I. Overview
Cerebral arteriovenous malformations are the most common type of cerebrovascular malformation and are located in the superficial or deep parts of the brain. The malformed vessels are composed of arteries and veins, and some contain aneurysms and venous aneurysms. Brain arteriovenous malformations have both blood supplying arteries and draining veins, and their sizes and shapes are diverse.
Intracranial and intraspinal vascular malformations are congenital abnormalities of central nervous system vascular development and can be divided into five types: (1) arteriovenous malformations (AVM); (2) cavernous hematoma; (3) capillary dilatation; (4) venous malformations; and (5) varicose veins. Among the above five types of vascular malformations, arteriovenous malformations are the most common, accounting for 62.7% of intracranial supratentorial vascular malformations. It accounts for 42.7% of the subcurtain vascular malformations.
Pathophysiology
The intracranial arteriovenous malformation (AVM) is a pathological brain vessel with congenital abnormal development. Its volume can grow with human development. The AVMs are formed by one or several curved and dilated arteries for blood supply and venous drainage, with a small diameter of less than 1 cm and a large diameter of up to 10 cm. The AVMs contain brain tissue, and the surrounding brain tissue is atrophied due to solid ischemia, with gliosis and sometimes with old hemorrhage. The arachnoid membrane on the surface of the malformed vessels is white and thick. The intracranial AVM can be located anywhere in the cerebral hemisphere, with a wedge-shaped tip pointing to the lateral ventricles.
III. Clinical manifestations
1.Hemorrhage The rupture of the malformed vessel can lead to intracerebral, intraventricular and subarachnoid control hemorrhage, resulting in impaired consciousness, headache and vomiting. Symptoms such as headache and vomiting. However, the clinical symptoms of small hemorrhage are not obvious. Most of the bleeding occurs in the brain, and 1/3 causes subarachnoid hemorrhage, accounting for 9% of subarachnoid hemorrhage, depending on the intracranial aneurysm. Bleeding has been reported to be the first symptom in 30% to 65% of AVMs. The age of predilection for hemorrhage is 20-40 years. It is generally believed that single supply artery, small size, deep site. As well as posterior cranial fossa AVMs are prone to acute rupture and bleeding. The risk of AVM rupture increases during pregnancy in women. Recent studies have found that the annual bleeding rate of unruptured AVMs in all age groups is about 2%. The risk of AVM bleeding is higher in younger patients than in older patients, and the rate of rebleeding and post-bleeding mortality are lower in AVMs than in intracranial aneurysms. This is due to the fact that the source of hemorrhage is mostly a vein of pathological circulation with lower pressure than cerebral arterial pressure. In addition, hemorrhage is less likely to occur in the basal pool, and cerebral vasospasm secondary to hemorrhage is rare.
2, convulsions in adults 21%-67% with convulsions as the first symptom, more than half occur before 30 years old, mostly in frontal and temporal AVM. frontal AVM mostly occurs convulsions of grand mal seizures, the top is mainly limited seizures. AVM occurs convulsions related to cerebral ischemia, progressive gliosis around the lesion, and stimulation of the cerebral cortex by iron-containing hemoglobin after bleeding. 14%-22% of AVM with bleeding will Convulsions occur. Early convulsions can be controlled with medication, but eventually medication is ineffective and convulsions are difficult to control. As a result of long-term intractable seizures, the lack of oxygen to the brain tissue is aggravated, resulting in the patient’s mental retardation.
3. Headache Half of the AVM patients have a history of headache. The headache can be unilateral and localized, or full headache. Intermittent or migratory. The headache may be related to the dilatation of blood supply arteries, drainage veins and sinuses, and sometimes related to small amount of bleeding, hydrocephalus and increased intracranial pressure in AVM.
4, neurological deficits Among AVMs with unruptured hemorrhage, 4%-12% have acute or progressive neurological deficits. Intracerebral hemorrhage can cause acute neurological deficits. Due to the role of AVM blood theft or combined with hydrocephalus. Patients have progressive neurological deficits, manifesting as motor, sensory, visual field and speech dysfunction. Individual patients may have cranial murmur or trigeminal neuralgia.
5.Children with large venous malformation of the brain, also called large venous tumor of the brain, can lead to heart failure and hydrocephalus.
IV. Diagnosis
1.CT of the head After enhanced scanning AVM shows a mixed density area, and the midline structure of cerebral hemisphere is not displaced. In the acute bleeding period, CT can determine the site and extent of bleeding.
2.MRI of the head can show the high speed blood flow in the lesion as flow-void phenomenon, in addition, MRI can show the good relationship between the lesion and brain anatomy, which can provide the basis for choosing the surgical access for resection of AVM.
3.Cerebral angiography is the necessary means to confirm the diagnosis of this disease. Whole brain angiography and continuous film. It is possible to understand the size and scope of the malformed vascular mass, the blood supplying artery, the draining vein and the blood flow rate, and sometimes it is also possible to see the phenomenon of blood theft by the contralateral internal carotid artery or vertebrobasilar artery system.
4.Electroencephalography Slow waves or spikes can be seen in and around the lesioned area of the affected cerebral hemisphere. Intraoperative EEG monitoring of patients with convulsions and removal of the epileptic lesion can reduce postoperative convulsive seizures.
V. Treatment
1. Surgical resection is the most fundamental method for the treatment of intracranial AVM, which can not only eliminate rebleeding of the lesion, but also stop the phenomenon of blood theft from malformed vessels, thus improving cerebral blood flow. As long as the lesion is located in the surgically resectable area, craniotomy should be performed. With the application of microsurgical techniques, surgical resection of intracranial AVMs is satisfactory. In emergency patients with AVM bleeding and hematoma formation, cerebral angiography should be completed preoperatively if available to clarify the malformed vessels. If the patient has brain herniation and is not qualified for cerebral angiography, emergency craniotomy can be performed. First remove the hematoma to lower the cranial pressure. Rescuing life, and then removing the malformed vessels in the second stage of surgery. It is dangerous to remove the deformed blood vessel without angiography.
2.Interventional treatment, intravascular embolization is simple, less painful for patients, less trauma to brain tissue, short operation time, no damage to the normal perivascular vessels, can create favorable conditions for surgical resection, and the results of follow-up after treatment confirm the efficacy. Interventional treatment should be preferred for patients who are suitable for interventional treatment.
3.Surgical resection is not suitable for AVMs located in deep brain important functional areas such as brainstem and mesencephalon. If the AVM remaining after surgical resection is less than 3 cm in diameter, γ a knife or X a knife treatment can be considered to make the endothelium of the malformed vessels slowly proliferate and the vessel wall thicken. The thrombus is formed and occluded, but during the treatment period. There is still the possibility of bleeding. If γ- or X- knife treatment is preferred, caution should be exercised for lesions containing aneurysms or cystic dilatation of arteries. Because in the arterial structure, the elastic fibers in the wall are more vulnerable to radiation damage than the endothelial cells, and early rupture will aggravate the fragility of the aneurysm wall, which may rupture and bleed before the whole lesion heals and worsen the condition.
4.Interventional embolization-based combination therapy. That is, after embolization, surgical resection or γ-one knife or X-one knife treatment is chosen according to the actual situation of the lesion, which can gradually cure AVM without damaging the quality of life.