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?
π₯ The Key Question
Does the aorta connect directly to the left ventricle?
This single question guides the differentiation.
1οΈβ£ Tetralogy of Fallot (TOF)
Structural Features
- Large VSD
- Overriding aorta (partially over septum)
- Pulmonary stenosis
- RV hypertrophy (postnatal finding)
Critical Point
β The aorta still maintains connection with the left ventricle
β 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
π The pulmonary artery problem is dominant.
2οΈβ£ Double Outlet Right Ventricle (DORV)
Structural Features
- Both great arteries arise predominantly from RV
- LV empties through VSD only
Critical Point
β There is no direct LVβaorta connection.
Ultrasound Clues
- Both Ao and PA appear to originate from RV
- LVOT does not show normal alignment
- Great vessels may appear parallel
π The origin problem is dominant.
π§ Practical Differentiation Strategy
| Feature | TOF | DORV |
| LVλ°o connection | Present | Absent |
| Override degree | Partial | Predominant RV origin |
| Main problem | Pulmonary stenosis | Abnormal vessel origin |
| 3VT | Ao dominance | Alignment abnormality |
π¨ 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.
π₯ 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.
