Clinical Pearls & Morning Reports
The clinical consequences of cerebral hemorrhage from an arteriovenous malformation depend on the extent of injury to adjacent brain structures. Of patients who survive the initial hemorrhage, approximately 25% ultimately have no neurologic deficit, 30% have mild-to-moderate deficits, and 45% have severe deficits. Three months after hemorrhage, almost 20% of initial survivors have died, and one third of patients remain moderately disabled. Read the new Review Article on this topic.
Q. What is the risk of cerebral hemorrhage associated with an arteriovenous malformation of the brain?
A. The annual risk of hemorrhage from a cerebral arteriovenous malformation is approximately 3%, but depending on the clinical and anatomical features of the malformation, the risk may be as low as 1% or as high as 33%. The risk of cerebral bleeding is increased if the patient has had previous episodes of bleeding or if the malformation is located deep within the brain or brain stem or is characterized by exclusively deep venous drainage. On the basis of various models, patients with none of these risk factors are at very low risk for cerebral hemorrhage (<1% annually), patients with one of these factors are at low risk (3 to 5% annually), patients with two factors are at medium risk (8 to 15% annually), and patients with all three factors are at high risk (>30% annually).
Q. Describe a limitation of stereotactic radiosurgery for treatment of arteriovenous malformations of the brain.
A. Stereotactic radiosurgery is a well-studied treatment for cerebral arteriovenous malformations. Successful obliteration of the arteriovenous malformation is predicted on the basis of the size of the lesion and the dose of radiation delivered to the margins of the malformation (the “marginal dose”). One of the greatest limitations of stereotactic radiosurgery for an arteriovenous malformation is the substantial delay in the radiographic obliteration of the lesion, which takes 2 to 4 years on average. Most data suggest that the risk of bleeding during this period is only slightly lower than the risk during the period before treatment.
Table 1. Spetzler–Martin Grading Scale for Arteriovenous Malformations of the Brain.
A: Embolization before radiosurgery has been proposed to reduce large arteriovenous malformations to a size that permits delivery of a more therapeutic marginal dose. The drawback of embolization before stereotactic radiosurgery is that embolic material in the malformation can shield the nidus from ionizing radiation and may obscure the outlines of the malformation, making targeting with radiotherapy difficult. In keeping with this limitation, nearly all studies have shown that preliminary embolization reduces the efficacy of subsequent stereotactic radiosurgery.
A: In a meta-analysis of 137 observational studies with a total of 13,398 patients and 46,314 patient-years of follow-up, procedure-related complications leading to permanent neurologic deficits or death occurred in 7% of patients who underwent microsurgery or embolization and in 5% of those who underwent stereotactic radiosurgery. Obliteration of the lesion, documented by either magnetic resonance imaging (MRI) or angiography, was achieved in 96% of patients after microsurgery, in 38% after radiosurgery, and in 13% after embolization alone. On the basis of these findings, surgery is generally regarded as the best initial option for patients with arteriovenous malformations associated with a low risk of a poor treatment outcome, particularly grade 1 or 2 lesions. In centers that treat large numbers of cerebral arteriovenous malformations, complete removal or obliteration of the lesion without complications has been achieved with surgery in more than 95% of cases and with radiosurgery in 70% of cases.