[A case of malignant pleural mesothelioma presenting as pneumothorax]

The patient was a 51-year-old woman who had no history of asbestos exposure and showed left pneumothorax with a small amount of pleural effusion. On admission to our hospital, she showed clinical and laboratory data similar to that of spontaneous pneumothorax except for a high concentration of hyaluronic acid in pleural fluid. After treatment of pneumothorax, pleural effusion appeared to decrease on chest X-ray. After 3 months, however, pleural effusion again increased, in spite of the improvement of pneumothorax. The patient received open lung biopsy and the histological examination showed mixed type malignant pleural mesothelioma.