I. Awareness, definition and significance of ischemia in the posterior circulation
The posterior cerebral circulation, also known as the vertebrobasilar system, consists of the vertebral artery, the basilar artery and the posterior cerebral artery, which mainly supplies blood to the brainstem, cerebellum, thalamus, hippocampus, occipital lobe, some temporal lobes and spinal cord. Posterior circulation ischemia (PCI) is a common ischemic cerebrovascular disease, accounting for approximately 20% of ischemic strokes.
1. History of the recognition of posterior circulation ischemia
In the 1950s, it was discovered that patients with trensient ischemic attack (TIA) had severe stenosis or occlusion of the arteries in the extracranial segment, which was presumed to be caused by the narrowing or occlusion of the arteries, resulting in a state of relative ischemia, called “carotid insufficiency”, where the tissues in the distribution area were supplied only by the collateral circulation. By extending this concept to the posterior circulation, the concept of “vertebrobasilar insufficiency” (VBI) was developed. As can be seen, the classical concept of VBI has two meanings: clinically, it refers to TIA in the posterior circulation, and etiologically, it refers to hemodynamic hypoperfusion due to severe stenosis or occlusion of the great arteries.
With the improved basic and clinical understanding of cerebral ischemia, the concept of “carotid insufficiency” is no longer used, as the only two forms of anterior circulation ischemia are TIA and infarction.
However, due to the lag in the understanding of posterior circulation ischemia, the concept of VBI is still widely used, and some misconceptions have arisen, such as attributing dizziness/vertigo and transient loss of consciousness to VBI, treating cervical spine osteophytes as an important cause of VBI, and even generalizing the concept of VBI to a “relative ischemic state” that is not normal and not ischemic. “. These situations are especially serious in China, leading to unclear concept of VBI, unclear diagnostic criteria and irregular treatment, which have considerably affected the medical level and health services in China.
2.Increased awareness of posterior circulation ischemia
After the 1980s, with the advancement of clinical research (e.g., the New England Medical Center’s Posterior Circulation Ischemia Registry Study, NEMC-PCP) and the development of research techniques, several important clinical and etiologic aspects of PCI have been recognized.
(1) The primary etiology of PCI is analogous to that of anterior circulation ischemia, primarily atherosclerosis, with cervical spondylolisthesis being only an extremely rare occurrence.
(2) The predominant mechanism of posterior circulation ischemia is embolism.
(3) Neither the clinical presentation nor the available imaging studies (CT, TCD, MRI, SPECT or PET) can reliably define the “relative ischemic state”.
(4) Although dizziness and vertigo are common symptoms of PCI, the common cause of dizziness and vertigo is not PCI.
Based on the above consensus, the concept of PCI has replaced the concept of VBI internationally.
3. Definition and meaning of posterior circulation ischemia
PCI means TIA and cerebral infarction in the posterior circulation. Its synonyms include ischemia of the vertebrobasilar system, TIA of the posterior circulation with cerebral infarction, vertebrobasilar artery disease, and vertebrobasilar thromboembolic disease.
Given that MRI diffusion-weighted imaging (DWI-MRI) reveals definite infarct changes in approximately half of patients with posterior circulation TIA and that the boundary between TIA and cerebral infarction is increasingly blurred, covering TIA of the posterior circulation with cerebral infarction with PCI facilitates clinical practice.
Using the concept of PCI and abandoning the concept of VBI can comprehensively improve the understanding of ischemic diseases of the posterior circulation among medical personnel of relevant departments (neurology, general internal medicine, orthopedics, geriatrics, otorhinolaryngology, neurosurgery, and traditional Chinese medicine) at all levels of hospitals, standardize the related diagnosis and treatment, and carry out scientific research and popularization of science to improve the medical level and health services in this field in China.
II. Pathogenesis and risk factors of posterior circulation
1, the main etiology and pathogenesis of PCI are.
(1) Atherosclerosis is the most common vascular pathology manifested by PCI, and the mechanisms leading to PCI include: large artery stenosis and occlusion causing hypoperfusion, thrombosis, arterial-derived embolism, and arterial entrapment. Atherosclerosis is more likely to occur in the beginning and intracranial segments of the vertebral artery.
(2) Embolism is the most common pathogenesis of PCI, accounting for about 40% of cases. Emboli mainly originate from the heart, the aortic arch, the beginning segment of the vertebral artery, and the basilar artery. The most common embolic sites are the intracranial segment of the vertebral artery and the distal basilar artery.
(3) Penetrating small artery lesions with damage such as lipohyalinosis, microaneurysms and atherosclerotic lesions at the beginning of small arteries, preferably in the pontine, midbrain and thalamus.
