The arteriovenous malformations (MAV) are defects of the circulatory system that usually occur during the development of the embryo or fetus or shortly after the birth of the baby. They constitute an entanglement of arteries and veins. The arteries carry the oxygenated blood of the heart to the cells of the human body; The veins bring the blood not oxygenated to the lungs and the heart. The presence of an arteriovenous malformation interrupts this vital cyclic process. Even though MAVs can be developed in various sites, which occur in the brain or spinal cord - both integral parts of the central nervous system - can have serious side effects on the body. The MAVs of the brain or spinal cord (neurological arteriovenous malformations) are usually affected approximately 300 thousand Americans. They also occur in males and women of any racial or ethnic group.
Most people suffering from arteriovenous malformations present very few symptoms of importance and malformations tend to be discovered only by chance, usually during an autopsy or in treatments for unrelated causes. However, at approximately 12 percent of the affected population (about 36 thousand of the 300,000 Americans who are estimated to suffer from MAV) these anomalies, also called lesions, cause symptoms whose degree of severity varies considerably. In a small number of individuals in this group, symptoms are serious enough to cause weakening or even cause death. Annually, approximately 1 percent of people suffering from MAV die as a direct consequence of these injuries.
The most widespread symptoms of MAVs include seizures and headaches, but a specific pattern of these symptoms has not been identified. Seizures can be partial or total, they can cause a loss of control in movement or a change in the person's level of consciousness. Headaches can vary significantly on frequency, duration and intensity, sometimes reaching as serious as migraines. In certain cases, a headache that constantly affects only one side of the head can be attributed directly to the location of an arteriovenous malformation. More often, however, the location of pain has no direct relationship with the injury and can cover most of the head.
Las MAV también pueden causar una amplia gama de síntomas neurológicos más específicos que varían de persona a persona, dependiendo sobre todo de la localización de la malformación arteriovenosa. Estos síntomas pueden incluir debilidad o parálisis muscular en una porción del cuerpo; pérdida de la coordinación (conocida como ataxia) que puede conducir a problemas en el modo de caminar; apraxia, o dificultades para realizar tareas que requieren ser planificadas; vértigo; problemas visuales tales como la pérdida de parte del campo visual; incapacidad de controlar el movimiento de los ojos; papiledema (hinchazón de una parte del nervio óptico conocida como el disco óptico); varios trastornos en la utilización o comprensión del lenguaje (afasia); sensaciones anormales tales como entumecimiento, hormigueo o dolores espontáneos (parestesia o disestesia); pérdidas de memoria y confusión, alucinaciones o demencia. Los investigadores han descubierto recientemente que las MAV pueden causar también en algunas personas pequeños trastornos en el aprendizaje o de conducta durante su niñez o adolescencia, mucho antes de que puedan observarse síntomas más graves.
One of the most palpable signals indicating the presence of an arteriovenous malformation is an auditory phenomenon called Bruit in English-term derived from a French word meaning noise-and that in Spanish is known as murmur or blow. (A signal is a physical effect detectable by a doctor and not by the patient). Physicians use this term to describe the rhythmic sound caused by blood when it crosses the arteries and veins of an MAV excessively fast. The sound is similar to the one that produces a torrent of water that crosses a narrow tubing. The murmur can sometimes become a symptom - that is, in an effect that patients notice - when it is gravity. When patients can hear the murmur, he can put hearing at risk, affect sleep or cause psychological disorders quite gravity.
Symptoms caused by MAV may appear at any age, but because these anomalies tend to be a product of a slow accumulation of neurological damage over time, they are notified more frequently in patients of 20, 30 or 40 years of age. If arteriovenous malformations do not come to present symptoms when the patient reaches the end of 40 years or the beginning of 50 years of age, injuries tend to remain stable and rarely produce symptoms. In women, sometimes pregnancy causes sudden start or worsening of symptoms, due to cardiovascular changes that accompany pregnancy, especially increases in volume of blood and blood pressure.
