Catamenial pneumothorax caused by diaphragmatic stromal endometriosis

A case of catamenial pneumothorax caused by stromal endometriosis of the diaphragm is described. A 40-year-old woman suffered two episodes of right-sided pneumothorax which occurred after onset of menstruation. Thoracoscopy revealed brownish spots in the right diaphragm and partial excision of the diaphragm was performed. Histological examination showed that the lesion was characterized by sheets of cells resembling endometrial stromal cells, small thin-walled blood vessels and extravasated erythrocytes in varying proportions. Some clusters of these cells were transmural. No endometrial-type glands were found. Immunohistochemically, the nuclei of the endometrial stromal cells were strongly positive for both estrogen and progesterone receptors. Therapy with a gonadotropin-releasing hormone analogue was started and the patient has since been asymptomatic for 6 months. Pathologists should not overlook diaphragmatic stromal endometriosis as a possible cause of pneumothorax.