Catamenial pneumothorax

Overview
Catamenial pneumothorax is a condition of collapsed lung occurring in conjunction with menstrual periods (catamenial refers to menstruation), believed to be caused primarily by endometriosis of the pleura (the membrane surrounding the lung).

Classification
Catamenial Pneumothorax is the most common form of thoracic endometriosis syndrome, which also includes catamenial hemothorax, catamenial hemoptysis, catamenial hemopneumothorax and endometriosis lung nodules]], as well as some exceptional presentations.

Symptoms and signs
Onset of lung collapse is less than 72 hours after menstruation. Typically, it occurs in women aged 30-40 years, but has been diagnosed in young girls as early as 10 years of age and post menopausal women (exclusively in women of menstrual age) most with a history of pelvic endometriosis.

Pathophysiology
Endometriosis can attach to the lung, 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 . How this endometrial tissue reaches the thorax remains enigmatic, although defects in the diaphragm can often be found.

The cysts can release blood; the endometrial cyst "menstruates" in the lung. Air can move in by an unknown mechanism. The blood and air cause the lung to collapse (i.e. catamenial hemopneumothorax).

Diagnosis
Diagnosis can be hinted by high recurrence rates of lung collapse in a woman of reproductive age with endometriosis. CA-125 is elevated. Nowadays, video-assisted thoracoscopy is used for confirmation.

Treatment
Pneumothorax is a medical emergency because it comes with severe pain and decreased lung function. A chest tube should be inserted after clinical assessment. This releases the air and menstrual blood, and the lung can re-expand.

Surgery, hormonal treatments and combined approaches have all been proposed, with variable results in terms of short and long term outcome. Surgical removal of the endometrial tissue should be endeavoured during menstruation for optimal visualisation of the cyst. Pleurodesis may also be helpful. Menstruation and accompanying lung collapse can be suppressed with hormone therapy, like with Lupron Depot, danazol or extended cycle combined oral contraceptive pills.

Epidemiology
Some sources claim this entity represents 3-6% of pneumothorax in women. In regard of the low incidence of (primary spontaneous, i.e. not due to surgical trauma etc.) pneumothorax in women (about 1/100'000/year), this is a very rare condition. Hence, many basic textbooks don't mention it, and many doctors have never heard of it. However, catamenial pneumothorax is probably under-recognised.