Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral radiographs of the chest demonstrate a moderate - sized partially loculated pleural effusion and persistent retrocardiac opacity , likely representing atelectasis versus pneumonia . There is mild cardiomegaly . The right lung is clear . The previously seen left apical pneumothorax has resolved .
    OUTPUT:
    
Moderate - sized partially loculated left pleural effusion with persistent retrocardiac opacity , likely representing atelectasis versus pneumonia .