Arteriovenous malformation
An arteriovenous malformation (AVM) is an abnormal connection between arteries and veins, bypassing the capillary system. Usually congenital, this vascular anomaly is widely known because of its occurrence in the central nervous system (usually as a cerebral AVM), but can appear anywhere in the body. The symptoms of AVMs can range from none at all to intense pain or bleeding, and they can lead to other serious medical problems.[1]
This article is about the anomaly generally. For its occurrence in the brain, see Cerebral arteriovenous malformation.Arteriovenous malformation
Genetics[edit]
AVMs are usually congenital and are part of the RASopathy family of developmental syndromes.
The understanding of the anomaly's genetic transmission patterns are incomplete, but there are known genetic mutations (for instance in the epithelial line, tumor suppressor PTEN gene) which can lead to an increased occurrence throughout the body.
The anomaly can occur due to autosomal dominant diseases, such as hereditary hemorrhagic telangiectasia.[8]
Pathophysiology[edit]
In the circulatory system, arteries carry blood away from the heart to the lungs and the rest of the body, where the blood normally passes through capillaries—where oxygen is released and waste products like carbon dioxide (CO2) absorbed—before veins return blood to the heart.[9] An AVM interferes with this process by forming a direct connection of the arteries and veins, bypassing the capillary bed.[10] AVMs can cause intense pain and lead to serious medical problems. Although AVMs are often associated with the brain and spinal cord, they can develop in other parts of the body.[10]
As an AVM lacks the dampening effect of capillaries on the blood flow, the AVM can get progressively larger over time as the amount of blood flowing through it increases, forcing the heart to work harder to keep up with the extra blood flow. It also causes the surrounding area to be deprived of the functions of the capillaries. The resulting tangle of blood vessels, often called a nidus (Latin for 'nest'), has no capillaries. It can be extremely fragile and prone to bleeding because of the abnormally direct connections between high-pressure arteries and low-pressure veins.[11] One indicator is a pulsing 'whoosh' sound caused by rapid blood flow through arteries and veins, which has been given the term bruit (French for 'noise'). If the AVM is severe, this may produce an audible symptom which can interfere with hearing and sleep as well as cause psychological distress.[1]
AVMs are diagnosed primarily by the following imaging methods:[12]
AVMs can occur in various parts of the body:
AVMs may occur in isolation or as a part of another disease (for example, Sturge-Weber syndrome or hereditary hemorrhagic telangiectasia).[22]
AVMs have been shown to be associated with aortic stenosis.[23]
Bleeding from an AVM can be relatively mild or devastating. It can cause severe and less often fatal strokes.[1]
Treatment[edit]
Treatment for AVMs in the brain can be symptomatic, and patients should be followed by a neurologist for any seizures, headaches, or focal neurologic deficits. AVM-specific treatment may also involve endovascular embolization, neurosurgery or radiosurgery.[1]
Embolization, that is, cutting off the blood supply to the AVM with coils, particles, acrylates, or polymers introduced by a radiographically guided catheter, may be used in addition to neurosurgery or radiosurgery, but is rarely successful in isolation except in smaller AVMs.[24] A gamma knife may also be used.[25]
If a cerebral AVM is detected before a stroke occurs, usually the arteries feeding blood into the nidus can be closed off to avert the danger.[26] Interventional therapy may be relatively risky in the short term.[27]
Treatment of lung AVMs is typically performed with endovascular embolization alone, which is considered the standard of care.[15]
Epidemiology[edit]
The estimated detection rate of AVM in the US general population is 1.4/100,000 per year.[28] This is approximately one-fifth to one-seventh the incidence of intracranial aneurysms. An estimated 300,000 Americans have AVMs, of whom 12% (approximately 36,000) will exhibit symptoms of greatly varying severity.[1]
History[edit]
Hubert von Luschka (1820–1875) and Rudolf Virchow (1821–1902) first described arteriovenous malformations in the mid-1800s. Herbert Olivecrona (1891–1980) performed the first surgical excision of an intracranial AVM in 1932.