Arteriovenous short circuit

Introduction The cause of epilepsy in patients with arteriovenous malformation is: arteriovenous short circuit makes the brain ischemic, adjacent to the glia-like changes of the brain tissue, and the igniting effect of the temporal and arteriovenous malformations. Cerebral arteriovenous malformation is a congenital disorder that is formed by the cerebral angiogenesis during embryonic development. The underlying cause of the disease is the lack of capillary structure between the arteries and veins in the AVM lesion. The arterial blood directly flows into the vein, and the blood flow resistance is suddenly reduced, resulting in a decrease in regional cerebral arterial pressure and an increase in cerebral venous pressure, resulting in a series of hemodynamics. Disorders and pathophysiological processes.

Cause

(1) Causes of the disease

Cerebral arteriovenous malformation is a congenital disorder that is formed by the cerebral angiogenesis during embryonic development. It is generally believed to occur at the 45th to 60th day of the embryo. At the 4th week of the embryo, the primordial vascular network begins to form, and the original blood circulation appears in the original brain. The original blood vessels then differentiate into arteries, veins, and capillaries. In the early embryonic period, the original arteries and veins communicate with each other. Later, due to local capillary dysplasia, the arteries and veins are still left in direct communication. Because there is no resistance to normal capillaries, blood flows directly from the artery into the vein, causing the vein to expand due to increased pressure. The artery is gradually thickened due to more blood supply, and the formation and expansion of the collateral vessels form distortion, tangles, and thickness. The abnormal vascular mass, the weakened blood vessel wall expands into a saclike shape, and there is no capillary between the internal cerebral artery and the vein, which directly communicates to form a number of sacral tracts. The blood flows from the blood supply artery into the malformed vascular group, passes through the sacral tract into the vein, and then converges to 1 to several drainage veins, then leaves the vascular mass and flows to the sinus. Due to the lack of capillary structure, a series of changes in cerebral hemodynamics occur, and corresponding clinical signs and symptoms appear.

(two) pathogenesis

AVM often begins with symptoms caused by intracranial hemorrhage and brain stealing. The underlying cause of the disease is the lack of capillary structure between the arteries and veins in the AVM lesion. The arterial blood directly flows into the vein, and the blood flow resistance is suddenly reduced, resulting in a decrease in regional cerebral arterial pressure and an increase in cerebral venous pressure, resulting in a series of hemodynamics. Disorders and pathophysiological processes.

1. Bleeding: a variety of factors can cause intracranial hemorrhage:

(1) The blood of a large flow distorts the arterial expansion of the abnormal wall structure, and the blood vessel wall is further damaged and destroyed, and the local rupture is bleeding once the blood flow pressure cannot be withstood.

(2) AVM-related aneurysm rupture and bleeding, with aneurysm lesion bleeding rate of 90% to 100%.

(3) A large amount of blood flow impinges on the drainage vein of the malformed vascular mass, and the thinner vein of the wall is locally expanded into a saclike or tumor-like shape, which is prone to rupture and bleeding.

(4) Because a large amount of blood passes through the arteriovenous fistula in the AVM, the artery is rapidly injected into the vein, and the local cerebral arterial pressure drops, resulting in the normal perfusion of the brain tissue around the lesion. The arterial blood flows to the AVM area, and the brain steals blood. "phenomenon. Long-term ischemia, the small arteries in the surrounding area are in an expanded state, and the wall structure changes accordingly. In some cases, such as a sudden increase in systemic blood pressure, this dilated blood vessel may also have a bleeding rupture.

The size of the AVM is related to the risk of bleeding. It is generally believed that the location of the small AVM also has a certain relationship with the bleeding tendency. The lesions in deep lesions such as the ventricles, ventricles, basal ganglia, thalamus, and insula are higher than those in the hemisphere AVM, up to 1.5 times, especially in the ventricles or ventricles. The reason may be that the deep lesions are generally small, the blood supply artery is short, the caliber is small, the arterial pressure is high, and the AVM is easily broken. At the same time, the drainage vein of the deep AVM is often a deep vein. There are many opportunities for stenosis in deep veins, which may lead to venous hypertension, which may cause rupture of veins or AVM masses, especially those with deep venous drainage. AVM located in the ventricles or ventricles, because of the lack of support around the brain tissue, is also prone to bleeding, often intraventricular hemorrhage.

