An arteriovenous malformation is a vascular malformation that creates a direct connection between the arterial and venous parts of the bloodstream without the interposition of the capillary system. This rare vascular malformation, which in many cases affects the central nervous system, usually occurs in the form of a plexus of veins. The walls of the blood vessels in the area of the vascular anomaly often do not reach normal strength, so that serious internal bleeding can occur in conjunction with the increased blood flow.
What is an arteriovenous malformation?
An arteriovenous malformation (AVM) is characterized by a plexus of arteries that connects directly to the venous vascular system. Normally, arterial blood must pass through the capillary system. In the case of this disease, before it enters the venous part of the circulation, it is practically short-circuited. AVM is exclusively defined as an arteriovenous short circuit created during the embryonic phase. It does not mean an acquired direct connection between arterial and venous blood flow or one artificially created for therapeutic purposes. The vascular anomaly usually consists of an inextricable tangle of veins, also called a nidus (nest), whose walls are extremely thin and prone to lesions. Often, the draining veins are severely dilated, putting the patient at high risk for developing bulges (aneurysms). Arteriovenous malformations are found primarily in the anterior region of the central nervous system (CNS), but in principle can occur anywhere in the body, including the lungs, spinal canal, retina of the eyes, and muscle tissue.
Causes
The causes for the development of arteriovenous malformations are not (yet) sufficiently known. It is considered likely that the malformations form during the early embryonic developmental period. It is not certain whether genetic defects are possible triggers. A familial clustering observed in certain manifestations of AVM supports the theory of one or more genetic defects. It is also not known whether exposure to certain pollutants or environmental toxins during the crucial early gestational period plays a role as a possible causative agent of AVM.
Symptoms, complaints, and signs
Symptoms and complaints of AVM cover a wide spectrum from only mildly noticeable symptoms and nonspecific headaches to comatose and life-threatening conditions. In most cases, arteriovenous malformations become conspicuous by internal bleeding. If the bleeding occurs in the brain or spinal cord, depending on the affected region, severe symptoms such as convulsive seizures, motor disturbances, and balance and visual disturbances may occur. Unconsciousness also frequently occurs due to more severe bleeding. Spatial involvement of cerebral hemorrhages can also cause epileptic seizures or paralysis of the arms and legs, as well as speech disorders.
Diagnosis and course
Four different diagnostic imaging techniques are available when AVM is suspected. Specifically, these are computed tomography (CT), magnetic resonance imaging (MRI), and angiography or digital subtraction angiography (DAS), an advanced form of conventional angiography. Color-coded duplex sonography can also be used for diagnostic purposes. In principle, these are non-invasive diagnostic procedures, unless – except in the case of duplex sonography – a contrast medium is applied to the blood vessels via catheter in order to improve the informative value of the images. For a diagnosis that is needed quickly, especially in the case of cerebral hemorrhage, a CT is usually obtained without contrast medium, which allows precise conclusions to be drawn about the location and size of the hemorrhage. The disease course of AVM can vary widely. Cases have also been observed in which the arteriovenous malformation has spontaneously regressed, but this does not correspond to the normal course of the disease. AVM always carries the risk of internal hemorrhage, which can lead to serious problems and neurological deficits, especially in the CNS. In the case of an extensive AVM, there is also the risk of severe blood loss with all the resulting health problems.
Complications
Arteriovenous malformation refers to a type of short-circuit connection of arteries and veins that supply the brain. The congestion causes a blood-enriched vascular tangle. If the vascular tangle bursts, a life-threatening cerebral hemorrhage is the result. Complications from an arteriovenous malformation may be far-reaching. Affected individuals may sustain irreversible neurologic deficits as a result of the symptom. If the symptom is located in the spinal cord, paraplegia is imminent. Epileptics in particular should seek medical attention immediately at the first sign of a severe headache. Other signs of hemorrhage include sensory disturbances, paralysis, speech disorders, and epileptic seizures leading to unconsciousness. Medical clarification is carried out by means of an MRI, if possible with the administration of a contrast medium, from which the extent of the vascular tangle and any cerebral hemorrhage that has already occurred can be easily identified. A brain wave measurement shows the extent of possible neurological deficits. Medical therapy is based on the patient’s medical history and is rarely problematic. Depending on the location of the vessel tangle, surgical intervention is considered. However, the occlusion itself can lead to complications if rupture or acute circulatory disturbances occur in the supply area during the operation. This can damage peripheral nerves or cause a stroke. If the symptom occurs in an unfavorable brain region, alternatives such as embolization or radiation therapy are initiated.
When should you see a doctor?
