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
Obliteration of Costophrenic angle is seen in 
Select and explain. 
A. Pneumothorax, B. Pleural effusion, C. Tuberculosis, D. Pneumonia
B: Pleural effusion
Answer: B: Pleural effusion 
Explanation: A Small Amount of free fluid may be undetectable on an erect PA chest radiograph as it tends initially to collect under the lower lobes. As the amount of effusion increases, the posterior and then the lateral costophrenic angles become blunted, by which time a 200 to 500-mL effusion is present