Cerebral arteriovenous vascular malformation is referred to as cerebral arteriovenous malformation (AVM). It is a congenital cerebrovascular disease. The main defect is the lack of capillaries between some of the arteries and veins of the brain, so that some of the cerebral arteries and cerebral veins are directly connected to form a cerebral arteriovenous fistula malformation, resulting in cerebral hemodynamic disorders, with recurrent intracranial hemorrhage, convulsions, transient ischemic attacks and progressive paralysis as the main clinical manifestations. It is the other common cause of spontaneous SAH after intracranial aneurysm. Its incidence is lower than that of intracranial aneurysm, only 1/7 to 1/4 of the latter, and compared with intracranial tumor, only 3% of it. It is two times more common in men than in women, with a peak age of 20-29 years and a mean age of 25 years. It is about 20 to 30 years earlier than intracranial aneurysm.
Etiology and pathology of cerebral arteriovenous malformation
[Pathogenesis].
The main pathophysiology of AVM is cerebral blood theft and loss of large amounts of cerebral arterial blood via AV fistula, resulting in a series of cerebral hemodynamic changes, summarized as follows.
1. the resistance to blood flow in the supplying arteries of AVM decreases and blood pressure drops, resulting in a reduced perfusion range and a relative ischemic state in the adjacent brain tissue, which can easily cause seizures. the larger the size of AVM, the greater the chance of seizures.
The smaller the AVM, the smaller the amount of stolen blood, the smaller the drop in arterial pressure, and the smaller the AVM, the weaker the walls of the smaller vessels than the large AVM, which cannot withstand the impact of high-pressure arterial blood and can easily rupture and bleed.
In order to obtain more collateral blood supply, the blood supplying arteries in the adjacent brain tissue are dilated, thus increasing the blood flow of AVM, which is a potential reason for the gradual increase of AVM.
4. The decrease of long-term arterial pressure leads to the decline of cerebral resistance vascular autoregulation function. Once the AVM is removed and the perfusion pressure returns to normal, the blood flow increases dramatically with the increase in perfusion pressure because the arteries cannot make immediate reactive contraction, resulting in the phenomenon of cerebral overperfusion, causing acute swelling, edema, diffuse hemorrhage and increased intracranial pressure in the brain.
5.The direct introduction of arterial blood into the vein increases the venous pressure, and the venous reflux of the adjacent brain tissue is resisted, causing depressed blood edema in the brain and possibly resulting in increased intracranial pressure
6.The small dilated veins are easy to rupture and bleed, causing SAH or intracerebral hemorrhage. In AVM, hemorrhage is not limited to AVM, but can sometimes occur in the surrounding brain tissue of AVM.
7.When a large amount of blood enters the vein, the emptying ability of cerebral vein cannot adapt for a while, causing the expansion, distortion and growth of the vein, even forming a huge venous bulb, if the venous bulb compresses or blocks the circulatory pathway of cerebrospinal fluid, it can cause obstructive hydrocephalus.
8. Repeated and repeated small amounts of SAH can cause extensive adhesions in the subarachnoid space, and the arachnoid granules are blocked by blood red blood cells, so that the balance of cerebrospinal fluid production and absorption is imbalanced, causing traffic hydrocephalus.
[Pathology
AVM is an arteriovenous fistula-type vascular malformation consisting of a mass of twisted cerebral arteries and cerebral veins, with no capillaries between the arteries and the static, but with a small amount of degenerated brain tissue. The size of the lesion varies from small, barely visible to the naked eye, to large, which can occupy the entire cerebral hemisphere. It has an irregular cone shape with the base of the cone facing the cerebral cortex and the tip of the cone pointing to the deeper part of the brain, mostly reaching the ventricular wall. One to multiple thickened blood supplying arteries enter it, draining the enlarged varices and directing bright red colored arterial blood into the intracranial venous sinuses. More than 90% of AVMs are located on the curtain. Superficial and deep ones each account for about half of the cases. The superficial ones are located in the subcortex, with the parietal lobe of the cerebral hemisphere having the greatest chance of occurrence, followed by the temporal lobe, frontal lobe, and occipital lobe in descending order. Those located deeper may be distributed in the base of the brain, basal ganglia, thalamus, corpus callosum, and ventricles. Less than 10% of AVMs are located in the subscripts, and are distributed throughout the cerebellar hemispheres, cerebellar earthworms, pontocerebellar horns, pontocerebellum, pontocerebellum, and the fourth ventricle.
