who smoked and had a family history of lung cancer was followed for a small lesion in segment 6 of the left lung. Over 1 year of CT surveillance, the lesion gradually enlarged to 8 mm. Before surgery, three-dimensional CT bronchography and angiography mapped the segmental anatomy, including the A6 arteries and V6 veins. During a left S6 segmentectomy, the surgical team first divided the A6 artery and fully expanded the lungs with 100% oxygen. As the lung began to deflate, the target S6 segment became visibly lighter than the neighbouring basal segment because its blood supply had been interrupted. This temporary colour boundary appeared within about 20 seconds and was marked immediately with electrocautery. Approximately 10 minutes later, the final inflation–deflation intersegmental plane formed and closely matched the earlier marking. Microscopic examination of the marked boundary also showed fewer red blood cells on the S6 side, supporting that the temporary colour change corresponded to the true segmental border. The approach allowed the team to identify the tissue boundary while preserving the surrounding lung. Final pathology of the resected lesion showed minimally invasive adenocarcinoma classified as pT1a(mi).