Arteriovenous malformation (AVM) is the most common type of malformation caused by abnormal cerebrovascular development, accounting for more than 90% of cerebrovascular malformations. The disease can occur in any part of the brain, and the distribution of lesions on the left and right side is basically equal. 90% of the lesions are located on the cerebellar curtain, and most of them are distributed in the cerebral cortex, accounting for about 70% of the lesions on the curtain. AVMs located in the longitudinal fissure of the brain, i.e., the medial aspect of the frontal, parietal and occipital lobes, are not uncommon, accounting for about 15% of the supratentorial lesions, while AVMs in the lateral fissure area are about 8%. AVMs involving deep structures, such as the thalamus in the striatum, account for about 1%, and those in the corpus callosum and other midline structures account for about 6%.
AVM in the subiculum, accounting for less than 10%, can be seen in the cerebellar hemispheres, cerebellar earth, cerebellar pontocerebellar horn and brainstem. Patients are more male than female, about 2:1, and the peak age of onset is 20-39 years old, with an average of 25 years old. According to statistics, 20% of cases develop before the age of 20, 69% before the age of 40, 81% before the age of 50, 95% before the age of 60, and less than 5% develop again beyond the age of 60.
Clinical presentation
Small arteriovenous malformations may not have any symptoms or signs, while the majority of arteriovenous malformations may have certain clinical manifestations, the common symptoms and signs are.
(1) Bleeding: The incidence is 20% to 88%, and it is mostly the first symptom. The smaller the arteriovenous malformation, the more likely it is to bleed. It usually occurs in young people. The onset is sudden and often occurs during physical activity or emotional stress. The headache is severe, accompanied by vomiting; the consciousness can be lucid, or there can be varying degrees of consciousness, or even coma; there can be symptoms of meningeal irritation such as cervical ankylosis, and there can be signs of increased intracranial pressure or neurological impairment such as hemiparesis and hemianesthesia.
If the AVM is a superficial cerebral vessel rupture, it can cause subarachnoid hemorrhage (SAH); if the rupture is a deeper vessel, it causes intracerebral hematoma; AVM rupture adjacent to the ventricle or intracerebroventricular is often an intracerebral hematoma with intraventricular hemorrhage or intraventricular hemorrhage only; AVM hemorrhage is mostly seen in the rupture of blood vessels in the vascular mass of the brain parenchyma, which has more chances to cause intracerebral hematoma. Therefore, it is usually not as aggressive as intracranial aneurysm hemorrhage.
AVM hemorrhage is usually located in the arterial ring at the base of the brain, and when it ruptures, blood fills the subarachnoid space at the base of the skull, causing severe cerebral artery spasm. 80% to 90% of patients with the first hemorrhage from AVM survive, whereas the survival rate for the first hemorrhage from aneurysm is only 50% to 60%. AVM hemorrhage can be recurrent, up to 10 times. As the number of bleeds increases, the signs and symptoms worsen and the condition deteriorates.
According to the literature, unruptured AVMs will have a bleeding rate of 2% to 4% per year, while AVMs that have ruptured and bled have a risk of rebleeding of about 6% in the first year and 2% to 4% per year from the second year onward, the same as unruptured AVMs. The annual mortality rate secondary to bleeding is 1%, the total mortality rate is 10%-15%, and the permanent disability rate is 2%-3% per year, of which 20%-30% is due to bleeding. This shows that AVM without bleeding and AVM with bleeding have potential or real danger to the health and life of patients, and both should be given high attention.
(2) Convulsions: About half of the patients have seizures that manifest as grand mal or focal seizures. The onset of convulsions is most frequent in AVMs of the frontal, parietal and temporal lobes, especially in patients with large, massive blood-stealing AVMs. Seizures may be the first symptom or may occur in the presence of hemorrhage or associated hydrocephalus. The incidence is related to the location and size of the arteriovenous malformation. The incidence of epilepsy in frontoparietal arteriovenous malformation is 86%, frontal lobe is 85%, parietal lobe is 58%, temporal lobe is 56%, and occipital lobe is 55%, the larger the arteriovenous malformation, the higher the incidence of epilepsy in large arteriovenous malformation with severe “brain theft”.
