Arteriovenous malformations (AVMs) are defects in the vascular system, consisting of tangles of abnormal blood vessels.
Arteriovenous malformations (AVMs) are defects in the vascular system, consisting of tangles of abnormal blood vessels (nidus) in which the feeding arteries are directly connected to a venous drainage network without interposition of a capillary bed. Arteries carry oxygen-rich blood away from the heart to the rest of the body’s tissues and cells, veins return oxygen-depleted blood to the lungs and heart; capillaries connect the arteries and veins. The presence of an AVM disrupts this vital cyclical process, causing a snarled tangle of arteries and veins that are connected to one another without the presence of any capillaries.
An AVM can occur anywhere in the body, but brain and spinal AVMs present substantial risks when they bleed. Because the brain and its blood vessels are formed together during embryological development, abnormal blood-vessel formation is often associated with abnormal brain tissue. Little is known about the etiology of brain AVMs. The cause of brain AVMs is debated, although it is likely multifactorial; with both genetic manipulation and angiogenic stimulation (the physiological process through which new blood vessels form from pre-existing vessels) appearing to play roles during AVM development. Some believe that AVMs develop in utero, while others advocate an angiopathic reaction, following either a cerebral ischemic or hemorrhagic event (sub-types of stroke) as a primary factor in their development.
Incidence and Prevalence
The incidence of AVM is estimated at one in 100,000.
The prevalence of AVM is estimated at 18 in 100,000.
An estimated two-thirds of AVMs occur before age 40.
Every year, about four out of every 100 people with an AVM will experience a hemorrhage.
Each hemorrhage poses a 15- to 20-percent risk of death or stroke, 30-percent neurological morbidity, and 10-percent mortality.
When hemorrhage occurs, it affects the following regions statistically: intracerebral (41%), subarachnoid (24%), intraventricular location (12%) and various combinations (23%).
AVMs are the second most identifiable cause of subarachnoid hemorrhage after cerebral aneurysms, accounting for 10 percent of all cases of subarachnoid hemorrhage.
About 1 percent of people with AVMs will develop epileptic seizures for the first time.
Approximately 50 percent of patients present initially with a bleed; often patients with an AVM experience no symptoms, and their AVMs are discovered only incidentally, usually either during an autopsy or during treatment for an unrelated disorder. The proportion of patients being diagnosed with un-ruptured AVMs has almost doubled in the past three decades, with improved non-invasive imaging. About 12 percent of people with AVMs will experience symptoms, varying in severity. AVMs can irritate the surrounding brain tissue and cause seizures or headaches. Any of the following symptoms may occur:
Seizures, new onset
Muscle weakness or paralysis
Loss of coordination
Difficulties carrying out organizational tasks
Abnormal sensations such as numbness, tingling, or spontaneous pain
Traditionally, the annual rupture rate of 4 percent has been cited for brain AVMs, based on a study on natural history of symptomatic AVMs; this study also included the AVMs that had previously ruptured. The bleeding risk of AVM’s range from 1-8% per year.
AVMs are usually diagnosed through a combination of magnetic resonance imaging (MRI) and angiography. These tests may need to be repeated to analyze a change in the size of the AVM, recent bleeding or the appearance of new lesions. Left untreated, AVMs can enlarge and rupture, causing intracerebral hemorrhage or subarachnoid hemorrhage, resulting in permanent brain damage. Deep bleeding is usually referred to as an intracerebral or intraparenchymal hemorrhage; bleeding within the membranes or on the surface of the brain is known as subdural hemorrhage or subarachnoid hemorrhage
The damaging effects and the extent of damage in the neurological status of patients from a hemorrhage are related to lesion location. Bleeding from AVMs located deep inside the interior tissues, or parenchyma of the brain, generally causes more severe neurological damage than does bleeding from lesions located in the dural or pial membranes or on the surface of the brain or spinal cord. AVM location is an important factor to consider when weighing the relative risks of surgical versus nonsurgical treatment. Preventing the rupture or re-rupture of vascular malformations is one of the major reasons that early neurosurgical treatment is recommended for AVMs.
The goal of brain AVM treatment is typically the prevention of new or recurrent hemorrhage from rupture. However, seizure control or stabilization of progressive neurological deficits are occasionally treatment goals.
he management options for brain AVMs (ruptured or un-ruptured) include observation or various treatment techniques, such as microsurgical techniques, endovascular embolization and stereotactic radiotherapy used alone or in combination with varying degrees of treatment-associated morbidity and mortality. A treatment plan is devised to offer the lowest risk, yet highest chance of obliterating the lesion.
Reproduced by permission of the copyright owner. American Association of Neurological Surgeons, 5550 Meadowbrook Dr., Rolling Meadows, IL 60008. Further reproduction prohibited without permission, 2016.