Chair of Neurosurgery, Medicomilitary Academy, Russia
Prevention and treatment of acute disorders of cerebral circulation of an ischemic type are the most urgent problem of clinical neurology and neurosurgery. The annual stroke rate varies from 260 up to 526.2 cases per 100 000 men. Stroke occupies the first place among the causes of persistent disability. The mortality rate during the first post-stroke year is 35-38%; on the whole, disorders of cerebral circulation are the cause of 1/4 of all fatal outcomes.
Lesions of pre-cerebral arteries in patients with an ischemic disease are widespread. Two and more arteries are affected in 87% of cases. Vessels of three and more vascular regions of the brain are impaired in 2/3 of observations. Complete occlusion of at least one pre-cerebral artery and hemodynamically significant stenosis are watched in 70% and 90% of cases respectively. Atherosclerotic changes are diagnosed mainly in initial segments of extracerebral parts of arteries supplying the brain. The rate of intracranial lesions is 4 times smaller. Occlusion and stenosis are more typical of carotid arteries (54-57% of patients) and carotid area as a whole (20% more frequent in comparison with a basilar area). Multi-level (echelon or tandem type) lesions of one of the vascular areas are observed in the carotid region rather often.
More than half a million strokes are registered in the USA annually; 20-30% of them are caused by lesions of carotid artery; the quota of asymptomatic stenosis is 2-5%.
A nature of stroke was studied during three hundred years, but a role of extracranial stenosis and occlusion of the internal carotid artery in development of stroke and transient disorders of cerebral circulation was clarified only in the 50s of the XXth century. A high rate of this lesion, its important role in stroke development and accessibility of an affected segment in direct interventions attracted great attention of vascular surgeons and neurosurgeons.
The first operation for local atherosclerotic lesion of the internal carotid artery (anastomosis between internal and external carotid arteries) was made by Carrea in 1951. DeBakey performed endarterectomy from the internal carotid artery in 1953, but there was no information on it till 1975. Analogous attempts were made in China and Argentina even earlier. The first official report on successful carotid reconstruction in a patient with transient disorders of cerebral circulation was published by Eastcott H. (1954). It gave rise to an “epidemic” of carotid endarterectomies in the USA and Europe, but an approach to this type of intervention acquired a “scientific” character only at the beginning of the 90s. It happened after carrying out randomized clinical studies which resulted in working out indications for various types of surgical interventions in different groups of patients.
Today 80 000-100 000 of endarterectomies are performed in the USA annually. It does not exceed 3000 in our country, though the rate of morbidity is considerably higher. This lag in surgery of brachiocephalic arteries is explained by unsatisfactory cooperation of cardiologists, therapeutists, neurologists on the one hand and vascular surgeons on the other. The majority of general practitioners and neuropathologists of polyclinics know little about the state of the art in the field of diagnosis and complex treatment of obliterating atherosclerosis of cerebral arteries.
Clinical manifestations of an ischemic disease, caused by atherosclerotic lesions of carotid arteries and their branches, can be classified in the following way:
Stenosis and occlusions of carotid arteries in patients of the first group and the second-forth group are referred to the so-called asymptomatic and symptomatic lesions respectively.
A degree of narrowing of the carotid artery on a neck is determined on the basis of a ratio between its diameter in a zone of maximum narrowing and diameter of a “referent” segment of a vessel which is represented by:
Thus, according to the chosen algorithm, a degree of narrowing is determined on the basis of the formula:
, where d is ICA diameter in a zone of maximum narrowing and D is diameter of a referent segment of a vessel.
A degree of stenosis of carotid artery should be estimated as precisely as possible using results of visualizing diagnosis. CCA index is the most objective one among the criteria given above; but NASCET and ECSR indices of stenosis, which were worked out during randomized studies carried out in the USA and Europe in 1991, are preferred owing to traditions and technical peculiarities.
According to a degree of stenosis, there are:
- minor stenosis (0-29%);
- moderate stenosis (30-50%);
- marked stenosis (50-69%);
- critical stenosis (70-99%);
- cclusion (100%).
Possibility of differentiation between stenoses of less than 50%, which are not liable to surgical treatment, and stenoses of more than 75%, being as a rule an object of surgical correction, is of principal importance.
An atherosclerotic plaque, which causes narrowing of a vessel, is classified according to the following characteristics:
structure- homogeneous (of low, moderate and high density);
- heterogenic (with dominance of zones of reduced/increased density);
spread- local (less than 1.5 cm);
- prolonged (more than 1.5. cm).
localization- segmental (occupying up to 1/4 of a vessel circumference);
- semiconcentric (occupying up to 1/2 of a vessel circumference);
- concentric (occupying more than 1/2 of a vessel circumference).
surface form- plane surface;
- rough surface.
presence of complications- uncomplicated;
- complicated (ulceration, intramural hemorrhage, intraluminal thrombus) (Fig. 1).
|Fig. 1. An endoscopic view of the ulcerated atherosclerotic plaque of CCA bifurcation: 1 - a lumen of the internal carotid artery; 2 - a lumen of the external carotid artery; 3 - a crater on the plaque surface being a source of microemboli.|
The whole complex of data is obtained on the basis of profound examination including visualization of a vascular bed lumen and vascular wall.
