Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . Lung volumes are low , resulting and pulmonary vascular crowding , otherwise the hilar and mediastinal contours are unremarkable . There is subtle increased opacity within the left perihilar region and upper lung . Streaky atelectasis is seen at the left lung base . There is no pneumothorax , or pleural effusion . The visualized osseous structures are unremarkable .
    OUTPUT:
    
Subtle increased opacity within the left perihilar region and upper lung , which could be secondary to pneumonia .