Introduction: Stereotactic radiosurgery is ideal for treating small cerebral arteriovenous malformations that are surgically inaccessible, but the inherent delay of AVM obliteration and the potential of radiosurgical failure necessitate safe and accurate follow-up imaging.
In this study, we aimed to determine the accuracy of an MRI diagnosis of complete thrombosis, establish the risk of hemorrhage in patients with an MR image indicating AVM obliteration, and identify variables that affect the precision of MRI assessment.
Methods: One hundred and twenty patients were reviewed after receiving radiosurgery at the University of Florida from 1990 to 2010. Each patient had an MRI demonstrating AVM obliteration and an angiogram either confirming or denying AVM thrombosis. AVM volume, MRI Tesla strength, and incidence of hemorrhage were documented.
Results: MRI correctly predicted AVM obliteration in 82% of patients. Comparison of nidus size demonstrated a significant correlation between AVM volume and MRI accuracy.
Logistic regression analysis revealed a significant linear relationship between the natural log of AVM volume and the probability of MRI agreement. A separate model showed significant evidence of a cutoff point in MRI accuracy near an AVM volume of 2.80 cm3, above which MRI agreement with angiography is 90%, and below which MRI agreement falls off sharply to remain roughly constant at 70%.
Only one patient experienced a hemorrhage after MRI indicated complete thrombosis. The average follow-up time was 2.05 years, and the risk of hemorrhage was 0.4% per year.
Conclusions: MRI is a useful diagnostic system for assessing AVM obliteration, but its accuracy is inherently linked to the volume it is measuring. Angiography is necessary for final confirmation of obliteration in smaller AVMs. However, the therapeutic benefit of evaluating larger AVMs with angiography is questionable. These results suggest MRI may be able to take on an increasingly independent role in the evaluation of AVM regression.
Patient Care: While angiography may be the ideal method of confirming AVM thrombosis after radiosurgery, the risks of permanent neurological complications, nephrotoxicity, endothelial damage, and exposure to radiation associated with the procedure remain a concern. In addition, patients are often lost to follow up due to an aversion of invasive imaging.
MRI is unique because it is a noninvasive imaging technique with high sensitivity that doesn’t rely on ionizing radiation. It is therefore important to determine if MRI is a safe and effective option to monitor AVM regression after radiosurgery, and to understand the risk of hemorrhage in patients with an MR image indicating thrombosis.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Understand the strengths and weaknesses of evaluating AVM occlusion with MR imaging after stereotactic radiosurgery
2) Identify how variables such as nidus volume influence the accuracy of MRI
3) Distinguish the incidence of hemorrhage in patients with an MRI showing thrombosis compared to the natural progression of hemorrhage in patients with untreated AVMs