A pathogenetic role of an atherosclerotic plaque of the carotid artery in development of stroke is connected with three main mechanisms:
Thus, occluding lesions of the carotid artery cause development of cerebral ischemia by embolic, hemodynamic and thrombotic mechanisms.
There is direct connection between a risk of ischemic stroke and a degree of narrowing of an artery lumen. According to Norris J.W. (1991) the annual risk of stroke in stenosis of the carotid artery of more than 75% is equal to 3%. The same index against a background of transient disorders of cerebral circulation is 13% a year. In accordance with data of the European randomized study of carotid endarterectomy (ECST, 1991) the annual risk of stroke in stenosis of 70-99% and stenosis of less than 30% is 5.7% and 1.8% a year respectively. As for asymptomatic stenosis of ICA of 75% and asymptomatic stenosis of 60 % this index is 5.5% a year and 11% during 5 years respectively. The rate of stroke caused by ICA occlusion reaches 40% during the first year after it and 7% during subsequent years. These statistical data are referred to the category of the so-called group prognostication. They are not related directly with individual prognostication of the risk of stenosis development in a patient with atherosclerotic lesion of ICA. Nevertheless, it is clear that symptomatic stenosis of ICA of more than 75% is an important independent risk factor of infarction in the carotid region.
Diagnosis of an ischemic disease of the brain (IDB) and occluding lesions of major arteries is complex. The main task at a stage of neurologic and general somatic examination is as follows:
Classic methods of neurologic, laboratory examination and estimation of a functional state of cardiovascular and respiratory systems are used. The main clinical symptoms of occluding lesion of major arteries of a neck are:
Presence of anamnestic signs indicative of acute ischemia of the brain or retina, atherosclerosis of arteries of lower extremities or coronary arteries is a basis for carrying out profound examination of the brain and its vascular system in order to confirm absence of local lesions, being risk factors of primary or repeated disorder of cerebral circulation. The list of instrumental methods, which can be used for these purposes, is rather big. Thus, it is expedient to stick to a definite algorithm which would permit to use diagnostic modalities in succession, passing from less invasive to more traumatic and informative methods.
The main tasks of diagnostic search are:
- diagnosis of occluding lesion of ICA;
- estimation of localization and a degree of severity of stenosis;
- determination of a state of structural and functional reserves of compensations;
- determination of a structure and embologenic activity of an atherosclerotic plaque;
- study of a morphologic and functional state of the brain;
- determination of a type of a disease course;
- estimation of risk factors of an intervention.
Optimum succession of applying methods of functional and radiation diagnosis for detecting occluding lesions of major arteries of the brain and neck can be as follows:
Estimation of Severity of Morphologic Changes:CT of the brain with intravenous administration of a contrast substance
MRI of the brain
Estimation of a Functional State:EEG
Somatosensory and evoked visual potentials
Estimation of Severity of Morphologic Changes:Transcranial Doppler
Duplex scanning of arteries of a neck
Spiral CT-angiography / MR-angiography
Estimation of a Functional State:Transcranial Doppler
Single photon emission or positron emission computer tomograpgy
The goal of radiation methods is to exclude any other causes of neurologic deficit. Today sensitivity of MRI at an early stage of detecting signs of cerebral ischemic lesions exceeds that of CT and is 90% versus 60% respectively. An initial sign indicative of possible disorder of cerebral circulation can appear during the first hours and even minutes after stroke. Correlation of data obtained with the help CT and MRI and concerning a size of an ischemic focus is rather important in choosing terms and a type of an intervention. When estimation of the brain volume is carried out, domination of this parameter accompanied by obvious changes of a signal in MRI above the same index obtained in CT is indicative of a potentially reversible character of neurologic disturbances.
Estimation of a functional state of the brain is carried out with the help of electrophysiologic methods. It is aimed at determination of a functional competence and “mobility” of a motor analyzer. Electrophysiologic diagnosis is indirect characterization of a state of conduction apparatus, integrative function of the brain, system of cerebral circulation.
Ultrasonic and radiation methods of diagnosis of vascular disorders are of the greatest importance in estimation of indications for surgical treatment of atherosclerotic lesion of major arteries of a head and neck. They make it possible to determine a character and degree of occluding lesion, a state of compensatory mechanisms, a functional state of cerebral hemodynamics.
Ultrasonic dopplerography is a leading method of screening in suspected occluding-stenotic lesions of major arteries of a head and neck. Stenosis of arteries of more than 50% in diameter is characterized by a combination of such specific dopplerographic patterns as stenosis, residual flow, and hampered perfusion at different levels of a precerebral vascular bed . It allows to make precise diagnosis (sensitivity of 79%, specificity of 88%) of a level and degree of arterial lesion in the majority of cases. Increase of systolic rate/blood flow velocity in the opening of affected artery is the most typical phenomenon in ICA stenosis. It permits to determine a degree of narrowing of the artery in its diameter rather precisely (see the table).
