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terial that are injected via a balloon catheter that has been navigated into a feeding vessel Complete obliteration of large AVMs is usually not possible by these methods but, they are highly effective in reducing the size of the AVM prior to surgery Kjellberg and Chapman pioneered the treatment of AVMs at the Massachusetts General Hospital using a single dose of subnecrotizing stereotactically directed proton radiation The technique of radiosurgery has been adopted by others using photon radiation sources, such as a linear accelerator, gamma knife, and other modes of focused x-ray radiation, as an accepted alternative to operative treatment of lesions situated in deep regions, including the brainstem, or in eloquent areas of the cortex Generally, malformations smaller than 3 cm diameter are treatable in this way Radiosurgical obliteration of AVMs occurs in a delayed manner, usually with a latency of at least 18 to 24 months after treatment During this early period the patient is unprotected from rebleeding The likelihood of successful treatment and the nature of the risks depend on the location and size of the AVM and the radiation dose delivered After 2 years, 75 to 80 percent of AVMs smaller than 25 cm in diameter have been obliterated Even for those AVMs that have not been totally eliminated, the radiation effect appears to confer some long-term protection from bleeding Of the larger ones, a majority are shrunken or appear less dense The rest have shown no change at this low dose level, but even in this group, the morbidity and mortality are lower than in the untreated group However, a proportion of larger AVMs that are obliterated will recanalize, and many of these will subsequently bleed Among more than 250 patients whose AVMs disappeared following proton beam Figure 34-26 Top: Angiogram of a large parieto-occipital AVM prior to treattherapy, there has been no recurrence of hemorrhage for up ment showing the malformation and greatly enlarged draining veins Bottom: to 10 years; in larger AVMs (approximately the last 1000 Obliteration of the malformation 2 years after proton beam treatment.

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cases) treated in this way, the frequency and severity of hemorrhage have been signi cantly reduced The results of treatment with focused gamma radiation have been about the same In one study, the risk of hemorrhage was reduced by 54 percent between the time of radiation and obliteration of the malformation and by 88 percent thereafter (Maruyama et al) Two types of complications of radiation occur at a combined rate of approximately 2 to 4 percent The rst is delayed radiation necrosis, which is predictable based on the radiation dose, and the second is a venous congestion that occurs several weeks or months after treatment The latter is indicative of the desired effect of thrombosis of the malformation Both cause local symptoms for weeks or months Radiation necrosis may be reduced by the administration of corticosteroids but the vascular problem generally is not helped The treatment of AVMs by endovascular techniques is increasingly popular but has not been fully evaluated Nearly every AVM has several feeding arteries, some not reachable by catheter, and some part of the AVM remains after treatment In most series, 25 percent or more of AVMs, mostly of small and medium size, could be completely obliterated, with a mortality rate below 3 percent and morbidity of 5 to 7 percent, which compares favorably with surgical outcomes These techniques are also particularly well adapted to lesions of a combined AVM and an aneurysm on the feeding vessel Most recently, combined therapy that begins with endovascular reduction of the lesion and is followed by either surgery or radiation has been viewed most favorably In series of patients using this approach, over 90 percent of lesions could be obliterated with a very low rebleeding rate over several years What is clear is that the plan for each patient must be individualized based on the size, location, nature of feeding vessels, the presence of other vascular lesions (aneurysm or additional AVM), and the age of the patient Even then, there will be differences of opinion based on local resources and experience Finally, if the primary problem is recurrent seizure, successful treatment with reduction or cessation of seizures is achieved in a very high proportion of cases The results are comparable to those from surgery and radiation, even if the AVM is not entirely obliterated.

Figure 34-27 Cerebral angiogram of a cerebral dural arteriovenous malformation The nidus is located at the cerebral convexity (arrow) There is rapid ling of the cerebral venous system after injection of dye into one internal carotid artery

These curious vascular abnormalities, occurring in both the cranial and spinal dura, have different presentations at each site; the latter form is discussed with other diseases of the spinal cord in Chap 46 The cranial type is being detected with increasing frequency as re nements continue to be made in imaging of the cerebral vessels, but its true incidence and pathogenesis are not fully known The de ning features are radiologic a nidus of abnormal arteries and veins with arteriovenous shunting contained entirely within the leaflets of the dura The lesion is fed by dural arterial vessels derived from the internal cranial circulation and often, more proli cally, from the external cranial circulation (external carotid artery and muscular branches of the vertebral artery) The venous drainage is complex and is largely into the dural venous sinuses (Fig 34-27) The rapid transit of injected angiographic dye through these stulas accounts for the early opaci cation of the draining venous structures; in the case of high- ow connections, this may not be seen unless images are taken almost immediately after the injection A number of potential feeding vessels must be injected to demonstrate all the conduits into the lesion On CT scanning and MRI, the stula is sometimes detected as a thickening or enhancement of a region

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