Question

What is the differentiating feature of an atrial septal defect (ASD) from a ventricular septal defect (VSD) on chest X-ray?

• A. Pulmonary hypertension
• B. Absence of left atrial enlargement
• C. Pulmonary congestion
• D. Aortic shadow

Hint:

In which defect does the extra volume bypass the left atrium?

Answer 1

The Correct Option is B

Step 1: Understand the shunt physiology.
Both ASD and VSD are left-to-right shunts and both cause increased pulmonary blood flow (plethora) and can lead to pulmonary hypertension. So those features do not separate them.

Step 2: Trace the chamber loading in VSD.
In a VSD, shunted blood enters the pulmonary circulation, returns to the left atrium, and then the left ventricle, so both the left atrium and left ventricle enlarge. Left atrial enlargement is therefore typical of a VSD.

Step 3: Trace the chamber loading in ASD.
In an ASD, the shunt decompresses at the atrial level; the extra return goes into the right atrium and right ventricle and pulmonary artery. The left atrium does NOT enlarge because the excess volume escapes through the defect rather than loading the LA.

Step 4: Identify the discriminator.
The absence of left atrial enlargement is the key X-ray feature that favours ASD over VSD. Pulmonary hypertension and congestion occur in both and so cannot differentiate them.

Hence the answer is absence of left atrial enlargement.