Congenital Variants and Anomalies of the Aortic Arch

A practical radiology review of Congenital Variants and Anomalies of the Aortic Arch, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

Embryology

• 4th arch → definitive aortic arch
• 5th arch → normally regresses (persistence = rare anomaly)
• 6th arch → ductus arteriosus / ligamentum arteriosum
• 22q11.2 deletion → favors 4th arch regression (Type B IAA, RAA)

Key imaging clue

• Arch sidedness = bronchus crossed (not vessel origin!)
• Vascular ring may be “invisible” if atretic → look for indirect signs:
• Distorted subclavian
• Kommerell diverticulum
• Ductal dimple opposite arch
• ↔ Descending aorta opposite side

Left Aortic Arch Variants

• Normal branching (70–80%): Brachiocephalic → LCCA → LSA
• “Bovine arch” misnomer → avoid term
• L vertebral from arch (5–6%) → procedure-relevant
• Aberrant Right Subclavian (ARSA)
• Most common anomaly
• Dysphagia lusoria (~10% adults)
• Kommerell diverticulum only in 15–30%
• No diverticulum → usually NO vascular ring
• With diverticulum → ductus is contralateral → vascular ring

Right Aortic Arch (RAA) — don’t confuse

• RAA + Aberrant LSA (from Kommerell)
• 2nd most common vascular ring
• Ring = L ductus → LPulA to diverticulum
• Rarely CHD (important!)
• RAA + Mirror Image Branching
• CHD in ~98% (TOF, truncus, TGA)
• Usually NO vascular ring
• Key: Left brachiocephalic artery, not separate LCCA+LSA

Circumflex Aorta

• Arch itself crosses midline posterior to esophagus
• Ductus completes ring
• Severe cases → aortic uncrossing surgery (not just ductal ligation!)

Double Aortic Arch

• Most common symptomatic vascular ring
• Stridor, wheeze, dysphagia from birth
• 4-artery sign = symmetric CCAs + SCAs
• Incomplete double arch ≠ RAA mirror image
• Atretic fibrous segment MUST be divided surgically

Isolation of Subclavian

• Vessel only via ductus to pulmonary artery
• Can cause subclavian steal
• Often with TOF

Interrupted Aortic Arch (IAA)

• Descending aorta supplied by PDA
• Type B = most common + 22q11

Know levels

• Type A: distal to LSA 22q11
• Type B: between LCCA–LSA 22q11
• Type C: between BCA–LCCA (rare)

Hypoplasia vs Coarctation

Hypoplasia thresholds

• Arch <60% (prox) / <50% (distal) of asc aorta
• Isthmus <40%

Coarctation

• Juxtaductal
• Collaterals common
• Rare in RAA (0.1%)

Pseudocoarctation

• Kinking only — NO gradient (<25 mmHg)
• No collaterals
• Can form aneurysm → rupture risk (don’t ignore!)