Unlike the vast majority of neurological arteriovenous malformations, there is a very serious type that causes symptoms to be seen at birth or very soon after birth. This injury is known as a defect of the Galen vein, so called because it affects a major blood vessel, and is located in the deepest part of the brain. It is frequently associated with hydrocephalus (swelling of the brain, often with the visible magnification of the head), visible swollen veins on the scalp, seizures, lack of energy and congestive cardiac arrest. Children who are born with this condition, and that survive beyond childhood, often present delays in development.
Arteriovenous malformations come to present symptoms only when the damage caused to the brain or spinal cord reaches a critical level. This is one of the reasons why a relatively small fraction of patients with these injuries suffer from significant health problems related to this condition. Arteriovenous malformations cause damage to the brain or spinal cord through three basic mechanisms: reducing the amount of oxygen that reaches neurological tissues; causing bleeding (hemorrhage) in close tissues and compressing or moving parts of the brain or spinal cord.
MAVs affect the transmission of oxygen to the brain or spinal cord by altering normal blood flow patterns. The arteries and veins are usually interconnected through a series of progressively smaller blood vessels that control and retard the flow of blood. The transport of oxygen to nearby tissues occurs through the fine and porous walls of the smallest interconnected vessels, known as capillary tubes , where blood flows more slowly. However, the arteries and veins that constitute the arteriovenous malformations lack this important capillary network. Instead, the arteries unload the blood directly to the veins through a conduit known as fistula . Blood flow is not controlled and is extremely fast - too fast as to allow oxygen to be dispersed between nearby tissues. When the cells constituting these tissues do not obtain the normal amounts of oxygen they need, they begin to deteriorate and sometimes die completely.
This abnormally rapid blood flow rate often causes blood pressure in the vessels located in the central portion of an arteriovenous malformation directly next to the fistula - an area that physicians commonly call the nest, from the Latin Nidus - Hazardous reach high levels. Often, the arteries that provide blood to the lesion swell and twist; The veins that drain blood from the injury frequently become abnormally narrow (a condition known as stenosis ). On the other hand, often, the walls of the arteries and the veins involved are abnormally thin and weak. The aneurysms - packages on the walls of the blood vessels that can be easily broken - could be developed in about half of the cases of neurological arteriovenous malformations, as a consequence of this structural weakness.
La combinación de la alta presión interna y la debilidad de las paredes de los vasos sanguíneos podrían resultar en hemorragias. Tales hemorragias son a menudo de tamaño microscópico, causando daños limitados y pocos síntomas significativos. Incluso, muchas MAV asintomáticas (que no presentan síntomas) muestran signos de hemorragias anteriores. Pero pueden ocurrir hemorragias masivas si las tensiones físicas causadas por la presión arterial extremadamente alta, un flujo muy rápido de la sangre y la debilidad en las paredes de los vasos son significativos. Si un volumen considerable de sangre se escapa al cerebro como consecuencia de una ruptura en la MAV, el resultado puede ser un derrame cerebral catastrófico. Las MAV suelen provocar el 2 por ciento de todos los derrames cerebrales que ocurren cada año.
Even when it is not about hemorrhages or major exhaustions at the oxygen level, MAVs can damage the brain or spinal cord simply by their presence. They can oscillate in size from a fraction of one inch to more than 2.5 inches in diameter, depending on the number and size of the blood vessels that form the lesion. The larger the lesion, the greater the amount of pressure it exerts in the close structures of the brain or in the spinal cord. Larger lesions can compress several inches from the spinal cord or alter the shape of a whole hemisphere of the brain. Said MAV can block the flow of cerebroospinal fluid - a transparent fluid that normally feeds and protects the brain and spinal cord - distorting or blocking open conduits and cameras (the ventricles ) inside the brain that allow That this liquid circulates freely. As the cerebroospinal fluid accumulates, the neurological tissues begin to swell, and in extreme cases a hydrocephalus occurs. The accumulation of this fluid further increases the pressure in fragile neurological structures, aggravating the damage caused by arteriovenous malformation itself.
