Arteriovenous malformation

Arteriovenous malformation or AVM in the majority of cases is a congenital disorder consisting of a connection between veins and arteries, this pathology is universally known because of its occurrence in the central nervous system, but can appear in any location.

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.

(Cerebral Arteriovenous Malformation)

Signs and symptoms

Symptoms of AVM vary according to the location of the malformation. Roughly (88% -needs citation) AVM are asymptomatic; often the malformation is discovered as part of an autopsy or during treatment of an unrelated disorder (called in medicine an incidental finding), rarely its expansion or a micro-bleed from it, could cause epilepsy, deficit or elicit pain.

The most general symptoms include headache and epilepsy, with more specific symptoms occurring that normally depend on the location of the malformation and the individual. Other possible symptoms include:

• Difficulties with movement or coordination, including muscle weakness and evenparalysis;
• vertigo (dizziness);
• Difficulties of speech (dysarthria) and communication, such as alogia;
• Difficulties with everyday activities, such as apraxia;
• Abnormal sensations (numbness, tingling, or spontaneous pain);
• Memory and thought-related problems, such as confusion, dementia or hallucinations.

Pathophysiology

Arteries and veins are part of the human cardiovascular system. Normally, the arteries in the vascular system carry oxygen-rich blood. Structurally, arteries divide and sub-divide repeatedly, eventually forming a sponge-like capillary bed. Blood moves through the capillaries, giving up oxygen and taking up waste products from the surrounding cells (CO2). Capillaries successively join together, one upon the other, to form veins that carry blood away. The heart acts to pump blood through arteries and uptake the venous blood.

If the capillary bed is thought of as a sponge, then an AVM is the rough equivalent of jamming a tangle of flexible soda straws from artery to vein through that sponge. On arteriogram films AVM formation often resemble a tangle of spaghetti noodles. This tangle of blood vessels forms a relatively direct connection between high pressure arteries and low pressure veins.

The result is a collection of blood vessels with abnormal connections and no capillaries. This collection, often called a nidus, can be extremely fragile and prone to bleeding.

Diagnosis

AVMs can occur in various parts of the body

• brain, causing a cerebral arteriovenous malformation
• spleen
  
• lung
• kidney
• spinal cord
• liver
• intercostal space
• iris
• spermatic cord

(The diagnosis of a brain AVM is made by CT scan, MRI, and catheter cerebral angiogram.)

AVMs may occur in isolation or as a part of another disease (e.g. Von Hippel-Lindau disease or hereditary hemorrhagic telangiectasia).

This bleeding can be devastating, particularly in the brain. It can cause severe and often fatal strokes. If detected before a stroke occurs, usually the arteries feeding blood into the nidus can be closed off, ensuring the safety of the patient.

Treatment

Treatment can be symptomatic, or it can involve surgery or radiation therapy. It can also be carried out via in interventinal radiography procedure using a glue to cut off the blood supply to the avm.

Epidemiology

An estimated 300,000 Americans have AVMs, of which 12% (approximately 36,000) will exhibit symptoms that differ greatly in severity.

Society and culture

• On December 13, 2006, Senator Tim Johnson was diagnosed with AVM and treated at George Washington University Hospital.

Cases in fiction

• The plot of William Finn's 1998 Off-Broadway musical, A New Brain, revolves around the main character's battle with AVM.
• The character Nate Fisher on the HBO television show Six Feet Under suffers from AVM.
• Patients with AVM appeared in an episode of the series House entitled DNR, as well as in a fictional British medical show called Harley Street.
• The main character in Robert J. Sawyer's book Mindscan suffers from an AVM that is at risk of reducing him to a permanent vegetative state.

Research directions

Despite many years of research, the central question of whether to treat AVMs has not been answered. All treatments, whether involving surgery 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.