**Question:** Double density sign in Mitral stenosis is a sign of enlargement of

A. Mitral valve
B. Left atrium
C. Left ventricle
D. Pulmonary artery

**Correct Answer:** B. Left atrium

**Core Concept:** Mitral stenosis is a valvular heart disease characterized by the narrowing of the mitral valve orifice, leading to increased resistance and reduced blood flow from the left atrium to the left ventricle. This narrowing results in compensatory mechanisms to maintain cardiac output.

**Why the Correct Answer is Right:** The double density sign is a radiographic finding seen on chest X-ray in patients with mitral stenosis. It indicates the presence of two densities within the left atrium, representing the mitral valve and the adjacent left atrial wall. This sign is specific for mitral stenosis and not seen in other heart diseases.

**Why Each Wrong Option is Incorrect:**

A. Mitral valve enlargement (mitral valve regurgitation) has a different clinical presentation and radiographic findings, not involving the left atrium.

B. Left atrial enlargement is a common finding in many cardiac conditions, including mitral stenosis, but the double density sign is more specific for mitral stenosis.

C. Mitral stenosis results in left ventricular enlargement but does not involve the left atrium to the extent that the double density sign is seen.

D. Pulmonary artery dilation is a feature of pulmonary arterial hypertension rather than mitral stenosis.

**Clinical Pearl:** The double density sign is a valuable clue for diagnosing mitral stenosis, especially when combined with other clinical, electrocardiographic, and echocardiographic findings. Early recognition and management of mitral stenosis are crucial to prevent complications like heart failure and cerebrovascular events.