Endometriosis lesions can more rarely be found outside of the pelvis, and the most common type of extrapelvic endometriosis is thoracic endometriosis. Although thoracic endometriosis is relatively rare, there has been an increase in diagnosis in recent years, probably because of increased awareness among medical professionals that endometriosis can occur outside of the pelvis. Thoracic endometriosis is often found in conjunction with severe pelvic endometriosis.
The average onset of symptoms of thoracic endometriosis is 35 years old, much later than for pelvic endometriosis, where symptoms often begin in adolescence. It is not clear why this is the case. In addition, the majority of thoracic endometriosis is right-sided, with a smaller number of cases being left-sided or bilateral.
Symptoms and Clinical Presentation
The most common symptom of thoracic endometriosis is catamenial chest pain, which is chest pain occurring right before or during menstruation. In one study, 80% of women with thoracic endometriosis had catamenial chest pain. In another study, 90% of women had chest pain, 30% had shortness of breath, and 7% coughed up blood. These symptoms occurred more often during menstruation, but were not necessarily limited to menstruation. In 40% of women, chest pain was the only symptom of thoracic endometriosis.
The four main clinical entities associated with thoracic endometriosis are catamenial pneumothorax, catamenial hemothorax, catamenial hemoptysis, and lung nodules. Of these, catamenial pneumothorax has been the most researched. This is when the lung collapses during menstruation. It is considered to be catamenial when the collapse occurs during the window of 24 hours prior to the onset of menstruation to 72 hours after onset. The majority of catamenial pneumothorax is caused by thoracic endometriosis; however, not all pneumothorax associated with endometriosis is catamenial. In one study of 150 thoracic endometriosis patients, 37% of the pneumothoraces were catamenial, and 63% were non-catamenial. Pneumothorax typically causes chest pain and shortness of breath.
Catamenial hemothorax is bleeding between the chest wall and the lung that occurs during menstruation. This is a rare cause of pleural effusion (fluid around the lung), and like pneumothorax, usually causes chest pain and shortness of breath. Catamenial hemoptysis is coughing up blood during menstruation, and is usually associated with chest pain and shortness of breath. Catamenial hemothorax and catamenial hemoptysis occur in thoracic endometriosis less frequently than catamenial pneumothorax. Pulmonary nodules are one of the least frequent manifestations of thoracic endometriosis, and are masses in the lung that can be mistaken for malignancy. They can be asymptomatic, or sometimes cause coughing up blood.
In most if not all cases of thoracic endometriosis, lesions are also found on the diaphragm. In the majority of women, diaphragmatic endometriosis penetrates through the diaphragm. However, in a small number of women, the endometriosis lesions are found only on the visceral (abdominal/pelvic) side of the diaphragm, or only on the pleural (thoracic/lung) side. Not all women with diaphragmatic endometriosis will also have thoracic endometriosis. The symptoms of endometriosis on the diaphragm are similar to the symptoms of thoracic endometriosis, with chest pain during menstruation. This pain may radiate to the shoulder, neck or arm.
In rare cases, endometriosis on the pericardium has been reported (here, and here). The pericardium is the membrane that surrounds the heart. These women also had diaphragmatic endometriosis, and one of them had severe pelvic endometriosis, and the other had an endometrioma in her liver.
How Does Thoracic Endometriosis Develop?
A common theory about the development of endometriosis, known as Sampson’s theory, suggests that retrograde menstruation, menstrual blood flowing backwards (away from the uterus) through the Fallopian tubes towards the pelvic cavity, deposits fragments of endometrium into the pelvis, which can then implant and grow into lesions. This theory has many flaws, as discussed here. The existence of endometriosis outside of the pelvis is one of several facts about endometriosis that cannot be explained by Sampson’s theory.
So how does endometriosis outside of the pelvis develop? There are three main theories, and it may be through one or a combination of these that endometriosis develops in the thorax. The fact that thoracic endometriosis develops later than pelvic endometriosis may suggest that there is something fundamentally different about the way it develops. The migration theory suggests that endometriosis moves through the peritoneum (the lining of the pelvis) to the diaphragm, and from there, can move into the thorax through small holes in the diaphragm. The embolization theory suggests that endometriosis can be transplanted to the thorax from the pelvis through the lymph circulation, or the blood. Lastly, the metaplasia theory suggests that certain cell types can be transformed or changed into endometriosis. Clearly, more research is needed to delineate how thoracic endometriosis develops, and even how pelvic endometriosis develops, as this is not fully understood either.
The definitive diagnosis of thoracic endometriosis, like all endometriosis, is through biopsy of endometriosis lesions/growths that have been removed surgically. Video-assisted thoracoscopic surgery can be used to visualize and remove endometriosis growths in the thorax. This type of surgery is similar to pelvic laparoscopy, where a small video camera scope allows the visualization of the surgical area, and instruments are inserted through small separate incisions. However, without surgery, a tentative diagnosis can be made through the clinical history and sometimes imaging results. In a woman with pelvic endometriosis, thoracic endometriosis may be suspected if catamenial chest pain is present, or any of the other clinical entities described above. Chest x-rays can show pneumothorax, pleural effusions, or lung nodules. CT scans may show certain findings characteristic of thoracic endometriosis, but sometimes CT scans are normal when a woman is not menstruating. MRI can also be helpful.
Hormone therapy such as birth control pills, depo-provera, and Lupron are associated with greater than 50% recurrence of symptoms within six months after treatment was stopped. Video-assisted thoracoscopic surgery has been shown to be a safe option for treatment of thoracic endometriosis, and it can be combined with pelvic laparoscopy in the same surgery if pelvic endometriosis also needs to be treated. As with all surgery to excise endometriosis, the goal is to locate all of the lesions and remove them completely, in order to minimize recurrence. Most studies of surgical treatment of thoracic endometriosis have a fairly short followup, typically median followup of 18 months, and the number of patients in the studies is usually a small number, so it is difficult to draw robust conclusions about the long-term effectiveness of surgery. In one study, all patients had improvements in symptoms after surgery, but two out of 25 had recurrence at nine and twelve months respectively. Overall, though, surgical excision of thoracic endometriosis appears to be effective in the majority of cases.