This is a very cohesive case which originally was unclear prior to the realization that this patient had recent rib fractures. 

At the time of diagnosis of the rib fractures, no effusion was present. However, it is likely that the patient developed hemothorax which went untreated, particularly given the degree of displacement of the rib fractures. This is the most likely cause of the pleural thickening and calcification, which is only present in the left lung. There is medium-sized left effusion with significant collapse in the left lower lobe and lingula. The swirled appearance on the sagittal reformatted images is characteristic of rounded atelectasis, which is likely due to fibrosis of the visceral pleura.