Although the exact cause is not known, a few theories come from metastatic, hormonal, and anatomical possibilities. The metastatic model proposes that endometrial tissue has migrated from the endometrium to the diaphragm or the pleural space, causing small holes in the diaphragm, allowing air into the pleural space. In the hormonal model, it is believed that prostaglandin F2 causes a narrowing of the bronchioles, the small tubes within the lungs. Narrowing of these can cause the alveoli to rupture which may trap air in the pleural space. 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<unk> es 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<unk>  (and hemothorax).
Catamenial pneumothorax
Pneumothorax ex vacuo
Tracheoinnominate fistula
Pulmonary hematoma
Tonic tensor tympani syndrome
Tracheal deviation
Hemothorax
Chylothorax