Pleural plaque. Coloured chest X-ray of a patient with occupational asbestos exposure, showing pleural plaque (dark green) on the right lung. Pleural plaque is a fibrous thickening of the parietal pleura, the membrane that lines the lungs and chest cavity. Pleural plaque develops at least seven years after asbestos exposure. It is generally asymptomatic and requires no treatment. In this patient, the lungs are also hyperinflated, consistent with chronic obstructive pulmonary disease (COPD) caused by emphysema or chronic bronchitis. Cigarette smoking is the most important risk factor for COPD.