Thoracic Endometriosis: When Endometriosis Affects the Diaphragm, Pleura, and Lungs

Thoracic endometriosis occurs when endometriosis involves structures in or around the chest, including the diaphragm, pleura, and, less commonly, the lung itself. Its best-known presentation is catamenial pneumothorax, a collapsed lung occurring in temporal relation to menstruation, but the disease can also cause cyclic chest pain, shoulder pain, shortness of breath, coughing, hemothorax, or subtle symptoms that remain unexplained for years.

The condition is often described as thoracic endometriosis syndrome. However, “syndrome” refers mainly to a recognizable pattern of symptoms and clinical events. A more complete understanding requires examination of the tissue itself: where the disease is located, how it affects the diaphragm and pleura, and whether histopathology confirms the presence of endometrial-type glands or stroma.

In many patients, it appears to be part of an anatomically connected disease pattern extending from the pelvis to the diaphragm, pleura, and lung.

What is thoracic endometriosis?

Thoracic endometriosis is endometriosis involving the diaphragm or tissues within the chest. It may affect the abdominal or thoracic surface of the diaphragm, the pleural lining, or the lung parenchyma (the lung’s functional tissue itself).

The term encompasses several manifestations:

• Catamenial pneumothorax, or menstrual-cycle-associated lung collapse
• Catamenial hemothorax, or blood in the pleural space around menstruation
• Cyclic chest, rib, upper abdominal, or shoulder pain
• Cyclic shortness of breath
• Catamenial hemoptysis, or coughing blood in association with menstruation
• Pulmonary nodules or other thoracic lesions associated with endometriosis

Not every patient has classic symptoms, and not every event occurs precisely during menstrual bleeding. The timing may vary, particularly in patients using hormonal treatment or those with irregular cycles.

Thoracic Endometriosis Symptoms and Warning Signs

The most important clue is a recurrent pattern of thoracic endometriosis symptoms linked to the menstrual cycle. Symptoms may begin shortly before menstruation, during bleeding, or within the following several days.

Possible warning signs include:

• Recurrent chest pain around menstruation
• Sudden or cyclic shortness of breath
• Right shoulder or shoulder-blade pain
• Pain beneath the ribs or in the right upper abdomen
• Pain traveling from the upper abdomen toward the neck or shoulder
• Repeated spontaneous pneumothorax
• Recurrent pleural effusion or hemothorax
• Coughing or, rarely, coughing blood around menstruation
• A history of severe pelvic endometriosis, infertility, or multiple pelvic surgeries

Right-sided symptoms are especially common. Published series reports right-sided involvement in roughly 90–95% of thoracic endometriosis cases, one of the most consistent features of the disease.

Sudden chest pain, significant breathing difficulty, fainting, bluish discoloration, or rapidly worsening symptoms require emergency assessment. A pneumothorax can be life-threatening and should never be managed as routine menstrual pain.

How can endometriosis cause a collapsed lung?

There is no single proven mechanism for every episode of catamenial pneumothorax. Several processes may act together.

Endometriosis can produce cyclic inflammation, bleeding, fibrosis, and tissue remodeling. On the diaphragm, this may be associated with microscopic pores or larger full-thickness openings called fenestrations. These defects may permit movement of fluid or air between the abdominal and pleural cavities. Endometriosis affecting the pleura or lung may also contribute to local air leakage.

One traditional theory, sometimes called the transdiaphragmatic passage or migration theory, proposes that air enters through the reproductive tract, travels through the fallopian tubes into the abdomen, and then passes through diaphragmatic defects. These defects appear to have multiple origins: some likely represent secondary damage from endometriotic implants and the chronic inflammatory destruction they cause, while others may be pre-existing congenital or anatomic variants that predate the disease and simply serve as passive conduits.

Yet pneumothorax can persist or first appear even after hysterectomy, when that route has been interrupted. This suggests that retained ovarian activity, established thoracic lesions, diaphragmatic defects, and pulmonary or pleural air leakage may also be important. A hormonal, prostaglandin-mediated theory has also been proposed, in which cyclic surges may directly affect pulmonary vessels and airway tone, independent of any physical migration route.

In other words, catamenial pneumothorax is likely multifactorial, not the result of one universal pathway. The diaphragm separates the abdomen from the chest, but in thoracic endometriosis, it may function as a critical disease interface.

Why can thoracic endometriosis be missed on pathology?

Endometriosis is commonly recognized by endometrial-type glands and stroma, but not every specimen contains both components. Some lesions, particularly in the chest, may be stromal-predominant, making them more difficult to recognize on routine examination.

How is thoracic endometriosis diagnosed?

There is no single test that definitively excludes thoracic endometriosis. Diagnosis usually combines history, imaging, operative assessment, and pathology.

Clinical history

A carefully constructed menstrual timeline is essential when evaluating symptoms of thoracic endometriosis. Patients should record when chest pain, shortness of breath, shoulder pain, coughing, or pneumothorax occurs in relation to the cycle. Previous pelvic symptoms and operations should also be reviewed.

