2.5.1 Definition and Historical Background
Carotid artery aneurysm can be defined as a more than 50% localized increase of carotid calibre diameter when compared to reference values:
• Internal carotid: 0.55±0.06 in men and 0.49±0.07 in women
• Carotid bulb: 0.99±0.10 in men and 0.92±0.10 in women.
Unlike occlusive or ulcerated atherosclerotic lesions carotid aneurysms are quite uncommon, with very few cases reported in the literature, which influences the correct knowledge of the natural history of this entity. In 1808 Sir Ashley Cooper made history when he performed, at Guy's Hospital in London, the first successful treatment of a carotid aneurysm. The operation consisted of ligation of the common carotid artery, and the patient, a 50-year-old man, left the hospital after a 3-month period of recovery (because of a "smouldering wound infection") [4, 5].
The patient died 14 years later from a cerebral haemorrhage.
Through autopsy, Sir Ashley Cooper noticed that the haemorrhage was on the same side as the previous carotid ligation, and there was a large posterior communicating artery supplying collateral circulation to the ipsilateral middle cerebral artery. In 1936 Nathan Winslow and colleagues reported an exhaustive review of 124 cases published in the literature. Surgical ligation of the carotid was the main therapeutical option (82 patients) with cure or improvement in 71%, and a mortality rate of 28%, while the conservative approach (42 patients) carried a mortality of 71% with 12% cure or improvement . Ligation remained the main therapeutical option until the late 1960s, when direct arterial reconstruction and/ or autogenous vein grafting had definitely become the best surgical option irrespective of the aetiology.
Since then several series have been published, such as those of McCollum and deBakey with 37 cases operated in 20 years, representing 0.5% of all aneurysms performed in the same period . More recently El Sabrout and Cooley  published, in 2000, the largest single centre series of 67 carotid an-eurysms operated between 1960 and 1995. Nowadays endovascular techniques are being used particularly for lesions that are inaccessible to surgery.
Extracranial carotid aneurysms are a rare situation representing 1-4% of all peripheral aneurysms and 0.5-2% of the total number of carotid operations [2, 8, 11, 16].
They are distributed almost equally in the internal and common carotid arteries and only 2% are located in the external carotid artery.
In the past, the main causes of the development of this disease were syphilis and infections in surrounding structures, such as the throat and ears, as well as trauma.
In recent times atherosclerosis, previous carotid surgery especially with patch closure, and trauma represent most of the cases reported .
• Representing 70% of all these aneurysms, they affect predominantly older and hypertensive patients, and are sometimes associated with manifestations of occlusive or aneurysmatic disease at other locations.
• They are localized at bifurcations and have a fusiform shape.
220.127.116.11 Previous Surgery/POS Endarterectomy
• False aneurysm has occurred after carotid surgery mostly with synthetic patch closure but sometimes even with vein patch angioplasty.
• The endarterectomized artery, infection, and the use of silk sutures (now abandoned) are the main factors implicated.
• Represents the second most important cause of these aneurysms.
• They are usually sacular and are really false aneurysms which as a group represent more than 50% of all cases in published series.
• Closed trauma may be associated with extension, with sudden head rotation promoting intimae disruption and parietal damage, or with direct compression of the atlas transverse process or styloid process, or with mandibular fracture.
• The extracranial high internal carotid is mainly affected, because it has no collaterals, thus promoting the mobility of this arterial segment compared to its intracerebral section.
• Open trauma may affect different parts of the carotids, but mostly in exposed areas such as the common carotid.
• Open trauma causes total or partial parietal disruption complicated by torrential haemorrhage, as well as false aneurysm and/or arterio-venous fistulae, as reported in World War II surgical registries .
• Syphilis was the main cause at the beginning of twentieth century and predominantly affects adults.
• Tonsillitis and otitis are main causes in children.
• Staphylococcus aureus infection is present in drug addicts and is carried by direct punctures with contaminated needles.
a break in the intimae followed by haemorrhage into the media, enlarging the vessel wall and reducing the true lumen.
• If haemorrhage dissects into a plane between the media and the adventitia, an aneurysm forms.
• This situation usually causes neurological symptoms owing to cranial nerve compression.
18.104.22.168 Other Possible Causes
Other possible causes are (Table 2.5.1):
• Fibromuscular dysplasia
• Congenital disorders
• More rarely associated with intracerebral or visceral aneurysms (systemic inflammatory vasculopathy)
• Marfan's syndrome
• Periarteritis nodosum
There is an association between saccular aneurysms and kinking and coils of the internal carotid artery (ICA), as personally observed by the authors. In these cases, the increased turbulence and shear stress on these vulnerable artery segments probably causes a locus of minor resistance, with intimae or transmural disruption and the formation of false or true aneurysms .
