User:Olivetabasco/Catamenial pneumothorax

Background
Catamenial pneumothorax is defined as at least two episodes of recurrent pneumothorax corresponding with menstruation. It was first described in 1858 when a woman presented with 12 episodes of right-sided pneumothorax over 1 year, recurring monthly with menstruation. Thoracotomy revealed thoracic endometriosis.

Endometriosis is defined as endometrial tissue that has implanted outside of the uterus. Mechanisms include retrograde menstruation resulting in abdomino-pelvic spread, blood-borne or lymphatic spread and deposition, and metaplasia.

Thoracic endometriosis is the most common non-abdominal site of involvement and is also the primary risk factor for catamenial pneumothorax. Catamenial pneumothorax is the primary clinical presentation of thoracic endometriosis, and symptoms include chest or shoulder pain, cough, dyspnea, and shortness of breath.

Pathophysiology
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 and Treatment
Clinical diagnosis can be made based on history and imaging, while the gold standard for definitive diagnosis remains video-assisted thoracoscopic surgery (VATS), which allows not only the visualization of the lesion, but also surgical treatment via cauterization of the ectopic endometrial tissue. Special staining under a microscope or utilizing a cell marker, such as PAX8, can be used to positively identify endometrial stroma.

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.