Catamenial Hemothorax: A Rare Presentation of Thoracic Endometriosis

Abstract Introduction: Catamenial hemothorax (CH) is a rare manifestation of thoracic endometriosis syndrome (TES), characterized by recurrent pleural effusions linked to the menstrual cycle. TES affects up to 12% of women with pelvic endometriosis, but CH accounts for less than 10% of these cases. This case report presents a 41-year-old female with recurrent right-sided pleural effusions, diagnosed with CH after comprehensive clinical and procedural evaluation, highlighting diagnostic challenges and emerging treatment options. Case Presentation: A 41-year-old woman with a history of pelvic endometriosis presented with exertional dyspnea. Initial chest imaging revealed a large right-sided pleural effusion, and diagnostic thoracentesis drained 2,464 mL of bloody fluid. Pleural fluid analysis showed elevated red blood cell counts (1992/mm³), LDH of 1564, and protein of 4.4 g/dL, consistent with an exudative effusion. No malignancy or infection was identified on cytology or microbiology. She had no history of lung disease, smoking, or environmental exposures, and previously underwent surgical resection of endometrial implants for endometriosis. Despite initial drainage, the pleural effusion recurred, necessitating further intervention.The patient underwent medical pleuroscopy by an interventional pulmonologist, during which 2,700 mL of bloody pleural fluid was drained. Multiple diaphragmatic fenestrations, parietal pleural nodules, and pleural adhesions were identified. Talc pleurodesis was performed, and biopsies confirmed mesothelium lined fibrous tissue and associated skeletal muscle with chronic inflammation and reactive mesothelial cells, consistent with TES. Given the cyclical nature of her symptoms, a diagnosis of catamenial hemothorax was made. Discussion: TES can present as catamenial pneumothorax, hemothorax, hemoptysis, or pulmonary nodules, with CH being the least common. TES is thought to arise from endometrial tissue in the pleura, which cyclically hemorrhages due to hormonal fluctuations. Two major theories suggest its development through transdiaphragmatic passage of endometrial cells or vascular/lymphatic dissemination. In this case, the recurrent hemothorax, diaphragmatic defects, and pleural nodules suggest transdiaphragmatic migration.Medical pleuroscopy, increasingly recognized as an emerging diagnostic and therapeutic tool in TES, offers advantages over video-assisted thoracoscopic surgery (VATS) by providing excellent visualization of pleural lesions with less invasiveness. Pleuroscopy allows real-time diagnosis and treatment, including pleurodesis, as seen in this case. Management of CH typically involves hormonal suppression to prevent recurrence, with definitive treatments such as pleurodesis or diaphragmatic repair. For patients desiring definitive resolution, hysterectomy may be considered. The patient was referred for further gynecological consultation to discuss potential surgical options.