Tetralogy of Fallot (TOF) and Double Outlet Right Ventricle (DORV) can look very similar on fetal ultrasound.
Both involve:
- VSD
- Aortic override
- Abnormal outflow tract alignment
So how do we differentiate them?
1️⃣ The Key Question
👉 Where does the aorta arise from?
That is the core difference.
TOF (Tetralogy of Fallot)
✔ Aorta overrides the VSD
✔ But still primarily connected to the left ventricle
✔ Pulmonary stenosis present
On 4-chamber view:
- VSD visible
- Overriding aorta partially over septum
On outflow tract view:
- Pulmonary artery smaller than aorta
👉 Aorta originates mainly from LV (with override)
DORV (Double Outlet Right Ventricle)
✔ Both aorta and pulmonary artery arise predominantly from the right ventricle
✔ Large VSD is required for LV output
Key point:
👉 Aorta arises entirely or mostly from RV
On imaging:
- Both great vessels aligned over RV
- VSD provides LV connection
2️⃣ Why They Look Similar
Because both show:
- Overriding aorta
- VSD
- Abnormal outflow relationship
But the degree of override matters.
TOF → partial override
DORV → near complete RV origin
3️⃣ Practical Ultrasound Clues
✔ Assess the relationship of great arteries to ventricles
✔ Trace the outflow tracts carefully
✔ Look at subaortic conus presence
✔ Evaluate pulmonary stenosis severity
If pulmonary stenosis is severe and aorta is mildly overriding → think TOF.
If both great arteries sit mostly over RV → think DORV.
4️⃣ Why It Matters
Because prognosis and surgical planning differ.
TOF:
- Well-defined surgical repair
- Often isolated
DORV:
- Multiple anatomical subtypes
- Surgical strategy depends on VSD location
Clinical Tip
When unsure:
👉 Ask: Does the LV have a direct connection to the aorta?
If yes → more likely TOF
If no → think DORV
