This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Valvular Heart Disease, Subject name: Medicine
In mitral stenosis double atrial shadow is due to enlargement of? 
Select and explain. 
A. Right atrium, B. Left atrium, C. Both atria, D. Left auricle
B: Left atrium
Answer: B: Left atrium 
Explanation: Ans. is 'b' i.e., Left atrium o Double Density sign in Mitral Stenosis is a sign of enlargement of Left Atrium.# Double density sign is seen on frontal chest radiograph in the presence of left atrial enlargement and occurs when the right side of the left atrium pushes behind the right cardiac shadows indenting the lung and forming its own district sihhouette.# If large enough it can actually reach beyond the border of the right atrium.