Table 1 Correlation of Maximum Systolic Rate (Velocity) in the ICA Opening with a Degree of Stenosis (Spencer M.P., 1997)
4CW probe kHz (cm/s)
|< 3 (<60)||0|
|< 4 (80)||20|
|4 - 5 (80 - 100)||30|
|5 - 7 (100 - 140)||40|
|7 - 8 (140 - 160)||50|
|8 - 10 (160 - 200)||60|
|10 - 12 (200 - 240)||70|
|12 - 14 (240 - 280)||80|
|> 14 (> 280)||90|
Besides gradation of a stenosis degree by the maximum linear blood flow velocity, dopplerography allows to estimate hemodynamic significance of a lesion on the basis of a sign indicative of functioning of collateral blood supply and a degree of reduction of perfusion pressure due to stenosis. This method permits to detect echelon-like stenoses/occlusions of intracranial segments of ICA/MCA. Results of compression tests (compression of the carotid artery on a neck) make it possible to prognosticate a risk of development of neurologic complications during transition of ICA stenosis into occlusion and to recommend an operation even in a lesser degree of artery narrowing. Transcranial Doppler is the only modality for on-line detection of microemboli, whose source is an unstable atherosclerotic plaque of the carotid artery (Fig. 2). Thanks to precise estimation of collateral blood supply in determining indications for carotid endarterectomy, transcranial Doppler helps to assess necessity of temporal intraluminal shunting at the stage of compression of the carotid artery. Its use in intraoperative monitoring during carotid endarterectomy and a postoperative examination has no alternative.
|Ðèñ. 2. Dopplerograms reflecting passage of mircoemboli from a surface of an atherosclerotic plaque.|
Duplex scanning ensures precise detection of stenoses of extracranial segments of carotid arteries, determination of their structure, size, shape, complications of an atherosclerotic plaque. Scanning in two-dimensional mode (B-mode) allows to assess atheroma density, an internal membrane of an artery and its state, i.e. depth of a layer of intima-media, and to characterize an extent of atherosclerotic lesion. Simultaneous use of Doppler mode provides carrying out spectral analysis of linear blood flow velocity in a zone of stenosis and its gradation. Visualization of flows of blood using modes of color mapping of Doppler spectrum and energy (ultrasonic angiography) is a noninvasive way of obtaining an image of a vascular bed lumen. This method proved to be both an effective means of preoperative diagnosis of stenosis and occlusion of carotid arteries and a means of postoperative control.
Spiral CT-angiography (SCTA) is a modern noninvasive modality of complex visualization of a vascular bed lumen, vascular wall and paravasal structures. An atherosclerotic plaque, watched on axial sections in applying SCTA, is a sign of atherosclerotic lesion of an extracranial segment of carotid arteries. It manifests itself in local changes of thickness and density of a vascular wall, defect of filling of a vascular lumen.
The optimum method of presentation of SCTA data in stenosing lesions of carotid arteries is a projection of maximum intensity, which makes it possible to estimate carotid arteries at a considerable length. Obtaining 8-12 projections at different angles permits to estimate an extent of a lesion zone and to determine a degree of narrowing. Signs of atherosclerotic lesion include uneven contour of a vessel, “defect of filling” seen on one or several projections. In case of its presence on several consecutive reconstructions, a percent of stenosis is calculated on the basis of the greatest narrowing (Fig. 3). Sensitivity and specificity of SCTA in diagnosis of a degree of stenosis is equal to 100% and 87.5% respectively.
Efficacy of magnetic resonance angiography (MR-A) in diagnosis of stenoses of carotid arteries is a bit lower due to limited resolution caused by a negative effect of high linear blood flow velocity, pulsation of arteries, respiratory movements. MR-A is advantageous in diagnosis of stenoses and occlusions of intracranial branches of carotid arteries. The goal of MR-A of an arterial circle is study of collateral blood flow. If this circle is closed, than anterior and posterior communicating arteries are visualized. They are not seen on typical three-dimensional time-flowing angiograms (3D TOF) in case of their hypoplasia or secondary impairment of filling in arteriolosclerosis. It is better to use phase-contrast (PC) MR-A for estimation of a state of an arterial circle.
|Fig. 3.Spiral CT-angiograms in atherosclerotic stenosis of ICA caused by petrified atherosclerotic plaques. Modes: projections of maximum intensity and “virtual angioscopy”; pathologic deformity of ICA; occlusion of ICA.|
SCTA and MR-A are competitive methods. Preference, given to this or that modality, depends on such factors as availability, a suspected level of lesion and diagnostic goals.
Cerebral angiography is a “golden standard” from the point of view of visualization of a vascular bed lumen. Unfortunately, an angiographic image is only an indirect characteristic of a vascular wall state, cerebral hemodynamics and collateral blood supply in occcluding lesions of major arteries.
At present angiographic examination is indicated in case of diagnosed, hemodynamically significant occluding-stenotic lesions of major arteries of the brain and neck, which are considered to be a potential object of surgical correction; it especially concerns cases characterized by divergence of data of various methods or suspected echelon-like stenosis of an intracranial segment of the internal carotid artery.
Decision on performing carotid endarterectomy is made without carrying out angiographic examination in 80% of cases, as it accounts for 4 % of ischemic strokes in patients with transient disorders of cerebral circulation; thus, taking into account a traumatic character of this method, cautious attitude to angiography allows to improve indices of outcome of surgical treatment.