(3) Headache: more than half of the patients have a history of long-term headache, similar to migraine, confined to one side, which can be relieved by itself, generally manifested as paroxysmal atypical migraine, which may be related to cerebral vasodilation. The headache is more intense than usual during bleeding, and is often accompanied by vomiting.
(4) Progressive neurological dysfunction: The incidence is about 40%, mainly motor or sensory dysfunction. It often occurs in larger AVMs and ischemic attacks caused by massive cerebral blood theft, with mild hemiparesis or limb numbness. Initially transient, the paralysis may worsen and become permanent as the number of episodes increases. In addition, multiple intracerebral hemorrhages can cause increased neurological impairment. In brain tissue with long-term ischemia due to cerebral blood theft, with ageing, extensive sclerosis or thrombosis of cerebral arteries, the progression of cerebral atrophy is faster than normal, and the progressive development of neurological dysfunction is also faster and more severe.
(5) Others: Huge AVMs, especially those involving bilateral frontal lobes, may be associated with mental retardation, and epilepsy and antiepileptic drugs may also affect mental development or contribute to the development of mental retardation. In larger AVMs involving extracranial or dura mater, the patient may feel an intracranial murmur. In subepicranial AVMs, there are fewer symptoms other than SAH, and they are not easily detected.
Diagnostic examination
1.History: Young people with a history of spontaneous subarachnoid hemorrhage or intracerebral hemorrhage, usually with headache, seizures and weakness of one limb, should be more suspicious of the disease, which often has a sudden onset and a causative factor.
2.Physical examination: Those with hemorrhage should be examined for signs of meningeal irritation, intracranial murmurs and signs of neurological deficits due to blood theft.
3.Cranial CT: local mixed density area can be seen, irregular enhancement area can be seen after enhancement, and tortuous dilated vessels can be seen, secondary changes such as hematoma and local calcification of brain atrophy can also be found.
5.Cranial MRI or MRA: the lesion area can be seen as a signal-free tortuous group of vascular shadow, and MRA can be seen as blood supply artery, malformed vascular group and drainage vein.
6.Transcranial ultrasonography (TCD): increased blood flow velocity and decreased pulsatility index of large arteries in the blood supply area.
7.Selective total cerebral angiography (DSA): the gold standard for diagnosing AVM, which can understand the location of AVM, blood supply arteries, size of malformed vascular masses and draining veins, and whether there are aneurysms, venous aneurysms, arteriovenous fistulas and cerebral blood theft. If necessary, external carotid arteriogram can be done to find out whether there is any involvement of external carotid artery in blood supply.
Treatment
The goal of treatment for cerebral arteriovenous malformation is to prevent bleeding, reduce or correct “cerebral blood theft”, improve blood supply to brain tissue, relieve neurological dysfunction, control epilepsy, and improve the patient’s life. Current treatment methods include conservative treatment, microsurgical resection, endovascular intervention and stereotactic radiation therapy.
Conservative treatment: For those who are older, have only epileptic symptoms or are located in important functional areas of the brain and deep brain lesions or have extensive lesions that are not suitable for surgery, conservative treatment should be used. The main purpose of conservative treatment is to prevent or stop bleeding and rebleeding, control epilepsy, and relieve symptoms.
Microsurgical resection: The application of microsurgical techniques has greatly improved the surgical total resection rate of cerebral AVM. So far, surgical resection is still one of the best methods to completely treat this disease.
3.Endovascular interventional embolization: Endovascular treatment started in the 1960s and is mainly used for deep AVM that is difficult to be treated surgically, so that the lesion can be reduced or completely occluded to facilitate surgery or radiotherapy. However, as a means of treating AVM alone, endovascular treatment still has great limitations, and only a few cases with a small number of blood supply arteries and simple structures can be cured by simple embolization therapy. The cure rate by embolization alone is about 10%-15%, and another 50% of lesions can be reduced to the extent that they can be treated with radiotherapy or surgery. Therefore, embolization is often used as an adjunct to surgery or radiation therapy. Super-selective catheterization technique can clearly show the blood supply artery of the lesion and deliver various embolization materials to the lesion through the catheter. At present, the commonly used embolization materials include permanent balloon, micro-spring coil, necrotizing drugs, various micro-gel and liquid embolization materials, etc.