MAVs can be formed virtually anywhere in the brain or spinal cord - wherever there are arteries or veins. Some are formed from the blood vessels located in the Duramadre or in Piamadre , the outer and more internal membrane, respectively, of the three membranes that coat the brain and spinal cord. (The third membrane, called Arachnoids , lacks blood vessels.) The arteriovenous malformations that affect the spinal cord are of two types: the arteriovenous malformations of the duramadre, which affect the function of the spinal cord, exerting excessive pressure to the venous spinal cord system and the arteriovenous malformations of the spinal cord proper, which affect the function of the spinal cord by means of hemorrhages reducing the flow of blood to the spinal cord or causing excess pressure in the veins. Frequently, the MAVs of the spinal cord cause sudden attacks of severe back pain, often concentrated at the roots of nerve fibers where the vertebrae end. The pain is similar to that caused by a diverted disk. These lesions can also cause disorders in sensitivity, muscle weakness or paralysis in the parts of the body affected by the spinal cord or by the nerve fibers that have suffered damage. The spinal cord injury, caused by the MAVs due to any of the mechanisms described above, can lead to the degeneration of the nerve fibers of the spinal cord below the level of the lesion, causing extensive paralysis in the controlled body parts by said nerve fibers.
The MAVs of the Duramadre and Piamadre can occur anywhere on the surface of the brain. Those located on the surface of the cerebral hemispheres - the outermost parts of the brain - exert pressure in the cerebral cortex , the "gray matter" of the brain. Depending on its location, such arteriovenous malformations can damage parts of the cerebral cortex that affect thought, speech, oral compression, hearing, taste, tact or start or control of voluntary movements. The MAVs located in the frontal lobe near the optic nerve or in the occipital lobe (the back of the brain where the images are processed) can cause a variety of visual disorders.
Los vasos sanguíneos localizados en la parte más profunda del cerebro también pueden generar las MAV. Estas MAV pueden afectar las funciones de tres estructuras vitales: el tálamo, que transmite señales nerviosas entre la médula espinal y las regiones superiores del cerebro; los ganglios basales que rodean el tálamo, los cuales coordinan los movimientos complejos; y el hipocampo, que desempeña un papel importante en la memoria.
MAVs can affect other organs in addition to the brain. The portion below the brain is constituted by two important structures: the cerebellum , which is located on the back of the brain, and the brain stem ( brain stem in English), which serves as a bridge to join the upper parts of the brain to the spinal cord. These structures control high coordination movements, maintain balance and regulate some functions of internal organs, including those of the heart and lungs. The damage caused by MAV to these parts below the brain can lead to dizziness, dizziness, vomiting, loss of coordination capacity of complex movements such as walking, uncontrollable muscle tremors or causing interruptions in the operation of the organs (for example , a cardiac arrest).
The greatest potential danger presented by arteriovenous malformations is hemorrhage. Researchers believe that each year between 2 and 4 percent of arteriovenous malformations cause hemorrhages. Most cases of bleeding go unnoticed at the time of occurrence because they are not severe enough to cause significant neurological damage. But there are cases of mass bleeding, which can even cause death. Current knowledge does not allow doctors to predict whether a particular person suffering from an MAV reaches an extensive hemorrhage. Injuries can remain stable or can be suddenly aggravated. In some cases, these injuries can be reduced spontaneously. Whenever an MAV is detected, the patient must be carefully supervised and constantly to detect any sample of instability that may indicate a growing risk of hemorrhage.
Some physical characteristics seem to indicate a greater probability of the normal of significant clinical hemorrhage. Smaller MAVs have a greater probability of hemorrhage than the largest, possibly because the increase in blood pressure within a comparatively smaller area tends to be more concentrated. The deterioration in drainage caused by unusually narrow veins located in deeper areas also increases blood pressure and, therefore, also increases the possibilities of hemorrhage. Pregnancy also seems to considerably increase the likelihood of significant clinical hemorrhage due mainly to increases in blood pressure and volume of blood. Finally, the MAVs that have presented hemorrhages once are probabilities about nine times higher than to bleed again during the first year after the initial hemorrhage that the injuries that have never bleed.