The manifestations of an arteriovenous malformation (AVM) range from minor to severe. It is always a direct connection, a kind of short circuit between the arterial and venous sides of the circulatory system bypassing the capillary system, so that the vascular resistance of the capillary system is also absent. Characteristically, AVMs are created during the embryonic phase for reasons not yet fully understood. Although an AVM can in principle be created anywhere in the bloodstream, it is predominantly found in the anterior part of the CNS. Strikingly, the vessel walls of an AVM, which are often braid-like, are not particularly strong, so that bleeding can occur, which can cause severe neurological complications in the CNS due to spatial stress. Some of the complications are similar to those of stroke. Smaller AVMs in the CNS area may be virtually asymptomatic and are often overlooked. In these cases, it is unnecessary to ask whether medical treatment should be sought. In the case of an already diagnosed AVM outside the CNS and outside the spinal canal, the risks and chances of therapy should be carefully weighed against each other. The primary goal is to arrest the AVM by surgical removal or by sclerotherapy or sclerotization. In the CNS, decommissioning of an AVM turns out to be much more complicated because bleeding must be avoided at all costs to avoid provoking additional neurologic damage.
Treatment and therapy
Therapeutic goals in the treatment of an AVM depend primarily on its location and size. For a smaller asymptomatic malformation, only regular observation is recommended. For arteriovenous malformations located outside the head and spinal canal, the therapeutic goal is usually complete removal of the AVM in a surgical procedure. In some cases, functional arrest in the form of sclerotherapy or embolization may also be used. While sclerotherapy is induced by direct injection of a special fluid into the vessels of the AVM, embolization is an artificial blockage of the affected veins. For the treatment of an AVM in the brain, there are several different treatment methods or forms of therapy available to stop the function of the malformed blood vessels. In the case of very small malformations, precision irradiation can lead to obliteration of the small vessels. However, the risk of bleeding is not eliminated immediately by irradiation, but is only reduced gradually over approximately two years. In some cases, a catheter can be advanced via the inguinal artery to the facial artery that supplies blood to the malformed vascular network.An embolizing fluid can then be introduced directly into the affected veins via the catheter. Regardless of the method used to immobilize or surgically remove the affected vascular network, it is very important that the malformed veins be completely captured or undesirable recurrences will develop.
Outlook and prognosis
The prognosis of arteriovenous malformation is very unfavorable without medical care. The vascular malformation leads to hemorrhage in most patients during their lifetime. An acute life-threatening condition occurs, which can have a fatal course. Various dysfunctions occur and multiple organ failure threatens the patient. If the affected person survives an acute condition that manifests itself via a heart attack or stroke, lifelong impairments remain. These include paralysis, speech disorders or motor problems that are beyond repair. In some cases, years of therapy can provide relief. Nevertheless, the initial situation is not restored. For patients who experience an early diagnosis and promptly participate in medical treatment, the likelihood of a positive prognosis increases. If there are no other pre-existing conditions, the patient has a good chance of being discharged as permanently healed after corrective surgery. Once wound healing is complete, normal participation in daily life can occur. Nevertheless, overexertion and heavy loads should be avoided. In the case of additional diseases, the prognosis must be assessed according to the overall situation. If chronic diseases are present or if there are additional vascular disorders, the prospect of complete recovery is minimized. In addition, the recovery process is prolonged immensely.
Prevention
Because the causes of arteriovenous malformation are not sufficiently known and, in certain manifestations, genetic defects probably play a role, preventive measures that could prevent the formation of an AVM are nonexistent. The only recommendation that remains is to seek medical help at the first suspicion.
Follow-up
In this malformation, in most cases the patient has no or very few measures and options for aftercare. First and foremost, the disease itself must be detected early and then treated to prevent further complications. In the worst case, these malformations can also cause internal bleeding, which can lead to the death of the affected person. Therefore, the main focus in this disease is early detection and treatment. In most cases, the symptoms are alleviated by surgical intervention. There are no particular complications. After the operation, the patient should rest and take care of his or her body. Stressful or strenuous activities should be avoided so that the body can recover. Further checks and examinations are also necessary by a doctor after the procedure to check that the wound is healing. After the treatment, no further measures of aftercare are necessary. However, if the patient notices any changes at the site of the procedure, it is recommended to consult a doctor in order to detect tumors quickly. With early and successful treatment, there is no decreased life expectancy due to this disease.
This is what you can do yourself
An arteriovenous malformation (AVM) can take very different forms. The immediate danger that an AVM can pose depends on its severity and location. Frequently, an AVM is located in the CNS or spinal canal. In these cases, specialist medical attention should be sought immediately. There is a risk of hemorrhage in the area of the AVM, which can lead to CNS deficits due to spatial stress and in some cases can be immediately life-threatening. An AVM of low severity outside the CNS and outside the spinal canal that does not show signs of rupture or hemorrhage should be evaluated from time to time. There are no known typical daily or self-help measures that could prevent the occurrence of an AVM. Nor are there any known measures that could minimize the risk of bleeding associated with an AVM.The risk of vessel rupture with subsequent hemorrhage is significantly greater in AVM than in healthy vessels because the individual wall layers of the vessels in the area of AVM are particularly thin or completely absent.