Parkinson (1980) divided the lesions into five categories based on the observation of 100 cases of supratentorial AVMs: ① Multi-unit type: a vascular mass consisting of multiple arteries and veins, containing multiple AV fistulas. It accounts for about 82% of the total number of AVMs. ②One-unit type: There is only one blood supplying artery and one draining vein forming a separate AV fistula. It is mostly a small lesion, accounting for about 10% of cases. (iii) Linear type: one artery is directly connected to a vein or venous sinus. Most often seen in infants, such as large cerebral venous tumors, accounting for about 3% of cases. ④Compound type: intracranial and extracranial artery double blood supply, return vein also has intracranial and extracranial, accounting for about 3%. ⑤ Venous wall type: the extracranial artery directly communicates with the intracranial venous sinus, or communicates with the intracranial venous sinus via the scalp, skull, and dural branches of the artery, which is rare and accounts for about 2%. According to 65 cases of surgically complete resected AVM specimens observed after perfusion of plastic, the author believes that AVM can be divided into four categories: ① varicose type: arteries and veins are obviously varicose, twisted together with each other, containing multiple AV fistulas, accounting for 64.6%. ②Broom type: arteries are straighter, dendritic branches occur from arteries and enter veins directly, veins are also less varicose, accounting for 11%. Arteriovenous aneurysm type: both arteries and veins are thick and have multiple irregular balloon-like enlarged structures, accounting for 12.2%. ④Mixed type: It is a mixture of the above three types.
Histological examination showed that the lesion consisted of vessels of different sizes, with varying wall thicknesses and sections at different angles, but all were more mature and had normal vascular levels. The intima showed varying degrees of hyperplasia, some of which protruded into the lumen and almost blocked the ducts. Atherosclerotic plaques were seen scatteredly. Thrombus formation was seen in some of the lumens. There was connective tissue and a small amount of degenerated brain tissue in the interstitial space, but no capillaries were seen. Signs of hemorrhage were seen everywhere.
There are ischemic changes in the brain tissue surrounding the AVM with vasodilatation, white matter edema, and a pseudo-envelope formed by gliosis. Secondary changes caused by hemorrhage, such as lumen formation and iron-containing heme deposits, are seen sporadically. The cerebral artery contralateral to the lesion may also be thickened due to the provision of collateral branches to the diseased side, and aneurysm formation may occasionally be seen. Giant high-flow AVMs can enlarge the right heart and even cause right heart failure due to increased blood return, especially in infants and children.
Clinical manifestations of cerebral arteriovenous malformations
Only a few occult and smaller AVMs can be asymptomatic for a long time, and the vast majority of AVM patients will develop by a certain age. There are several types of morbidity.
(a) Stroke type is mostly seen in adolescents after 1 physical activity or mood swing, and can also have a sudden onset without any causative factors at all, with severe headache, vomiting, neck tonicity, positive Kernig’s sign, and in severe cases followed by impaired consciousness or coma, waking up with aphasia, hemiparesis, hemianesthesia, and hemianopsia.
(b) Epileptic type is mostly seen in larger AVM cases, with intermittent convulsive seizures, either partial or generalized, or starting with partial convulsions and later spreading to the whole body secondary to them. This type is seen in 20-40% of AVM cases. The long-term result of the convulsions may be mild paralysis with mild limb atrophy. The diagnosis of AVM can be established in patients with seizures followed by SAH seizures.
(iii) Transient ischemic type, also known as TIA, presents with recurrent transient limb paralysis or weakness, usually following physical activity or exercise, but of short duration and returning to normal quickly. The condition is very similar to ischemic stroke, but the patient is young and has no history of atherosclerosis or hypertension.
(d) The tumor type has a slow onset and progressive limb paralysis, mainly due to progressive cerebral ischemia or AVM with partial thrombosis.
In addition to the above-mentioned different types of onset, patients may also have the following symptoms.
1.Headache More than 60% of patients have a history of long-term headache, mostly confined to one side, similar to migraine, which may be related to the dilatation of cerebral arteries and meningeal arteries.
2. Progressive mental retardation is seen in huge AVM, where there is diffuse ischemia and developmental disorders in brain tissue due to the severity of cerebral blood theft. In some cases, due to frequent seizures, brain function is doubly inhibited by seizure discharges and antiepileptic drugs, resulting in mental retardation.
3. Intracranial murmurs are felt by patients themselves more than those who can be heard by others. The murmur is more obvious when the AVM is huge and located in a superficial area or involves the dura mater or extracranial tissues. Compression of the ipsilateral common carotid artery can make the murmur disappear.
4. Eye protrusion is a less common symptom of AVM. It can be seen in the anterior temporal lobe or when there is a large vein draining into the cavernous sinus, causing an increase in venous pressure in that sinus. However, there is no ocular pulsation.
Subscopic AVMs are more insidious and less symptomatic than supratentorial AVMs. Most are detected due to spontaneous SAH. A few are detected because of increased intracranial pressure, secondary optic nerve atrophy, visual impairment, and progressive ataxia.
Diagnosis and Differentiation of Cerebral Arteriovenous Malformation
In adolescents with spontaneous SAH or intracerebral hemorrhage, this disease should be considered as a possibility, and it is more likely if there are convulsions in the medical history.
(a) CT scan of the head without hemorrhage shows irregular hypodense areas, representing ischemia and degeneration of the brain around AVM, or brain lacunae formed by past hemorrhage. After contrast enhancement, the dense aberrant vascular mass and its thickened blood supply arteries and draining veins can be seen.
