Intraoperative pulmonary air-leak sites in catamenial pneumothorax: a retrospective 15-case surgical series.

BACKGROUND: The mechanism by which catamenial pneumothorax develops remains unclear. Although diaphragmatic lesions are characteristic findings, the actual pulmonary sources of air leakage have not been well documented. Therefore, this study aimed to investigate intraoperatively confirmed pulmonary air-leak sites in surgically treated patients with pathologically confirmed catamenial pneumothorax. METHODS: We retrospectively reviewed 76 female patients who underwent surgery for pneumothorax at Yokohama Municipal Citizen's Hospital between October 2008 and December 2025. Patients with histopathologically confirmed thoracic endometriosis in resected diaphragmatic and/or pulmonary specimens were included. Clinical, intraoperative, pathological, and postoperative data were collected, with particular attention to directly observed intraoperative pulmonary air leakage. RESULTS: Among 76 female patients who underwent surgery for pneumothorax, 15 had pathologically confirmed thoracic endometriosis. The median age was 42 years (range, 27-54 years). All patients had right-sided pneumothorax and macroscopically identifiable diaphragmatic defects or thinning. Intraoperative pulmonary air leakage was detected in nine patients (60.0%). The leakage sites were located in segment S4 in six patients and in segments S1, S6, and S8 in one patient each. Endometrial tissue was identified in all resected pulmonary air-leak lesions. During a median follow-up of 18.0 months (range, 2.5-136.5 months), postoperative recurrence developed in five patients (33.3%). Recurrence was observed in 1 of 9 patients with an intraoperatively identified leakage site and in 4 of 6 patients without an identified leakage site. CONCLUSIONS: In this consecutive surgical series of catamenial pneumothorax, intraoperative pulmonary air leaks were frequently identified, particularly in segment S4 near the three-lobe confluence, despite the consistent presence of diaphragmatic lesions. These findings suggest that surgery performed during an active or clinically suspected air-leak state may increase the likelihood of identifying responsible pulmonary lesions. Direct confirmation and resection of these lesions may help distinguish responsible pulmonary air-leak lesions from associated thoracic endometriotic abnormalities and support more targeted and comprehensive surgical management.