Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a mild left - sided posterior sulcus opacity which might represent a small pleural effusion . Pleural effusion can be confirmed with a left down decubitus study . If diagnostic sample of the fluid is desired , thoracentesis under ultrasound guidance would be recommended . The heart is within normal limits for size . The aorta is tortuous and heavily calcified . There is severe thoracic dextroscoliosis which distorts the lung bases . The diaphragm is seen in the higher position relative to previous studies . No acute infiltrates are identified . There is no evidence of pneumothorax . The pleural surfaces are unremarkable .
    OUTPUT:
    
Left posterior basal opacity might represent small pleural effusion . Thoracentesis , if warranted , should be performed under ultrasound guidance .