4, stereotactic radiation therapy: radiation therapy is the therapy carried out in the past 20 years, important γ knife, χ knife, proton beam, linear gas pedal, etc.. It is the use of contemporary advanced stereotactic and computer systems to intracranial targets, using a high dose of irradiation, radiation from multiple directions, multiple angles to accurately gather the target, causing radiobiological response, so as to treat the disease method.
The occlusion rate after radiotherapy for AVM increases year by year, and the occlusion rates in the 2nd, 3rd and 4th years after radiotherapy are 32%, 50% and 80%, respectively. However, radiotherapy is not effective for lesions >3 cm and has a high complication rate; therefore, it is currently used mainly for AVMs with diameters <3 cm, deep and aggressive locations, lesions located in major functional areas, not easily operable, or difficult to treat endovascularly and for the complementary treatment of residual lesions after craniotomy and endovascular embolization. Radiation therapy is easily accepted by patients because it does not require craniotomy and has a short hospital stay. However, less than 25% of all brain AVMs are fully suitable for radiation therapy.
5.Comprehensive treatment: Microsurgery, intravascular interventional embolization and stereotactic radiosurgery have been widely used in the treatment of cerebral AVM, but for large, giant AVM or lesions located in important structures or deep brain, it is difficult to achieve ideal efficacy with a single treatment method. In recent years, we have significantly improved the cure rate of AVMs and minimized the disability and mortality rates through the combined application of two or three treatments.
Small (<3 cm in diameter) and superficial AVMs are surgically resected, and small (<3 cm in diameter) and deep lesions are treated with radiosurgery. For AVM >3cm in diameter, endovascular embolization should be performed first, and if the AVM disappears completely, no further treatment is needed, but follow-up is required; if the diameter is still >3cm, lesions with high surgical risk are temporarily treated conservatively, and radiotherapy is not advocated; lesions with reduced diameter and superficial <3cm in diameter can be surgically resected, and deep ones are treated radiosurgically.
(1) Interventional embolization plus surgical resection: the combined application of these two methods is the most widely carried out at present. Preoperative embolization can reduce the volume of AVM, blood flow and intraoperative bleeding, especially the obstruction of deep blood supply artery is beneficial to the separation of vascular mass and total resection of malformation. Preoperative fractionated intravascular embolization is of greater significance in preventing intraoperative and postoperative cerebral hyperperfusion phenomena. It is generally believed that surgery is most appropriate 1 to 2 weeks after embolization, while revascularization occurs with NBCA embolization, which is more common after 3 months, so surgery can be delayed appropriately. In conclusion, endovascular interventional embolization has been an important adjunct before surgical resection of AVM.
(2) Interventional intravascular embolization plus stereotactic radiation therapy: The application of stereotactic radiosurgery, γ-knife and χ-knife for the treatment of cerebral AVM has the advantages of non-invasive, small risk and short hospital stay, but the efficacy of single radiation therapy is inferior to the combined treatment of both. Intravascular embolization before radiotherapy can reduce the size of AVM, decrease the radiation dose and reduce the radiation response of surrounding brain tissue, which can improve the cure rate. Endovascular embolization can also occlude AVM complicated by aneurysm and associated large arteriovenous fistula, reducing the risk of rebleeding during radiotherapy observation. However, embolization before radiotherapy can make the residual AVM mass more irregular in shape, which makes it difficult to accurately estimate the target volume of AVM and calculate radiation dose.
(3) Stereotactic radiotherapy plus microsurgical resection: large cerebral AVM can also be treated with stereotactic radiotherapy as an adjunct before surgical resection. After radiotherapy, thrombosis within the AVM mass is formed, the volume is reduced, the number of vessels is decreased, and intraoperative bleeding is low. Converting large AVM into a lesion with low complications facilitates surgical operation and improves the success rate of surgery. Surgery, in turn, removes large AVMs that cannot be occluded by radiotherapy, improving the cure rate.