Overview 

Mood swings, cravings, and cramps all sound like familiar symptoms around that time of the month, but have you ever heard of a collapsed lung as one? For some women, this is a painful reality. A small number of women experience a collapsed lung in connection with their menstrual cycle – a condition called catamenial pneumothorax (CP) (cat-uh-MEE-nee-uhl new-mo-THOR-axe).¹

A pneumothorax is defined as air inside the chest cavity. The word catamenial comes from the Greek word “katamenios”, meaning monthly occurrence, which roughly translates to “in association with a menstrual cycle”.² Therefore, a catamenial pneumothorax describes the air inside the pleural space (the small space between your lungs and the chest wall) that occurs approximately 72 hours after menstruation begins, which causes the lung to collapse.³

This condition mostly affects women of reproductive age, with the average age of onset being 32-35 years old. The majority of cases of CP (85-95%) occur unilaterally (on one side), mainly on the right side of the chest. However, there have been reports where patients felt pain either on the left side of the chest or bilaterally (on both sides).⁴

CP is typically caused by thoracic endometriosis. Endometrial-like tissue, which is normally found in the lining of the uterus, is found in the chest, which is abnormal. This damages parts of the lung and allows air to enter the pleural space, causing a collapsed lung. Hence, CP is considered a manifestation of thoracic endometriosis syndrome (TES).^5,6

CP is constantly misdiagnosed as a pneumothorax due to a lack of awareness and oversight to consider the menstrual cycle as a cause. This article explores the pathophysiology of catamenial pneumothorax: how and why it happens.⁷

Understanding the pathophysiology of catamenial pneumothorax

What is a pneumothorax? 

The lungs can be found in the chest cavity, also known as the thorax. The outside surface of your lungs is covered with a layer called visceral pleura, whereas the inside of your chest wall is covered by parietal pleura. The pleural space is a fluid that helps the lungs glide smoothly each time you breathe, and it is found in the small space between these layers. Your lungs stay inflated as the air pressure inside the lungs is greater than the pressure inside the pleural space.³ However, if air somehow gets inside the space from either: 

• Outside the body (a surgery or accident causing chest injury), or
• Inside the body (if parts of the lung are damaged or burst) 

It can put pressure on the lung and cause it to collapse, making it very hard to breathe — this is called a pneumothorax. CP occurs when this happens around the time of menstruation.⁸ 

How does endometrial tissue get inside the chest? 

CP is linked with a condition called thoracic endometriosis. Endometriosis is the presence of ectopic endometrial tissue outside the uterus. The most common form that women experience is pelvic endometriosis, with symptoms like pelvic pain, painful cramps, dyspareunia, and infertility. While this condition occurs in the pelvis, thoracic endometriosis occurs in the thoracic cavity. However, not everyone with CP has endometriosis.⁹ 

There are a handful of theories to explain how endometrial tissue travels from the abdomen to the chest, the most widely accepted theory being transdiaphragmatic migration. This theory suggests that endometrial tissue travels to the chest through tiny holes in the diaphragm, a muscle which separates the chest from the abdomen.¹⁰ During menstruation, retrograde menstruation can occur, whereby the flow of menstrual blood goes backwards through the fallopian tubes into the uterus and the abdomen. This process can carry some endometrial cells from the uterus, which can pass through the diaphragm, creating small perforations (holes) that allow air to escape into the pleural space. The diaphragm sits on the right-hand side, which can offer an explanation why most cases of CP occur on the right side. Once inside the chest, this tissue can implant on the lung surface.^1,11 

What role does menstruation play? 

There have been several mechanisms proposed for how menstruation influences the development of CP. 

• One theory suggests air travels through the genital tract into the abdomen and through the diaphragmatic perforations into the chest. This occurs during a woman's period, as the cervical mucus plug is not there
• Another theory involves the shedding of the abnormal endometrial tissue on the lung surface or diaphragm. The implanted endometrial tissue in the lungs would react to signals from hormones during a menstrual cycle, as it would normally do in the uterus. These tissues then slough or “break down”, weakening lung tissue and allowing air to escape inside
• A third theory focuses on the prostaglandin hormone, which increases during a menstrual cycle. This causes small airways and lung vessels to narrow, which leads to lung tissue injury, causing air to leak inside the chest cavity¹² 

It is likely that CP is caused by a combination of these mechanisms. They may act together to weaken tissue and trigger lung collapse in women, with menstruation being a key factor in this.^13,14

Clinical manifestation of catamenial pneumothorax

Women with CP may experience sharp and intense chest pain, sometimes accompanied by shoulder pain, a painful cough, or a rapid heartbeat, or they may struggle to breathe properly. It's important to note that these symptoms tend to appear within 72 hours of their period starting.¹ 

To confirm a CP diagnosis, a doctor may take: 

• A detailed history of the patient's menstrual cycle 
• Imaging scans (e.g. chest CT or MRI, to see the collapsed lung or any diaphragmatic perforations)
• VATS (video-assisted thoracoscopic surgery). This allows doctors to observe and remove any endometrial implants and repair the diaphragm, as well as confirm histopathology¹⁵ 

Treatment follows a two-pronged approach: 

1. Medication: Gonadotropin-releasing hormone analogues (GnRH), a type of hormone suppression typically used to suppress regular hormonal changes. This can reduce menstrual bleeding and related symptoms
2. Surgical Intervention: VATS with pleurodesis (a procedure to stop air or fluid from building inside the pleural cavity). This surgery will address any structural damage to the lung and diaphragm

Combining surgery with GnRH has shown positive outcomes in patients, considerably lowering the reappearance of a pneumothorax.⁵

Frequently asked questions (FAQs)

Is spontaneous pneumothorax the same as catamenial pneumothorax?

No, they are not the same. While they both involve a collapsed lung, catamenial pneumothorax is linked to menstruation specifically.¹⁶

Can catamenial pneumothorax happen to women without endometriosis?

Yes. Whilst the majority of cases are linked to endometriosis, not all women with CP have confirmed endometriosis.¹⁷

Why does CP usually happen on the right side?

The right side of the diaphragm is more prone to small perforations, and this allows endometrial tissue or air to travel into the right side of the chest.⁶

Can CP be cured?

There is currently no cure, but a combination of surgical and hormone treatment can significantly reduce symptoms and recurrence.⁵

Should women who experience similar symptoms to CP during menstruation seek a gynaecological consult?

Definitely. A regular pattern of CP symptoms coinciding with the monthly menstrual cycle should prompt evaluation by a specialist.¹⁸

Conclusion 

Catamenial pneumothorax presents with intense chest pain and shortness of breath in people who experience it. Although these symptoms may be treated and detected as a pneumothorax, the underlying cause, which is the monthly menstrual cycle, is often overlooked. Connecting the dots between a pneumothorax and the onset of a period is very important to avoid a regular monthly appearance of a collapsed lung.

Awareness of CP and the links between pneumothoraxes and menstrual cycles should be improved so that necessary steps can be taken to provide proper care. If you notice yourself experiencing chest pain and shortness of breath, whether or not you are on your period, it is always important to reach out to a doctor immediately. These symptoms may indicate a serious issue.