Arteriovenous malformations are congenital anomalies of cerebral vessels characterized by the formation of a local vascular conglomerate in which there are no capillary vessels, and the arteries pass directly into the veins. Arteriovenous malformations are manifested by persistent headaches, epileptic syndrome, intracranial bleeding with rupture of malformation vessels. Diagnosis is carried out using CT and MRI of the cerebral vessels. Surgical treatment: transcranial excision, radiosurgery, endovascular embolization or a combination of these techniques.
Q28.2 Arteriovenous malformation of cerebral vessels
Arteriovenous malformations (cerebral AVM) are altered areas of the cerebral vascular network, where instead of capillaries there are numerous branches of convoluted arteries and veins forming a single vascular conglomerate, or tangle. Arteriovenous malformations refer to vascular abnormalities of brain development. They occur in 2 people out of 100 thousand of the population. In most cases, they make their clinical debut in the period from 20 to 40 years, in some cases — in people over 50 years old. The arteries forming the AVM have thinned walls with an underdeveloped muscle layer. This causes the main danger of vascular malformations — the possibility of their rupture.
In the presence of disease, the risk of its rupture is estimated at about 2-4% per year. If the hemorrhage has already taken place, then the probability of its recurrence is 6-18%. Mortality in intracranial hemorrhage from AVM is observed in 10% of cases, and persistent disability is noted in half of patients. Due to the thinning of the arterial wall, a protrusion of the vessel – an aneurysm — may form on the AVM site. The mortality rate in case of rupture of a cerebral aneurysm is much higher than in case of AVM, and is about 50%. Since AVMs are dangerous intracranial hemorrhage at a young age with subsequent mortality or disability, their timely diagnosis and treatment are urgent problems of modern neurosurgery and neurology.
Arteriovenous malformations of the brain occur as a result of intrauterine local disorders of the formation of the cerebral vascular network. The causes of such disorders are various harmful factors affecting the fetus during the antenatal period: increased radioactive background, intrauterine infections, diseases of a pregnant woman (diabetes mellitus, chronic glomerulonephritis, bronchial asthma, etc.), intoxication, bad habits of a pregnant woman (drug addiction, smoking, alcoholism), taking medications during pregnancy that have a teratogenic effect.
Cerebral arteriovenous malformations can be located anywhere in the brain: both on its surface and in depth. There is no capillary network at the site of AVM localization, blood circulation occurs from the arteries to the veins directly, which causes increased pressure and vein dilation. At the same time, the discharge of blood bypassing the capillary network can lead to a deterioration in the blood supply to the cerebral tissues at the location, leading to chronic local ischemia of the brain.
According to their type, cerebral vascular malformations are classified into arteriovenous, arterial and venous. Arteriovenous malformations consist of an adductor artery, a draining vein, and a conglomerate of altered vessels located between them. There are fistulous AVM, racinous AVM and micromalformation. About 75% of cases are occupied by racinous AVMs. Isolated arterial or venous malformations, in which there is tortuosity, respectively, only of the artery or only of the vein, are quite rare.
By size, cerebral arteriovenous malformations are divided into small (diameter less than 3 cm), medium (from 3 to 6 cm) and large (over 6 cm). According to the nature of drainage, AVMs are classified into having and not having deep draining veins, i.e. veins flowing into the rectus sinus or the system of the large cerebral vein. There are also AVMs localized in or outside of functionally significant areas. The latter include the sensorimotor cortex, brain stem, thalamus, deep zones of the temporal lobe, sensory speech area (Wernicke’s zone), Broca’s center, occipital lobes.
In neurosurgical practice, AVM gradation is used to determine the risk of surgical intervention for cerebral vascular malformations, depending on the total score. Each of the features (size, type of drainage and localization in relation to functional zones) is awarded a certain number of points from 0 to 3. Depending on the points scored, the AVM is classified from having a minor operational risk (1 point) to being associated with a high operational risk due to the technical complexity of its liquidation, a high risk of death and disability (5 points).
In the clinic of arteriovenous malformations, hemorrhagic and torpid variants of the course are distinguished. According to various sources, the hemorrhagic variant accounts for 50% to 70% of AVM cases. It is typical for small-sized AVMs with draining veins, as well as for AVMs located in the posterior cranial fossa. As a rule, in such cases, patients have arterial hypertension. Depending on the location, subarachnoid hemorrhage is possible, which accounts for about 52% of all cases of AVM rupture. The remaining 48% are complicated hemorrhages: parenchymal with the formation of intracerebral hematoma, shell with the formation of subdural hematoma and mixed. In some cases, complicated hemorrhages are accompanied by hemorrhage in the ventricles of the brain.