Los efectos perjudiciales de una hemorragia se relacionan con la ubicación de la lesión. Las hemorragias de las MAV localizadas en los tejidos internos del cerebro (llamados parénquima) causan típicamente un daño neurológico más severo que las hemorragias de las lesiones en las membranas dural o pial o en la superficie del cerebro o de la médula espinal. (La hemorragia localizada en partes profundas se conoce generalmente como hemorragia intracerebral o parenquimatosa; el sangramiento en de las membranas o en la superficie del cerebro se conoce como hemorragia subdural o subaracnoidea.) Por lo tanto, la ubicación es un factor importante al tomar en cuenta los riesgos de un tratamiento quirúrgico versus no quirúrgico de las MAV.
In addition to arteriovenous malformations, three other main types of vascular lesions in the brain or spinal cord can be presented: cavernous malformations, capillary telangiectasis and venous malformations . These lesions can be formed anywhere in the central nervous system, but unlike MAVs, are not caused by the high speed of the blood flow of the arteries towards the veins. On the other hand, cavernous malformations, telangiectasias and venous malformations are all injuries low flow . That is, instead of a combination of arteries and veins, these injuries involve only a type of blood vessel. These lesions are less unstable than MAVs and do not pose the relatively high risk of extensive hemorrhages. In general, low-flow lesions tend to cause few neurological care symptoms and require less aggressive treatment than MAVs.
- cavernous malformations. These lesions are formed from groups of very compact blood vessels of abnormally thin walls, which displace normal neurological tissue in the brain or spinal cord. The vessels are filled with slow flow or stagnant blood that is usually coagulated or found in a decomposition state. Like arteriovenous malformations, cavernous malformations can oscillate in size of some inch fractions up to several inches in diameter, depending on the number of blood vessels involved. Certain patients have multiple lesions. Although cavernous malformations generally do not cause hemorrhages as serious as MAVs, they sometimes let blood escape towards brain tissues or spinal cord because the walls of the blood vessels in question are extremely fragile. Although they often do not present as many symptoms such as MAVs, cavernous malformations can cause seizures in some patients. After the MAV, the cavernous malformations are the type of vascular injury that is more likely to require treatment.
- capillary telangiectasias. These lesions consist of groups of capillary tubes with abnormal swellings and which usually measure less than one inch in diameter. The capillary tubes are the smallest blood vessels, with smaller diameters than a human hair; They have the ability to transport only small amounts of blood and blood pass through these vessels very slowly. Due to these factors, telangiectasias rarely cause deep damage to tissues adjacent to the brain or spinal cord. Any isolated hemorrhage that occurs is usually microscopic size. Therefore, the lesions are generally benign. However, in some hereditary disorders in which patients develop a large number of these lesions (see below), telangiectasias can contribute to the development of non-specific neurological symptoms, such as headaches or seizures.
- venous malformations. These injuries consist of an abnormal growth of veins. The structural defect does not usually interfere with the function of the blood vessels, which is draining non-oxygenated blood from the tissues of the body and return it to the lungs and the heart. Venous malformations rarely cause hemorrhages. As in the case of telangiectasias, most venous malformations do not produce symptoms, go unnoticed and are benign.
Although the causes of these vascular abnormalities of the central nervous system are not yet fully understood, scientists believe that anomalies are mostly due to errors that occur during embryo or fetus development. These errors can be associated with genetic mutations (alterations of genes) in some cases. Some types of vascular malformations are known to be hereditary and that have a genetic origin. Certain findings also suggest that at least some of these injuries are best acquired in life as a result of damage that occurred in central nervous system.
During fetal development, new blood vessels are continually formed and then disappear as the human body changes and grows. These changes in the vascular map of the body continue after birth and are controlled by the angiogenic factors , chemical substances produced by the body that stimulate the formation and growth of blood vessels. Researchers have recently identified changes in the chemical structures of several angiogenic factors in some patients suffering from MAV or other vascular abnormalities of the central nervous system. However, it is still not clear how these chemical changes really cause changes in the structure of blood vessels.
