Case Presentation: A 33-year-old nulliparous female with no past medical history presented with 10 months of postmenstrual umbilical pain. She denied vomiting or bowel habit changes, but noted recent orthopnea and nocturnal wheezing. She had regular, monthly menstrual cycles associated with dysmenorrhea since menarche at age 11.  She had not been sexually active for 4 years. A CT abdomen/pelvis revealed signs of endometriosis, mild perihepatic ascites and an incidental right-sided pleural effusion. Given the suggested endometriosis and hydropneumothorax on CT, a catamenial pneumothorax (CP) secondary to thoracic endometriosis was considered. Thoracentesis demonstrated dark, serosanguinous fluid with pleural fluid studies revealing an exudative effusion. Cytology exhibited mesothelial cells and small lymphocytes (Table 1).  A chest tube placed for 24 hours yielded 1200cc of fluid. An MRI with contrast of the pelvis confirmed multiple areas of hemorrhagic endometrial implants and moderate ascites. The patient was started on combined oral contraceptives (COC’s) to suppress menses and a one-month dose of the gonadotropin releasing hormone (GnRH) agonist, Lupron – creating a hypoestrogen state. 10 weeks after discharge the patient pursed elective video-assisted thoracoscopic surgery (VATS).  A large hemothorax was evacuated, revealing diffuse pleural implants anddiaphragmatic fenestrations with liver visible beneath. The fenestrations were repaired intraoperatively. Given the diffuse pleural implants, a complete right hemithorax parietal pleurectomy was performed, followed by doxycycline chemical pleurodesis. A wedge resection was also performed. Both the wedge resection and pleural biopsies were positive for foci of endometriosis on pathology. The surgery was well tolerated without complications.

Discussion: This case reminds us that endometriosis can involve areas outside of the abdomen and provides insight into the diagnosis and treatment of CP. Guidelines for the initial management of a spontaneous pneumothorax (SP) with pleural effusion were followed – evaluation by thoracentesis followed by tube thoracostomy. However, CP is prone to recurrence. In order to prevent repeat thoracostomies, further interventions are necessary. Pharmacologic therapy alone is only a temporizing measure to reduce symptoms and aid in the perioperative period. Studies comparing surgery alone versus hormonal therapy alone demonstrated 1-year recurrence rates of 30% and 60%, respectively. VATS is often followed by pleurectomy and/or pleurodesis, removing ectopic endometrium to prevent recurrence – as in this case.  

Conclusions: The diagnosis of CP comes from a high index of suspicion and quality of presentation.  In this case, the hemopneumothorax was an incidental finding on CT abdomen. Even with pelvic endometriosis and a new hydropneumothorax, CP remains a challenging diagnosis to prove.  Cytology was non-confirmatory in this case, which is not abnormal, as many cases cannot be histologically diagnosed and there are no diagnostic radiographic qualifications.8 VATS is considered the gold standard in diagnosis of CP via the visualization of endometrial plaques or pleural fenestrations, which held true in this case.