Stromal-only endometriosis catamenial pneumothorax: A diagnostic algorithm with potential pitfalls

Catamenial pneumothorax (CP) is a rare form of recurrent spontaneous pneumothorax occurring synchronously with menstruation and represents the most common manifestation of thoracic endometriosis. CP predominantly involves the right hemithorax as a result of the transdiaphragmatic migration of endometrial tissue through congenital or acquired diaphragmatic defects, a phenomenon thought to be facilitated by the clockwise circulation of peritoneal fluid and by the absence of an effective anatomical barrier on the right side to limit transdiaphragmatic spread. Diagnosis may be particularly challenging when endometrial implants are composed exclusively of stromal cells without identifiable glands, are focal in distribution, and minute in size. We herein describe two challenging cases of recurrent right-sided pneumothorax in women of reproductive age, in whom paucifocal endometrial deposits were consistent with stromal-only endometriosis in the absence of endometrial glands. Based on these cases, we propose a practical diagnostic flowchart addressing the major pitfalls in the recognition of stromal-only thoracic endometriosis and highlighting the critical importance of close clinicopathologic correlation, particularly in gland-deficient lesions. Data availability All data presented in this article are available upon request.

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Not applicable. Funding Not applicable (no funding was received for this study) Author information Authors and Affiliations Contributions R.P.: conceptualization, methodology, original draft preparation, review, editing and manuscript finalization; A.M. and M.I.: thoracic resection performance, clinical data collection, and manuscript finalization. G.P.: conceptualization, review, editing, and manuscript finalization. All authors commented on previous versions of the manuscript. All authors read and approved the final version of the manuscript. The patients kindly provided informed consent for the processing of their personal data for this scientific publication Corresponding author Ethics declarations Artificial Intelligence technology No tools of AI were used in the paper. Conflict of interest The authors declare that they have no conflicts of interest. Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rights and permissions About this article Cite this article Papa, R., Meroni, A., Incarbone, M. et al. Stromal-only endometriosis catamenial pneumothorax: A diagnostic algorithm with potential pitfalls. Virchows Arch (2026). https://doi.org/10.1007/s00428-026-04585-0 Received: Revised: Accepted: Published: Version of record: DOI: https://doi.org/10.1007/s00428-026-04585-0