How to Tell Them Apart on Fetal Ultrasound
Tetralogy of Fallot (TOF) and Double Outlet Right Ventricle (DORV)
often look similar on fetal ultrasound.
Both may show:
- Ventricular septal defect (VSD)
- Overriding aorta
- Abnormal outflow tract alignment
So what truly differentiates them?
๐ฅ The Key Question
Does the aorta connect directly to the left ventricle?
This single question guides the differentiation.
1๏ธโฃ Tetralogy of Fallot (TOF)
Structural Features
- Large VSD
- Overriding aorta (partially over septum)
- Pulmonary stenosis
- RV hypertrophy (postnatal finding)
Critical Point
โ The aorta still maintains connection with the left ventricle
โ Override is partial, not complete
Ultrasound Clues
- LVOT shows continuity between LV and aorta
- RVOT shows pulmonary narrowing
- 3VT shows Ao dominance with small PA
๐ The pulmonary artery problem is dominant.
2๏ธโฃ Double Outlet Right Ventricle (DORV)
Structural Features
- Both great arteries arise predominantly from RV
- LV empties through VSD only
Critical Point
โ There is no direct LVโaorta connection.
Ultrasound Clues
- Both Ao and PA appear to originate from RV
- LVOT does not show normal alignment
- Great vessels may appear parallel
๐ The origin problem is dominant.
๐ง Practical Differentiation Strategy
| Feature | TOF | DORV |
| LV๋ฐo connection | Present | Absent |
| Override degree | Partial | Predominant RV origin |
| Main problem | Pulmonary stenosis | Abnormal vessel origin |
| 3VT | Ao dominance | Alignment abnormality |
๐จ Why It Matters
TOF and DORV may require different surgical strategies.
In DORV, outcome depends on:
- VSD location (subaortic vs subpulmonary)
- Great artery relationship
- Associated anomalies
So accurate prenatal distinction is important.
๐ฅ Bottom Line
In TOF, the aorta overrides but still belongs to the LV.
In DORV, the aorta belongs to the RV.
The outflow tract tracing is everything.