When studying patterns of family incidence, researchers have been able to establish that a type of cavernous malformation, which involves the formation of multiple lesions, is caused by a genetic mutation on chromosome 7. This genetic mutation is presented in many ethnic groups , but it is much more frequent in a large population of Hispanic Americans residing in the southwest of the United States. These individuals have an ancestor in which genetic change is evidenced. Other types of vascular defects of the central nervous system are part of more complex medical syndromes of hereditary nature. These syndromes include the hereditary hemorrhagic telangiectasia (also known as the Osler-Weber-Rendu disease), the STURGE-Weber syndrome, the Klippel syndrome Trenaunay, the Parkes-Weber syndrome and the Wyburn-Mason syndrome .
At present, doctors use a variety of traditional and new image processing technologies to detect the presence of arteriovenous malformations. A procedure called angiography provides the most precise images of the structure of the blood vessels of the MAV. The technique requires injecting into an artery a special solution that is diluted in water, called contrast agent. This contrast agent highlights the structure of the blood vessels allowing us to register using conventional x-rays. Although angiography can record the smallest details of vascular lesions, the procedure is a bit annoying and involves a small risk of causing a spill. However, the level of risk has recently been decreased by the development of more accurate techniques to inject the contrast agent at the place of the MAV. The super selective angiography involves inserting into an artery a fine and flexible tube called catheter. The doctor directs the catheter to the place of the injury and then injects a small amount of the contrast agent directly into the injury.
Dos de las tecnologías no invasoras para el procesamiento de imágenes, que son empleadas con mayor frecuencia para detectar las malformaciones arteriovenosas, son los estudios de imágenes por medio de la tomografía axial computarizada (CT por su sigla en inglés) y la resonancia magnética (MRI por su sigla en inglés). Las exploraciones tipo CT utilizan radiografías para crear una serie de imágenes de secciones transversales de la cabeza, el cerebro o de la médula espinal y resultan especialmente útiles en detectar la presencia de hemorragias. La resonancia magnética, sin embargo, ofrece una información de diagnóstico superior usando campos magnéticos para detectar cambios sutiles en los tejidos neurológicos. Una aplicación desarrollada recientemente -la angiografía por resonancia magnética (MRA por su sigla en inglés) - puede registrar el patrón y la velocidad con la que la sangre atraviesa las lesiones vasculares, así como el flujo del líquido cerebroespinal a través del cerebro y de la médula espinal. Las exploraciones de tipo MRI y MRA pueden proporcionar representaciones tridimensionales de las MAV tomando imágenes desde múltiples ángulos.
Medications can often relieve general symptoms, such as headache, back pain and seizures caused by arteriovenous malformations and other vascular injuries. However, the definitive treatment of MAV is surgery. Venous malformations and capillary telangiectasides very rarely require surgery. Moreover, its structures are diffuse and generally can not be corrected with surgery. The cavernous malformations are well-defined enough to be surrendered surgically, but surgery in these injuries is less common than in MAV because they do not have the same risk of causing hemorrhage.
The decision to conduct surgery in a patient who suffers from an MAV requires careful consideration of possible risks and benefits. The behavior of a particular MAV is difficult to predict. However, if it is not treated, it has the potential to cause important hemorrhages that can lead to serious neurological problems or even death. On the other hand, surgery in any part of the central nervous system also has its own risks. The surgery of an MAV has an estimated level of risk in 8 percent that serious complications occur or that the patient dies. There is no easy formula that allows doctors and their patients to make a decision regarding treatment to follow in these cases - all therapeutic decisions must be taken on a case-by-case basis.
Currently there are three surgical options for the treatment of MAV: the conventional surgery, Endovascular embolization and radiosurgery . The selection of treatment depends largely on the size and location of the MAV. Conventional surgery involves penetrating the brain or spinal cord and withdrawing the central part of the MAV, including fistula, trying to cause the minimum possible damage to nearby neurological structures. This surgery is the most appropriate when an MAV is located on a superficial part of the brain or spinal cord and is relatively small. The MAVs located in the deep parts of the brain generally can not be achieved with conventional surgical techniques since there is a too large possibility of damaging or destroying functionally important brain tissue.