The main diagnostic goals of cerebral angiography carried out in patients with cerebral atherosclerosis are as follows:
Typical angiograms of carotid arteries in stenosis and occlusion of ICA on a neck are presented in fig. 4.
|Fig. 4. A) Critical stenosis (90%) of the ICA opening with ulceration of an atherosclerotic plaque;|
B) Chronic atherosclerotic occlusion of ICA.
The leading clinical method of estimation of a functional state of cerebral hemodynamics is transcranial Doppler with functional test-loads. Testing reactivity and autoregulation of cerebral blood flow allows to determine a degree of insufficiency of cerebral circulation and hemodynamic reserve. It is necessary to differentiate between structural and functional reserves of compensation.
The first characterizes quality of collateral blood supply of a vascular region of stenotic/occluded carotid artery. Values of linear blood flow velocity in MCA and indices of peripheral resistance, a degree of interhemispheric asymmetry, direction of flow in communicating arteries and periorbital anastomosis of blood supply make it possible to make a conclusion on sufficiency of collateral circulation. Decompensated collateral blood supply is a basis for choosing surgical methods, when all other indices are identical.
A state of functional reserve of compensation is determined according to reactivity values and autoregulation indices in affected vascular region. Absent or inverted reactivity watched, as a rule, in decompensated collateral blood supply, is indicative of a higher risk of hemodynamic cerebral infarction and necessity of surgical revascularization of the brain.
Surgical treatment of cerebral atherosclerosis has a preventive character, being a part of a complex of measures aimed at secondary prevention of ischemic infarction of the brain. Different methods of surgical revascularization have been worked out by now:
- carotid endarterectomy and other reconstructive operations on ICA bifurcation;
- extraanatomic anastomosis (EICMA);
- transcutaneous transluminal angioplasty with stents;
- correction of deformed extracranial parts of major arteries;
- interventions on the vegetative nervous system.
Numerous cooperative studies show that only carotid endarterectomy, out of all methods on the above list, possesses preventive efficacy. Due to insufficiency of clinical observations, preventive effectiveness of transluminal angioplasty has not been proved yet, though preliminary results suggest that it is rather high. In spite of considerable experience, one cannot say for sure that EICMA, correction of artery deformities and interventions on the vegetative nervous system are important means of prevention. According to data of the International cooperative study (1985-1987), efficacy of surgical correction does not differ from that of drug treatment. However, it does not exclude use of these methods for correction of occluding lesions in selected groups of patients.
Up-to-date views on preventive efficacy of carotid endarterectomy (CE) have been formed owing to randomized clinical trials carried out in 1990-2000 in symptomatic and symptom-free patients. Their main results are given in tables 2 and 3.
Table 2Results of Cooperative Trials in Patients with Symptomatic Stenosis of ICA
|Index||NASCET (ÑØÀ)||ECST (Åâðîïà)|
|A number of clinics and centers||50||97|
|A number of patients||990||2741|
|Indications for surgical treatment|
|Was not studied||No|
|Yes (in a complication level of less than 3%)||Yes (in a complication level of less than 3%)|
Note: NASCET - North American Stenosis Carotid Endarterectomy Trial
ECST - European Carotid Stenosis Trial
Table 3 Results of Cooperative Trials in Patients with ICA Asymptomatic Stenosis
|Index||VACT (ÑØÀ)||ACAS (ÑØÀ)|
|A number of clinics and centers||11||97|
|A number of patients||444||1 659|
|Indications for surgical treatment|
|Yes||Yes(stenosis of more than 60%)|
Note: VACT - Veteran Affairs Cooperative Trial
ACAS - Asymptomatic Carotid Artery Stenosis
The results in patients with symptomatic stenosis show, that:
Conclusions, concerning asymptomatic stenosis, are less categorical. CE can be indicated only after profound study of several factors: a stenosis degree, progression of artery narrowing, a degree of stenotic lesion of contralateral artery, estimation of collateral blood supply, presence of silent cerebral infarctions detected by CT, presence of an ulcerated plaque. The operation should be performed only in patients with a low risk of complications (3-4%).
Today there are the following indications and contraindications for CE:
The operation is indicated
!!! stenosis of more than 70% in a perioperative rate of complications of less than 6%;
!? acute thrombosis of ICA;
!? developing stroke;
!? embologenic stenosis of 30-69%;
!? one-stage aortocoronary shunting;
!? acute stratification of aorta;
?? stenosis of less than 30% .
The operation is contraindicated
stenosis of less than 30% without taking aspirin.
chronic ICA occlusion
The operation is indicated
!!! stenosis of more than 60% in a prognosticated rate of complications of less than 2%;
!? stenosis of more than 60% in a prognosticated rate of complications of less than 4-6%.
The operation is contraindicated
- stenosis of more than 60%;
- chronic occlusion of ICA;
- carotid artery stratification ;
- stenosis of more than 60% and a risk of complications of less than 6%.
