Imaging Findings
The Contrast Chest CT scan shows a branch arising from the distal left
aortic arch which is traveling behind the oesophagus and coursing as the
right subclavian artery. This is an aberrant right subclavian artery and
sometimes may cause ‘dysphagia lusoria’.
Discussion
This is the most
common congenital vascular anomaly of the aortic arch (present in about
0.5 to 1% of the population). The right subclavian artery arises just
distal to left subclavian artery as the last branch of the aortic arch
(beyond the ligamentum arteriosum) and runs to the right POSTERIOR to
the esophagus (this produces a posterior indentation from lower left to
upper right on barium esophagram). Affected patients are typically asymptomatic,
but the condition may cause dysphagia ("dysphagia lusoria"),
particularly in patients with a 'Diverticulum of Kommerell'. This is a
wide based take-off of the aberrant vessel. A vascular ring encircling
both the trachea and esophagus may be completed if there is a ductus associated
with the aberrant vessel.
There can be anomalous origin from the proximal descending aorta of either
the right or left subclavian artery. An aberrant right subclavian artery
arises distal to the left aortic arch. An aberrant left subclavian artery
arises distal to the right aortic arch (nonmirror-image right aortic arch);
an aortic diverticulum exists at the site of origin. In a right arch with
aberrant left subclavian artery, a right-sided ligamentum arteriosum connects
the diverticulum and the proximal left pulmonary artery producing a complete
vascular ring. In both types of aberrant subclavian arteries, the vessel
runs behind the oesophagus. The aberrant right subclavian artery produces
an impression on the back of the oesophagus while the left one usually
causes anterior displacement and severe compression of the oesophagus.
The latter also frequently causes airway compression. The right aberrant
artery can be associated with dysphagia in adults while the left usually
causes symptomatic airway and oesophageal obstruction during infancy or
early childhood.
Plain radiography with barium swallow displays a right-sided aortic arch
impression and posterior impression of the aberrant left subclavian on
the oesophagus or left-sided aortic arch impression and posterior impression
of the aberrant left subclavian artery on the oesophagus. The lateral
view also reveals anterior displacement and compression of the trachea
by the aberrant left subclavian artery. Thoracic aortography demonstrates
the relationship of the arch to the trachea or oesophagus (simultaneous
barium swallow) and origin of the aberrant subclavian as the fourth major
branch of the aortic arch.
Definitive diagnosis is now usually accomplished by CT or MRI. Both display
the severity of airway narrowing and the retro-oesophageal aberrant artery
(as seen in the pitures).
Dr Santosh Rai,
Asst Professor, Dept of Radiodiagnosis, KMC Mangalore. Manipal Academy
of higher education.
Consultant Radiologist, Global radiology center, WIPRO-MAHE, Bangalore.
|
