<s>[INST] My chest xray Roentgenological Findings state that; Linear densities are seen in the left lower lung field. heart is not enlarged. Pulmonary vascularity is within normal limits. Diaphragm and costophrenic sulci are intact. IMPRESSION : Subsegmental atelectasis versus fibrosis , left lower lung field. Doctor, what does this mean? Thank you. [/INST] Thanks for your question on Chat Doctor. Atelectasis is partial collapse of lung segment. It is due to intraluminal obstruction by retained secretions (mucus plugging). Fibrosis is scar tissue. It is seen most commonly after any lung insult like pneumonia or Tuberculosis or trauma. So fibrosis is healed scar. So in your case we need CT THORAX to rule out atelectasis and fibrosis. CT gives excellent imaging of lung parenchymal and thus will be diagnostic in your case. </s>