Determining indications for CE, one should not forget about its preventive significance; thus, a rate of complications should not exceed a risk of a natural course of the disease. The Committee on CE of the Stroke Council of the American Association of Cardiologists worked out permissible range of complications in this operation. The rate of fatal outcomes should not exceed 2%.
|À||Asymptomatic stenosis||3 %|
|B||Transient disorders of cerebral circulation||5 %|
|C||Ischemic stroke||7 %|
|D||Carotid restenosis||10 %|
The following scheme of prognostication of craniocerebral complications can be used for determining “permissible” and individual risk, when CE is planned (Sundt T.M., 1975). An expected risk of complications is determined by an individual combination of neurologic, angiographic and somatic risk factors (Table 5).
|A risk degree||Neurologic||Somatic||Angiographic||% of complications|
|III||-||+||+ / -||4.0|
|IV||+||+ / -||+ / -||8.5|
Thus, if there are clinical-angiographic indications for CE, a risk of surgical complications can be prognosticated individually and brought into correlation with a risk of stroke against a background of existing stenosis. CE is not expedient, when a risk of complications is higher than a risk of stroke in a natural course of the disease. Less traumatic methods of stenosis correction, for example carotid angioplasty, are preferable in such situations.
CE is performed in departments of vascular surgery or neurosurgery. As a rule, multi-component general anesthesia with trachea intubation is used. Local infiltration or locoregional anesthesia with 0.5-1% solution of trimecaine or lidocaine is recommended too. Regardless of a chosen method, the main goals of anesthesia consist in providing adequate perfusion of the brain and myocardium at operation stages, characterized by changes of perfusion pressure. As a rule, a central venous approach and direct monitoring of arterial pressure are necessary. Systemic heparinization (100 units/kg of body weight), induced arterial hypertension, medicamental protection of the brain from ischemia are used during anesthesia at stages of carotid artery compression. Barbiturates in high doses are the drugs of choice. Continuous EEG monitoring at the stage of carotid artery compression is expedient, as it allows to optimize dosage of thiopental sodium, propofol or etomidat (up to the level of burst-suppression). Vasoactive drugs for timely correction of arterial pressure are necessary.
The operation is performed in a supine position of a patient with his head thrown back and turned to the side opposite to the affected one. The skin is cut (linear or S-shaped incision) from the top of the mastoid process down the medial margin of the sternocleidomastoid muscle. After dissection of the skin and subcutaneous muscle down the linea alba, the sheath of the neurovascular bundle of the neck is exposed widely at the medial margin of the sternocleidomastoid muscle. CCA is identified, isolated and a tourniquet is brought under it. Blunt preparation of an area of CCA bifurcation is performed while moving upwards stage by stage. The hypoglossal nerve, which crosses the internal carotid artery perpendicularly, is identified above the bifurcation, prepared upwards and pushed medially. A distal part of ICA is exposed carefully at least 1 cm above the upper edge of an atherosclerotic plaque. An approach to the internal carotid artery should be as short and straight as possible. Preparation of the posteroexternal wall of ICA, which usually carries a plaque, should be made with special care. As a rule, a more or less marked periarterial adhesive process is watched along this segment. During dissection one should avoid palpation, displacement of vessels; it especially concerns a zone of localization of an atherosclerotic plaque.
When the arteries are ready to compression, heparin in an average dose of 100 units/kg of body weight is administered intravenously. Clips or bulldog-type forceps are put on internal and external carotid arteries. The common carotid artery is blocked with the help of DeBakey clamp or a tourniquet. An anesthesiologists times compression from the moment of blood flow cessation.
Today there are two widespread methods of endarterectomy proper: classical and eversion endarterectomy.
In classical CE arteriotomy is performed along the anteroexternal wall of CCA and ICA in projection of an atherosclerotic plaque. The latter is identified in the artery lumen and the wall section. As a rule, it can be separated from the external layer of media and adventitia quite easily. An atherosclerotic plaque is separated from the vascular wall along the whole length of arteriotomic incision with the help of a curved dissector and cut off from intact intima in proximal (CCA) and distal (ICA) parts. Intima scraps in a distal segment are fixed along the vessel circumference with the help of Ï-sutures and atraumatic thread. Plaque residues are removed from the ECA lumen as well. Plasty of the vessel with an expanding patch is performed in order to prevent restenosis. An autovein (subcutaneous vein of the shin or external jugular vein), autoartery (superior thyroid artery), autopericardium (in simultaneous operations on the heart), lyophilized dura mater, xenomaterial are used for a patch. The artery lumen is filled with blood before final suturing, measures on prevention of air embolism are carried out. When blood flow is restored, insufficient bleeding from needle insertions is watched. It is controlled during 3-5 minutes by pressing a dry gauze tampon. In case of incompetent collateral blood supply (high functional significance of the artery), a temporary intraluminal shunt (a Teflon tube with a heparinized inner layer and diameter of 2-4 mm) is inserted into the lumen of CCA and ICA after arteriotomy. It is removed before placing the last stitches in artery plasty.
When eversion CE is performed, ICA is dissected away from CCA in the opening. External layers of the wall are turned inside out as a stocking and separated from an atherosclerotic plaque until it “comes to naught”. Placing fixing sutures on intima in a distal part of the artery is unnecessary. After removal of an atherosclerotic plaque from ICA and CCA, a normal state of the internal carotid artery is restored and it is reimplanted into CCA. Integrity of a vascular bed is achieved by placing circular continuous suture.
