Limitations of magnetic resonance imaging and magnetic resonance angiography in the diagnosis of intracranial aneurysms

OBJECTIVE: Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are being used with increasing frequency for the diagnosis of intracranial aneurysms. Although the literature suggests that MRI and MRA are accurate, we have observed that both are associated with a high likelihood of false-positive results in the diagnosis of aneurysms. We prospectively evaluated and compared the accuracy of MRI/MRA versus digital subtraction angiography (DSA) for the diagnosis of intracranial aneurysms. METHODS: Over the course of 2 years, 133 patients diagnosed with one or more unruptured intracranial aneurysms by MRI/MRA were prospectively evaluated in an outpatient setting. The patients were advised to undergo cerebral four-vessel DSA, and the results from DSA were compared with MRI/MRA findings. RESULTS: In 59% of cases, the DSA and MRI/MRA findings were markedly different. Specifically, in 38% of MRI/MRA-positive cases, DSA findings were completely normal, showing no aneurysms. In an additional 21% of cases, although DSA confirmed the presence of an aneurysm, it differed substantially from MRI/MRA findings in terms of aneurysm location, number of aneurysms, or aneurysm type. In general, the false-positive aneurysms by MRI/MRA were smaller than 5 mm and were most commonly identified in the anterior communicating artery region. CONCLUSION: MRI/MRA studies are often inaccurate in the diagnosis of intracranial aneurysms and should not be used as the sole diagnostic studies for intracranial aneurysms. Other radiographic modalities should be further investigated as alternatives to MRI/MRA for the diagnosis of intracranial aneurysms.