AVM (arteriovenous malformation) is a congenital condition that manifests itself in the form of abnormal blood vessels plexus and arteriovenous anastomosis (abnormal connections between the veins and arteries). If not treated, this condition results in a brain haemorrhage for 2/3 patients who suffer from AVM.
AVM is a congenital condition, but not a genetic one. Arteriovenous malformations develop as a result of the improper brain vessels development during week 4 of embryogenesis. This abnormality can be caused by genetic mutations.
There are three morphological types of AVM:
1. Plexiform, when the fetal capillaries remain. In the future they develop abnormal vascular plexus.
2. Fistula, when the fetal capillaries are completely destroyed but the connection between a vein and artery remains.
3. The most frequent option of AVM is when the fetal capillaries are partially destroyed and abnormal vascular tangles with lots of fistulas are formed.
Some vessels of AVM are hard to attribute to veins or arteries. They have direct connection, mixed blood flow and peculiarities of their structure resemble both veins and arteries.
Types of AMVs depending on location:
Types of AMVs according to the size:
To make the correct choice of treatment, one must take the functions of the brain areas into consideration where the abnormal plexuses are located.
AVMs’ locations are differentiated as following:
AVMs are also distinguished as: intercerebral (localization within the brain), extracerebral (meninx fibrosa, soft tissues of the skull), and both.
AVM may have a different clinical course, and is divided depending on the 4 degrees of severity:
1 - asymptomatic
2 - rare cases of seizures and headaches
3 - stroke-or pseudo tumor development (the symptoms are the same as for stroke or brain tumor - frequent seizures, persistent and intractable by painkillers headache, passing cerebrovascular accidents with loss of certain functions - speech disorder, coordination, paresis and paralysis of muscles, etc. )
4 - apoplectic type is characterized by recurrent bleeding into the brain.
AVM leads to bleeding for 50-70% of patients. Depending on the location of the ruptured blood vessels, there is a corresponding clinic associated with a lesion of certain parts of the central nervous system.
Methods used for the diagnostics of AVMs are given below:
Electrophysiological diagnostics is not specific, but helps a doctor to suspect AVM. Rheoencephalography is also used for the determination of the electrical resistance of the various parts of the brain, and electroencephalography helps to determine the bioelectric activity of the brain.
Ultrasonic Doppler examination can detect changes in the blood flow in certain areas of the brain. Transcranial Doppler allows to set "bypass phenomenon" (mixing of blood between the connected arterial and venous vessels).
CAT scan is an X-ray method of investigation that identifies the AVM of 2 cm. The method is also used to determine the localization of bleeding in case of rupture of arteriovenous malformations.
Cerebral angiography is the most informative though dangerous method of diagnostics. Therefore it is applied only if indicated (in the case of haemorrhage, after surgery, as well as in cases of suspected AVM, if controversial results were obtained while the non-invasive examination). The contrast agent is injected into the blood vessels, then, using an X-ray their scan is produced.
AVM can be eliminated only through surgery. Though, not all patients are treated like that. Surgery is required only for those who have high risk of ischemic stroke, haemorrhage into the brain or suffer from the condition’s side effect.
The surgery is necessary if a patient has:
While making a decision about the surgery a patient should remember that 45% of AVMs eventually disrupt even if there are no any symptoms of the disease.
Even if it is not accompanied by symptoms, AVM carries the two major hazards:
1. Ischemia (lack of blood supply) of the brain. The larger the size of AVM, the more blood enters into the abnormal vascular plexus, causing a "steal syndrome" to other parts of the brain. As a consequence, there may be transient ischemic attack or ischemic stroke.
2. Bleeding (hemorrhagic stroke). It is related to possible rupture of arteriovenous malformations. This outcome is observed among 50-70% of patients. Increased risk of bleeding associated with high blood pressure in the vessels of AVM. Mortality after the first bleeding is about 15%.
It is advisable to start the treatment of AVM, without waiting for the first bleeding in the brain. This greatly improves the prognosis.
AVM excision. This is a very complicated type of surgery that demands a highly qualified and experienced neurosurgeon and modern medical equipment. Point of surgery is to remove the abnormal vascular plexuses and retain the normal blood flow. The results of surgery depends largely on the doctor’s skill and modern equipment.
Endovascular occlusion of AVM is used more and more often as it has an obvious advantage: it doesn’t require a craniotomy. It is used if there are high risks, when AVM is large or giant or located in functionally active brain parts.
While chemical occlusion the thrombosing substances are injected into the blood vessels. Blood clots block them interrupting the blood flow through the abnormal vascular plexuses.
Embolization with platinum coils has been used frequently in recent years. The coils are placed inside the vessel that lead to blood clots formation and blocking the lumen of the veins and arteries.
Gamma knife. Congelation of the small and medium vessels is performed with the help of the directed radiosurgical effects. Gamma- rays are directed to the relevant location, which are focused on the one spot. As a result of the vascular endothelium damage and blood clots, blood flow through the veins and arteries of the AVM is completely or partially terminated. The main advantage of this method of treatment is that it is non-invasive and painless. The procedure takes place without any surgical incision.
AVM congelation by the directed proton beam is basically the same as the previous method, but its more precise (gamma knife may have an error in 0,2-0,3 mm). High-tech procedure is rarely applied in fact, because costly equipment is necessary for it. Therefore, it is held only in the best clinics of the developed countries.
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