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Arteriovenous malformation (AVM) is a group of blood vessels that are abnormally interconnected to each other. AVM can occur in different organs, but ATV's of the brain are the most problematic.
A CT image of a AVM is seen in figure 1.1 .
Approximately 0.1% of brain AVMs are present at birth. Symptoms usually start to present at ages between 10-30 years of age. The most common age of diagnosis is 50 years old.
Figure 1.1 Ct image of AVM.
It is believed that an AVM develops during fetal development. Cause is unknown. There does seem to be a slight increase in the male incidence over female. AVMs disrupt the normal blood flow throughout the brain causing damage to the brain slowly over time. AVMs commonly do not present symptoms until early adulthood. Increases blood flow from pregnancy can worsen these symptoms.
Signs & 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 or during treatment of an unrelated disorder; 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 and epilepsy, 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 and even paralysis
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.
If a patient is suspected of having an AVM, imaging studies should be done to confirm the diagnosis. Angiography has been used in the past. However, it is a fairly invasive procedure and carries a slight risk of bleeding (which could cause a stroke). More recently, modalities such as CT and MRI have been used as diagnostic procedures. MRA combines MRI and Angiography making it a great diagnostic tool.
AVMs have no specific histology.
Lymph Node Drainage:
There is no lymphatic drainage in the brain due to the Blood Brain Barrier.
A benign tumor usually does not spread to distant sites but it can press on structures near it causing symptoms.
GX Grade not assessable
G1 Well differentiated
G2 Moderately differentiated
G3 Poorly differentiated
There is no universal staging system for
Arteriovenous malformation (AVM).
Radiation Side Effects:
Side Effects of SRS:
Swelling: As with all radiation treatments, the cells of the irradiated tumors lose their ability to regulate fluids, and edema or swelling may occur. This does not happen in all treatments. If welling does occur, and it causes symptoms that are unpleasant, then a mild course of steriod medication may be given to reduce the fluid within the tumor cavity.
Necrosis: The tumor tissue that remains after the radiation treatment will typically shrink. On rare occasions this necrotic or dead tissue can cause further problems and may require removal. This occurs in a very small percentage of cases.
The most important prognostic factor is if the AVM is diagnosis before hemorrhage. Prognosis is also directly related to the size, symptoms and location to vital areas of the brain.
Treatment options include:
"Resection is usually done when the AVM can be removed with acceptable risk to prevent hemorrhage or seizures. AVMs that are in deep brain regions carry a higher risk of complications." When that is the case, other treatment options need to be considered.
Removal of small AVM's is relatively safe and effective. To do this, a section of the skull is removed to gain access to the AVM. Using a high-powered microscope, a neurosurgeon seals off the AVM with special clips and removes it from the brain. In somce cases, this is done with a laser. The bone is then reattached and closed with stitches.
This is a procedure in which a catherter is inserted into the groin and threaded through the body to the brain arteries. "The catheter is positioned in one of the feeding arteries to the AVM, and small particles of glue-like subrstance are injected to block the vessel and reduce blood flow into the AVM. This procedure can be done by itself, prior to other treatments to reduce the size of the AVM, or during surgery to reduces chances of it bleeding during the procedure. "In some large brain AVMs, endovascular embolization may reduce sroke-like symptoms by redirecting blood back to normal brain tissue."
"This treatment uses precisely focused radiation to destroy the AVM. The radiation causes the AVM vessels to slowly clot off in the months or years following treatment. This treatment works best for small AVMs and for those that have not caused a life-threatening hemorrhage."
Sometimes, AVM's are treated with stereoractic radiosurgery in just one high-dose fraction to a small stereotactically defined volume to sclerose the AVM and prevent it from hemorrhaging. The minimum dose that should be given to an AVM is 15 to 30 Gy prescribed in the periphery of the target. In 71% to 89% of patients, complete obliteration of the AVM is seen within 2 years. "Sterotactic radiosurgery is more effective when the AVM is less than 2 cm and when all feeder vessels are irradiated. Stereotactic radiotherapy with 2 to 3 sessions of 8 to 10 Gy is equally effective." Using fractionated radiation therapy has been shown to be inferior to using stereoractic radiosurgery. "Doses of 40 to 55 Gy in 1.8- to 3.5-Gy fractions yielded complete responses in 20% of patients." Preop doses of 30 Gy has shown and increase in resectability and decrease in intraoperative hemorrhage for extracerebral cavernous hemangiomas of the middle fossa
The Gamma Knife is one type of stereotactic radiosurgery equipment used to treat AVMs. The Gamma Knife aimes highly focused gamma rays at small to medium size lesions. Children with AVMs are good candidates for Gamma Knife treatment because it is precise and noninvasive. The AVM can be treated with minimal effects to surrounding healthy brain tissue. Figure 1.2 is an example of a Gamma Knife helmet.
Figure 1.2 Gamma Knife helmet.
Figure 1. TD 5/5 for areas that areas around the treatment field.
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