Endovascular embolization and radiosurgery are less invasive than conventional surgery and offer safer options for the treatment of MAV located in deep parts of the brain. In Endovascular embolization, the surgeon directs a catheter through the arterial network until the catheter reaches the MAV site. The surgeon then injects a substance that covers the fistula, thus correcting the abnormal pattern of blood flow. This process is known as embolization because it causes a plunger (a blood clot) trails the blood vessels, stays in a particular blood vessel and obstruct the flow of blood. The materials used to create an artificial blood clot in the center of an MAV include biologically inactive glues that rapidly dry, fibrous titanium wires and tiny balloons. Because the embolization usually does not eliminate the MAV permanently, this process is commonly used in parallel to surgery to reduce blood flow through MAV and make surgery safer.
La radiocirugía es una alternativa terapéutica mucho menos invasora. Involucra la utilización de un rayo de radiación de alta precisión directamente en la MAV. La alta dosis de radiación daña las paredes de los vasos sanguíneos que forman la lesión. Varios meses después del procedimiento, los vasos irradiados se degeneran gradualmente y eventualmente se cierran, lo que causa la eliminación de la MAV.
Although Endovascular embolization and radiosurgery are low invading procedures, they are often not as effective as conventional surgery. Embolization tends to be incomplete or temporary, although in recent years the new materials that are used have generated better results. In general, radiosurgery also produces incomplete results, particularly when MVA is large and has the additional risk of damage caused by radiation of normal neighboring tissues. In the same way, in cases where the procedure is successful, the complete closure of an MAV occurs in a period of many months after radiosurgery. During this period, the risk of hemorrhage is still present. However, both techniques now offer the possibility of treating the MAVs in deep locations, which were previously inaccessible. In many patients, the embolization followed by surgical intervention is carried out, resulting in fewer complications or deaths.
Because MAV treatment involves many variables, doctors must determine the danger of procedures in each patient and to a large extent, case by case. The consequences of hemorrhage are potentially disastrous, which makes many doctors recommend surgical intervention in those cases in which the physical characteristics of the MAV seem to indicate a greater probability of the normal of relevance hemorrhages and consequent neurological damage.
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In the Federal Government, the National Institute of Neurological Disorders and Cerebrovascular Accidents (NINDS) A Division of the National Institutes of Health (NIH), has the main responsibility to sponsor the Research of neurological disorders. As part of its mission, the NINDS conducts research on arteriovenous malformations and other vascular lesions of the central nervous system and supports studies through donations to important medical institutions across the country.
In partnership with the School of Medicine of the University of Columbia, the NINDS has established a long-term study group of arteriovenous diseases in order to discover more closely the natural course of MAV in patients and improve the Surgical treatment of these injuries.
Another group of researchers sponsored by the NINDS is currently conducting studies in large populations of patients with arteriovenous malformations in order to formulate the criteria that will allow physicians to predict the risk of hemorrhage in each patient. The role played by high blood pressure in the injury in the production of hemorrhage is of vital importance. Other scientists are examining the genetic basis of family cavernous malformations and other hereditary syndromes that cause neurological vascular lesions, including ataxia-telangiectasia.
Other scientists are currently trying to refine the available techniques for the treatment of MAVs. Radiosurgery is a field of special interest because this technology is still very new. A study currently underway is closely examining the exact effects that exposure to radiation causes vascular tissues to improve the predictability and consistency of treatality results.
Finally, several ongoing studies are dedicated to developing new non-invasive technologies of neurological image processing to increase the effectiveness and safety of MAV surgery. Some scientists are initiating the use of magnetic resonance for measuring the amounts of oxygen present in the brain tissue of patients suffering from vascular lesions to predict brain response to surgical therapies. Others are developing a new microcamera that can be inserted into catheters to increase the accuracy of angiography. In addition, new types of non-invasive devices are being developed for the processing of images to detect functional activity of the brain through changes in the emission or reflection of light on the tissue. This technology may be more sensitive than magnetic resonance and other mechanisms currently available, providing surgeons with a new tool to improve the efficacy and safety of arteriovenous malformation surgery.
For additional information about NINDS research programs, contact the New Year's Neurological Resource and Information Network (Brain) at:
Brain
P.O. Box 5801
Bethesda, MD 20824
(800) 352-9424
http://www.ninds.nih.gov