Imaging

Chest X-ray and CT are important for detecting an active pneumothorax, pleural fluid, or other urgent thoracic findings. MRI may help characterize diaphragmatic or pleural abnormalities in selected cases. However, small, superficial, nonpigmented, or fibrotic lesions may not be visible on imaging. A normal scan does not necessarily rule out disease.

Surgery and histopathology

Video-assisted thoracoscopic surgery (VATS) allows examination of the pleura, thoracic diaphragm, and lung. Laparoscopy or robotic surgery permits evaluation of the pelvis, upper abdomen, liver dome, and abdominal surface of the diaphragm. Tissue diagnosis remains important because visual appearance alone is not always specific.

Why may both the pelvis and chest need evaluation?

Thoracic-only treatment may address the immediate chest event but leave pelvic, abdominal, or diaphragmatic disease untreated. Conversely, pelvic surgery alone cannot fully evaluate lesions on the thoracic side of the diaphragm or within the lung.

For appropriately selected patients, a dual-compartment approach combines:

• Complete laparoscopic or robotic assessment of pelvic and abdominal disease
• Inspection of the liver dome, subhepatic space, and abdominal diaphragm
• VATS evaluation of the thoracic diaphragm, pleura, and lung
• Excision of suspicious lesions for compartment-specific pathology
• Repair or reinforcement of clinically significant diaphragmatic defects
• Management of pulmonary or pleural abnormalities when indicated

This approach requires coordination among an experienced endometriosis surgeon, thoracic surgeon, anesthesiology team, pathology specialists, and, in complex upper-abdominal cases, a hepatobiliary (liver and bile duct) surgeon. Bowel, urinary-tract, or vascular specialists may also be needed.

The operation must be individualized. If pelvic disease is more extensive than anticipated, a staged procedure may sometimes be safer than attempting every component during one prolonged operation.

Can thoracic endometriosis return after surgery?

Yes. Recurrence depends on disease extent, the structures involved, completeness of treatment, repair of diaphragmatic defects, ovarian function, and postoperative management. Long-term care may include postoperative hormonal suppression when appropriate, symptom surveillance, repeat imaging for recurrent respiratory symptoms, and coordinated gynecologic and thoracic follow-up.

What should patients ask before thoracic endometriosis surgery?

Useful questions include:

• Will both the pelvis and thorax be evaluated?
• Which surgeons will be present, and what is their experience with thoracic endometriosis?
• Will the abdominal and thoracic surfaces of the diaphragm both be inspected?
• How will full-thickness diaphragmatic defects be repaired?
• Will pleural and lung lesions be assessed and treated when necessary?
• Will each anatomic compartment be submitted separately for pathology?
• Does the pathology team use deeper sections or immunohistochemistry when appropriate?
• What are the risks of bowel, bladder, ureteral, vascular, or thoracic procedures in my case?
• Should treatment be combined or staged?
• How could surgery or hormonal treatment affect fertility and ovarian function?
• What is the plan for recurrence prevention and long-term follow-up?

The key clinical message

Thoracic endometriosis should be considered when chest pain, shoulder pain, breathing difficulty, pleural bleeding, or pneumothorax repeatedly occur near menstruation, especially in a patient with pelvic pain, infertility, or known endometriosis.

For patients with suspected thoracic endometriosis, timely recognition and coordinated multidisciplinary assessment can help replace fragmented emergency care with a more complete, anatomy-based treatment plan.

References:

1. Nezhat C, Main J, Paka C, Nezhat A, Beygui RE. Multidisciplinary treatment for thoracic and abdominopelvic endometriosis. JSLS. 2014;18(3):e2014.00312. doi:10.4293/JSLS.2014.00312.
2. Inoue T, Chida M, Inaba H, Tamura M, Kobayashi S, Sado T. Juvenile catamenial pneumothorax: institutional report and review. J Cardiothorac Surg. 2015;10:83. doi:10.1186/s13019-015-0289-7.
3. Fukuda S, Hirata T, Neriishi K, Nakazawa A, Takamura M, Izumi G, et al. Thoracic endometriosis syndrome: comparison between catamenial pneumothorax or endometriosis-related pneumothorax and catamenial hemoptysis. Eur J Obstet Gynecol Reprod Biol. 2018;225:118–123. doi:10.1016/j.ejogrb.2018.04.021.
4. Soriano D, Schonman R, Gat I, Schiff E, Seidman DS, Carp H, et al. Thoracic endometriosis syndrome is strongly associated with severe pelvic endometriosis and infertility. J Minim Invasive Gynecol. 2012;19(6):742–748. doi:10.1016/j.jmig.2012.08.773.
5. Liu L, Seckin S, Goldstein K, Seckin T. Dual compartment surgery for pulmonary endometriosis. J Minim Invasive Gynecol. 2020;27(3):559–560. doi:10.1016/j.jmig.2019.07.019.