In the anatomical model, researchers believe that the absence of the cervical mucous plug, which is normally there during the menstrual cycle, allows air to pass from the genital tract to the pleural space through fenestrations in the diaphragm. Another theory is that hormonal changes that come with the menstrual cycle can cause blebs to spontaneously rupture. Blebs are small blisters/pustules filled with air or fluid and can develop on the lungs.Endometrial tissue attaches within the thoracic cavity, forming chocolate-like cysts. Generally the parietal pleura is involved, but the lung itself, the visceral layer, the diaphragm, and more rarely the tracheobronchial tree may also be afflicted. The mechanism through which endometrial tissue reaches the thorax remains unclear. Nearly 90% of cases occur on the right hemithorax, a phenomenon thought to potentially be due to the direction of flow of retroperitoneal fluid. Peritoneal flow occurs in a clockwise pattern, which could likely explain the tendency for catamenial pneumothoraces to be right-sided. Defects in the diaphragm, which are found often in affected individuals, could provide an entry path, as could microembolization through pelvic veins. Such diaphragmatic defects may be either congenital or acquired. The cysts can release blood; the endometrial cyst "menstruates" in the lung. Endometrial cells undergo structural changes during the secretory phase of the menstrual cycle, in a process called decidualization. Decidualized pleural endometrial implants can disrupt the pleura and lead to pneumothorax (and hemothorax). Diagnosis
Diagnosis can be hinted by high recurrence rates of lung collapse in a woman of reproductive age with endometriosis.
An additional procedure involves a mesh that is placed over the diaphragm to block any holes that may have been missed in the first surgery. Hormonal therapies can also be used to suppress ovulation. Surgical removal of the endometrial tissue should be endeavored during menstruation for optimal visualization. Pleurodesis may also be effective in removing the space between the lung and the chest wall; preventing air build up between these layers. Non-surgical treatment includes pharmacological treatment via continuous oral contraceptive therapy to avoid cyclical bleeding with monthly menstruation. Oral contraceptives appear to be preferable for patients due to fewer negative side effects than treatment with GnRH agonist therapy, which can lead to hypoestrogenic effects including osteoporosis, resulting in discontinuation of therapy and thus a higher likelihood of recurrence of catamenial pneumothorax. Epidemiology
Some sources claim this entity represents 3 to 6% of pneumothorax in women. In regard of the low incidence of primary spontaneous pneumothorax (i.e. not due to surgical trauma etc.) in women (about 1/100000/year), this is a very rare condition. Hence, many basic textbooks do not mention it, and many doctors have never heard of it. Therefore, catamenial pneumothorax is probably under-recognized. See also
Catamenial epilepsy
Catamenial migraine

References


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