Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single portable AP chest radiograph was provided . The right pleural effusion is unchanged in size since the prior radiograph . Overlying opacity has slightly increased since the prior exam but most likely represents atelectasis . The left lung is clear . Cardiomediastinal silhouette is unchanged . Bony structures are intact .
    OUTPUT:
    
Stable moderate right pleural effusion with opacity at the right base , which is likely overlying atelectasis .