|Year : 2013 | Volume
| Issue : 1 | Page : 38-41
Subclavian artery aneurysm with incidental bovine aortic arch branch
Godwin I Ogbole, Abiodun O Adeyinka, Eric O Umeh
Department of Radiology, University College Hospital, Ibadan, Nigeria
|Date of Web Publication||18-Oct-2013|
Godwin I Ogbole
Department of Radiology, University College Hospital, Ibadan
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aneurysms of the Subclavian artery are uncommon, accounting for less than 0.2% of all arterial aneurysms. The most common causes are arteriosclerosis, thoracic outlet obstruction, and trauma. Anomalous branching aortic arrangements are less uncommon, occurring in some 35% of subjects. We report a case of subclavian artery aneurysm in a 62-year- old man presenting with a painless right supraclavicular swelling of approximately 30 years duration. He was a known hypertensive diagnosed 21 years previously and compliant with medication. His serum lipid profile was normal. Doppler Ultrasound of the right subclavian artery showed a thin walled fusiform aneurysmal dilatation located 3.6 cm from its origin with fine internal echoes, and measuring 2.74 cm in diameter. Peak systolic velocity (PSV) within the aneurysm was 33 cm/s, compared with 55 cm/s and 45 cm/s in the right pre-aneurysmal segment and left subclavian arteries respectively. There was turbulent flow and spectral broadening within the aneurysm. Computerized Tomographic (CT) angiography of the aortic arch confirmed a right subclavian aneurysm, and showed an anomalous origin of the left common carotid and subclavian arteries. An anomalous common origin of the left common carotid from the brachiocephalic trunk representing a bovine type variant is a rare condition, its association with subclavian artery aneurysm an even rarer finding.
Keywords: Aneurysm, anomalous aortic branch, subclavian artery
|How to cite this article:|
Ogbole GI, Adeyinka AO, Umeh EO. Subclavian artery aneurysm with incidental bovine aortic arch branch. Ann Nigerian Med 2013;7:38-41
| Introduction|| |
True aneurysms of the subclavian artery are rare in comparison with other peripheral aneurysms, accounting for less than 0.2% of all arterial aneurysms. However, the subclavian artery is the most common site of upper extremity aneurysm.  Common causes are arteriosclerosis, thoracic outlet obstruction, and trauma. Rare causes include an aberrant right subclavian artery, abnormalities of the vessel wall (fibromuscular dysplasia), Marfan syndrome, Ehlers-Danlos syndrome More Details, cystic medial necrosis, Turner syndrome,  as well as infections involving arterial walls such as tuberculosis and syphilis. 
The finding of an anomalous branching aortic arrangement which occurs in about 25% of individuals being associated with a subclavian artery aneurysm is uncommon. The true value of such detection is in the diagnostic gain before vascular surgery on the supra-aortic arteries. 
We report a case of a right subclavian artery aneurysm in a 62-year-old male, illustrating the complementary role of CT angiography in demonstrating an associated anomalous bovine type supra-aortic branch.
The aim of this report is to review the literature and to present the symptoms, and diagnostic possibilities of this rare pathology.
| Case Report|| |
A 62-year-old male presented with a painless right pulsatile supraclavicular swelling of approximately 30 years duration. He was a known hypertensive diagnosed 21 years ago and compliant with his medication. On examination, he was well oriented in time, place, and person and showed no obvious neurological deficits. His blood pressure was 145/90 mmHg and pulse 68 beats per minute with normal rhythm and character. Chest was clear and heart sounds were normal, while his gastro-intestinal and urogenital systems revealeded no abnormality. Serum lipid profile was also normal. Doppler Ultrasound of the right subclavian artery [Figure 1] showed a fairly rounded, thin walled aneurysmal dilatation located approximately 3.6 cm from its origin, measuring 2.7 × 2.9 cm in diameter. Peak systolic velocity (PSV) within the aneurysm was 33 cm/s, compared with 55 m/s in the proximal segment and 45 cm/s in the left subclavian artery.
|Figure 1: B-mode ultrasound scans (a) Longitudinal and (b) transverse showing a thin walled fusiform aneurysmal dilatation of right subclavian artery located approximately 3.6 cm from its origin. It contains relatively clear internal echoes and measures 2.47 cm in diameter|
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Three-dimensional CT angiography of the aortic arch confirmed a true aneurysm in the middle third of the right subclavian artery without any sign of a rupture or mural thrombosis [Figure 2]. It also demonstrated an anomalous common origin of the left common carotid from the brachiocephalic trunk representing a bovine type variant [Figure 3].
|Figure 2: Transverse computed tomography (MIP) image showing the aneurysmal dilatation of right subclavian artery (white arrow) located approximately 3.6 cm from its origin|
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|Figure 3: CT angiography, volume rendered image showing the anomalous origin of left common carotid artery from the brachiocephalic trunk (white arrow) and a right subclavian artery aneurysm (red arrow)|
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No pathology belonging to the thoracic outlet syndrome complex (TOS) was found. Ultrasound evaluation of the contralateral subclavian artery, the common carotid arteries, abdominal aorta and the common iliac arteries showed no aneurysmal dilatation. The patient opted for a non surgical conservative management having understood the possible complications. He is presently scheduled to have regular follow-up clinic visits.
| Discussion|| |
Subclavian artery aneurysms are usually monolateral, but as many as 33 to 47% of patients have an associated aortic, iliac or other peripheral aneurysms.  Abrahams and Cockshott working in the same region reported four patients with non-luetic subclavian artery aneurysm at Ibadan in southwestern Nigeria over a 2-year period. All had co-existing aneurysms in the aorta or carotid arteries.  The cause of aneurysm in these reported cases were speculative, as none of the patients showed evidence of an infective process such as tuberculosis or syphilis, nor was there a family history. Also none showed stigmata of connective tissue disease such as Marfan's disease. Our patient however demonstrated no other aneurysmal swelling in other parts of his body or a family history. Anyanwu et al. in eastern Nigeria showed that subclavian aneurysms may not frequently be post-traumatic as have been reported for the femoral or carotid arteries. 