(b) Magnetic resonance imaging of cerebral AVM can be shown in magnetic resonance images without contrast. Because of the rich blood flow in AVM, it can be shown as high signal area in SR scan image if short TR is used. Associated thrombosis, large venous tumors, hemorrhagic foci, and peripheral edema can also be visualized. In IR and SE scans, low signal or even no signal area can be shown due to the “flow-void effect” of blood flow in AVM, so that the morphology of AVM can be fully displayed.
(C) The purpose of cerebral angiography is to see the details of AVM supply artery and drainage vein and side branch supply, so that the preoperative access and steps can be planned more reasonably. For AVM with high flow rate, bilateral angiography or whole brain angiography should be performed, which can help to see the whole picture of AVM. The use of subtraction angiography provides a clearer image and is more appropriate for lesions in the posterior cranial fossa and the base of the brain. Dynamic angiography (cineangiography) can show the filling procedure of AVM, which is helpful to identify the blood supplying arteries and draining veins of AVM, and can avoid cerebral overperfusion during surgery. The images of arterial digital subtraction angiography (IADSA) are comparable to those of normal cerebral arteriography. The images of bones and soft tissues have been removed and a purely vascular image is obtained, which is clearer, but the results may not be better than those of normal cerebral arteriography because smaller arteries cannot be shown.
In AVM cerebral arteriogram, a pile of irregular vascular masses can be seen, representing the main body of AVM, with one or more thick and deeply developed blood supplying arteries and one or more dilated and distorted early appearing draining veins. This is a characteristic feature of AVM arteriography. Unless there is a large hematoma present generally no obvious displacement or occupying effect of cerebral vessels can be seen, which can be differentiated from other intracranial lesions.
[Differential diagnosis
Stroke onset AVM needs to be differentiated from the following diseases.
(a) intracranial aneurysm
(b) cavernous vessels may bleed repeatedly without other characteristic signs and symptoms. CT scans may show fibrous tissue of varying density with calcified plaques in the lesion area. There may be slight enhancement after contrast injection, but the enlarged supply arteries and early appearing draining veins are not visible.
(c) Venous cerebrovascular malformation can cause SAH or intracerebral hemorrhage, as AVM, and is often accompanied by increased intracranial pressure. There is no malformed vascular mass or thickened supply artery on cerebral angiography, but only a large abnormal vein with multiple small veins converging.
(d) Patients with stroke are older and have a history of hypertensive atherosclerosis. CT scans and cerebral angiograms show intracerebral hematoma or cerebral infarct foci, but no malformed vascular masses.
(v) Other diseases that can cause SAH such as hematologic diseases, leukemia, intracranial inflammation, various arteritis, moyamoya disease, systemic lupus erythematosus, etc. Each disease should be ruled out by examination or laboratory tests according to the characteristics of each disease.
AVM with epileptic onset should be differentiated from epilepsy. Common idiopathic epilepsy rarely has objective neurological signs, no history of hemorrhage during the course of the disease, EEG shows epileptic waves, and CT and cerebral angiography are negative.
Tumor-onset AVM should be differentiated from various brain tumors with rich blood supply, the more important of which are.
1. Glioma with rich blood supply has a fast progression and may have symptoms of increased intracranial pressure at a relatively early stage; CT scan shows enhanced tumor tissue and cerebral angiography shows obvious vascular displacement, but the abnormal vascular mass is scattered and there are no thick supply arteries or early appearing veins.
2.Hemangioblastoma is found in cerebellar hemispheres and earthworms, with familial tendency, tends to form cysts, and shows hemoglobinemia; CT and cerebral angiogram both show vascular masses and supply arteries, but in addition, there may be displacement of cerebral vessels.
3.Angioblastoma meningioma has obvious symptoms of increased intracranial pressure, the morphology of tumor vascular mass is different from that of AVM, and the displacement of normal cerebral arteries is obvious.
4. Brain metastasis of metastatic cancer, especially lung cancer, breast cancer, kidney cancer, choriocarcinoma and melanoma, can often cause SAH, but the development of the disease process is fast and the patient has a history of primary cancer, so it is not difficult to find clues from the medical history. In addition, neurological dysfunction is obvious before hemorrhage and often accompanied by increased intracranial pressure, which can also help to differentiate, not necessarily relying on CT and cerebral angiography.
5. Jugular venous bullae often have a history of ear canal hemorrhage, intracranial vascular murmur, multiple cranial nerve damage, especially partial involvement of 6-12 cranial nerves, and obvious rock cone and skull base fracture damage, etc., which can help to differentiate. However, cerebral angiography is sometimes confusing because of the presence of obviously dilated blood supply arteries (usually the thick pharyngeal ascending artery and its branches) and the presence of obvious arteriovenous fistulas. AVM with cerebral ischemic onset needs to be differentiated from various diseases that can cause cerebral ischemia, such as carotid artery stenosis and occlusion, carotid artery entrapment aneurysm, various cerebral arteritis, moyamoya disease, cerebrovascular embolism and TIA. The difference can be made by cerebral angiography.