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26-01-2012 | Surgery | Article

MRA suitable for monitoring most cerebral aneurysms


Free abstract

MedWire News: Magnetic resonance angiography (MRA) can be used for routine follow up of all but the smallest cerebral aneurysms after coiling, say researchers.

But Pascale Lavoie (Centre hospitalier affilié de l'Université Laval, Quebec, Canada) and team caution that MRA mistakenly identifies some occluded aneurysms as having residual flow. Digital subtraction angiography (DSA) "should be performed before any therapeutic decision is made when a recurrent aneurysm is seen on MRA," they write in Stroke.

The team prospectively studied 149 patients who had 160 coiled aneurysms imaged with MRA and DSA. DSA is the gold standard for assessing aneurysms, but MRA is noninvasive and does not expose patients to radiation.

Immediately after coiling, 92% of the aneurysms had no residual flow. On follow-up imaging, performed between 6 and more than 20 months after coiling, 25% of these had recanalized. Nine of the 37 recanalized aneurysms were retreated.

Time of flight (TOF) MRA was 76% sensitive and 85% specific for detection of DSA-diagnosed recanalization (distinct residual flow into the aneurysm sac; Class 3). The positive and negative predictive values were 67% and 90%, respectively.

This did not change notably with the addition of the contrast-enhanced (CE) MRA sequence reading.

Eight aneurysms diagnosed as Class 3 on DSA were misclassified as Class 2 (subtotal occlusion, little or no residual flow) on TOF MRA and nine were misclassified on CE MRA. Also, three Class 3 aneurysms were misclassified as Class 1 (complete occlusion) on TOF MRA.

Aneurysms diagnosed as Class 1 or 2 on DSA, were falsely diagnosed as Class 3 in 17 instances on TOF MRA and 18 instances on CE MRA.

Lavoie et al note that achieving a higher sensitivity with MRA would come at the price of a lower specificity, and potentially an increased retreatment rate. "Because it is unclear whether the rebleeding risk after aneurysm coiling is worth the risks of recurrent aneurysm retreatment, we must question the benefit and cost-effectiveness of using very high [sensitivity] criteria," they say.

However, the sensitivity of MRA was low for small aneurysms (2-6 mm), at 46% with both TOF and CE sequences, compared with 54% and 92%, respectively, for larger aneurysms (>6 mm). The specificities were similar regardless of aneurysm size.

"Routine use of MRA to follow small aneurysms should wait better estimation of its performance in this particular subgroup," conclude the researchers.

By Eleanor McDermid

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