- Umbilical vein varix
- Timing of Cranial Markers in Open NTD
- Real world experience Open Neural tube defect and Brain Signs
- Real world experience First Trimester Megacystis – Management
- Real world experience Fetal Megacystis
- Abnormal facial profile
- Azygous Vein & ARSA
- Blakes Pouch Cyst
- Absent nasal bone (ANB)
- Choroid plexus cysts
- Chronic placental abruption
- Fetal Alcohol Syndrome
- Placenta-First Risk Stratification
Azygous Vein and ARSA
Dilated azygos vein vs ARSA: core differences
• Azygos vein: venous structure, posterior, drains into the SVC.
• ARSA (aberrant right subclavian artery): arterial branch from the descending aorta, courses posterior to the trachea and esophagus.
Azygos → SVC (venous), ARSA → descending aorta (arterial).
Plane and position
Three-vessel–trachea (3VT) view
• ARSA
o Seen posterior to the trachea
o Usually oblique or horizontal
o Originates from the descending aorta
• Dilated azygos vein
o Seen posterior and to the right of the trachea
o More vertical or gently curving
o Joins the SVC superiorly
Doppler behavior
| Feature | Azygos vein | ARSA |
|---|---|---|
| Doppler pattern | Low-velocity, phasic venous flow | High-velocity arterial flow |
| Pulsatility | Respiratory variation | Cardiac pulsatility |
| Color aliasing | Minimal | Common |
| Direction | Toward SVC | Away from descending aorta |
Connectivity tracing
• Trace inferiorly
o ARSA connects to descending aorta
o Azygos continues as a venous channel alongside the spine
• Trace superiorly
o Azygos drains into SVC
o ARSA goes to the right arm
ARSA
• Often isolated
• Soft marker for trisomy 21
• No venous enlargement elsewhere
Dilated azygos vein
• Often seen with:
o Interrupted IVC with azygos continuation
o Absent or hypoplastic ductus venosus
o Elevated central venous pressure
• SVC may appear prominent
When azygos vein is truly dilated
True azygos dilatation usually implies rerouted venous return
• Interrupted IVC with azygos continuation
• Absent ductus venosus
• Significant cardiac inflow obstruction
In these cases:
• Azygos vein is consistently large
• Seen in multiple planes
• Accompanied by systemic venous anomalies
If:
• Normal IVC
• Normal ductus venosus
• Normal venous Dopplers
and only a prominent vessel posterior to the trachea,
→ think physiologically prominent azygos,
The azygos vein is frequently visible
Especially in:
• Second and third trimester
• Thin maternal habitus
• Good venous color sensitivity
• When the left brachiocephalic vein is well seen
Left atrial isomerism (LAI), the azygos vein becomes the main venous pathway, not just a small accessory vein.
| Normal fetus | Left atrial heterotaxy |
|---|---|
| IVC present | IVC interrupted |
| Azygos is small or moderate | Azygos is large and dominant |
| Venous return via IVC → RA | Venous return via azygos → SVC |
| Often seen incidentally | Seen inevitably and prominently |
Red flags
• IVC not seen below the liver
• “Double vessel” sign next to the descending aorta in abdominal view
• Large, straight, continuously visible azygos vein
• Abnormal hepatic venous drainage
• Cardiac clues:
o AVSD
o Bradyarrhythmia / heart block
o Abnormal pulmonary venous connections
• Visceral clues:
o Midline liver
o Stomach malposition
o Polysplenia
Azygos appearance
• Small to moderate calibre
• Curved, tapering
• Intermittently conspicuous
• Best seen near SVC junction
→ NORMAL AZYGOS
vs
• Large, straight, dominant vessel
• Seen in multiple planes continuously
• Runs parallel to descending aorta
• Comparable in size to SVC
→ PATHOLOGICAL AZYGOS
If ANY of the following are present, escalate:
• Midline liver
• Abnormal stomach position
• Polysplenia
• AVSD
• Bradycardia / heart block
• Abnormal pulmonary venous return
→ Think heterotaxy / left atrial isomerism