A limiting factor of preventive efficacy of CE is a rather high rate of perioperative cerebrovascular complications, varying from 1.6% up to 24%; approximately 60% of complications develop intraoperatively. Persistent attempts to reduce the risk of CE resulted in appearance of numerous methods of monitoring for adequate protection of the brain. Usually they are based on estimating either a vascular bed state (measurement of occlusion pressure, residual blood flow, intraoperative Doppler or scanning, angiography) or brain function (EEG-EVP-monitoring). Use of intraoperative Doppler monitoring allowed to reduce the rate of perioperative cerebrovascular complications from 4.8% up to 0.8% (n=301) (Jansen C., 1994) and from 7% up to 2% (n=500) (Spencer M., 1997).
During the first 12-48 hours after the operation treatment is carried out in an intensive care unit. Monitoring of vital functions and cerebral blood flow is continued. Great attention is paid to normalizing systemic blood pressure, indices of electrolyte balance. After estimating quality of artery correction with the help of duplex scanning, spiral CT-angiography and transcranial Doppler, a patient can be dismissed from the hospital (the 3rd-7th day). Further treatment is carried out in an outpatient clinic.
The most spread complications of an early postoperative period (up to 30 days) are as follows (their rate according to NASCET is given in brackets):
Acute myocardial infarction (4%)
Ischemic stroke or death (5.8%)
Hematoma of soft tissues, bleeding (5.5%)
Infectious complications (3.4%)
Early thrombosis of ICA
Impaired function of cranial nerves (7.6%):
Great auricular nerve
Myocardial infarction is a frequent complication of reconstructive interventions on carotid arteries; its rate varies from 0.5% up to 18.2%. Angina pectoris of the 3rd functional class, lesions of three coronary arteries and a trunk of the left coronary artery, reduction of output fraction of the left ventricle up to 40% and less, low tolerance (> 50 W) to physical loads, and spontaneous ischemia, watched in monitoring according to Holt, are risk factors of postoperative coronary complications.
Ischemic stroke is a severe complication of CE. Ischemic disorders of cerebral circulation are observed in 4.2-6.7% of cases. Reversible neurologic deficit, minor stroke and hemispheric stroke are seen in 1/3, 1/4 and 1/2 of all cases with acute disorders of cerebral circulation respectively. Cerebral embolism (76%) and circulatory ischemia in CCA compression and postoperative thrombosis (34%) are causes of ischemic disorders. Measures of preventing intraoperative strokes include intraoperative Doppler monitoring of microembolism episodes (especially during surgical access), postoperative monitoring and estimation of neurologic status, as well as selective approach to intraluminal shunting at the stage of carotid artery compression. Metabolic protection of the brain during the operation, delicate handling of vessels, heparin prescription, prevention of residual stenosis and intraluminal thrombi or intima scraps, support of adequate blood pressure in a postoperative period are of great importance.
Remote complication are represented by restenosis/occlusion of carotid artery due to hyperplasia of intima media. The rate of restenoses is 25%; however, the majority of them are asymptomatic. Usually they appear when CE was performed without using a patch.
Carotid angioplasty with stenting is a method under study. It is an alternative to CE. The goal of both interventions lies in prevention of cerebral stroke due to occluding lesion of an extracranial segment of carotid arteries. Stenting is less invasive, traumatic and expensive means of achieving this purpose.
The first reports on balloon angioplasty and its use in treatment of ICA stenosis appeared in 1987. Theron J. et al. published a report, describing results of dilation of ICA stenosis in 48 patients. The operation led to development of hemispheric stroke in 4 cases. Application of only ballooon dilation of stenosis turned out to be traumatic and rather insufficient. The rate of restenosis exceeded 25%, and the level of complications (stroke+fatal otcomes) varied from 3 to 30%. Inetrnal plasty of an arterial wall by means of implantation of net stents allows to overcome drawbacks of angioplasty.
Angioplasty is characterized by the following complications:
Mortality is equal to 0.2-1.4%. The total rate of stroke and death, as complications of angioplasty, is 3-3.5% for patients under 80 and 11.9-21% for cases of more than 80 years old.
Lesions of cranial nerves, hematoma in a zone of access and wound infection are extremely rare. Thus, the rate of systemic and local complications typical of CE is much lower in angioplasty.
The total rate of neurologic complications in symptomatic and asymptomatic patients under 80 corresponds to that of CE. It is necessary to use the so-called protective devices, preventing intraoperative embolism of a vascular bed, in patients of more than 80 years old.
These devices are either an occluding balloon (PercuSurge GUARDWIRETM; Medicorp H.A.F.R.) or a net filter (Accunet (Guidant); Angioguard (Cordis); E-Trap Filter Wire (EPI); Neuroshield (Mednova); Medtronic; Microvena; Intratherapeutics). Examples of protective devices are given in fig. 5. Use of protective devices makes it possible to reduce the rate of neurologic complications up to 4.5%.
|Fig. 5 Protective devices used in carotid angioplasty. a) PercuSurge GUARDWIRETM occluding balloon with a catheter for washing of a vessel; b) Guidant ACCUNETTM filter.|
Remote results of carotid stenting are favorable as well. A three-year follow-up showed that all types of ischemic stroke were absent in 88% of patients. Restenoses of operated carotid arteries were diagnosed in 8% of cases during the first year and 6% of patients during subsequent years.
