**2. Incidence**

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 [4, 8–10, 19, 22–29].

Yet, the incidence of catamenial pneumothorax was much higher among women at reproductive age who were referred for surgical treatment because of recurrent spontaneous pneumothorax, ranging between 18 and 33% [9–12, 22].

In a recent study [24, 29, 30], 156 premenopausal women who underwent surgery for spontaneous pneumothorax were reviewed retrospectively, and 31.4% (49/156) of the patients were classified as CPX.

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 number of the lesions [24, 30].
