Arteriovenous Malformations of the Central Nervous System
WELCOME!
Welcome to this information page on arteriovenous malformations (AVMs) of the central nervous system. This page is meant to provide a brief overview of what AVMs are, how they may affect individuals and families who have been diagnosed with AVMs and what can be done about them. In addition, this page will provide you with the necessary resources to obtain further information about AVMs and the experts in this centre who will be able to work with you and help you or someone you know decide what can and should be done to treat this disease.
WHAT IS AN AVM?
In brief, an AVM is an abnormal nest of tangled blood vessels that can be present essentially in any part of one’s body. To better understand what an AVM is and how it comes about, one needs to compare it to the “normal” state of things in the human body. In general, as can be seen in the accompanying figure, blood travels from the heart to all the body’s tissues via muscular vessels called arteries. These arteries get progressively smaller to the point where they become very thin-walled capillaries which allow nutrients in the blood to enter the tissues. The nutrient-poor blood then returns to the heart via a system of moderately thin-walled vessels-- the veins.
In the case of an AVM, there is an absence of capillaries in this "circuit" As a result, the vessels of an AVM have rather abnormal flow patterns that may be harmful to a person, especially if a particular AVM has a high amount of blood flow or high pressures. This is particularly a potentially serious problem in instances where AVM’s involve parts of the central nervous system (the brain, spinal cord and their respective coverings, specifically the dura).
There are certain terms that are used to help identify the various parts of an AVM:
Feeding vessels--the arteries and arterioles that provide blood to the AVM
Nidus--the "nest" or central portion of an AVM that includes numerous loops of vessels that gives the appearance of a "bowl of spaghetti"
Draining veins--the veins that collect the blood from the AVM and return it to the normal systemic circulation.
ARE ALL AVMS HARMFUL AND WHAT HARM CAN THEY DO?
The potential for harm that an AVM can cause depends on a number of factors which includes primarily the type of AVM, and its location. Depending on the type of AVM people may present to medical attention because of severe headaches, seizures or most commonly because of an "ictus"-- a sudden onset of severe headache which may be accompanied by a variable period of loss of consciousness, caused by the AVM bleeding or haemorrhaging into the brain, fluid filled ventricles within the brain or the spaces surrounding the brain known as the subarachnoid spaces. Though the seizures are not life-threatening and may indeed be controlled through the use of medications , the greater concern is that these haemorrhages are potentially incapacitating and even life threatening. It is for this reason that all AVMs, regardless of their type, location within the central nervous system or whether or not they have bled, should be carefully evaluated by experts in the field.
WHAT KINDS OF AVMS ARE THERE?
In general, AVMs can be divided into a number of categories based on location or its supposed mechanism of origin. In the interest of space, we will separate these lesions primarily by location and include mechanisms of origin within the individual descriptions:
Brain (so-called "cerebral AVMs"):
These involve primarily the brain matter itself. Over the course of many years, numerous studies have shown that, depending on the size, vessel quality and location, one can predict (though not with 100% accuracy) which AVMs have a high risk bleeding. Currently the theory is that these lesions are most-likely congenital (that is you are born with it).
Dural (may also be referred to as dural fistulas):
These AVMs affect the coverings of the brain principally the outer tough covering called the dura mater. Studies have suggested that these may be acquired in nature, namely environmental events such as head trauma and even infections may be a cause of these lesions. Not all dural AVMs are dangerous or require treatment, in that there are a large number that will not bleed over the course of the individualís life-time.
Spinal:
These AVMs occur in the spinal cord. In this group, there again seems to be various types which may affect the coverings of the spinal cord or the spinal cord itself.
HOW CAN YOU TREAT THESE AVMS?
As briefly discussed above the decision to treat let alone the method to be used to treat it is a decision that requires careful consideration of each individual case. Therefore there is no formula by which one can easily conclude an ideal mode of therapy for any given AVM. However, we will briefly present the various modes of therapy available to you and/or your family/friends that are offered at our institution.
1) OBSERVE: For numerous reasons, the option to follow the course of an AVM is valid. Though this will not cure the AVM, there are times when this is the best mode of therapy at that point in time.
2) RADIOSURGERY: Over the last several years, focal radiation therapy for the obliteration of AVMs and other lesions has made significant progress. In general, small ( < 2.5cm) lesions located in areas of the brain that are not easily accessible by conventional means are excellent candidates for this treatment modality. With the recent addition of the Gamma Knife to the current linear accelerator technology at our institution, Radiosurgery is certainly a strong option in appropriate instances.
3) EMBOLISATION : The last five to ten years has seen a dramatic increase in the role of interventional neuroradiology for the treatment of AVMs. In general, embolization of an AVM serves to obliterate most, if not all of the feeding arteries and parts of the nidus so as to make resection of the AVM safer. Serving primarily as an adjunct to conventional surgery, most patients with AVMs undergo one or several courses of embolization.
4) SURGICAL RESECTION: Ultimately, in order to eliminate the risks of hemorrhage from the rupture of an AVM, the AVM can be resected. As previously mentioned, with the advent of interventional techniques, the surgical resection of AVMs has become safer, thus significantly reducing the risks of the surgery itself.
Situations that may require various other combinations of therapy exist. One of the many benefits of having these options available in one institution is that experts in all the fields listed (i.e. neurosurgeons, neurologists, neuroradiologists, interventional neuroradiologists, radiation oncologists, neuroanesthesiologists, neuroscience nursing) participate in a weekly interdisciplinary conference where all cases are presented and discussed so as to incorporate all necessary disciplines and ultimately develop an indivualized treatment plan for a patient with any given AVM. Such interactions ensure that all aspects of the patientís care are recognized and addressed, while also helping the institution learn more about the disease. It is this kind of interaction that enables institutions such as this push the boundaries of knowledge for a relative rare disease such as this.