2. Brain stealing blood: The range of cerebral ischemia caused by stealing blood is larger than the range of deformed vascular mass, and the resulting symptoms and signs are also more extensive than the corresponding functional changes in the lesion area. The severity of stealing blood is related to the size of the AVM. The larger the malformed vascular mass, the greater the amount of blood stealing and the greater the degree of cerebral ischemia. Small AVM steals small amounts of blood, cerebral ischemia is light, and even does not cause ischemia, there is no clinical symptoms. Severe ischemia can cause epilepsy or transient ischemic attack or progressive neurological deficit. Such as somatosensory or hemiplegia.

3. Brain hyperperfusion: a large amount of brain stealing blood causes the blood vessels in the adjacent brain tissue to expand, so as to obtain more blood flow to supply the brain tissue, so that the long-expanded arterial wall gradually weakens, the wall becomes thin, and the blood vessels The auto-tuning function drops, the upper threshold is lowered, and even the state. Once the cerebral perfusion pressure rises above the upper limit of the cerebral vascular autoregulation threshold, the arteries with autoregulatory dysfunction not only do not contract but become acutely dilated, and cerebral blood flow increases linearly with perfusion pressure, ie, brain hyperperfusion occurs. As the local venous pressure rises, the venous blood flow in the surrounding brain tissue is blocked and a series of phenomena such as brain swelling, cerebral edema, increased intracranial pressure, and extensive small blood vessel rupture and bleeding occur suddenly. Especially in the case of large-type high-flow AVM (maximum diameter > 6cm), it is very easy to occur. According to reports, the incidence of brain hyperperfusion is 1% to 3% after large and medium-sized AVM, and 12% to 21% for giant AVM. The disability and mortality rate is as high as 54%. This phenomenon can also occur in the intravascular interventional therapy of AVM and is the most serious risk that may occur during AVM treatment.

AI-Rodhan (1993) presented another explanation for cerebral edema and residual venous bleeding after AVM, which is considered to be due to stump stenosis, thrombosis or embolism of the drainage vein after AVM resection, and venous return obstruction of surrounding brain tissue. To. Venous occlusive congestion

4. Increased intracranial pressure: AVM itself has no mass effect, but many patients show signs of increased intracranial pressure. On the one hand, arterial blood directly enters the vein in AVM, resulting in increased cerebral venous pressure, obstructing venous return of surrounding brain tissue, causing long-term congestion and edema of the brain tissue, and increased intracranial pressure; on the other hand, AVM patients are often accompanied by hydrocephalus The cause of hydrocephalus may be the drainage of deep veins in deep brain lesions, enlargement into spherical venous tumors or intraventricular hemorrhage to block cerebrospinal fluid circulation pathway, or cerebral venous hypertension affecting the absorption or bleeding of cerebrospinal fluid leading to partial subarachnoid space. Blockage of occlusion or arachnoid granules reduces cerebrospinal fluid absorption, which can cause obstructive or traffic hydrocephalus. On the other hand, intracerebral hematoma caused by hemorrhage and cerebral edema around the hematoma are also important causes of increased intracranial pressure.