Indications for carotid angioplasty with stenting do not differ from those of CE. Besides, a number of factors, conditioning a high risk of complications in CE, are not regarded to be contraindications for stenting. Among them one can mention:
- patients of more than 80 years old;
- a short neck;
- high (above C2) or low bifurcation;
- fixed segments of the cervical spine (arthrosis, operations);
- diseases, causing a higher risk of anesthesia;
- irradiation of cervical organs carried out earlier;
- endarterectomy, performed earlier;
- expected aorto-coronary shunting;
- echelon-like stenosis of intracranial arteries.
Contraindications for carotid angioplasty with stenting include:
- asymptomatic patients of more than 80 years old;
- difficult access into the artery;
- severe neurologic deficit;
- marked atrophy of the brain/lacunar infarctions;
Local risk factors in stenting are as follows:
- marked concentric calcification of a plaque;
- total occlusion of ICA;
- marked deformity of a distal segment of carotid artery.
In general, the overwhelming majority of systemic risk factors increases probability of dangerous complications of CE. Thus, carotid angioplasty with stenting can become a reasonable alternative of open operations in carotid artery stenosis. Fig. 6 illustrates the results of carotid angioplasty with a self-dilating stent.
|Fig. 6. a - complex stenosis of the right ICA of 90%; b - control angiographic examination after angioplasty with stenting; there is no stenosis (OVitec J., 2001).|
Authors of observation: Jean Claude Laborde è Irene Bossi, Clinique Pasteur, Toulouse, France.
A clinical case:
a male patient aged 79.
Risk factors: smoking, arterial hypertension, dyslipemia.
A clinical picture of unstable angina pectoris watched during 3 years. Transient disorder of cerebral circulation in a region of the right MCA observed 3 years before an operation. Bilateral ICA stenosis, critical stenosis of the left ICA diagnosed in duplex scanning. CT-examination of the brain - no pathology.
Carotid angioplasty with stenting of the left ICA.
When carotid angioplasty is planned, its is necessary to pay attention to:
An acute angle and marked atherosclerosis hamper performing the operation.
Selective stenting can be performed in patients with symptomatic stenosis of intracranial segments of carotid arteries and their branches. Coronary stents with a diameter of up to 4 mm or specialized carotid stents, designed during the last years, are used for these purposes. The experience of such interventions is not enough for recommending their wide use.
Revascularization of the brain in ICA occlusion was an unsolvable problem for a long period of time. A high rate of complications of thromboendarterectomy in chronic occlusion of ICA forced neurosurgeons to give up direct interventions. Numerous studies showed that the main cause of progressive cerebrovascular insufficiency in ICA occlusion was incompetence of natural collateral blood supply of the brain. Circulation deficiency led to development of recurrent strokes in 9-12% of cases during the first year and 20-50% of observations subsequent during five years; mortality reached 40%. Collateral anastomosis was considered to be one of the most adequate ways of increasing perfusion pressure in the region of occluded artery.
The idea of such an operation was put forward by Crutrie E. in 1912 and only in 1967 Donaghy and Yasargil reported about the first successful creation of extra-intracranial microvascular anastomosis (EICMA) between superficial temporal and middle cerebral arteries in chronic occlusion of ICA. The operation was widely practiced in the 70-80s. Its preventive and marked curative effect in mild and moderate neurologic deficit, watched after completed stroke, was described in several articles.
Neurosurgeons of the whole world used EICMA not only in ICA and MCA occlusion, but also in echelon-like stenoses, ICA stenoses in extracranial segment, CCA occlusion. This situation existed up to 1982. Some authors suggested creating EICMA in patients with a clinical picture of ischemic stroke in the region of carotid artery and absence of any pathology according to data of cerebral angiography (Schnidek P. Et al., 1978). However, other researchers wrote about absence of a supposed effect in patients with EICMA. At first it was explained by remoteness of the disease onset, then by marked manifestations of ischemic stroke in some patients, presence of good natural paths of collateral circulation or their absence. Neurosurgeons failed to work out common indications for creation of EICMA during that time. According to the statement of one of the participants of the working conference, devoted to these problems, “it was easier to determine contraindications for EICMA, than to point out a group of patients, to whom it was indicated” (Cupch A.Ya., 1987).
A negative attitude to this operation intensified after publication of the results of the International cooperative trial (1976-1985). According to its conclusion, EICMA was of no importance in prevention of ischemic stroke. All attempts to prove its efficacy in patients with bilateral occlusion of ICA failed. The majority of European countries, USA refused to recommend EICMA as a measure, preventing stroke in patients with cerebral atherosclerosis. Technical results of the operation were estimated as well. Patency of microanastomosis was watched in 96% of cases. Perioperative mortality and invalidism were 0.6% and 2.5% respectively. Thus, preventive efficacy of the operation was identical to taking aspirin. However, methodology of the trial was subject to sharp criticism in further publications and at the VIIIth International Symposium on Microsurgical Anastomoses Used in Cerebral Ischemia (Florence, 1986). Total study of remote results, without taking into account indications and contraindications for EICMA, was one of the most vulnerable points of the trial. One of the reporters remarked: “The results of the cooperative trial are valuable at least from the point of view of determining a group of patients with contraindications for surgical treatment”. The Symposium recommended to work out more precise indications for EICMA and to carry out one more cooperative trial with taking into account all critical remarks (Diaz F.G. et al., 1987). Today research in this field is being continued; a number of operated patients becomes greater; new operative methods are being developed; precise indications are being worked out.
