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The abnormal development or formation of blood vessels are known as vascular malformations. Vascular malformations are usually present at birth or congenital and affect the organization and function of veins or arteries in the body.
The most common vascular malformations are arteriovenous malformations. These are discussed in detail below.
Other less common vascular lesions include:
- Cavernous malformations: large blood-filled cavities
- Venous malformations: lesions with abnormally large veins
- Telangiectases: lesions characterized by swollen capillaries.
- Lymphatic malformations
- Combined vascular malformations
Ateriovenous malformation (AVM) is a vascular disorder in which arteries and veins are connected directly rather than through capillaries. This direct connection produces enlarged, tangled masses of blood vessels that are prone to rupture, bleeding and stroke.
Abnormal blood vessels may interfere with the normal flow of blood by preventing an adequete supply of oxygenated blood from filling capillaries, tiny blood vessels connecting arteries and veins in the body. This can result in blood traveling directly from the arteries into the veins completely bypassing the capillary system. This causes a lack of oxygen and accumulation of wastes in body tissue that would ordinarily receive blood from the capillaries. These potentially dangerous malformations are known as arteriovenous malformations, or AVMs.
AVMs can develop in many different areas of the body, including the lungs, kidney, liver, iris, spermatic cord and the areas between the ribs. Those located in the brain or spinal cord can have especially widespread effects on the body. AVMs of the brain or spinal cord are believed to affect approximately 300,000 Americans. They occur in males and females of all racial or ethnic backgrounds at roughly equal rates.
Scientists believe that arterialvenous malformations are most often the result from mistakes that occur during embryonic or fetal development. The genetic transmission patterns of AVM, if any, are unknown.
Approximately 88% of people affected with AVM do not have any symptoms.
The most general symptoms of a cerebral AVM include headache and seizures. More specific symptoms depend on the location of the malformation and the individual. These symptoms include:
- Difficulties with movement or coordination, including muscle weakness and even paralysis
- vertigo (dizziness)
- Difficulties of speech and communication
- Difficulties with everyday activities
- Abnormal sensations (numbness, tingling, or spontaneous pain)
- Memory and thought-related problems, such as confusion, dementia or hallucinations
The greatest potential danger posed by an AVM is hemorrhage. Researchers believe that each year between two and four percent of all AVMs hemorrhage.
Treatments for arteriovenous malformations vary on a case-to case basis and depend on the size and location of the AVM. Treatments include the following:
- Medications can often alleviate general symptoms such as headache, back pain, and seizures but are not a definitive treatment for an AVM.
- Conventional surgery involves removing the central portion of the AVM while causing as little damage as possible to surrounding structures. This surgery is most appropriate when the AVM is superficially located and relatively small in size.
- Radiosurgery is a less invasive therapeutic approach involving aiming a beam of highly focused radiation at the AVM. The radiation damages the walls of the blood vessels, creating a lesion. Over the course of the next several months, the irradiated vessels gradually degenerate and eventually close, leading to the resolution of the AVM.
- Endovascular embolization is less invasive than conventional surgery and involves the surgeon guiding a catheter through the arterial network until the tip reaches the site of the AVM. The surgeon then introduces a substance that will become lodged in a vessel of the AVM and obstruct blood flow. Since embolization does not permanently obliterate the AVM, it is usually used as an adjunct to surgery or radiosurgery to reduce the blood flow through the AVM and make surgery safer.
Because so many variables are involved in treating AVMs, doctors must assess the danger posed to individuals on a case-by-case basis. The consquences of hemorrhage are potentially dangerous, leading many clinicians to recommend surgical interventon whenever the physical characteristics of an AVM appear to indicate the likelihood of significant bleeding and possible neurological damage
In some cases, it might be better to avoid treatment and simply accept a small risk of coming to harm from the AVM. This question is currently being addressed in clinical trials.