Table 2.5.1 Causes of extracranial carotid aneurysms
• Mycotic (syphilis, tuberculosis, otitis, tonsillitis)
• Association with intracerebral aneurysms
• Association with visceral aneurysms
• Marfan's syndrome and Behçet's disease
As these are spontaneous or traumatic they cause acute occlusion or chronic aneurysm, by developing
The symptoms of extracranial carotid aneurysms vary according to their location, size and aetiology. They can be fusiform or saccular in shape. The most frequent are fusiform aneurysms. Most often these affect the bifurcation of the common carotid artery and have a bilateral predilection, whereas the saccular type is mainly unilateral and located in the retrostyloid region .
• They are mainly asymptomatic, and present as a pulsating mass in the neck, with bruit and thrill . They may cause symptoms, due to either compression of adjacent structures or cerebral embolization.
• At present, neurological manifestations, such as transient ischaemic attack (TIA) or cerebral vascular accident, are the most frequent revealing sign of the fusiform type [1, 17].
• The symptoms of compression, of which pain is the most common local symptom, caused by the pulsated and expansible cervical mass (Fig. 2.5.1) characteristic of the saccular type can cause laryngeal and oesophageal compression or glossopharyngeal nerve or sympathetic nerve (Horner's syndrome) compres
Fig. 2.5.1 Cervical mass sion  and cranial nerve dysfunction (II, III, IV, V and VI).
• Raeder's paratrigeminal syndrome, characterized by oculosympathetic paresis and intermittent facial pain, in some cases has been caused by a carotid aneurysm at the base of the skull .
• There are references in the literature to the propensity of the extracranial carotid aneurysms to imitate peritonsillar abscess, which were drained with consequent mortal haemorrhage . The classic paper by Shipley's group emphasized that aneurysms of the ICA present inwardly into the throat, whereas those of the common carotid present outwardly in the neck .
• Cerebral embolization, causing TIA or stroke, is the most frequent complication.
• Haemorrhage from spontaneous rupture is rare . If rupture occurs into the oropharynx, the bleeding can be massive and can lead to suffocation and death.
22.214.171.124 Recommended European Standard Diagnostic Steps of Investigation
• Colour Doppler (Fig. 2.5.2) is the most simple diagnostic tool, but has limitations, especially if the patient has a short neck or if the lesion is localized too distal in the carotid artery . B-mode gray-scale imaging allows excellent definition of the size and extent of the arterial dilatation, and the use of colour flow imaging can determine the presence of thrombus and the flow characteristics .
• Enhanced CT scanning with three-dimensional reconstruction gives the most information. It allows complete analysis of the aneurysm, estimating the upstream and downstream ICA, and assesses the possible existence of a false lumen channel, representing the existence of a previous dysplastic or traumatic dissection. It also estimates the distance between the upper limit of the aneurysm and the temporal bone .
• The two-dimensional magnetic resonance inflow angiography technique with reconstruction (Fig. 2.5.3)
Fig. 2.5.2 Colour Doppler
Fig. 2.5.2 Colour Doppler
yields good opacification of the ICA, but the lesion may be underestimated in the case of a partially or completely thrombosed aneurysm .
• Arteriography (Fig. 2.5.4) precisely defines the location, and detects any associated lesion, such as stenosis, or wall irregularities . It also has the advantage of preoperative assessment of the patient's ability to tolerate carotid artery occlusion using an angiographic
Fig. 2.5.4 Angiography balloon catheter , which is relevant to defining the surgical strategy. One clear disadvantage of arteriography is that it sometimes fails to visualize the aneurysm due to intramural thrombus formation .
• Two angiographic features help to differentiate saccular from fusiform aneurysms: saccular aneurysms show an outpouching off the arterial lumen, usually with a neck, whereas the fusiform type shows frank dilatation of the arterial lumen with no additional contrast outside the lumen. This latter type of aneurysm is usually accompanied by distortion of the arterial lumen and dilatation or stenosis in other segments of the vessel .
Conservative treatment based on anticoagulation is recommended for some small aneurysms especially postdissection and requires regular ultrasonography control . In 1984 Zwolak  described an overall stroke/major complications rate of 21% managing one-fifth of these aneurysms nonoperatively, but the group only included 6 cases. However, conservative treatment can be indicated for a subgroup of young patients with traumatic and
spontaneously dissecting small aneurysms. Surgical repair is mandatory whenever neurological complications appear or progressive expansion occurs.
• Nowadays, surgery is generally accepted as the main treatment of extracranial carotid artery aneurysms, thus preventing cerebral embolization and rupture.
• There is however some degree of uncertainty regarding the few cases treated in each institution (mean of one per year), and the different aetiologies, types and technical options chosen.
• Aetiology and the type of presentation are the main factors that influence the surgical approach, which, until we have a better understanding of the natural history and results of the different therapeutical options, represents the gold standard for treatment.
