Thoracic Endometriosis-Related Catamenial Pneumothorax: Case Report and Literature Review

Endometriosis is a gynecological disorder where endometrial-like tissue grows outside the uterus. Though its exact cause is unclear, it is known to be hormone-dependent and linked to the menstrual cycle. It is the primary cause of chronic pelvic pain in women, affecting 1–2% of those of reproductive age and 15–25% of those with infertility.[] Endometriosis can be classified as either endopelvic or extra-pelvic, depending on the location of the ectopic endometrial tissue. In the pelvis, common sites include the ovaries, fallopian tubes, and uterosacral ligaments. Though less frequent, extra-pelvic endometriosis can affect the abdominal wall, episiotomy scars, urinary and gastrointestinal tracts, nasal mucosa, and even the thoracic cavity.[] Thoracic endometriosis is a type of endometriosis that can be categorized as either pleural or pulmonary. This condition is extremely rare and has complex, not well-understood causes and development processes. This report describes a case presenting as recurrent hemothorax synchronized with the menstrual cycle. The purpose of this case presentation is to increase clinical awareness, as pulmonary endometriosis can be easily misdiagnosed as a systemic disease due to its nonspecific clinical presentation and imaging findings. CASE HISTORY A 43-year-old woman presented with chief complaints of shortness of breath and bilateral chest pain for the past six months. She was diagnosed with bilateral hydropneumothorax and experienced partial relief from dyspnea following bilateral intercostal drain (ICD) insertion. The patient has a history of two previous ICD insertions bilaterally, performed one year ago. There is a noted history of bloody drainage from the bilateral ICDs, with increased drainage observed during her menstrual cycle. The patient has no history of antitubercular treatment, trauma, or other surgical interventions. She has been married and infertile for 10 years, having received multiple oral medications (hormone therapy) and undergone in vitro fertilization, which were unsuccessful. Upon examination, the patient was conscious, oriented, of thin build, and undernourished. Pallor was noted, and other general physical examination findings were unremarkable. Respiratory system examination showed decreased breath sounds on both sides. Hemorrhagic fluid was present in bilateral ICD bags, with no air leak detected. A chest X-ray revealed bilateral hydropneumothorax [Figure 1a and b] with an ICD in place. Pleural fluid analysis showed multiple red blood cells, predominantly lymphocytic, exudative with low ADA levels (10.2 U/L). The patient underwent a left-sided thoracoscopy for an undiagnosed pleural effusion, which identified multiple small chocolate-colored nodules [Figure 2]. Biopsy of these nodules confirmed endometrial glands with ER and PR positivity, leading to a diagnosis of thoracic endometriosis [Figure 3a–c]. The patient was prescribed 2 mg dienogest daily and chose not to undergo surgical intervention. After one year on oral medication, the patient’s clinical condition improved and drainage decreased.

