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: Differential cyanosis means one part of the body is pink while another is cyanotic. This happens when deoxygenated blood reaches some parts of the body but not others, which requires a connection between the systemic and pulmonary circulations distal to the head and upper limb vessels.

Step 2: In a patent ductus arteriosus (PDA), the duct connects the aorta to the pulmonary artery beyond the origin of the vessels supplying the head and arms. When pulmonary hypertension develops and the shunt reverses (Eisenmenger physiology), deoxygenated blood from the pulmonary artery flows into the descending aorta. This makes the lower limbs cyanotic and clubbed while the upper limbs and face stay pink.

Step 3: A VSD or ASD with shunt reversal mixes blood centrally, so cyanosis is uniform and not differential. Tetralogy of Fallot also causes central, generalized cyanosis. Hence PDA with reversal of shunt is the correct answer.