Arteriovenous malformations (AVMs) are congenital lesions composed of a complex tangle of arteries and veins connected by one or more fistulae (see the image below). They most commonly occur in young adults, with morbidity and death occurring in 30–50% and 10–15% of patients, respectively.
T1 axial MRI showing a small subcortical arteriovenous malformation in the right frontal lobe.
Signs and symptoms
Considerations regarding patient history include the following:
AVMs tend to be clinically silent until the presenting event occurs; therefore, the diagnosis usually is made at the time of the first seizure or hemorrhage
A history of minor learning disability is found in as many as two thirds of patients; such dysfunction is rarely apparent in adult life
A history of headaches is found in as many as half of all patients with cerebral AVM; the headaches subsequently may take the form of classic migraine or more generalized headache
If seizures have occurred, a careful seizure history should be obtained; seizures are simple, partial, or secondarily generalized
Considerations regarding the physical examination of patients with AVM include the following:
Focal neurologic findings are rare in the absence of seizure or hemorrhage in patients with cerebral AVMs; they are more common in AVMs that are deeply located or in the brainstem
Detailed neuropsychological testing may disclose subtle right or left hemisphere dysfunction
If parenchymal hemorrhage is present, the physical findings are indistinguishable from those produced by intracranial hemorrhage from other causes
Intraventricular hemorrhage generally produces a less severe neurologic deficit than does hemorrhage into other areas of the brain
In the rare patients in whom focal neurologic deficits are present, the deficit may reflect the location of the AVM
See Clinical Presentation for more detail.
The following imaging studies are used in the diagnosis and assessment of cerebral AVM:
Computed tomography (CT) scanning: Easily identifies intracerebral hemorrhages, raising suspicion of AVM in a younger person or a patient without clear risk factors for hemorrhage; however, this modality can identify only large AVMs.
Magnetic resonance imaging (MRI): Essential for the initial diagnosis of AVMs; the malformations appear as irregular or globoid masses anywhere within the hemispheres or brainstem; a retrospective analysis demonstrated that silent intralesional microhemorrhage on CT scan/MRI may be a risk factor for intracerebral hemorrhage from a brain AVM rupture
Cerebral angiography: Required for hemodynamic assessment, which is essential for planning treatment
Superselective angiography: Performed with standard cerebral angiography, with access via a femoral artery puncture
See Workup for more detail.
Invasive treatment is recommended for younger patients with 1 or more high-risk features for an AVM rupture. Older individuals and patients with no high-risk features may be best treated through management of the medical aspects of the illness alone; in such patients, anticonvulsants for seizure control and appropriate analgesia for headaches may be the only treatment recommendations necessary.
Invasive treatment of AVMs may include endovascular embolization, surgical resection, and focal beam radiation, alone or in any combination. The current American Heart Association multidisciplinary management guidelines for the treatment of brain AVMs recommend the following approach:
Surgical extirpation is strongly suggested as the primary treatment for AVMs of Spetzler-Martin grade I or II if they are surgically accessible with low risk
Radiation therapy alone is recommended for AVMs of Spetzler-Martin grade I or II if they are less than 3 cm in size and surgery has an increased surgical risk based on location and vascular anatomy
Brain AVMs of Spetzler-Martin grade III can often be treated with a multimodal approach that uses embolization followed by surgical extirpation. If the lesion has a high surgical risk based on location and vascular anatomy, radiation therapy may be performed after embolization
AVMs of Spetzler-Martin grade IV or V are often not amenable to surgical treatment alone because of the high procedural risk; these AVMs can be treated using a combined multimodal approach that includes embolization, radiosurgery, and/or surgery
In general, embolization should be performed only if the goal is complete AVM eradication with other treatment modalities; the only exception is palliative embolization in patients with an AVM of Spetzler-Martin grade IV or V with venous outflow obstruction or true steal phenomenon, in order to reduce arterial inflow to control edema or to reduce the amount of shunt, respectively
See Treatment for more detail.