Catamenial pneumothorax due to heterotopic endometriosis in the pericardium

A 46-year-old woman presented with a right pneumothorax at a regular medical examination during menstruation. The pneumothorax resolved without intervention; however, 6 months later, she was referred to our hospital due to chest pain and dyspnoea. A chest X-ray showed grade III pneumothorax and surgery was performed. During surgery, the patient was found to have pleural adhesions around the right upper lung, pores in the diaphragm and a blueberry spot in the pericardium. The margins of the upper lobe and diaphragm were covered with a polyglycolic acid sheet at the operation. Eight days after surgery, she was referred to our hospital again due to massive haemothorax. The reoperation suggested that the aforementioned blueberry spot in the pericardium was the source of bleeding. The spot was resected and shown to be oestrogen and progesterone receptor-positive, providing evidence of heterotopic endometriosis.