Report from MDCT Symposium: Modalities seesaw for advantage in cerebral aneurysm detection

Multislice CT angiography boasts multiple advantages over MRA and digital subtraction angiography for detecting cerebral aneurysms, but the playing field is changing. Advances in rotational DSA (rDSA) are turning that technique into a powerful tool, said Dr. Nancy Fischbein, a neuroradiologist at Stanford University, speaking at the seventh annual Symposium on Multidetector-Row CT in San Francisco.

Key advantages of CT include speed and ease of use, high resolution, and the ability to visualize veins and adjacent anatomy and to demonstrate active bleeding. Where CT weakens compared with MRA and DSA is its dependence on radiation, iodinated contrast, bolus injection, and complex postprocessing.

MRA also offers high resolution, albeit lower than CTA. But postprocessing, repeat exams, and follow-up are all easily performed. MRA drawbacks in cerebral aneurysm detection include contraindications, inability to scan very sick or uncooperative patients, and flow and susceptibility artifacts, Fischbein said.

DSA is the accepted gold standard, with high resolution and a rotational option. But its invasive nature and complications rate are significant drawbacks.

For screening to determine if an aneurysm is present, both CTA and MRA are useful, according to Fischbein. In diagnostic mode, to address acute symptoms or suspected subarachnoid hemorrhage, CTA is preferred. DSA is the winning technique for use in treatment.

For initial evaluation and diagnosis, however, the question remains whether both CTA and DSA are needed, she said.

"CTA can guide and limit the DSA exam, providing a road map for surgeons if patients cannot complete angiography," she said. "Many patients are simply unable to hold still long enough."

Use of CTA alone is an increasingly viable option, but all three techniques are constantly evolving, Fischbein said. A review of the literature shows that rDSA is more accurate than CTA in aneurysm detection, but the findings have not been statistically significant.

CTA advances in progress will overcome limitations related to skull base evaluations and postprocessing methods. But one of its biggest pitfalls - when radiologists miss multiple aneurysms because they stop looking after finding one - can be avoided simply by paying better attention, she said.

"I call it the rule of 'n-plus-one'," Fischbein said. "Where there is one aneurysm there might be more. Keep looking. Don't assume you've satisfied your search just because you've found one or even two cerebral aneurysms."