The clinic of an AVM rupture depends on its localization and the rate of blood flow. In most cases, there is a sharp deterioration of the condition, an increasing headache, a disorder of consciousness (from confusion to coma). Parenchymal and mixed hemorrhages, along with this, are manifested by focal neurological symptoms: hearing disorders, visual disorders, paresis and paralysis, loss of sensitivity, motor aphasia or dysarthria.
The torpid variant of the course is more typical for cerebral AVMs of medium and large size located in the cerebral cortex. It is characterized by cluster cephalgia — successive paroxysms of headache, lasting no longer than 3 hours. Cephalgia is not as intense as when the AVM ruptures, but it is regular. Against the background of cephalgia, a number of patients have convulsive seizures, which often have a generalized character. In other cases, torpid cerebral AVM may mimic the symptoms of an intracerebral tumor or other volumetric formation. In this case, the appearance and gradual increase of focal neurological deficit is observed.
In childhood, there is a separate type of cerebral vascular malformation — AVM of the Galena vein. The pathology is congenital and consists in the presence of AVM in the area of the large vein of the brain. Galen’s AVM veins account for about a third of all cases of cerebral vascular malformations occurring in pediatrics. They are characterized by high mortality (up to 90%). Surgical treatment performed in the first year of life is considered the most effective.
The reason for contacting a neurologist before the AVM rupture may be persistent headaches, first-time epiprime, the appearance of focal symptoms. The patient is undergoing a routine examination, including EEG, Echo-EG and REG. In case of rupture, diagnostics is carried out in an emergency. Tomographic methods are the most informative in the diagnosis of vascular malformations. Computed tomography and magnetic resonance imaging can be used both for visualization of brain tissues and for vascular examination. In case of AVM rupture, brain MRI is more informative than CT. It makes it possible to identify the localization and size of the hemorrhage, to differentiate it from other volumetric intracranial formations (chronic hematoma, tumor, brain abscess, cerebral cyst).
With a torpid course, MRI and CT brain may remain normal. Only cerebral angiography and its modern analogues — vascular CT and MR angiography – can detect vascular malformation in such cases. Studies of cerebral vessels are carried out using contrast agents. Diagnosis is carried out by a neurosurgeon, who also assesses the operational risk and the feasibility of surgical treatment of AVM. At the same time, it should be borne in mind that in case of rupture, due to vascular compression in conditions of hematoma and cerebral edema, the tomographic size may be significantly smaller than the real one.
Arteriovenous malformations of the brain in case of their rupture or in case of danger of such a complication are subject to removal. Preferably planned surgical treatment of AVM. In case of rupture, it is carried out after the elimination of the acute period of hemorrhage and resorption of the hematoma. In the acute period, according to indications, surgical removal of the resulting hematoma is possible. Simultaneous elimination of both hematoma and AVM is carried out only with lobar localization of vascular malformation and its small diameter. In case of ventricular hemorrhage, external ventricular drainage is primarily indicated.
Classical surgical removal of AVM is carried out by trepanation of the skull. Coagulation of adducting vessels, isolation of AVM, ligation of vessels departing from malformation and excision of AVM is performed. Such radical transcranial removal of AVM is feasible with its volume not exceeding 100 ml and location outside of functionally significant zones. With a large AVM size, combined treatment is often resorted to.
When transcranial removal of AVM is difficult due to its location in functionally significant areas of the brain and deep structures, radiosurgical removal of AVM is performed. However, this method is effective only for malformations no larger than 3 cm. If the size does not exceed 1 cm, then its complete obliteration occurs in 90% of cases, and with sizes over 3 cm — in 30%. The disadvantage of the method is the long period (from 1 to 3 years) required for complete obliteration. In some cases, gradual irradiation of the malformation is required for a number of years.
The methods of elimination of cerebral AVMs also include X-ray endovascular embolization of the arteries leading to AVM. It is possible to conduct it when there are adducting vessels available for catheterization. Embolization is carried out in stages, and its volume depends on the vascular structure. Complete embolization can be achieved only in 30% of patients. Subtotal embolization is obtained in another 30%. In other cases, embolization is only partially possible.
Combined stage-by-stage treatment consists in the stage-by-stage use of several of the methods listed above. For example, with incomplete embolization, the next step is transcranial excision of its remaining part. In cases where complete removal is not possible, radiosurgical treatment is additionally applied. Such a multimodal approach to the treatment of cerebral vascular malformations has proved to be the most effective and justified in relation to large-sized AVMs.