Occlusion of the carotid arteries is a partial or complete obturation of the lumen of the carotid arteries supplying blood to the brain. It may have an asymptomatic course, but is more often manifested by repeated TIA, a clinic of chronic cerebral ischemia, ischemic strokes in the basin of the middle and anterior cerebral arteries. Diagnostic search for carotid artery occlusion is aimed at establishing the location, genesis and degree of obturation. It includes ultrasound of carotid vessels, cerebral angiography, magnetic resonance angiography, CT or MRI of the brain. The most effective surgical treatment is endarterectomy, stenting of the affected area of the artery or the creation of a bypass vascular shunt.
General information
Modern research in the field of neurology has shown that in most patients suffering from cerebral ischemia, the extracranial (extracranial) parts of the blood vessels supplying the brain are affected. Intracranial (intracranial) vascular changes are detected 4 times less often. At the same time, occlusion of the carotid arteries accounts for about 56% of cases of cerebral ischemia and causes up to 30% of strokes.
Occlusion of the carotid arteries may be partial, when there is only a narrowing of the lumen of the vessel. In such cases, the term “stenosis” is more often used. Complete occlusion is an obturation of the entire diameter of the artery and, with acute development, often leads to an ischemic stroke, and in some cases to sudden death.
Anatomy
The left common carotid artery (CCA) starts from the aortic arch, and the right — from the brachiocephalic trunk. Both of them rise vertically upwards and are localized in the neck area in front of the transverse processes of the cervical vertebrae. At the level of thyroid cartilage, each WASP is divided into internal (ICA) and external (ESA) carotid arteries. The ESA is responsible for the blood supply to the tissues of the face and head, other extracranial structures and parts of the dura mater. ICA passes through the channel in the temporal bone into the cranial cavity and provides intracranial blood supply. It feeds the pituitary gland, frontal, temporal and parietal lobes of the brain of the same side. The ocular artery departs from the ICA, giving blood supply to various structures of the eyeball and orbit. In the region of the cavernous sinus, the ICA gives a branch anastomosing with the branch of the ESA passing to the inner surface of the base of the skull through the opening of the sphenoid bone. According to this anastomosis, collateral blood circulation occurs during ICA obturation.
Causes
The most common etiological factor of carotid artery occlusion is atherosclerosis. The atherosclerotic plaque is located inside on the vascular wall and consists of cholesterol, fats, blood cells (mainly platelets). As the atherosclerotic plaque grows, it can cause complete occlusion of the carotid artery. On the surface of the plaque, the formation of a blood clot is possible, which with the blood flow moves further along the vascular bed and causes thrombosis of intracranial vessels. With incomplete occlusion, the plaque itself can break away from the vascular wall. Then it turns into an embolus, which can lead to thromboembolism of cerebral vessels of a smaller caliber.
Carotid artery obturation can also be caused by other pathological processes of the vascular wall, for example, with fibromuscular dysplasia, Horton’s disease, Takayasu arteritis, moya-moya disease. Traumatic occlusion of the carotid arteries develops as a result of TBI and is caused by the formation of a subintimal hematoma. Other etiofactors include hypercoagulation conditions (thrombocytosis, sickle cell anemia, antiphospholipid syndrome), homocystinuria, cardiogenic embolism (with valvular acquired and congenital heart defects, bacterial endocarditis, myocardial infarction, atrial fibrillation with the formation of blood clots), tumors.
Factors contributing to stenosis and obturation of the carotid arteries are: features of the anatomy of these vessels (hypoplasia, tortuosity, kinking), diabetes mellitus, smoking, improper nutrition with an increased content of animal fats in the diet, obesity, etc.
Symptoms
The carotid artery obturation clinic depends on the location of the lesion, the rate of occlusion (suddenly or gradually) and the degree of development of vascular collaterals providing alternative blood supply to the same areas of the brain. With the gradual development of occlusion, there is a restructuring of the blood supply due to collateral vessels and some adaptation of brain cells to the prevailing conditions (reduced intake of nutrients and oxygen); a clinic of chronic cerebral ischemia is formed. The bilateral nature of obturation has a more severe course and a less favorable prognosis. Sudden occlusion of the carotid arteries usually leads to an ischemic stroke.
In most cases, occlusion of the carotid arteries manifests as a transient ischemic attack (TIA) — a transient disorder of cerebral circulation, the duration of which primarily depends on the degree of development of vascular collaterals of the affected area of the brain. The most typical symptoms of TIA in the carotid system are mono- or hemiparesis and sensitivity disorders on the opposite side (heterolateral) in combination with monocular visual disorders on the affected side (homolateral).
Usually, the onset of the attack is the occurrence of numbness or paresthesia of half of the face and fingers of the hand, the development of muscle weakness in the entire arm or only in its distal parts. Visual disturbances range from the sensation of spots in front of the eyes to a significant decrease in visual acuity. In some cases, retinal infarction is possible, triggering the development of optic nerve atrophy. More rare manifestations of TIA in carotid artery obturation include: dysarthria, aphasia, facial paresis, headache. Some patients indicate dizziness, nausea, swallowing disorders, visual hallucinations. In 3% of cases, local seizures or large seizures are observed.