The rare lesions and pathogenesis of PCI are: arterial entrapment, migraine, aneurysm, subclavian steal, fibromuscular dysplasia, venous sclerosis, and coagulation abnormalities. Fibrous tethering at the entry of the vertebral artery into the skull, turning of the neck or trauma, giant cell arteritis, genetic disorders, intracranial infections, autoimmune diseases, etc.
2.Risk factors for posterior circulation ischemia
The risk factors for PCI are similar to those for anterior circulation ischemia, mainly non-modifiable and modifiable factors. The non-modifiable factors include age, gender, race, genetic background, family history, personal history, etc. The modifiable factors include lifestyle (diet, smoking, lack of activity, etc.), obesity and various vascular risk factors, the latter including hypertension, diabetes, hyperlipidemia, heart disease, history of stroke/TIA, carotid artery disease, peripheral vascular disease, hypercoagulable state, hyperhomocysteinemia, oral contraceptives etc.
3. Cervical spine osteophytes are not the main cause of posterior circulation ischemia
In the past, it was thought that turning the head/neck caused the osteophytes to compress the vertebral artery, resulting in posterior circulation ischemia, and due to the sensitivity of the vestibular nucleus to ischemia, dizziness/vertigo was produced. This is a typical model of traditional medicine that substitutes hypothesis or experience for evidence, and is a major cause of the current confusion in the diagnosis of VBI. In contrast, numerous clinical studies have demonstrated that aging-related cervical spine osteophytes are by no means a major risk factor for PCI because.
(1) PCI patients have cervical spine osteophytes in addition to atherosclerosis, and it is not possible to determine that the osteophytes, rather than atherosclerosis, are responsible for the disease. There is no significant difference in the degree of cervical spine osteophytes between middle-aged and elderly populations with and without PCI, but only in vascular risk factors.
(2) Pathological studies demonstrated that the vertebral artery initiation segment is a good site for atherosclerosis, while the stenosis/occlusion of the intravertebral segment is not severe.
(3) In 203 consecutive vertebral artery dynamic imaging cases, only 2 cases had lateral displacement of the artery due to osteophytes.
(4) In 1018 patients with various vascular risk factors who underwent Doppler ultrasonography after turning the neck, it was found that 5% of the patients had compression of the vertebral artery in the external carotid segment; only 9% of the 136 patients with posterior circulation symptoms had compression; of these 136 patients, 28 had symptoms at the time of turning the head and only 4 had compression; the ratio of compression between the 882 patients without symptoms and the 108 patients with posterior circulation symptoms who did not have symptoms at the time of turning the head was not different. There was no difference in the pressure ratio between 882 cases without symptoms and 108 cases with posterior circulation symptoms without head turn.
Clinical manifestations and diagnosis of posterior circulation ischemia
1.Main clinical manifestations of posterior circulation ischemia
The brainstem is an important neural activity site, in which the cerebral nerves, the reticular upstream activation system and the important upstream and downstream conduction bundles pass. When the blood supply is impaired and neurological impairment occurs, various but overlapping clinical manifestations will occur. Thus the clinical manifestations of PCI are diverse, lack a stereotypical or fixed form, and are difficult to identify clinically.
Common clinical symptoms of PCI include dizziness, vertigo, numbness in the limbs or head and face, limb paralysis, sensory abnormalities, gait or limb ataxia, dysarthria or dysphagia, fall episodes, hemianopia, hoarseness, and Horner’s syndrome. The presence of crossover of neurological damage on one side of the brain and motor-sensory damage on the other side is a characteristic manifestation of PCI.
The common types of PCI are TIA, cerebellar infarction, lateral delayed brain syndrome, basilar artery cusp syndrome, Weber syndrome, atresia syndrome, posterior cerebral artery infarction, lacunar infarction (pure motor stroke, ataxia with mild hemiparesis, dysarthria-clumsy hand syndrome, pure sensory stroke, etc.).
Current evidence suggests that the overall prognosis of PCI is not worse than that of those with anterior circulation ischemia, e.g., 79% of 407 patients in the NEMC-PCR had a good prognosis.
2. Clinical manifestations that are often mistaken for posterior circulation ischemia
The dense structure of the brainstem and the non-one-to-one correspondence between vascular innervation and neural structure determine that most of the PCI presents multiple overlapping clinical manifestations, and rarely presents only a single symptom or sign. For example, in NEMC-PCR, less than 1% of patients present with a single symptom or sign. Single signs or symptoms, such as dizziness, vertigo, lightheadedness, headache, syncope, fall episodes and transient loss of consciousness, are mostly caused by systemic diseases, circulatory diseases, periventricular diseases and psychiatric disorders, and rarely by PCI.
