Subclavian artery aneurysm.
Aneurysms of the subclavian artery represent about 1 per cent of all peripheral arterial aneurysms. Their causes, presentation, and treatment can be classified in morphological terms as those of the intrathoracic and those of the extrathoracic portion of the subclavian artery. They are rare in childhood, increasing in incidence with age.
The subclavian artery may be compressed at the thoracic outlet by a cervical rib, an abnormal first rib, or muscular and fibrous bands associated with the scalenus anterior or medius muscles. Post-stenotic dilatation of the subclavian artery may occur. The 'thoracic outlet syndrome' or 'scalene syndrome' and previous trauma account for about three-quarters of extracranial aneurysms and are generally seen in young adults. Atherosclerosis accounts for the majority of the aneurysms in elderly people. Other, rarer causes include congenital (aneurysms of an aberrant right subclavian artery), infective, and degenerative conditions (Behçet's syndrome and Takayasu's arteritis), and there is an increasing number of reports on the adverse sequelae of central venous catheters in relation to subclavian aneurysm.
An incidental finding of a mediastinal shadow on routine chest radiography is the most common presentation for intrathoracic aneurysms. They are largely asymptomatic, but may present with chest and back pain, Horner's syndrome, venous congestion, and hoarseness secondary to local compression. Distal embolization to the arm is unusual at this site, but is seen in about two-thirds of patients with extrathoracic aneurysms. The signs must be differentiated from Raynaud's phenomenon, which also presents with episodic symptoms related to the digital vessels. Neurological symptoms of brachial-plexus compression are present in 90 per cent patients with 'thoracic outlet syndrome' and so the relative importance of the aneurysm may be difficult to determine. Large aneurysms may result in subclavian-steal syndrome. Rarely, the aneurysm ruptures. Intense local pain and swelling may be accompanied by signs of compression of the brachial plexus and ischaemia of the arm. Rupture into the apex of the lung presenting with haemoptysis has been reported.
Careful physical examination may reveal a pulsatile mass in the supraclavicular fossa, a bruit, or pulse deficits, and there may be evidence of associated compression of the thoracic outlet or upper mediastinum. Coexisting aneurysms should be identified at other sites. Plain radiographs of the thoracic outlet and upper mediastinum may show the extent of the mass, a calcified arterial wall, or cervical ribs. Further morphological data can be acquired by using spiral CT. Magnetic resonance imaging can detect fibrous bands and soft-tissue anomalies causing deviation and compression of local structures. Conventional or digital-subtraction angiography will demonstrate the arterial anatomy, the extent of aneurysmal disease, associated stenosis or thrombus, and the patency of the distal vessels.
Intra-arterial thrombolysis may be administered in cases of acute ischaemia of the limb secondary to aneurysmal thrombosis. However, elective surgical treatment is recommended for most subclavian aneurysms. Intrathoracic aneurysms are approached through a lateral thoracotomy on the left or a median sternotomy for the right side. The approach for the extrathoracic subclavian artery varies according to the morphology and cause of the aneurysm. It can be approached through a supraclavicular incision after medial retraction of the phrenic nerve and division of the scalenus anterior. Additional exposure can be achieved by resection of the middle third of the clavicle or by dissection of the axillary artery below the clavicle. In cases of 'thoracic outlet syndrome' it may also be necessary to resect a cervical rib or band, or the first rib if this is implicated. A transaxillary approach may be utilized for this procedure.
The aim of the surgery is to exclude or remove the aneurysm, with restoration of arterial continuity. Direct arterial repair or patch angioplasty may be appropriate in some patients with false aneurysms. In most cases, resection is possible, the arterial supply being maintained by either direct anastomosis or replacement with a venous or prosthetic graft. Rarely, ligation of the artery proximally and distally with excision of the aneurysm can be performed if there is sufficient collateral circulation. This approach can also be used in hazardous cases, the circulation being restored by extra-anatomical axilloaxillary or caroticosubclavian bypass when the collateral supply does not suffice. Percutaneous embolization using steel coils has also been reported.
Clagett GP. Upper extremity aneurysms. In Rutherford RB, ed. Vascular surgery, 4th edn, pp. 1112–18. Saunders, Philadelphia,1995. [An overview of upper limb arterial aneurysms.]
Dougherty MJ, Calligaro KD, Savarese RP, DeLaurentis DA. Atherosclerotic aneurysm of the intrathoracic subclavian artery. A case report and review of the literature. Journal of Vascular Surgery 1995; 21: 521. [A case of surgically treated asymptomatic atherosclerotic aneurysm of the left subclavian artery, with a review of the literature.]
Fedullo LM, Meranze SG, McLean GK, Burke DR. Embolisation of a subclavian artery aneurysm with steel coils and thrombin. Cardiovascular and Interventional Radiology 1987; 10: 134–7. [Report describing endovascular management for a subclavian artery aneurysm.]
Hobson RW, Israel MR, Lynch TG. Axillosubclavian arterial aneurysms. In Bergan JJ, Yao JST, eds. Aneurysms: diagnosis and treatment, pp. 435–47. Grune and Stratton, New York, 1982. [A review of upper limb inflow arterial aneurysms covering epidemiology and management.]
Scher LA et al. Staging of arterial complications of cervical rib: guidelines for surgical management. Surgery 1984; 95: 644–9. [A series of 12 patients with 15 arterial lesions is reviewed and a staging system proposed to provide guidelines for managing patients with this condition.]