Keywords
subclavian artery - agenesis - aortic arch - anomaly
Introduction
Unilateral absence of a brachial, radial, and ulnar pulse in a pediatric age patient
is rare. Possible etiologies include congenital abnormalities, trauma, vasculitis,
embolus, or possibly sequelae of arterial thoracic outlet syndrome. We present an
asymptomatic 12-year-old patient who, on examination, was found to have no palpable
right radial or brachial pulse.
Case Presentation
A 12-year-old male presented to the emergency department for evaluation after a concussion,
and there was reported difficulty in palpating his right radial artery. He was sent
to a vascular surgeon for evaluation where blood pressure was 125/80 mm Hg in the
left arm and 80/40 mm Hg in the right arm. On physical examination, his right brachial,
radial, and ulnar pulses were decreased as compared with the left. The patient had
no acute medical concerns and denied ischemic symptoms in the arm.
A chest X-ray demonstrated normal anatomy and no evidence of a cervical rib. Computed
tomography angiography (CTA) of the chest revealed that the right subclavian artery
did not have an origin from the brachiocephalic artery but rather filled distally
from the right internal mammary artery ([Fig. 1]). There was no definitive soft tissue mass at the thoracic outlet region and there
were no cervical ribs. Interestingly, there was also no vertebral artery identified
on the right side ([Fig. 2]). A three-dimensional reconstruction was performed from the CTA showing a discrete
area of absence of the right subclavian artery ([Fig. 3]).
Fig. 1 There is an anastomosis between the intercostal and internal mammary.
Fig. 2 Right vertebral artery is not present.
Fig. 3 Three-dimensional reconstruction of aortic arch and thoracic vessels.
Discussion
Aortic arch anomalies are present in 35% of the population and result when segments
of the primitive aorta do not disappear and persist, or vice versa.[1] Most commonly, the left common carotid artery originates from the brachiocephalic
trunk rather than from the aortic arch and is termed a bovine arch as in ruminant
animals. In this most common arch anomaly, the brachiocephalic trunk gives rise to
the right subclavian, right common carotid, and left common carotid arteries, leaving
the left subclavian to originate directly from the aortic arch. The remaining variations
occur in less than 3% of the population.[1] These are reported as follows: First, a shortened brachiocephalic trunk can bifurcate
immediately into the right subclavian and right common carotid arteries with the left
common carotid arising from the aortic arch at the base of the brachiocephalic trunk
and a normal origin for the left subclavian artery from the aortic arch. Second, the
left vertebral artery can originate directly from the aortic arch between the left
common carotid and subclavian arteries. Third, the aortic arch can be right sided,
and the right subclavian artery can be retroesophageal, and termed the arteria lusoria.
Also, in this setting, the isolated left subclavian artery fills by retrograde flow
from the left vertebral artery creating a congenital left subclavian steal.[2] Most of these anomalies are asymptomatic except for the aberrant right subclavian
artery in which 5% of patients have compression of the esophagus causing difficulty
in swallowing resulting in the condition, dysphagia lusoria. This anomaly is also
prone to aneurysmal development, Kommerell diverticulum, or a bulbous configuration
of the origin of an aberrant left subclavian artery which can lead to compressive
symptoms, thromboembolism, or rupture. An image recreated to visualize these anomalies
has been provided ([Fig. 4]).[3]
Fig. 4 Aortic arch anomalies. 1, brachiocephalic artery; 2, left common carotid artery;
3, left subclavian artery; 4, right common carotid artery; 5, left vertebral artery;
6, aberrant right subclavian artery. Reproduced with permission from Dumfarth et al.[3]
The innominate artery is formed by the right horn of the aortic sac and the left becomes
the proximal ascending aorta. The 3rd aortic arch forms the common carotid arteries
while the 4th aortic arch separates and forms a left and right portion. The left portion
of the 4th aortic arch forms the area of the aortic arch between the left common carotid
and the left subclavian arteries. The right portion of the 4th aortic arch becomes
the proximal segment of the right subclavian artery with root segments three through
seven. The distal aspect of the proximal right subclavian artery is derived from the
right dorsal aorta and its right 7th intersegmental artery. Also arising from the
right 7th is the right vertebral artery.
Subclavian arteries are the embryological product of 7th intersegmental arteries.[4] During normal embryogenesis, the distal segment of the right dorsal aorta involutes,
allowing the 4th vascular arch and the 7th intersegmental artery on the right side
to become the brachiocephalic and the subclavian arteries.[4] In 0.5% of population, the right 4th vascular arch and proximal right dorsal aorta
involute, leaving the right 7th intersegmental artery attached to the left descending
aorta via the distal part of the right dorsal aorta forming the aforementioned Kommerell's
diverticulum.
Our other differential diagnoses consisted of thoracic outlet syndrome, an embolic
event, vascular agenesis, some type of vasculitis, or trauma. The arterial form of
thoracic outlet compression is present in less than 1% of cases of thoracic outlet
syndrome.[1] Patients present with microembolization to the hand and ischemic symptoms. This
disease is defined by the presence of arterial compression, poststenotic dilation,
aneurysmal degeneration, and a secondary embolism. The compression can be secondary
to a cervical or anomalous first rib, clavicular fracture, or anomalous insertion
of the anterior scalene muscle. This syndrome is evaluated using duplex ultrasound
looking for an aneurysm, thrombus, turbulence, and elevated velocities, or CTA with
the patient's arms at the sides and again hyper abducted and externally rotated.
Few reports of vascular agenesis exist in current literature, with the most relevant
to our case being unilateral congenital absence of the internal carotid artery (ICA).
So far eight cases of bilateral total absence of the ICA, and seven cases of unilateral
partial congenital absence of the ICA with an intercavernous anastomosis between the
contralateral “normal” and ipsilateral partially aplastic ICA have been identified
by angiography.[5] Events that lead to absence of the carotid arteries is unknown. These anomalies
are usually identified during angiography for patients who present with intracerebral
hemorrhage as they have concurrent intracerebral aneurysms.[5]
We believe our patient may have had an intrauterine vascular insult to the 7th intersegmental
arteries or to the 4th aortic arch thus causing there to be an absence of the right
subclavian artery and right vertebral artery. What would be the subclavian or proximal
axillary artery is formed by a branch of the internal mammary and an anterior continuation
or a posterior intercostal artery. A few of the branches appear hypertrophied including
the lateral thoracic artery and the anterior intercostal, likely as a response to
demand from the arm. The patient has no symptoms, and therefore further investigation
will not be undertaken.
