This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Radiology, Subject name: Radiology
Deep sulcus sign is seen in 
Select and explain. 
A. Pneumothorax, B. Pleural effusion, C. Tuberculosis, D. Pneumonia
A: Pneumothorax
Answer: A: Pneumothorax 
Explanation: Deep Sulcus sign is seen On Supine chest x-ray in Expiration phase in a case of Pneumothorax where the lucency of air in the costophrenic angle gives the appearance of a deep sulcus. Other Findings of Pneumothorax on CXR: Absent Bronchoalveolar markings Visceral Pleural Reflection