In the NEMC-PCR, none of the patients presented with a simple fall attack without other manifestations; therefore, a simple fall attack is not a common manifestation of PCI.
3. Evaluation and diagnosis of posterior circulation ischemia
A detailed history, physical examination and neurological examination are the basis for diagnosis. Take a particularly careful history, especially the onset, form, duration, concomitant symptoms, evolution and possible precipitating factors; pay attention to various possible vascular risk factors; when neurological examination, pay special attention to the examination of cerebral nerves (vision, eye movements, facial sensation, hearing, vestibular function) and ataxia. Dix-Hallpike examinations should always be performed in those with dizziness/vertigo as the main complaint.
Neuroimaging should be performed in all patients suspected of PCI, mainly when MRI is performed. DWI-MRI is most diagnostic for acute lesions. CT cranial examination is susceptible to bone artifacts. It has little diagnostic value and is only applicable to exclude blood and patients who cannot undergo MRI examination.
Various vascular examinations should be actively carried out, such as digital subtraction angiography (DSA), CT angiography (CTA), MRI angiography (MRA) and vascular Doppler ultrasonography, all of which can help to detect and clarify large intracranial and extracranial vascular lesions. Each test has its own characteristics, and there is a lack of correlation studies between different tests. Transcranial Doppler ultrasonography (TCD), which is widely used in China, can detect stenosis or occlusion of the intracranial segment of the vertebral artery and the proximal segment of the basilar artery, but it cannot be a diagnostic basis for PCI.
Electrocardiography, cardiac ultrasound and rhythm testing are important tests to detect the source of cardiac or aortic embolism, especially important for unexplained, non-hypertensive PCI.
Imaging tests related to the cervical spine are not the preferred or important tests for the diagnosis of PCI and are mainly used for differential diagnosis.
IV. Treatment of posterior circulation ischemia
1. Acute treatment of posterior circulation ischemia
There is still a lack of results of large randomized controlled studies specifically for PCI, so the acute treatment of PCI should be basically equivalent to the treatment of anterior circulation ischemic stroke. An organized treatment model for stroke units should be actively pursued. Intravenous rt-PA thrombolysis can be performed in appropriate patients with 3 hours of onset. Arterial arterial thrombolysis is feasible where available, and the treatment time window can be relaxed appropriately. For all unsuitable patients with no contraindications to thrombolytic therapy, aspirin 100-300 mg/d should be administered. Other treatment measures can be referred to the relevant treatment guidelines at home and abroad.
2. Prevention of posterior circulation ischemia
The control of various vascular risk factors should refer to the relevant domestic and international prevention and treatment guidelines. In view of the fact that about 40% of posterior circulation ischemic diseases are due to embolism, it is recommended to actively carry out etiological examination. Those with a clear diagnosis should be treated with antithrombotic therapy.
The use of antiplatelet agents (aspirin, clopidogrel, etc.) alone or in combination has a preventive effect. The efficacy of treatments such as angioplasty, stent placement, and intracranial and extracranial vascular bypass should be explored. Unless the relationship between cervical spine osteophytes and PCI is clear, cervical spine surgery should not be performed just for the treatment of PCI.
3. Education on posterior circulation ischemia
Medical education on PCI should be actively carried out, especially the continuing re-education of physicians to update the concept, update the concept, update the knowledge, and stop using the concept of VBI.
The missionary education should be strengthened to correctly grasp the early manifestations of PCI to achieve early detection and early diagnosis.
Education should be strengthened to correctly understand the risk factors of PCI and to establish a scientific view of prevention.
V. Clinical research on posterior circulation ischemia
Linchuan research in the field of PCI in China should be actively promoted, and the establishment of a national or regional database of the registration system should be actively promoted.
Diagnostic criteria and preventive and curative measures for PCI should be standardized
Emphasis should be placed on the identification and intervention of vascular risk factors in patients and on the detection of vascular lesions.
VI. Several important understandings about posterior circulation ischemia
1, PCI includes TIA (i.e., classical VBI) and cerebral infarction.
2, The main cause of PCI is the same as anterior circulation ischemia, and cervical spondylosis is not the main cause of PCI.
3, Dizziness/vertigo is a common manifestation of PCI, mostly accompanied by other manifestations, and simple dizziness/vertigo is rarely a manifestation of PCI.
4, The main etiology of dizziness/vertigo after neck turn or position change is not PCI.
5, Diagnostic tests, treatment and prevention of PCI should be consistent with anterior circulation ischemia.