Aneurysms of the extracranial carotid artery are uncommon, the largest single reported series representing 37 of 8500 aneurysms treated at Baylor University over a 21-year period. They usually affect the common or internal carotid artery, rarely the external artery, and are bilateral in about 10 per cent of cases. True aneurysms are most commonly atherosclerotic, although mycotic and syphilitic aneurysms do occur, along with rarer degenerative and dysplastic conditions (Fig. 1) 276. False aneurysms may occur following trauma and are seen increasing as a complication of previous carotid endarterectomy.

Most carotid aneurysms present as an asymptomatic, pulsatile neck swelling, or with transient or fixed neurological defects due to cerebral emboli. More rarely, they present with local pressure symptoms such as dysphagia or as an emergency following rupture. Examination usually demonstrates a pulsatile mass just below the angle of the jaw which may have a bruit and can sometimes be observed or palpated in the tonsillar fossa. They may, however, be sited anywhere from the root of the neck to the base of the skull.

The most common differential diagnosis of a pulsatile neck swelling is the more common and benign condition of a tortuous carotid artery (Fig. 2) 277. This is usually seen in the root of the neck on the right and is asymptomatic. Other differential diagnoses should include masses overlying the carotid vessels with transmitted pulsation, particularly carotid body tumour, branchial cysts, and lymphadenopathy. Duplex ultrasonography is the first line of investigation: this is non-invasive, provides useful information about the size and extent of the aneurysm, and allows assessment of the contralateral carotid vessels. Angiography is usually required for accurate assessment of the anatomy (Fig. 3) 278, with digital subtraction techniques providing enhanced images. CT or magnetic resonance techniques can provide excellent images showing the extent and situation of the aneurysm.

The natural history of untreated carotid aneurysms is not well documented, although small asymptomatic aneurysms may be treated conservatively, especially if the operative risks are high. Such treatment should include the use of antiplatelet agents such as aspirin to reduce the risk of cerebral emboli. The earliest reported surgical treatment was simple ligation of the carotid artery. This operation was first reported by Pare in 1552 for trauma and was carried out by Sir Astley Cooper in 1805 for a carotid aneurysm. His first attempt resulted in hemiplegia and early postoperative death but he successfully carried out the procedure on a similar case 3 years later.

Because of the risk of major stroke following carotid ligation the first choice for treatment is excision of the aneurysm with restoration of flow by direct anastomosis or graft. Primary anastomosis is frequently possible, as elongation of the artery often accompanies aneurysmal dilatation. Where this cannot be achieved the use of the external carotid artery, vein, or prosthetic graft is necessary. For false aneurysms the use of a patch angioplasty may be sufficient but the use of prosthetic materials should be avoided where possible, due to the implication of infection as a possible aetiological factor. The need for a peroperative shunt is controversial but it should be considered if there is a stump pressure of less than 55 mmHg or if there are EEG changes on applying clamps.

High aneurysms present the most difficult problem since surgical approaches require the removal of part of the mastoid bone or dislocation of the mandible. Where distal control would be difficult or dangerous, carotid occlusion may be the only alternative, but attempts should be made to improve upon the success of simple ligation. Graded occlusion may achieve this or one of a range of percutaneous techniques, such as inflatable, detachable occlusion balloons with concomitant extra-intracranial bypass if required.

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