Embryology of aortic arch and its branches
The most common anatomy of the aortic arch,
present in approximately 70% of humans,
is represented by three great vessels originating from it: innominate artery (IA),
left common carotid artery (LCCA) and left subclavian artery (LCSA).
The IA subsequently branches into the right common carotid artery (RCCA) and the right subclavian artery (RSCA).
The vertebral arteries originate from the corresponding subclavian arteries.
The most widely recognized aortic arch development theory is the Rathke's diagram.
According to it,
six pairs of the branchial arches connect two primitive aortas,
ventral and dorsal.
The branchial arches are numbered from 1 to 6 from cephalad to caudad.
The development of these arches begins in the second week of gestation and is completed by the seventh week.
The first,
second,
and fifth arches regress before the development of the sixth arch.
The third arch and the ventral and dorsal portions of the aortic arches contribute to the formation of the arteries of the neck and head (common carotid arteries,
external carotid arteries, and internal carotid arteries).
The fourth arch forms the aortic arch and the ventral of sixth arches become the pulmonary arteries.
The dorsal portion of the right sixth arch disappears,
and on the left it persists as the ductus arteriosus.
The intersegmental arteries migrate cephalically to form the subclavian arteries
Another theory is useful to understand the aortic arch anomalies,
the Edwards hypothetical double arch.
According to this theory,
there is the double aortic arch with the ductus arteriosus on each side,
encircling the trachea and esophagus,
carotid and subclavian arteries arise from their respective arches.
Descending aorta is in midline.
Specific anomalies can be explained by showing the effect of interrupting the double arch at different locations.
Normal aortic arch is formed by interruption of dorsal segment of right aortic arch between right subclavian artery and descending aorta,
with regression of right ductus arteriosus.
Congenital aortic arch malformations present a large spectrum of variations and anomalies that originated from disordered embryogenesis of branchial arches,
previously described.
These variations result from abnormal persistence or involution of embryonic vascular segments.
Fig. 1
These anomalies are relatively frequent findings in chest and neck imaging studies.
They are usually incidental radiological findings in asymptomatic patients but may present vague symptoms such as chest pain and dysphagia.
Understanding aortic arch anomalies can help radiologists guide treatment and interventions.
Imaging techniques
Echocardiography,
magnetic resonance imaging,
and computed tomographic angiography are noninvasive imaging modalities used to identify aortic arch anomalies.
These modalities can be useful in preoperative surgical planning and percutaneous interventions.
Besides,
they largely replaced catheter angiography and barium esophagogram in the diagnosis of suspected vascular rings.
Echocardiography can be used particularly in children as an initial imaging modality to assessment of non-complex aortic arch anomalies.
However,
cross-sectional imaging with CT angiography or MR angiography is necessary in the setting of more complex anomalies in older children and adults with inadequate echocardiographic visualization of the mediastinum.
CT angiography is a noninvasive technique that allows fast and high-spatial-resolution evaluation of vascular anomalies but has the disadvantages of exposure to ionizing radiation,
use of iodinated contrast material,
and limited ability to evaluate functional changes.
MRI also allows assessment of the aortic arch and has the advantage of non-exposure to ionizing radiation.
However,
the acquisition time is long,
and sedation may be necessary in pediatric settings. Both methods have the advantage of evaluating tracheal or esophageal compression.
Fig. 2