Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low , and there is slight elevation of the right hemidiaphragm . While there is no focal consolidation , there are diffusely increased coarse interstitial markings , with peribronchial cuffing . There is no effusion or pneumothorax . Heart is normal in size , and the hilar and mediastinal contours are normal . There is mild tortuosity of the aortic knob . A rounded 3 .7 - cm structure with a sharply - defined lateral margin projects over the heart at left lung base , which is unchanged from the prior radiographs and per previous reports , may represent a posterior mediastinal mass , presumably a neurogenic tumor .
    OUTPUT:
    
Diffuse interstitial markings , suggestive of an atypical infectious process , or possibly interstitial pulmonary edema .