According to various data, the risk of ischemic stroke within 1 year after the appearance of TIA ranges from 12 to 25%. Approximately 1/3 of patients with carotid artery occlusion have a stroke after one or more TIA, 1/3 develop it without previous TIA. Another 1/3 are patients whose ischemic stroke is not observed, but TIA continues to occur. The clinical picture of ischemic stroke is similar to the symptoms of TIA, but it has an ongoing course, i.e. neurological deficit (paresis, hypesthesia, visual disorders) does not go away with time and can decrease only as a result of timely adequate treatment.
In some cases, the manifestations of occlusion do not have a sharp onset and are so unexpressed that it is very difficult to assume the vascular genesis of the problems that have arisen. The patient’s condition is often interpreted as a clinic of a cerebral tumor or dementia. Some authors indicate that irritability, depression, confusion, hypersomnia, emotional lability and dementia may develop as a result of occlusion or microembolism of the ICA on the dominant side or on both sides.
Obturation of the common carotid artery occurs only in 1% of cases. If it develops against the background of normal patency of the ESA and ICA, then the collateral blood flow going through the ESA to the ICA is sufficient to avoid ischemic brain damage. However, as a rule, atherosclerotic changes in the carotid arteries have a multilevel character, which leads to the occurrence of the symptoms of occlusion described above.
The bilateral type of carotid artery occlusion with well-developed collaterals may have a low-symptom course. But more often it leads to bilateral strokes of the cerebral hemispheres, manifested by spastic tetraplegia and coma.
Diagnostics
In diagnostics, along with neurological examination of the patient and the study of anamnesis data, instrumental methods of carotid artery examination are of fundamental importance. The most accessible, safe and sufficiently informative method is the ultrasound of the vessels of the head and neck. With occlusion of the carotid arteries, the ultrasound of extracranial vessels usually reveals accelerated retrograde blood flow along the superficial branches of the ESA. In conditions of occlusion, the blood moves through them to the ocular artery, and through it to the ICA. During ultrasound, a test is performed with compression of one of the superficial branches of the ESA (more often the temporal artery). A decrease in blood flow through the ocular artery with finger compression of the temporal artery indicates occlusion of the ICA.
Angiography of cerebral vessels allows you to accurately determine the level of occlusion of the carotid arteries. However, due to the risk of complications, it can be performed only in difficult diagnostic cases or immediately before surgical treatment. MRA — magnetic resonance angiography has become an excellent and safe replacement for angiography. To date, in many clinics, MRA in combination with MRI of the brain are the “gold standard” for the diagnosis of carotid artery occlusion.
Ischemic damage to cerebral structures is visualized using MRI or CT of the brain. At the same time, the presence of “white” ischemia indicates a gradual atherosclerotic nature of the obturation of the carotid arteries, and ischemia with hemorrhagic impregnation indicates an embolic type of lesion. It should also be taken into account that in about 30% of patients with ischemic stroke, focal changes in brain tissues are not visualized in the first days.
Treatment
With regard to occlusion of the carotid arteries, it is possible to use various surgical tactics, the choice of which depends on the type, level and degree of obturation, the state of collateral circulation. In cases when the operation is performed after 6-8h from the onset of a progressive ischemic stroke, the mortality rate of patients reaches 40%. In this regard, surgical treatment is advisable before the development of a stroke and has a preventive value. As a rule, it is carried out in the intervals between TIA when the patient’s condition is stabilized. Surgical treatment is carried out mainly with the extracranial type of occlusion.
Among the indications for surgical treatment of stenosis and obturation of the carotid arteries, there are: a recent TIA, a completed ischemic stroke with minimal neurological disorders, asymptomatic occlusion of the cervical ICA site of more than 70%, the existence of sources of embolism in the extracranial arteries, a syndrome of insufficient arterial blood supply to the brain.
With partial occlusion of the carotid arteries, the operations of choice are: stenting and carotid endarterectomy (eversion or classical). Complete obturation of the vascular lumen is an indication for the creation of an extra-intracranial anastomosis — a new way of blood supply, bypassing the occluded area. With the preservation of the lumen of the ICA, subclavian-general prosthetics is recommended, with its obturation — subclavian-external prosthetics.
Prognosis and prevention
According to generalized data, asymptomatic partial occlusion of the carotid arteries up to 60% in 11 cases out of 100 is accompanied by the development of stroke within 5 years. With narrowing of the artery lumen to 75%, the risk of ischemic stroke is 5.5% per year. In 40% of patients with complete occlusion of ICA, ischemic stroke develops in the first year of its occurrence. Carrying out preventive surgical treatment allows minimizing the risk of developing ACVA.
Measures aimed at preventing arterial occlusion include getting rid of bad habits, proper nutrition, weight loss, correction of blood lipid profile, timely treatment of cardiovascular diseases, vasculitis and hereditary pathology (for example, various coagulopathies).