Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is opacity in the left superior and posterior basal segments . There is associated volume loss of the left lower lobe . Heart size is within normal limits . Mediastinal and hilar contours are unremarkable . There is no evidence for pulmonary edema , pleural effusion , or pneumothorax .
    OUTPUT:
    
Left lower lobe opacity in the superior and posterior basal segments with substantial volume loss . Although potentially due to an acute infectious pneumonia with a component of atelectasis from mucous plugging , a post obstructive process from obstructing neoplasm such as carcinoid may have a similar radiographic appearance . Depending on clinical presentation , short - term follow - up chest radiograph in 2 weeks after antibiotic therapy or immediate chest CT with contrast is recommended . The latter would be suggested if the patient has been experiencing recurrent symptoms or if the process fails to substantially improved after treatment .