Introduction

Catamenial pneumothorax (CP) is a medical condition in which air leaks into the space surrounding the lungs, causing lung collapse. This can occur spontaneously during menstruation (catamenial, relating to menstruation and pneumothorax, means air in the chest cavity).¹

Thoracic structures refer to the lung and chest regions of the body; therefore, thoracic endometriosis syndrome (TES) refers to the presence of endometrial tissue in the chest cavity. Endometriosis is more commonly found on the diaphragm, but it may also be found in the lungs.²

The relation between catamenial pneumothorax and thoracic endometriosis syndrome

Catamenial pneumothorax is the most common manifestation of endometriosis syndrome, and is accountable for around 18-33% of spontaneous pneumothorax seen in women.³ Women withTES experience endometrial tissue growing in the thoracic cavity (space surrounding the lungs), causing swelling and bleeding as a response to the hormonal fluctuation during their menstrual cycle. Subsequently, the swelling and bleeding into the thoracic region lead to a pneumothorax(the collapse of a lung), which is recurrent in individuals with catamenial pneumothorax and is typically present in less than 72 hours after menstruation.⁴

Pathophysiology

Mechanisms linking TES to CP

Diaphragmatic defects

Diaphragmatic defects (E.g. a small hole or incomplete formation of the diaphragm) or fenestrations link TES to CP by creating a pathway for both endometrial tissue and air to flow from the peritoneal cavity to the pleural space. Endometrial tissue present in the thoracic region, specifically the diaphragm, can cause weakening and over time, tears in the diaphragm, resulting in small openings (fenestrations). During menstruation, there is a lack of cervical mucus plug in the uterus (mucus seal during pregnancy to prevent infection in the uterus). This allows air to enter the uterus, where it can then travel from the peritoneal cavity to the thoracic cavity due to the diaphragm defects, causing a pneumothorax.⁵

Translocation of endometrial cells

Endometrial cells travel to the thoracic cavity by way of the lymphatic or vascular pathways, a mechanism referred to as metastatic endometriosis. The endometrial cells shed during menstruation and travel through these pathways, where they can then embed and grow in the thorax, cause damage to the tissue, and result in diaphragmatic fenestrations, inducing subsequent catamenial pneumothorax.⁶

Hormonal influence on ectopic endometrial tissue

Elevated estrogen levels during the follicular phase of the menstrual cycle are responsible for the rapid increase of endometrial cells found in the thoracic cavity.⁷ During menstruation, normal endometrial cells break down and exit the uterus; however, endometrial-like cells found in the thoracic cavity, as seen in TES, break down and do not leave the body. This causes inflammation and possible diaphragmatic fenestrations or other alveolar lesions. This repeated mechanism of endometrial cells in the thoracic cavity rapidly increasing and breaking down due to hormonal changes can cause a pneumothorax. Thus demonstrating catamenial pneumothorax as a manifestation of thoracic endometriosis syndrome.⁶

Right-sided predominance of catamenial pneumothorax

Catamenial pneumothorax predominantly affects the right side of the body due to the abdominal and pelvic involvement in individuals with TES.⁸ The endometrial cells travel across the abdomen to the diaphragm, affecting the right side due to the nature of fluid flowing through the abdominal cavity in a clockwise manner.⁹

Clinical features 

The symptoms of catamenial pneumothorax as a manifestation of thoracic endometriosis syndrome include chest pain, coughing, shortness of breath, and sometimes right-sided pain around the shoulder or neck due to diaphragmatic irritation.⁶ There are significantly high recurrence rates of catamenial pneumothorax with currently no effective treatment.

These symptoms often recur during menstruation, specifically within 72 hours of menstruation, due to the increased levels of prostaglandin F2 and endometrial tissue changes, causing thoracic endometrial implants. During this period of the menstrual cycle, the impact of hormonal fluctuations and breakdown of endometrial tissue within the thoracic cavity can result in the lungs collapsing.

Diagnosis 

A medical professional may suspect catamenial pneumothorax when symptoms present or recur at the time of menstruation. A diagnosis can involve detecting diaphragmatic endometriosis using various tests, including imaging of the thoracic cavity and specifically the membrane between the lungs during menstruation, such as a chest X-ray or CT scan. 

A definitive diagnosis for thoracic endometriosis includes the gold standard method of using video-assisted thoracoscopic surgery (VATS) - a minimally invasive surgery - to enable visualisation of lesions in the thoracic cavity.⁶ 

Management 

Surgical

The recommended management for thoracic endometriosis syndrome can involve a surgical or medical approach or a combination of both. Video-assisted thoracic surgery is used to diagnose and manage TES, as this allows for the surgical removal of endometrial lesions in the diaphragm and also repairs any defects.

During a VATS procedure, pleurodesis (a procedure that creates adhesions between the two linings of the chest wall and lung together) can be performed to prevent any future air leaks or fluid build-up in the pleural cavity.¹⁰

Diaphragmatic repair during surgery usually involves identifying the defect from endometrial implants during a VATS procedure and closing them via methods of stitching, stapling and artificial mesh.¹¹ 

Medicinal

Hormone therapy has been identified as an adjunctive treatment method for catamenial pneumothorax, specifically gonadotropin-releasing hormone (GnRH). GnRH manages the condition by suppressing ovarian function; therefore, the hormone fluctuations that occur during the menstrual cycle. This prevents the formation of endometrial implantation in the diaphragm, which can induce catamenial pneumothorax.¹² 

Although hormone therapy of GnRH is more commonly used and more effective in preventing the recurrence of CP, hormone contraceptives are also used in combination with a surgical approach, as they can suppress ovulation and menstruation.¹³

Combined approach

A combined approach of both surgical intervention and hormone therapy for the management of catamenial pneumothorax gives the most favourable outcomes. Findings show that a surgical approach alone addresses the physical issues of the condition, i.e. diaphragmatic repair, but has greater recurrence rates, while hormone therapy manages underlying hormonal fluctuations that induce recurrence of CP. When used in conjunction, individuals have reduced recurrence of pneumothorax compared to each treatment used alone.¹⁴ 

Prognosis and recurrence

Catamenial pneumothorax is defined by its recurrence of pneumothoracic episodes, and if not treated, has high recurrence rates. Without both surgical intervention and hormone therapy to repair and remove endometrial lesions and suppress hormonal fluctuations, the fundamental cause - thoracic endometriosis- will not be addressed, and the condition will therefore recur following menstruation. 

The prognosis for CP is favourable with appropriate management of the underlying thoracic endometriosis, as this is evident in reduced recurrence rates of CP. ⁴ Thus, highlighting the importance of early recognition of the condition to enable timely management involving a multidisciplinary approach of surgery and hormone therapy to address all aspects of the condition.

Summary 

Catamenial pneumothorax (CP) is a recurrent lung collapse associated with thoracic endometriosis syndrome (TES), wherein endometrial tissue travels and implants itself in the chest cavity as a direct response to hormone fluctuations from menstruation. Symptoms involve inflammation, bleeding, and air leaking into the chest cavity, causing a pneumothorax, and it is usually on the right side and occurs within 72 hours after menstruation. 

Diagnosis of the condition includes methods of imaging and video-assisted thoracoscopic surgery (VATS), and treatment involves the surgical repair following the findings of the VATS procedure, combined with hormone therapy to manage the hormone fluctuations that aggravate the endometrial cells during menstruation and result in recurrent pneumothorax. 

Early recognition and a multidisciplinary approach exhibit reduced recurrence rates and provide an overall favourable outcome. Understanding the link between TES and CP is significant to improving the outcome and preventing recurrent pneumothoracic episodes.