Follow-up chest radiograph shows the placement of a left-sided chest tube with improved aeration of the left lung and diminished left pleural effusion. However, the left costophrenic angle is not fully visualized, and a deep sulcus sign cannot be completely excluded. Additionally, there is air-space opacity in the left lower lung retrocardiac region, which may indicate consolidation or atelectasis.
Simple pleural effusion (Absent) Atelectasis (Uncertain)