Arteriovenous malformation or AVM is an abnormal connection between veins and arteries, usually congenital

Congenital disorder

A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...

. This pathology is widely known because of its occurrence in the central nervous system, but can appear in any location. An arteriovenous malformation is a vascular anomaly

Vascular anomaly

A vascular anomaly is a kind of birthmark caused by a disorder of the vascular development, although it is not always present at birth. A vascular anomaly is a localized defect in blood vessels that can affect each part of the vasculature...

. It is a RASopathy

RASopathy

The RASopathies are developmental syndromes caused by germline mutations in genes that alter the Ras subfamily and Mitogen-activated protein kinase that control Signal transduction, including:*Capillary malformation-AV malformation syndrome...

.

The genetic transmission patterns of AVM, if any, are unknown. AVM is not generally thought to be an inherited disorder, unless in the context of a specific hereditary syndrome

Syndrome

In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...

.

History

Emmanuel, Luschka, and Virchow first described arteriovenous malformations in the mid 1800s. Olivecrona performed the first surgical excision of an intracranial AVM in 1932.

Definition

AVMs are lesions of the vasculature that develop such that blood flows directly from the arterial system to the venous system without passing through a capillary system.

Signs and symptoms

Symptoms of AVM vary according to the location of the malformation. Roughly 88% of people affected with AVM are asymptomatic; often the malformation is discovered as part of an autopsy

Autopsy

An autopsy—also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction—is a highly specialized surgical procedure that consists of a thorough examination of a corpse to determine the cause and manner of death and to evaluate any disease or injury that may be present...

 or during treatment of an unrelated disorder (called in medicine "an incidental finding"); in rare cases its expansion or a micro-bleed from an AVM in the brain can cause epilepsy, deficit or pain.

The most general symptoms of a cerebral AVM include headache

Headache

A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...

 and epilepsy

Epilepsy

Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

, with more specific symptoms occurring that normally depend on the location of the malformation and the individual. Such possible symptoms include:

• Difficulties with movement or coordination, including muscle weakness
  Muscle weakness
  Muscle weakness or myasthenia is a lack of muscle strength. The causes are many and can be divided into conditions that have true or perceived muscle weakness...
  
   and even paralysis
  Paralysis
  Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
  
  ;
• vertigo
  Vertigo (medical)
  Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
  
   (dizziness);
• Difficulties of speech (dysarthria
  Dysarthria
  Dysarthria is a motor speech disorder resulting from neurological injury of the motor component of the motor-speech system and is characterized by poor articulation of phonemes...
  
  ) and communication, such as aphasia
  Aphasia
  Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
  
  ;
• Difficulties with everyday activities, such as apraxia
  Apraxia
  Apraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements...
  
  ;
• Abnormal sensations (numbness, tingling, or spontaneous pain
  Pain
  Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
  
  );
• Memory and thought-related problems, such as confusion
  ConFusion
  ConFusion is an annual science fiction convention organized by the Stilyagi Air Corps and its parent organization, the Ann Arbor Science Fiction Association. Commonly, it is held the third weekend of January. It is the oldest science fiction convention in Michigan, a regional, general SF con...
  
  , dementia
  Dementia
  Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
  
   or hallucination
  Hallucination
  A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...
  
  s.

Cerebral AVMs may present in a number of ways

• Hemorrhage (45% of cases)
  • Acute onset of severe headache. May be described as the worst headache of the patient's life. Depending on the location of hemorrhage, may be associated with new fixed neurologic deficit. In unruptured brain AVMs, the risk of spontaneous hemorrhage may be as low as 1% per year. After a first rupture, the annual bleeding risk may increase to more than 5%.

• Seizure (46%)

• Headache (34%)

• Progressive neurologic deficit (21%)
  • May be caused by mass effect or venous dilatations. Presence and nature of deficit depend on location of lesion and the draining veins.