Diagnostic methods do not differ from those used in examination of patients with cerebral atherosclerosis, as ICA occlusion in its essence is stenosis of 100%. A peculiar attention is paid to estimation of collateral blood supply of an affected hemisphere and cerebral perfusion reserve. It has been proved, that hemodynamic efficacy of EICMA is a necessary condition, which should be taken into consideration in estimating indications for surgical intervention.
A clinical and preventive effect can be ensured only in adequate functioning of a newly created path of collateral blood supply. EICMA is hemodynamically significant in case of initial insufficiency of natural collateral blood supply of an affected carotid region; its criterion is critically low or inverted cerebrovascular reactivity (according to results of functional load with CO2), which can be estimated in Doppler examination.
Factors, which have an impact on clinical and preventive efficacy, are a type of cerebral circulation disorder, a degree of neurologic disturbances before an operation, size and localization of ischemic foci according to CT findings and a degree of hemodynamic efficacy of anastomosis.
At present indications for EICMA can be formulated in the following way:
- Inoperable segmental lesions of major vessels (ICA/MCA), which are inaccessible for extracranial surgical correction.
- A course of cerebral ischemic disease with clinical manifestations in the form of transient disorders of cerebral circulation, reversible ischemic neurologic deficit (minor stroke) and sequelae of completed stroke with mild residual effects.
- Absence of vast and deep postischemic changes in the brain substance and prevalence of functional (reversible) disorders over organic changes.
- Decompensated circulatory insufficiency in a region of ipsilateral MCA.
- Absence of signs of cardiogenic embolism.
Criteria of decompensated insufficiency of circulation in MCA on the side of ICA occlusion (or other lesions of a carotid region) are as follows:
Transcranial Doppler is the optimum diagnostic modality for determining a degree of circulatory insufficiency in a carotid region. Dopplerographic criteria of the above-mentioned disorders include:
- marked reduction of average linear blood flow velocity in MCA (asymmetry index of more than 25%);
- marked reduction of an index of peripheral resistance in MCA (transmission index of pulsations <0.5);
- presence of functioning nasoorbital anastomosis and cortical collaterals from the system of PCA;
- reduction of reactivity indices in loads with CO2 and autoregulation coefficients below critical levels or presence of inverse responses.
Today there is a conditional group of indications for EICMA. It includes the so-called “curative”, “preventive” and “protective” indications (Spiridonov A.A. et al., 2000).
When ICA occlusion is combined with lesions of other major arteries of a neck, priority interventions are those performed on extracranial segments, as it provides maximum favorable conditions for EICMA functioning.
Introduction of microsurgical technique raised efficacy of neurovascular operations. However, it does not eliminate a certain risk of technical defects in such operations. Control of quality of microvascular reconstruction is pledge of success and creation of functioning anastomosis (fig. 7).
|Fig. 7. Control cerebral angiograpgy after creation of hemodinamically significant microvascular anastomosis (a) between the superficial temporal artery and a cortical branch of the middle cerebral artery (an arrow). Retrograde filling of the right MCA with blood (b) up to the level of artery bifurcation (M2) is seen in anteroposterior projection.|
Functioning of microvascular anastomosis in a postoperative period is verified with the help of both linear and scanning ultrasonic Doppler systems. It permits to obtain approximate estimation of volumetric blood flow in anastomosis, which varies from 40 up to 200 ml/min.
A preventive effect of this operation depends on a degree of compensation of neurologic functions before intervention and hemodynamic significance of anastomosis (table 6).
Table 6 Preventive Efficacy of EICMA in Various Degrees of Neurologic Disorders and Anastomosis Types
(% of patients free from ischemic stroke) (Spiridonov A.A. et al., 2000)
|5 years||7 years|
|Progressive transient disorders of cerebral circulation||100||100|
|Transient disorders of cerebral circulation||95||92|
|Hemodynamic type of EICMA|
Thus, the mere fact of occlusion of a major vessel is not a reason for intervention. Only careful selection, based on clinical-hemodynamic criteria, permits to determine a group of patients, who need revascularization of the brain by means of creation EICMA.
Postoperative treatment of patients after reconstructive and revascularizing interventions should include careful monitoring of neurologic functions, correction of disorders of systemic hemodynamics and first of all arterial hypertension, drug therapy. The latter consists in prescription of drugs, effecting the system of hemostasis. A drug of choice is aspirin (100-325 mg/day) in combination with curantyl (300 mg/day). In case of repeated thromboembolic episodes an indirect anticoagulant is prescribed (phenylin, pelentan, varfarin) in a dose, providing reduction of a prothrombin index up to 60-80%.
Control examination should be carried out every 6 months; its purpose is estimation of the artery state in a zone of reconstruction. It is expedient to use ultrasonic methods. When restenosis of an affected segment is diagnosed, a decision on indications for reoperation is made.
It is quite clear, that even “reckoned-by-the head surgical treatment” will not solve the problem of stroke in our country, characterized by an extremely low level of prevention of cardiovascular diseases. Though only 20% of acute disorders of cerebral circulation are caused by obliterating lesions of major cerebral arteries, timely surgical correction promotes prevention of vascular “catastrophes” in the most valuable (from the social point of view) group of able-bodied population.