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The Echography
in the supraortic Vessel Surgery

Neurochirurgia, Ospedale Civile, Caserta, *Centro Diagnostico  Napoli, Italia

The vascular echo-color-doppler represents the standard examination in studying the atherosclerosis pathology of the supraortic vessels. The high-resolution echography, the pulse doppler and the color doppler together contribute to the ultrasound information and complement each other. The echo-tomography is well able to show even the least wall lesions, but it is not reliable for the quantitative evaluation of the highly stenosing lesions. The doppler is scarcely sensitive in the case of lesions with a low haemodynamic profile; on the contrary it is very accurate in case of haemodynamically significant stenosis. The color-doppler gives a panning view of the blood flow, highlighting the low echogenic lesions projecting into the vessel lumen as a lack of staining, not visible in the echo-tomography. The information resulting from the contemporaneous use of these three techniques allow to accurately define an atherosclerotic lesion. Normally, these information are included in the echo-color-doppler clinical reports. However, there are some information, purely concerning the anatomy, not included in the examination reports that may influence the choice of the surgical tactics. Some topics related to the echographic anatomy in the surgical perspective will be discussed hereafter.

Normally, the carotid bifurcation is located at the level of the upper edge of the thyroid cartilage, at the height of C4 transverse process. However, there is a great variability in the bifurcation position. It may be located more proximally, up to 6 cm. from the lower edge of the jawbone body, corresponding to the carotid tuberculum. The first sign that leads to the suspect of a low location of the bifurcation is given by the display of a particularly long segment of the external or internal carotid. If the internal carotid is displayed with a length greater than 3 cm., we may think that the bifurcation is proximally located (Fig. 1). In this case, the relations between the bifurcation and the omohyoid muscle and the lower edge of the plaque need to be studied and then the information should be given to the surgeon. The aggression on a low bifurcation requires sectioning of the omohyoid muscle (Fig. 2), not always necessary in case of normal or high bifurcation. If the surgeon is not supplied with this information, it may happen that he dissections a vessel considering it a common carotid and cranially extends the vessel isolation searching for the bifurcation; instead, he deals with the internal carotid, and eventually he will need to caudally prepare the artery, unnecessarily lengthening the intervention duration. The bifurcation position is to be located in relation to the lower edge of the plaque; in fact, when there is a low bifurcation, with a plaque very much extended proximally to the common carotid, a low cervicotomy may not be sufficient; instead, a cervico-sternotomy is needed.
Equally important for the surgeon is the knowledge of a high bifurcation. This information must be always supplied with a description of the plaque distal edge; in fact, if the bifurcation is high, but the plaque is short, the surgeon may decide to undertake a normal cervicotomy, and, if it is the case, to remove the plaque using an endarterectomy by eversion. On the contrary, if the bifurcation is high and the plaque is long (Fig. 3), the surgeon must plan a distal internal carotid exposure, with a skin cutting from the mastoid apex to the pretragus (Fig. 4) and he should foresee the sectioning of the biventral muscle posterior venter, the stylohyoid muscle and the stylomandibular ligament.
(Fig. 5).

There are three types of morphological anomalies due to the lengthening of the extracranial internal carotid. They are:
"Tortuosity": lengthening with an scarce change of direction, regular curves and no angulations. The haemodynamic effects of these lengthenings are usually nil.
"Coiling": lengthening with a rolling up in the shape of a circle or a coil more o less tight on the longitudinal axis (Fig. 6). This anomaly is often bilateral or symmetrical; it is found in young patients and it is considered congenital. It is located in a high position with respect to the bifurcation, near the retrostylohyd space. This anomaly has generally no haemodynamic effects as well. However, it may have some haemodynamic repercussions during the neck rotation movements when it is associated to a communicating artery agenesis. In this case it must be surgically corrected. The surgical treatment consists in a high exposure of the internal carotid as it has been previously described.
"Kinking": lengthening with abrupt change of direction configuring a consistent angulation with a lumen constriction. The reduction of the flow and the pressure downstream a kinking is proportional to the angulation degree. The surgical correction must be undertaken when an atherosclerosis pathology is concomitant, that is when the association "plaque + kinking" occurs (Fig. 7). In fact, there is a reciprocal influence between the kinking and the plaque, in the meaning that when the kinking is proximal, the whirls and turbulence generated by it induce the plaque progression and the insurgence of complications (see ulceration); the kinking haemodynamic repercussions are instead aggravated by the presence of stenosis. The technique we prefer for the treatment of these associated pathologies is the modified Lorimer technique, which is performed by a resectioning of the internal carotid and a proximal reimplant of it.

The follow-up on the operated patient must first evaluate the vessel patency. The onset of neurologic signs during the immediate post-operation period is an indication of the need to undertake an echo-color-doppler on urgency to exclude or confirm the vessel thrombosis and try again the surgical exploration. The diagnosis of thrombosis using the color-doppler is easy and it is given by a "lack of staining" of the occluded vessel (Fig. 8). The so-called fibro-intimal hyperplasia is practically constant in the operated carotid. It is a neo-endarterium that recent studies have showed to be constituted by an accumulation of fibrin, and it can be seen as a remedial process by the arterious wall. In the echography it is displayed as a hypoecogenous striation adherent to the endarterectomized wall. In the area of the fibrointimal hyperplasia, a systolic peak speed equal to 120cm\sec is often detected on the pulse doppler while on the color doppler clear turbulence phenomena can be observed. These findings often remain unchanged during the serial checks. Sometimes, the remedial process evolves, and from the tissue point of view we have a proliferation of fibroblasts and smooth muscular cells thus configuring the restenosis
(Fig. 9). A tardive complication of the operated carotid is represented by the formation of aneurysms. These aneurysms can be real ones, both fusiform and sacciform, more frequent when patches in saphena are used, or false aneurysms, generally consequent to a suture dehiscence due to the surgical wound infection. The aneurysm appears as a round anechogenic formation; in its lumen there are echoes of different intensity resulting from the presence of thrombi (Figg. 10 and 11). Inside the aneurysm the flow is turbulent and at low speed.

The importance of the echo-color-doppler in defining the cerebral ischaemic desease from an etiopathogenic perspective is universally accepted. It gives the surgeon important information. However, there is also a "negative" aspect of this method, that is in patients suffering from TIA, crescendo TIA or with stroke it detects absolutely nothing. In these cases, we maintain that it is the duty of the operator to involve another specialist, the echocardiographist, to undertake an examination: the trans-oesophageal echocardiography, which is not yet part of the diagnostic routine for the patient affected by a cerebral ischaemic vasculopathy. In our opinion, at this stage this method seems to be the most sensitive to diagnose the pathologies related to the ictus still defined cryptogenetic. In particular, it has been chosen a population of patients, comprising young subjects (aged < 45), with no known cardiopathy, negative echo-color-doppler for carotid vessel pathology, which showed a significant prevalence (30-50%), of left atrial thrombosis, patent oval foramen, endocardial vegetations, aortic debris, and suffering from ictus. This specimen, also considering a positive cost Æ benefit ratio, is the one to undertake the trans-oesophageal echography. (TEE).

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