Patients presenting with subclavian aneurysm are often asymptomatic.  However, in some cases there is a pulsatile mass either above or below the clavicle.  Symptoms such as dysphagia, stridor, chest pain, hoarseness, upper extremity fatigue, and gangrene or ulceration of the fingers may develop with progressive enlargement of the aneurysm.  Neurological involvement with compression of the brachial plexus or the sympathetic chain resulting in numbness of affected limb has been reported. , No such symptom was reported in this patient except for the disfiguring swelling, Also, no obvious neurological deficit was observed on physical examination. This may have been responsible for his late presentation.
In situ thrombosis, antegrade and retrograde emboli can complicate the subclavian artery aneusysm with the danger of cerebral infarcts and limb ischaemia.  Rupture is also a dangerous complication with significant late mortality. , However, our patient reported no symptomatology suggestive of a ruptured aneurysm or an ischemic injury to the brain or limbs.
Subclavian artery aneurysm can be diagnosed with duplex ultrasound or with digital subtraction angiography (DSA).  Computed tomography and magnetic resonance imaging studies may confirm diagnosis and show other incidental anomalies. 
We performed a CT angiography of the carotids including the aortic arch following which we discovered an anomalous branching of the arch of the bovine variety. Complete aortic arch and upper extremity angiography is mandatory to delineate the extent of the aneurysm. This may be done by an intra-arterial or venous DSA preferably using an iodinated contrast agent.  The outlined right subclavian aneurysm will be seen as a rounded area of increased density in the right supraclavicular region.  Observed filling defects will be interpreted as endoluminal thrombi, while extraluminal contrast will suggest leakages through the aneurysmal walls due to rupture. This technique will also facilitate evaluation of the contralateral vertebral circulation competency when the ipsilateral vertebral artery originates from an aneurysmal vessel.  These points are usually crucial for planning appropriate surgical reconstruction. 
This patient's anomalous branching aortic arrangement is symptom-free and may not call for urgent treatment. However, the aneurysm, given its size, will ultimately benefit from various treatment options. Open surgical management is the standard treatment for subclavian aneurysms  especially if they are larger than 2 cm in diameter.  However interventional radiological options are less invasive and may be associated with less risk than open surgical repair.  Access to the sites of vascular occlusion is facilitated for cases of associated thromboembolism. Satisfactory albeit short term results have been achieved with commercially prepared endografts (stent grafts) delivered through a trans-brachial access for treatment of subclavian aneurysm. , Also, the successful endovascular treatment of subclavian aneurysm using a Mamotherm stent has been documented.  An alternative management approach involves minimally invasive open repair combined with endovascular treatment. , This combined surgical and interventional radiological treatment option has dual benefits of avoiding a sternotomy and a lateral thoracotomy, as well as achieving revascularization of the affected arm. Endovascular exclusion of the aneurysm may be achieved by inserting an endoprosthesis to occlude the aortic exit of the aneurysm accompanied by a distal ligation of the aneurysm.  Carotid / subclavian bypass is then created to preserve function of the subclavian artery. 
The true value of detecting anomalous origins is in the diagnostic gain before vascular surgeries of supraaortic arteries, as variations of the branches of the aortic arch are likely to occur as a result of the altered development of certain branchial arch arteries during the embryonic period of gestation.  CT angiography may be preferable to DSA for assessment of the aortic arch and its branches due to the formers capability for 3D imaging  and image reformatting. CT angiography is also less invasive and stressful to the patient. 
The standard three-branched arrangement of the aortic arch is found in 64.9% of individuals  or may range between 65-75%.  However, prevalence of anomalous aortic arch branch variations as low as 9.8% has been reported in India.  These variations usually asymptomatic include a common origin of the brachiocephalic trunk and left common carotid arteries (13-15%), , and the bovine variant which is an origination of left common carotid artery from the brachiocephalic trunk as described in this case report (9%).  Others include a left vertebral artery arising from the aortic arch 3%, left and right brachiocephalic trunks (1%), and an aberrant right subclavian artery arising as the last branch of the aortic arch (<1%).  This has a known association with right subclavian artery aneurysm.  Detailed knowledge of an anomalous origin of supra-aortic arteries is also important for patients who have to undergo four-vessel angiography in an emergency, in order to rule out the possibility of intracranial aneurysm after subarachnoid hemorrhage. If the detection of a vertebral artery in the normal position is not possible, the presence of such a variant must be taken into consideration.  The anatomic and morphologic variations of the aortic arch and its branches are significant for diagnostic and surgical procedures in the thorax and neck. Patients with aortic arch anomalies may also benefit from genetic screening as Momma et al. had described that arch anomalies are associated with chromosome 22q11 deletion. 
| Conclusion|| |
A subclavian artery aneurysm associated with a bovine aortic arch branch variation is a very rare finding. In the absence of symptoms, patients are likely to present late or following the onset of a complication. Doppler ultrasound is usually sufficient for diagnosis, but CT angiography may provide a more comprehensive evaluation.
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[Figure 1], [Figure 2], [Figure 3]