Aneurysms of the subclavian artery represent about 1 per cent of all peripheral arterial aneurysms. They fall into two distinct groups in terms of aetiology, presentation, and treatment: those of the intrathoracic and those of the extrathoracic portion of the subclavian artery. Those in the extrathoracic site are the more common, and about three-quarters of aneurysms at this site are related to thoracic outlet syndrome or to previous trauma (Figs. 1 and 2) 279,280. The other major cause is atherosclerosis, which is responsible for the majority of intrathoracic aneurysms. Other, rarer causes include infection and degenerative conditions, and there have been a number of reports of aneurysms of an aberrant right subclavian artery. As would be expected the epidemiology parallels that of the underlying cause: atherosclerotic aneurysms occur in the elderly, while those associated with thoracic outlet syndrome are seen in young adults.

Intrathoracic aneurysms present most often with an asymptomatic mediastinal shadow on a routine chest radiograph or with symptoms of local compression, and they must be differentiated from other mediastinal masses. Reported symptoms include chest and back pain, Horner's syndrome, venous congestion, and hoarseness. Symptoms due to distal embolization to the arm are an unusual presentation at this site but are seen in about two-thirds of patients with extrathoracic aneurysms. The emboli tend to be small, affecting digital vessels and leading to episodic symptoms, and may be confused with Raynaud's phenomenon. Whenever such symptoms are unilateral the possibility of a proximal arterial lesion should always be considered. Extrathoracic aneurysms are often associated with neurological symptoms of brachial plexus compression, although it may be difficult to determine the relative importance of the aneurysm and any associated thoracic outlet compression. Rupture of a subclavian aneurysm is a rare event but has been reported, as has acute ischaemia due to thrombosis.

Careful physical examination may reveal a pulsatile mass in the supraclavicular fossa, a bruit, or pulse deficits, and there may be evidence of associated thoracic outlet or upper mediastinal compression. Attention should also be directed to identifying coexisting aneurysms 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. Magnetic resonance imaging is also proving a useful investigation of the thoracic outlet, and is often able to detect fibrous bands causing obstruction. Conventional or digital subtraction angiography will demonstrate the arterial anatomy, extent of aneurysmal disease, and associated stenosis or thrombus, as well as showing occlusions of distal vessels if there have been previous emboli.

Because of the high risk of complications resulting in limb loss, elective surgical treatment is recommended for most subclavian aneurysms. Access to the intrathoracic subclavian artery is achieved through a lateral thoracotomy on the left or a median sternotomy for the right side. The extrathoracic subclavian vein 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.

The aim of the surgery is to exclude or remove the aneurysm with restoration of circulation. 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 prosthesic graft. In difficult cases ligation may be less hazardous, the circulation being restored by extra-anatomical axilloaxillary or caroticosubclavian bypass.

Gordon RD, Garrett HE. Atheromatous and aneurysmal disease of the upper extremity. In: Rutherford I, ed. Vascular Surgery. Philadelphia: WB Saunders, 1984: 688–92.

Hobson RW, Israel MR, Lynch TG. Axillosubclavian arterial aneurysms. In: Bergan JJ, Yao JST, eds. Aneurysms: Diagnosis and Treatment. New York: Grune and Stratton, 1982: 435–47.