• Pediatric patients
  • Heart failure
  • Macrocephaly
  • Prominent scalp veins

Pathophysiology

Arteriovenous malformations, also known as AVMs, are deficiencies of the cardiovascular system. In a normal functioning human body, arteries carry oxygen-rich blood away from the heart to the rest of the body, and veins return oxygen-depleted blood to the lungs and heart. An AVM interferes with this cyclical process. Instead of the gradual transition through the capillaries from arteries to veins that is typical of normal functioning vasculature, AVMs cause direct associations of the arteries and veins. 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 any part of the body.

Arteries and veins are part of the human cardiovascular system

Circulatory system

The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

. Normally, the arteries in the vascular system carry oxygen-rich blood, except in the case of the pulmonary artery. Structurally, arteries divide and sub-divide repeatedly, eventually forming a sponge-like capillary bed. Blood moves through the capillaries

Capillary

Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...

, giving up oxygen and taking up waste products, including , from the surrounding cells. Capillaries in turn successively join together to form veins that carry blood away. The heart acts to pump blood through arteries and uptake the venous blood.

An AVM lacks the dampening effect of capillaries on the blood flow; it also causes the surrounding area to be deprived of the functions of the capillaries — removal of and delivery of nutrients to the cells. The resulting tangle of blood vessels, often called a nidus (Latin for "nest") has no capillaries and abnormally direct connections between high-pressure arteries and low-pressure veins. It can be extremely fragile and prone to bleeding. The resultant sign, audible via stethoscope, is a rhythmic, whooshing sound caused by excessively rapid blood flow through the arteries and veins. It has been given the term "bruit", French for noise. On some occasions a patient with a brain AVM may become aware of the noise, which can compromise hearing and interfere with sleep in addition to causing psychological distress.

Diagnosis

AVMs can occur in various parts of the body:

• brain
  Human brain
  The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
  
  , causing a cerebral arteriovenous malformation
  Cerebral arteriovenous malformation
  A cerebral arteriovenous malformation is an abnormal connection between the arteries and veins in the brain.-Signs and symptoms:The most frequently observed problems related to an AVM are headaches and seizures while at least 15% of the population at detection have no symptoms at all...
  
  
• spleen
  Spleen
  The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
  
  
• lung
  Human lung
  The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...
  
  
• kidney
  Kidney
  The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
  
  
• spinal cord
  Spinal cord
  The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
  
  
• liver
  Liver
  The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
  
  
• intercostal space
  Intercostal space
  The intercostal space is the space between two ribs . Since there are 12 ribs on each side, there are 11 intercostal spaces, each numbered for the rib superior to it.-Structures in intercostal space:* several kinds of intercostal muscle...
  
  
• iris
  Iris (anatomy)
  The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
  
  
• spermatic cord
  Spermatic cord
  The spermatic cord is the name given to the cord-like structure in males formed by the ductus deferens and surrounding tissue that run from the abdomen down to each testicle.-Contents of spermatic cord:...
  
  

AVMs may occur in isolation or as a part of another disease (for example, Von Hippel-Lindau disease

Von Hippel-Lindau disease

Von Hippel–Lindau is a rare, autosomal dominant genetic condition in which hemangioblastomas are found in the cerebellum, spinal cord, kidney and retina. These are associated with several pathologies including renal angioma, renal cell carcinoma and pheochromocytoma...

 or hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia , also known as Osler-Weber-Rendu disease and Osler-Weber-Rendu syndrome, is a genetic disorder that leads to abnormal blood vessel formation in the skin, mucous membranes, and often in organs such as the lungs, liver and brain.It may lead to nosebleeds, acute...

).

AVMs have been shown to be associated with Aortic Stenosis.

