Aberrant right subclavian artery & 22q Microdeletion
Aberrant right subclavian artery (ARSA)
Most common aortic arch branching variant
• Isolated and benign
• Or associated with chromosomal, genetic, structural, and syndromic abnormalities
In ARSA:
• the vessel arises distal to the left subclavian artery
• courses behind the trachea/esophagus toward the right arm
On 3-vessel trachea view: vessel is seen posterior to trachea
Overall Prevalence
• 0.5–2% of all fetuses
• Around 1% average prevalence in euploid populations
Higher prevalence is seen in aneuploid fetuses, especially:
• Down syndrome
• 22q11.2 deletion syndrome
| Category | Approximate Frequency |
|---|---|
| Isolated ARSA | ~70–90% |
| ARSA with additional findings | ~10–30% |
Trisomy 21
In fetuses with Down syndrome: ARSA is present in roughly 15–35%
In contrast: only ~1% of euploid fetuses have ARSA.
22q11.2 Deletion and ARSA
| ARSA | Approximate 22q11 Risk |
|---|---|
| Truly isolated ARSA | <1% (very low) |
| ARSA + cardiac anomaly | 3–15% |
| ARSA + conotruncal defect/right aortic arch | can exceed 15–20% |
ARSA is reported in approximately: 15–30%
especially when associated with:
• conotruncal cardiac defects, abnormal thymus, right-sided arch anomalies
Soft Markers Commonly Associated
Aneuploidy markers
• Increased NT
• Absent/hypoplastic nasal bone
• Echogenic bowel
• Mild ventriculomegaly
• Pyelectasis
• EIF
• Short femur/humerus
• Single umbilical artery
Major Structural Anomalies Associated Cardiac
• VSD, AVSD
• Tetralogy of Fallot, Coarctation
• Right aortic arch, Double outlet right ventricle
Conotruncal defects particularly important
Prognosis
Truly isolated ARSA
Generally:
• excellent prognosis, normal neurodevelopment
Rare Postnatal Issues
Occasionally:
• dysphagia lusoria, feeding difficulty, respiratory compression
Facial Features on Prenatal Ultrasound
Prenatal facial dysmorphism is usually subtle,
Nasal region
• bulbous nose
• broad nasal bridge
• prominent nose
• tubular nose
• hypoplastic nasal alae
Midface findings
• mild midface hypoplasia
• flat facial profile
• retruded maxilla
Mouth and chin
• micrognathia
• small chin
• asymmetric mouth
• downturned mouth corners
Ear abnormalities
Difficult prenatally but may include:
• low-set ears
• posteriorly rotated ears
• dysplastic ears
Relative Predictive Value of Findings
| Prenatal Finding | Association Strength |
|---|---|
| Interrupted aortic arch B | Very high |
| Truncus arteriosus | Very high |
| TOF with absent thymus | Very high |
| Right aortic arch | Moderate-high |
| ARSA alone | Low |
| Isolated facial features | Low |
| Hypoplastic thymus | High |
| Cleft palate + CHD | High |