The fate of the arches…

Trisha J. OuraRadiology Resident

9/21/09

But first…

• Early embryogenesis:– Thickenings of mesenchyme, ecto and endoderm– Mesenchyme migrates ventrolaterally pharngeal

bulges– Neural and cardiac tissue follow, form concentric

hemi-rings

TW Sadler, Langman’s Medical Embryology, Lippincott, Williams & Wilkins, 2003

• Enlarged mesoderm stacks (like donuts) to form bilateral pharyngeal (branchial) arches

• Ectoderm clefts (between donuts)• Endoderm pouches (within donuts)

TW Sadler, Langman’s Medical Embryology, Lippincott, Williams & Wilkins, 2003www.gettyimages.com

• Each pharyngeal arch contains:– Aortic arch– Cartilage core– Muscle– Nerves

BM Patten, BM Carlson, Foundation of Embryology, McGraw-Hill Publishing Co, 1974MSA Kumar, Developmental Anatomy, Tufts, 2009.

Where did those aortic arches come from?

• Early heart = tube • “S” shaped looping creates

cranial truncus arteriosus• Truncus aortic sac

aortic arches

DM Noden and A DeLahunta, The Embryology of Domestic Animals, Williams & Williams, 1985

KL Moore and TVN Persaud, The Developing Human, Clinically Oriented Embryology, Saunders, 2003

Now what?

• I, II = disappear early• III = common carotids• IV:

– Right: common brachiocephalic trunk (R subclavian a.)

– Left: arch of aorta• V: transient• VI: pulmonary a.

– Right: no connection to dorsal aorta

– Left: ductus arteriosus (ligamentum arteriosus)

R L

TW Sadler, Langman’s Medical Embryology, Lippincott, Williams & Wilkins, 2003

Vascular ring anomalies:aberrations, anomalies, and…. avians?• Birds:

– RIGHT IV arch becomes arch of the aorta (vs. left in mammals)

• PRAA (dextroaorta):– mammals = birds– Most common– Poss w/ persistent L CrVC– On radiographs:

• DV/VD = trachea often midline or left

DM Noden and A DeLahunta, The Embryology of Domestic Animals, Williams & Williams, 1985

PRAA

Normal PRAA

http://cal.vet.upenn.edu/projects/cardiosf/project/embprs/embprs14.htm

PRAA (Acc 71349)

Aberrant Subclavians

Right subclavian a.:- Direct from arch of aorta or

w/ the left in bi-subclavian trunk

- Esophagus constricted dorsally w/o complete ring

- R subclavian crosses left right, causes indentation/half ring stricture of esophagus

Normal

Aberrant R. subclavian a.

Left subclavian a.:- Right IV arch aortic arch (PRAA)- Left IV arch L subclavian- Retains connection to dorsal aorta- Crosses retroesophageally on left - L subclavian constricts esophagus

at heart base

Normal

Anomalous L. subclavian a.

R. subclavian

PRAA

• Double Aortic Arch– Complete persistence of

both sides of the fourth arch vascular ring anomaly

– Fuse distally to form the descending aorta

– More caudal compression– ONLY vascular ring

anomaly with clinically important tracheal compression

– Treatment: ligate smaller aorta

Normal

Double Aortic Arch

L. subclavian

R. subclavian

Acc 115803

References:

1. http://cal.vet.upenn.edu/projects/cardiosf/project/embprs/embprs21.htm

2. MSA. Kumar, Developmental anatomy syllabus, Tufts, 2009.