Is an Early Angiogram Needed?

The value of arteriovenous malformation (AVM) radiosurgery is its noninvasive nature, and efforts should be made to minimize the invasiveness that is relevant to associated diagnostic imaging procedures. MR imaging, for diagnosis, treatment guidance, and follow-up is the most helpful tool to meet this purpose. For many AVMs that have a classic MR appearance, we may reconsider the use of diagnostic X-ray angiography to determine the feasibility of radiosurgery. For radiosurgical guidance, stereotaxic X-ray angiography remains the standard of reference imaging technique (1), and for those AVMs with repeated episodes of hemorrhage or previous partial surgical extirpation, X-ray angiography is mandatory. Stereotaxic MR imaging, however, is of great value in providing three-dimensional delineation of the AVM nidus, which is the only target in AVM radiosurgery (2). In AVM radiosurgery, stereotaxic X-ray angiography and stereotaxic MR imaging are performed on the same stereotaxic system, and the location and coordinates of the target lesion in the stereotaxic space is transferable. We are, therefore, able to integrate the information derived from MR imaging and X-ray angiography for a better delineation of the AVM nidus. This imaging strategy improves the delivery of effective dose levels and provides a better irradiation volume in AVM radiosurgery. It, consequently, safely expands the indication of radiosurgery for larger AVMs and explores new indications, such as dural arteriovenous fistulas of the cavernous sinus with radiosurgery (3–5).

After radiosurgery, the involuting AVM seems to be equally “visible” on both MR images and X-ray angiograms. MR imaging can show a decreasing size as early as 3 months after radiosurgery (6). Concerning the bleeding rate of AVMs treated radiosurgically in the time lag prior to complete obliteration, the data available in the literature is controversial. Our data, based on follow-up of our protocol of AVM patients, have shown that the clinical bleeding rate in this time period is lower than the natural history of bleeding. Subclinical hemorrhage, however, (eg, petechia in AVM regions), as depicted on MR images, is much more frequent than expected (7). In documenting complete obliteration in AVM radiosurgery, MR imaging plays a vital role (8). The challenge to neuroradiologists should be to use MR imaging exclusively to verify complete AVM obliteration.