Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The aorta is mildly tortuous . The pulmonary vascularity is not engorged . Opacification within the left lung base near the left costophrenic angle on the frontal view suggests a small left pleural effusion with adjacent atelectasis . The right lung is grossly clear . No pneumothorax is identified . There are no acute osseous abnormalities .
    OUTPUT:
    
Left basilar opacification likely reflects atelectasis with small left pleural effusion though infection can not be excluded .