*passage.* **Table 1.**

*Pneumothorax*

**2. Incidence**

[4, 8–10, 19, 22–29].

The mean age of onset is reported to be 32–35 years [3, 4, 12, 14–17]. CPX may also develop as late as at 39 years of age [18, 19]. CPX occurs most often (85–95%) unilaterally, usually occurring on the right side of the chest, but there are cases on

CPX is generally considered to be a rare entity, and there is an incidence less than 3–6% among women who suffer from spontaneous pneumothorax. Such a low incidence rate may be a result of decreased disease awareness and underdiagnosis

In a recent study [24, 29, 30], 156 premenopausal women who underwent surgery for spontaneous pneumothorax were reviewed retrospectively, and 31.4%

Yet, the incidence of catamenial pneumothorax was much higher among women at reproductive age who were referred for surgical treatment because of recurrent

In a retrospective study, Alifano et al. reported thoracic endometriosis in 13 out of 35 (37%) patients who underwent reoperation for recurrent spontaneous pneumothorax [29]. Catamenial pneumothorax was the initial diagnosis in eight cases and idiopathic pneumothorax in four cases [29]. Under/misdiagnosis of thoracic endometriosis can be referred to several causes, including decreased disease awareness, incomplete scanning for the lesions, variations in the size, appearance, and

The etiopathology of catamenial pneumothorax remains unclear, but there are some theories explaining the etiopathogenesis of catamenial pneumothorax. These theories include physiological, migrational, microembolic-metastatic, and the

According to the physiologic hypothesis, high levels of circulating prostaglandin F2 during menstrual cycle cause vasoconstriction and this induces alveolar rupture and pneumothorax. Pulmonary bullae blebs may be more sensitive to ruptures during hormonal changes. There are no pathognomonic lesions in such cases and this

In metastatic or lymphovascular microembolization theory, endometrial tissue spread through the venous and/or the lymphatic system to the lungs, and subsequent catamenial necrosis of endometrial parenchymal site adjacent to visceral pleura causes pneumothorax. If parenchymal endometrial focus is located centrally, hemoptysis may be present as a symptom [3, 4, 7, 8, 22, 24, 30–32]. Endometrial tissue can be detected in the lung parenchyma, at knee, in the brain, and in the eye.

According to the transgenital-transdiaphragmatic passage of air theory, absence of cervical mucus during menstruation provides air passage from the vagina to the uterus, through the cervix. Then, air enters the peritoneal cavity straight through the fallopian tubes and reaches to the pleural space by diaphragmatic defects [4, 7, 8, 22, 24, 31]. This passage is facilitated by the difference in atmospheric pressures between pleural space and peritoneal space since the atmospheric pressure in the

which pneumothorax also occurs on the left side or bilaterally [11, 15–21].

spontaneous pneumothorax, ranging between 18 and 33% [9–12, 22].

(49/156) of the patients were classified as CPX.

diaphragmatic theory of air passage [17] (**Table 1**).

issue supports the physiologic theory [4, 7, 8, 24, 31].

pleural cavity is less than the pressure in the peritoneal cavity.

This supports the metastatic theory [12].

number of the lesions [24, 30].

**3. Etiology**

**42**

*The etiopathology of catamenial pneumothorax remains unclear, but there are some theories explaining the etiopathogenesis of catamenial pneumothorax.*

There are few reports in the literature regarding transgenital-transdiaphragmatic passage of air theory. There are rare cases reporting simultaneous [33, 34] or undulating episodes CPX and pneumoperitoneum [35], and also case reports defining radiologic findings of small diaphragmatic defects associated with ipsilateral CPX [21]. But repeated episodes of pneumothorax after hysterectomy, fallopian tube ligation, and diaphragmatic resection provide evidence that all the CPX cases can be explained by this theory [7, 24, 29, 36].

Migration theory is based on retrograde menstruation which causes in pelvic seeding of endometrial tissue and migration of this tissue to the subdiaphragmatic sites through the peritoneal fluid flow. Endometrial tissue is mostly implanted to the right hemidiaphragm because peritoneal circulation prefers a clockwise flow through the right paracolic gutter to right hemidiaphragm and the liver facilitates flow with its piston-like activity. Catamenial necrosis of this diaphragmatic endometrial implants results in diaphragmatic perforations. Endometrial tissue then passes through this diaphragmatic perforation and spreads into the thoracic cavity. Ectopic endometrial tissue implants to the visceral pleura and following catamenial necrosis of this tissue cause rupture of the underlying alveoli, and pneumothorax occurs [3, 4, 7, 8, 22, 24, 30, 31]. Endometrial diaphragmatic implants exist along with diaphragmatic perforations [37], and endometrial tissue can be seen at the edges of the diaphragmatic perforations in many cases of CPX [22]; these findings may support the migration theory in the etiopathology of catamenial pneumothorax.