pathology

Brain AVM can occur anywhere in the brain. 80% to 90% are located on the screen, the top of the cerebral hemisphere, especially the cerebral artery supply area, the outer surface of the temporal lobe is the most common, followed by the frontal cerebral artery supply area and the inner side of the brain, other parts of the occipital lobe The basal ganglia, thalamus, cerebellum, brainstem, corpus callosum, and ventricles are less common. Most of the supratentorial lesions are supplied by the middle cerebral artery or the anterior cerebral artery. The under-AVM is supplied by the upper cerebellar artery or the anterior or posterior inferior cerebellum. There is usually only one blood supply artery, and there are two or three blood supply veins. The reflux vein is mostly one, and occasionally two. The blood supply artery and the reflux vein are much thicker, which is 1 to several times larger than normal movement and vein. According to statistics, the middle cerebral artery of the blood supply artery accounts for 60%, the branch of the anterior cerebral artery accounts for 20%, and the combined supply of the middle cerebral artery and the anterior cerebral artery accounts for 10%. The choroidal artery and the branch of the vertebral-basal artery are rare, and the branch of the posterior cerebellum 2% or so. The reflux vein is divided into the sagittal sinus, the great cerebral vein, the parasagittal venous plexus, the sinus sinus, the transverse sinus, the straight sinus, and the superior sinus. Since the embryonic cerebral blood vessels first develop in the pia mater, the arteriovenous malformation is often located on the surface of the brain, and may also be located in the sulci or in the deep brain tissue. The typical cerebral arteriovenous malformation is conical, the cone bottom is on the surface of the brain, the cone tip is toward the ventricle, deep into the ventricle wall, and some extend into the ventricle and connect with the choroid plexus of the lateral ventricle. A few arteriovenous malformations are spherical, elongated or irregular, with irregular edges.

The size of the deformed vascular mass varies, and the disparity is very large. The small one can only be seen under careful examination. The cerebral angiography can not be displayed. It can only be found in the postoperative pathological examination, and some even the routine pathological examination is difficult to find. Large lesions can reach more than 8~10cm in diameter, which can affect more than two lobes, accounting for 1/3~1/2 of the cerebral hemisphere or widely distributed in one side or bilateral brain or cerebellar hemisphere. The deformed blood vessels in the lesion are entangled into a mass, and the diameter of the blood vessel is different, sometimes small, sometimes extremely dilated, twisted, or even the stroke of the curve is spiral or rounded. Different sizes of arteriovenous capillaries are intertwined. In the meantime, brain tissue can be mixed.

Under the microscope, the characteristics of arteriovenous malformation are composed of arteries and veins of different sizes and different directions. The lumen is dilated, the intima hyperplasia of the wall arteries is hypertrophic, and some of them are protruding into the lumen. The inner elastic layer is extremely weak or even missing. The middle layer is not thick. The atherosclerotic plaque and the mechanized blood clot may be attached to the arterial wall, and some of the lumens are partially blocked, and some are aneurysmal-like expansion. The veins often have fibrosis or glassy changes and thickening, and occasionally calcification. But arteries and veins are often difficult to distinguish. There is a hemosiderin deposition around the malformed blood vessels, and the brain tissue is variably necrotic between the blood vessels.

Because there are no capillaries between arteries and veins of arteriovenous malformation, blood flows directly into the vein through the artery, lacking vascular resistance, local blood flow increases, and blood circulation speed increases. This blood flow changes, causing a lot of "brain stealing blood" phenomenon. As the arterial blood directly flows into the vein, the intra-arterial pressure is greatly reduced, and the intra-arterial pressure of the blood supply is reduced from 4% of the normal arterial pressure to 45.1% to 61.8%, and the venous pressure rises, causing venous return within the lesion range. Obstructed and caused venous anger and distortion. The decrease in arterial pressure and the phenomenon of "cerebral ischemia" cause the arterial autoregulation to be lost, causing the arteries to dilate to compensate for the lack of blood supply to the distal brain. The impact of blood flow in the arteries causes the formation of aneurysms, and the long-term anger and distortion of the veins, forming a large venous tumor. These are all factors that cause rupture of arteriovenous malformations. The blood flow in the vein is accelerated, the blood vessel wall is thickened, and the vein contains arterial blood. The vein is bright red during surgery, which is difficult to distinguish from the artery. This is called arterialization of the vein. With the expansion of arteries and veins, the amount of stealing blood is increasing, and the range of lesions is gradually expanding.

an examination

Related inspection

Brain CT examination of cerebral angiography

History

Young people have a history of spontaneous subarachnoid hemorrhage or intracerebral hemorrhage. When there are headaches, seizures, and weakness of one limb, the disease should be suspected. It is often a sudden onset and has incentives.