Fig. 2.5.5 Resection and interposition
Resection and Reconstruction using Saphenous Vein or PTFE
Resection of the aneurysm and reconstruction using sa-phenous vein is the preferred technique (Fig. 2.5.5). The external carotid may be ligated or anastomosed to the graft. Shunt is used if there is evidence of impaired intracranial collateral perfusion or in cases of a previous stroke . A high aneurysm location requires some technical details for achieving distal carotid control, such as:
• division of the sternocleidomastoid muscle from its mastoid attachment with elevation of the parotid,
• division of the digastrics,
• removal of the styloid process and its attached muscles,
• control of back bleeding by balloon catheter.
The Marseille group  obtained reasonably good results in 25 ICA reconstructions, using an aggressive approach to get access to the last segment of the ICA via an anterior infratemporal route. This approach was used in ten cases, and included:
• cutting the external auditory canal,
• isolating the branches of the facial nerves,
• retracting the styloid process and
• luxation of the mandibular condyle.
The mastoid process was reduced and the intrapetrous segment of the ICA exposed .
Resection and Primary Anastomosis or Reimplantation
• In the case of a long and tortuous ICA, aneurysms can be treated simply by resection and primary anastomosis or reimplantation (Fig. 2.5.6).
• The most frequent complications associated with this type of surgery are strokes related to embolization during manipulation and injury of the cranial nerves, particularly the X and the XII.
• Occasionally neurogenic hypertension can result from transection of the carotid sinus and loss of barorecep-tor function .
To avoid cranial nerve injury, El-Sabrout and Cooley , in their article describing the Texas Institute experience, express their preference for partial aneurysmectomy and patch closure of large fusiform aneurysms evolving carotid bifurcation. This option avoids extensive dissection of the posterior wall of the aneurysm, reducing the rate of cranial nerve dysfunction to 6%.
Results of reconstructive surgery for atherosclerotic carotid aneurysms are reasonably acceptable with:
Fig. 2.5.6 Resection and reimplantation
The meta-analysis of the results of reconstructive surgery for all causes shows:
• a cumulative morbidity-mortality risk of 7.2% .
Worse results can be expected when surgery is performed on an emergency basis for rupture or neurological manifestations, for re-operation and for high located aneu-rysms, which also promotes a higher incidence of cranial nerve injury .
The timing of surgery depends on aetiology and can influence the results. In post-traumatic or post-dissection cases, a delay of at least 3 months for revascularization is preferable, allowing the performance of a distal anastomosis on sclerotic and recovered scar tissue . After a neurological event the delay depends on the presence of a stable neurological status and the absence of recent cerebral lesions defined by CT scan .
• When reconstruction is not feasible, endoaneurysmorraphy reducing the aneurysm diameter is an option in fusiform aneurysms, but long-term success has not been established .
• Ligation nowadays is rarely used, being reserved for cases when reconstruction is not technically possible (about 10% of cases), where there is extensive local infection or for high-risk patients .
• McCann, in a literature survey with this technique, showed a stroke risk of 25% and a mortality rate of 20%  and others a death/stroke rate of 12%, in correlation with the back pressure of the clamped carotid artery .
• To obviate these effects some propose extracranial-intracranial by-pass graft, which is rarely used (4% of cases) but its effectiveness and long-term patency have not been demonstrated.
• Endovascular techniques using stenting and embolization are now being used especially in inaccessible surgical cases, such as far distal lesions or re-operation.
• The immediate and late results of a consistent number of cases are awaited but there are already some reports of good experiences using bare or covered stents, the latter being preferred in large defects in pseudoaneu-ryms complicating trauma or endarteriectomy [6, 11].
• McCready reports two cases, out of his experience of four, of embolization of branches of the middle cerebral arteries during the procedure and one stent occlusion at 12 months .
• So embolization constitutes a major hazard of this kind of therapy and the use of filters for cerebral protection is recommended.
• Doubts about the natural history of carotid artery aneurysms still persist, and, as Hertzer  said, one can ask if they are sufficiently dangerous to justify operations of the magnitude described by Rosset et al.  or if patients can be managed just as safely, or perhaps even more so, by modern antiplatelet therapy or oral anticoagulation.
• However, the combined stroke and mortality rate of surgical reconstruction from the series of the Texas Heart Institute and in 12 previously published studies cited by this group was 9%.
• In comparison the rate was 12% for patients submitted to carotid ligation and 21% for patients receiving conservative treatment [2, 4].
• We can conclude that surgical treatment appears to be appropriate for most aneurysms located near the carotid bifurcation, although the stroke risk is higher than that associated with carotid endarterectomy, probably because of the higher potential for emboliza-tion from the thrombus and the tendency for the vein graft to kink and occlude.
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