Bleeding from an AVM can be relatively mild or devastating. It can cause severe and less often fatal stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

s. 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. However, interventional therapy may also be relatively risky

Treatment

Treatment for brain AVMs can be symptomatic, and patients should be followed by a neurologist for any seizures, headaches or focal deficits. AVM-specific treatment may also involve endovascular embolization, neurosurgery or radiation therapy.
Embolization, that is, cutting off the blood supply to the AVM with coils or particles or glue

Glue

This is a list of various types of glue. Historically, the term "glue" only referred to protein colloids prepared from animal flesh. The meaning has been extended to refer to any fluid adhesive....

 introduced by a radiographically guided catheter, can be used in addition to either, but is rarely successful in isolation except for in smaller AVMs. The neurological risk of any such intervention is roughly 10%.
For unruptured brain AVMs, the benefit for endovascular, neurosurgical or radiation therapy is as yet unknown. Therefore, the best way to follow an unruptured brain AVM is to join the NIH/NINDS funded international study designed for patients with an unruptured brain AVM.

Epidemiology

The estimated detection rate of AVM in the US general population is 1.4/100,000 per year. This is approximately one fifth to one seventh the incidence of intracranial aneurysms. An estimated 300,000 Americans

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 have AVMs, of whom 12% (approximately 36,000) will exhibit symptoms of greatly varying severity.

Society and culture

• On December 13, 2006, Senator
  United States Senate
  The United States Senate is the upper house of the bicameral legislature of the United States, and together with the United States House of Representatives comprises the United States Congress. The composition and powers of the Senate are established in Article One of the U.S. Constitution. Each...
  
   Tim Johnson was diagnosed with AVM and treated at George Washington University
  George Washington University
  The George Washington University is a private, coeducational comprehensive university located in Washington, D.C. in the United States...
  
   Hospital.

• On August 3, 2011, Mike Patterson of the Philadelphia Eagles
  Philadelphia Eagles
  The Philadelphia Eagles are a professional American football team based in Philadelphia, Pennsylvania. They are members of the East Division of the National Football Conference in the National Football League...
  
   collapsed on the field and suffered a seizure during a practice. After he collapsed, Patterson was rushed to the hospital where he quickly texted Eagles employees and teammates that he was fine. He was described as alert and stable in the hospital, where he stayed overnight. Patterson was diagnosed with AVM on August 4.

• Six Feet Under, an American television series that ran on HBO from 2001–2005, featured a protaganist, Nate Fisher
  Nate Fisher
  Nathaniel Samuel "Nate" Fisher, Jr. is a fictional character on the HBO television series Six Feet Under, played by Peter Krause.-Prior to the Pilot:...
  
  , that suffered from AVM, a recurring feature in the storyline of this character.

• On August 1, 2007, NIH/NINDS decides to launch the first international study evaluating the best treatment strategy for patients with unruptured brain AVMs: ARUBA — A Randomizd trial of Unruptured Brain AVMs.

• Actor Ricardo Montalbán
  Ricardo Montalbán
  Ricardo Gonzalo Pedro Montalbán y Merino, KSG was a Mexican radio, television, theatre and film actor. He had a career spanning six decades and many notable roles...
  
   was born with spinal AVM. During the filming of the 1951 film, Across the Wide Missouri
  Across the Wide Missouri
  Across the Wide Missouri is a 1947 historical work by Bernard DeVoto. It is the second volume of a trilogy that includes The Year of Decision and The Course of Empire ....
  
  , Montalbán was thrown from his horse, knocked unconscious, and trampled by another horse which aggrevated his AVM and resulted in a painful back injury that never healed. The pain increased as he aged, and in 1993, Montalbán underwent 9½ hours of spinal surgery which left him paralysed below the waist and using a wheelchair.

Research directions

Despite many years of research, the central question of whether to treat AVMs has not been answered. All treatments, whether involving surgery, radiation, or drugs, have risks and side-effects. Therefore it might be better in some cases to avoid treatment altogether and simply accept a small risk of coming to harm from the AVM itself. This question is currently being addressed in clinical trials. Interested patients are welcome to contact participating centers worldwide.

External links

• AVM Support Groups from the DMOZ Open Directory.
• University of California San Francisco AVM research.
• http://www.arubastudy.org
• http://www.cervco.fr