Cranial Dural Arteriovenous Malformations
Paul W. Detwiler, MS, MD,
Cesar de Paula Lucas, MD†
Joseph M. Zabramski, MD
Cameron G. McDougall, MD
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona
†Division of Neurological Surgery, Hospital Orthopedico de Goiania, Goiania, Brazil
Dural arteriovenous malformations represent 10 to 15% of intracranial vascular malformations. They are characterized by the presence of an abnormal arteriovenous fistula or nidus located in the dura. Common nidus locations include the transverse, sigmoid, and cavernous sinuses as well as the falx and floor of the frontal fossa. The natural history of these lesions varies with location and pattern of venous drainage. Certain patterns of venous drainage, especially retrograde leptomeningeal venous drainage, are associated with a high risk of hemorrhage. Therapeutic options for the management of these lesions include transarterial and/or transvenous embolization, direct surgical obliteration, or a combination of the two. This review examines the natural history of these lesions, the indications for treatment, and the selection of approaches for their management.
Key Words: arteriovenous malformation, dural fistula, embolization, resection
Intracranial dural arteriovenous malformations (DAVMs) consist of an abnormal arteriovenous fistula or nidus within the dura. They occur about one-tenth as frequently as their intraparenchymal counterparts. Most DAVMs behave benignly, occasionally even involuting on their own. However, they also can become symptomatic with an aggressive neurological course that includes seizures, focal neurological deficits, and hemorrhage.[5,8,9,17] To manage these lesions effectively, one must be able to identify the risk factors associated with a poor natural history.
The idea that the natural history of these lesions could be predicted by the pattern of venous drainage was first suggested by Houser et al. in 1972. They concluded that intracranial hemorrhage occurred when venous drainage of the lesions was limited to the pial (leptomeningeal) veins. These findings were confirmed and expanded by others.[3-6,8-10,16,19,20] Lesions that drain freely into a dural sinus tend to have a benign course, whereas those with evidence of cortical (leptomeningeal) venous drainage are associated with hemorrhage and neurologic deficits and symptoms.
In certain locations, such as the floor of the anterior cranial fossa and the tentorium cerebelli, DAVMs appear to be associated with an aggressive course. Lesions in these locations, however, are commonly associated with extensive retrograde pial drainage as an independent risk factor. No location is immune to the risk of hemorrhage and neurological deficits. Location only raises the index of suspicion for the presence of dangerous venous anatomy.
Treatment options for the management of DAVMs include endovascular embolization by transarterial or transvenous routes, surgical obliteration, or a combination of these two. Location and the pattern of venous drainage determine the best approach to an individual lesion. The purpose of this review is to examine the natural history of these lesions, their indications for treatment, and the selection of therapeutic options.
DAVMs may be either congenital or acquired lesions.[2,7,12,13,15] Patients with a presumably acquired dural AV fistula often have a history of previous trauma, craniotomy, or venous sinus thrombosis.
Two mechanisms have been proposed to account for the formation of acquired dural AV fistulae. The first is based on the proximity of dural arteries and veins, which presumably predisposes to direct connections after trauma. The second model assumes that inflammation (e.g., secondary to trauma, infection, surgery, tumor) or spontaneous thrombosis leads to occlusion of a sinus with the opening of preexisting, minute AV fistulae that exist in the walls of the sinus.[2,13,15] This theory has been tested in a rat model. Dural AV fistulae were produced in rats subjected to a combination of venous sinus thrombosis and increased venous sinus pressure.
Despite advances in noninvasive neuroimaging, angiography remains the "gold standard" for the diagnosis of DAVMs. Evaluation should include selective, bilateral injections of the internal (ICA) and external carotid (ECA) arteries as well as the vertebral artery because lesions are often fed by multiple branches on both sides regardless of anatomic location. The ability to define both the magnitude and direction of blood flow highlights the value of angiography compared to computed tomography or magnetic resonance imaging.
The successful treatment of DAVMs requires a thorough understanding of both arterial and venous anatomy. The location of the lesion and the venous characteristics are the most important features determining the approach to treatment.
Natural History and Classification
The clinical presentation of patients with DAVMs is quite variable. Their course can be benign with spontaneous involution of the fistula or frankly aggressive, manifesting with seizures, focal neurological deficits, or intracranial hemorrhage. The clinical presentation and natural history of these lesions are related to their venous anatomy.
Pulsatile tinnitus is a common initial symptom of DAVMs draining into the transverse and sigmoid sinuses.[3,8] The bruit itself is benign but may be disabling to patients. A significant change in the character of the bruit requires reassessment. A decrease in the intensity of a bruit can reflect involution of the DAVM but can also result from obstruction of the draining dural sinus and diversion of outflow into the leptomeningeal venous system.
Neurological symptoms other than tinnitus can be caused by three physiopathological mechanisms: (1) direct compression of neural structures by a dysplastic vein(s); (2) venous hypertension;[3,8,16] or (3) an intracerebral, subarachnoid, or subdural hemorrhage of ruptured leptomeningeal draining veins.[5,17] Nonspecific headache related to venous hypertension can be the only symptom of a DAVM and should be explored if the patient has a history of cranial trauma or paranasal sinus infection. Ocular pain associated with chemosis (red eye syndrome), with or without pulsatile exophthalmos, suggests a DAVM in the cavernous sinus. Atypical facial pain or trigeminal neuralgia can be caused by direct compression of the respective cranial nerves by dilated venous channels. Seizure activity and hydrocephalus or papilledema are less common clinical manifestations of DAVMs related to the effects of local and generalized venous hypertension, respectively.