2. Physical examination

Bleeding should be checked for signs of meningeal irritation, with or without intracranial murmurs and signs of neurological deficits due to stealing blood.

3. Lumbar puncture

Measure intracranial pressure; understand whether cerebrospinal fluid is bloody and count red blood cells.

4. Head CT

The local mixed density zone can be seen. After the enhancement, the irregular enhancement zone can be seen, and the dilated vasodilation can be seen. The secondary changes such as hematoma and local atrophy of brain atrophy can also be found.

5. Skull MRI or MRA

It can be seen that there is no signal distortion in the lesion area, and MRA can be seen in the blood supply artery, malformed vascular group and drainage vein.

6. Transcranial ultrasound examination

The blood flow velocity of the aorta in the blood supply area increased, and the pulsation index decreased.

7. Selective whole brain angiography

You can understand the location of cerebral arteriovenous malformation, the blood supply artery, the size of the deformed vascular mass and the drainage vein to understand whether it is accompanied by aneurysm, venous tumor, arteriovenous fistula and brain stealing. If necessary, add external carotid artery angiography to see if any external carotid artery participates in blood supply.

Differential diagnosis

Cerebral arteriovenous malformation needs to be differentiated from other cerebrovascular malformations, moyamoya disease, primary epilepsy, intracranial aneurysms.

Cerebral cavernous hemangioma

It is also one of the common causes of repeated subarachnoid hemorrhage in young people. Patients often have no obvious clinical symptoms before bleeding. Cerebral angiography is often negative or pathological vascular mass, but no thickened blood supply artery or dilated draining vein is seen. CT plain scan can be expressed as a honeycomb low-density area, and the lesions are slightly enhanced after enhancement. But in the end, surgical resection and pathological examination are needed to distinguish from arteriovenous malformations.

2. Primary epilepsy

Cerebral arteriovenous malformations often occur epilepsy, and arteriovenous malformations of thrombosis are more likely to have intractable seizures. At this time, cerebral angiography is often not developed, so it is often misdiagnosed as epilepsy. However, primary epilepsy is common in children. For young people with epilepsy and subarachnoid hemorrhage or epilepsy after subarachnoid hemorrhage, arteriovenous malformation should be considered. In addition, in addition to epilepsy in patients with arteriovenous malformations, there are other signs and symptoms, such as headache, progressive hemiparesis, ataxia, visual impairment. CT scans help to differentiate the diagnosis.

3. Cerebral aneurysms

It is the most common cause of subarachnoid hemorrhage. The age of onset is about 20 years older than that of cerebral arteriovenous malformation, that is, it is more common in 40 to 50 years old, and more common in women. Patients often have a history of hypertension and arteriosclerosis. Seizures are rare and oculomotor nerve palsy is more common. According to cerebral angiography is not difficult to identify.

4. Venous vascular malformations

Less common, sometimes ruptured bleeding caused by subarachnoid hemorrhage, and increased intracranial pressure. There is no obvious abnormal vascular display in cerebral angiography. Sometimes there is only one large vein with some drainage branches. The CT scan showed a low-density area, and the enhanced scan showed enhanced lesions.

5. Moyamoya disease

The disease is more common in children and young adults, children with cerebral ischemia as the main manifestation, and adults with intracranial hemorrhage as the main symptom. Clear differential diagnosis depends on cerebral angiography. The cerebral angiography of moyamoya disease is characterized by internal carotid artery stenosis or occlusion, and there are cloud-like and slender abnormal vascular clusters at the base of the brain.

6. Blood-rich brain tumors

Cerebral arteriovenous malformation still needs to be differentiated from blood-rich gliomas, metastases, meningioma, and hemangioblastoma. Because these tumors are rich in blood supply, cerebral angiography shows traffic between arteries and veins and early veins, which is confused with cerebral arteriovenous malformations. However, according to the age of onset, medical history, course of disease, clinical symptoms and signs, etc., CT scan can help to identify the differential diagnosis.

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