Two cases of bronchial ischemia and one case of bronchial perforation associated with SCS were first reported by Shibano et al. in 2015 . Severe mucosal ischemia was noted by intra- or postoperative bronchoscopy in the former 2 cases, and a bronchopleural fistula at the lateral wall of the right B4 had developed in the other patient on POD 15 after right lower lobectomy. Hashimoto et al. have reported a case of tracheal perforation following right upper lobectomy and superior mediastinal lymph node dissection, which was noticed on POD 37 . In all 4 cases, the location of ischemia or perforation was exactly the same site, where the ball electrode tip connected to SCS was directly applied for hemostasis; therefore, the authors undoubtedly assumed that soft coagulation caused the bronchial wall damage.
Distinct from previously reported cases, the patient in this case report had bronchial perforation after bulla cauterization, even though the electrode tip was not directly in contact with the bronchial wall. Based on the operative findings and preoperative CT images, we speculated that the IBT was damaged through the giant bulla during cauterization, which required a relatively long time. Tissues with low blood flow, such as the bronchus, are prone to thermal damage because of the lack of blood flow, which acts as a radiator. Compared with normal lung parenchyma and mediastinal tissues, which are rich in moisture content, low-moisture tissue is also estimated to be easily thermally damaged. The unexpected thermal damage to the IBT by relatively low temperatures with SCS was thought that the bulla inside was heated by prolonged soft coagulation, and the heat was directly transferred to the bronchial wall adjacent to the cyst. This finding warns us to take careful precautions against possible severe damage to the bronchial or tracheal wall by SCS, regardless of whether there is direct contact of the electrode tip with the airway. When SCS is inevitably applied to the airway wall or its adjacent tissue for a long time, intraoperative bronchoscopy should be performed.
Moreover, note that 3 reported cases of airway perforation associated with SCS, including the patient in this case reported, occurred on PODs 13, 21, and 37, respectively. Verkindre et al. have chronologically examined the histological changes in large airways after endobronchial application of soft coagulation in animals . They have shown that coagulation necrosis of the mucosa alone and acute inflammation of the bronchial structure in the early phase (48 h) dramatically resulted in transmural fibrosis and cartilage destruction in the late phase (6 weeks). This suggests that tissue damage to the airway wall by SCS remains over several weeks and that the damage caused by SCS, depending on the extent of the damage, is irreversible. Though covering the damaged area with biological tissue, such as muscle or adipose flap, is deemed appropriate to prevent airway perforation, the effect of this technique is unknown.