Original contributionNoncontrast dynamic MRA in intracranial arteriovenous malformation (AVM): comparison with time of flight (TOF) and digital subtraction angiography (DSA)
Introduction
Intracranial arteriovenous malformations (AVMs) are congenital vascular abnormalities characterized by direct arteriovenous shunts through a nidus of coiled and tortuous vascular connections without a normal intervening capillary bed. The principal presentation of AVM patients is hemorrhage which accounts for 2%–4% of overall hemorrhagic strokes [1], conferring significant morbidity and mortality. Detailed information about the architecture and hemodynamics of AVM is of great value with respect to adequate diagnosis and ensuing therapeutic approaches [2].
Digital subtraction angiography (DSA) remains the gold standard for the characterization and delineation of intracranial AVMs. However, as an invasive technique, it exposes both doctors and patients to the radiation of X-rays and carries risks related to puncture of femoral artery, catheter placement, contrast agents and experience of doctors [3]. Time-resolved contrast-enhanced magnetic resonance angiography (CE-MRA) is a promising technique in the assessment of both anatomic and hemodynamic information, but its temporal resolution is relatively low (generally on the order of seconds), which might not be sufficient to capture the fast-flow hemodynamic information. Also, complications may occur with the application of gadolinium-based contrast agents such as nephrogenic systemic fibrosis when the glomerular filtration rate is lower than 30 ml/min [4]. Standard time-of-flight (TOF) MRA provides static vascular images with high spatial resolution; however, it cannot provide hemodynamic information. Recently, an unenhanced four-dimensional (4D) time-resolved dynamic MRA (dMRA) technique was introduced by combining arterial spin tagging with a multiphase true fast imaging with steady-state precession (TrueFISP) sequence [5], [6]. In preliminary studies, this 4D dMRA technique was able to delineate the dynamic course of blood flow through an AVM with a temporal resolution of a few tens of milliseconds and a spatial resolution of a few cubic millimeters.
In this paper, we attempted to evaluate the clinical utility of the 4D dMRA technique in a cohort of AVM patients using Spetzler–Martin grading scale (size, eloquence of adjacent brain and pattern of venous drainage) [7] ( Table 1), which has been traditionally used to estimate the risk of surgical intervention, as the reference. In addition, other factors that are important for the evaluation of AVMs or deemed as significant determinants of risks and outcomes such as the pattern of supplying artery and draining vein, AVM-related aneurysms, presence of arteriovenous fistula (AVF) and detailed hemodynamic information were evaluated [8], [9], [10]. These results were then compared with those of DSA and TOF MRA, respectively, to test whether the information derived from dMRA is consistent with the gold standard of DSA and whether dMRA will improve the existing diagnosis based on TOF MRA.
Section snippets
Patients
This study was approved by the institutional review boards, and written informed consent was obtained from all patients. The general contraindications for MR examination were applied and defined as exclusion criteria.
Between July 2009 and November 2010, 19 patients (12 women, 7 men, mean age 26.2±10.7 years) with intracranial AVM scheduled for DSA examination were included in this prospective study. Among them, four patients experienced spontaneous intracranial hemorrhage (all occurred within 4
Results
All the 19 AVMs demonstrated a typical appearance with one or more feeding arteries, an appreciable nidus and at least one readily identifiable draining vein entering venous sinuses, and no AVM-related aneurysm or AVF was found on DSA. Dynamic MRA was able to depict the entire dynamic blood circulation from arterial feeders to draining veins of cerebral AVM in accordance with DSA ( Fig. 1, Supplemental Video 1). It failed to detect AVM lesions in three patients (patient nos. 1, 7, 12). In
Discussion
Spetzler–Martin grading scale has been traditionally used to estimate the risk of surgical intervention for intracranial AVM and has been validated by its correlation with outcomes for surgically treated patients. All AVMs fall into one of six grades, and the higher the grade is, the poorer the outcome for operative treatment. Many risk factors have been studied to predict hemorrhage of intracranial AVM. Some research showed that patients with small (≤3 cm) AVMs presented more frequently with
Conclusion
As a newly emerging and promising technique, noncontrast unenhanced dMRA can be easily implemented in clinical routines due to its noninvasive feature and relatively fast acquisition time. In this pilot study performed on 19 AVM patients, dMRA was capable in depiction of the size and location of AVM, moderate in description of feeding arteries and poor in detection of draining veins. Most information it provided was in accordance with DSA. Although it cannot replace either DSA or TOF for
Acknowledgment
This work was supported by the National Natural Science Foundation of China (30830101) and the Ministry of Science and Technology of China grants (2010IM030800). This work was also supported by US National Institutes of Health grant MH080892.
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