Question

In which of the following conditions is differential cyanosis found?

• A. VSD with reversal of shunt
• B. PDA with reversal of shunt
• C. ASD with reversal of shunt
• D. Tetralogy of Fallot

Hint:

Think of a shunt sited distal to the head and arm vessels.

Answer 1

The Correct Option is B

Step 1: The clue here is the word differential. A pink upper body with a blue lower body is only possible when impure blood is delivered selectively to the descending aorta after the great vessels to the head and arms have already branched off.

Step 2: The patent ductus arteriosus joins the pulmonary artery to the aorta just past the left subclavian artery. Normally flow is left to right. Once pulmonary pressures climb high enough to reverse the shunt, venous blood crosses into the post-subclavian aorta and travels only to the trunk and legs.

Step 3: Therefore the toes look blue and clubbed while the fingers and lips remain rosy. Septal defects (VSD, ASD) cause complete intracardiac mixing and TOF produces right-to-left shunting at the ventricular level, so all four limbs share the same colour in those lesions.

\[\boxed{\text{PDA with reversal of shunt}}\]