Endometriosis can affect pelvic organs as well as extra-pelvic organs and tissues. When endometrial implants are found in the airways, pleura, and lung parenchyma, this is referred to as thoracic endometriosis syndrome (TES). TES includes catamenial pneumothorax, catamenial hemothorax, catamenial hemoptysis, and pulmonary nodules. Among reported cases, catamenial pneumothorax occurs in 73%, catamenial hemothorax in 14%, catamenial hemoptysis in 7%, and lung nodules in 6%.[] Extra-pelvic endometriosis most commonly involves four anatomical locations: the lungs, bowel and omentum, urinary tract, and central nervous system. A systematic review conducted by Andres et al. (2019) identified the thorax as the predominant site of extra-pelvic endometriosis.[] The condition affects 5–15% of women during their reproductive years, with an average age at presentation of 35 ± 0.6 years and an observed range from 15 to 54 years. Approximately 92% of thoracic endometriosis syndrome (TES) cases are reported in the right hemithorax, 5% in the left hemithorax, and 3% exhibit bilateral involvement. In the present case, the patient falls within the typical age range and demonstrated right hemithoracic involvement.[] Several theories have been proposed: the first suggests lymphatic or hematogenous embolization from the uterus; the second is the coelomic metaplasia theory; and the third proposes retrograde menstruation, in which endometrial tissue from the uterus and fallopian tubes migrates through the abdomen and enters the pleural cavity via congenital or acquired diaphragmatic defects.[] Recognizing catamenial pneumothorax is key to promptly diagnosing and treating thoracic endometriosis syndrome. Haga et al. identified four distinguishing features: right-sided pneumothorax, pelvic endometriosis history, age 31, and nonsmoking status. These factors strongly predict thoracic endometriosis syndrome-related pneumothorax versus spontaneous pneumothorax.[] Patients commonly experience catamenial symptoms within 24–48 hours after the onset of menstruation. The most frequently reported symptom is chest pain (90%), followed by dyspnea (31%), hemoptysis (7%), and cough (which is uncommon). Initial diagnostic evaluations indicate that pneumothorax occurs in 73% of cases, hemothorax in 14%, hemoptysis in 7%, and pulmonary nodules in 6%.[] In this case, the patient primarily presented with dyspnea and chest pain, whereas cough was infrequently reported. Notably, hemoptysis was absent. According to a study by Channabasavaiah and Joseph,[] chest pain is the most prevalent symptom (90%), while dyspnea (31%), hemoptysis (7%), and cough are observed less frequently. The patient presented with early onset, mild respiratory tract symptoms. Repeated admissions to the pulmonology department indicate a recurrent and cyclical pattern of the condition. Retrospective evaluation demonstrated that dyspnea episodes consistently preceded hospitalizations, supporting the diagnosis of catamenial pneumothorax. Diagnostic approaches for thoracic endometriosis syndrome (TES) include chest X-ray, CT scan, or MRI. Video-assisted thoracoscopy can identify diaphragm perforations and nodular or plaque-like brown/violet deposits smaller than 1 cm. Bronchoscopy may detect small red submucosal lesions, and bronchial biopsy and brush cytology can reveal the presence of endometrial cells.[] Histopathological analysis of the biopsy demonstrated round to oval endometrial glands encased within endometrial stroma. Immunohistochemical studies verified that these glands exhibited positivity for estrogen receptor (ER) and progesterone receptor (PR). Kawaguchi et al. (2018) identified endometrial glands, stroma, and hemosiderin-laden macrophages as key histopathological features of thoracic endometriosis, findings also noted by Yoshinobu Ichiki et al.[] Minimally invasive procedures, like bronchoscopy and video-assisted thoracoscopic surgery, are effective for diagnosing and treating thoracic endometriosis in over 60% of cases, though there is still some risk of morbidity and mortality.[] TES commonly presents with menstrual-related symptoms, helping clinicians recognize the condition. Diagnosis involves radiological and histological assessments. Management requires a multidisciplinary strategy—combining clinical, imaging, surgical, pharmaceutical approaches, and pleural fluid drainage to alleviate symptoms. The primary objective of medical management is the suppression of ovarian estrogen production through pharmacological agents, such as danazol and gonadotropin-releasing hormone (GnRH) agonists. In this case, the patient was prescribed dienogest, which led to improvement in her clinical condition. She elected to avoid surgical intervention and continues to be monitored with regular follow-up appointments.

Pulmonologists should possess a comprehensive understanding of the clinical features associated with this potentially manageable etiology of spontaneous hemothorax. Pathological confirmation is attainable when examinations are performed within an appropriate clinical context and effective collaboration between clinicians and pathologists is maintained, thereby minimizing unnecessary surgical diagnostic interventions for both patients and surgeons. Management remains complex due to a high recurrence rate, highlighting the need for further assessment of optimal therapeutic approaches. Current evidence suggests that integrating surgical intervention with hormonal therapy may improve relapse-free survival outcomes. Take-home message Thoracic endometriosis is a rare condition that poses diagnostic challenges for clinicians and pathologists. Its clinical manifestations, such as catamenial pneumothorax, hemothorax, or pulmonary nodules, often mimic more common thoracic conditions, potentially causing delays in diagnosis. Histopathological confirmation can be difficult due to the subtle and nonspecific appearance of endometrial tissue, especially in small or poorly preserved biopsy specimens. Immunohistochemistry may assist in identifying endometrial stroma and glands; however, sampling limitations and similarities with other pathologies necessitate careful consideration. A multidisciplinary approach involving gynecologists, pulmonologists, thoracic surgeons, and pathologists is essential for accurate diagnosis and effective management of this condition. Data availability statement De-identified patient data supporting the findings of this case report are available from the corresponding author upon reasonable request, subject to institutional and ethical restrictions. Author contribution YG: conceptualization, case management, manuscript drafting. AJ: histopathology analysis, manuscript editing, correspondence. SSK: literature review, figure preparation, manuscript revision. All authors read and approved the final manuscript. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

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