Percent insula infarction may help predict stroke treatment response



SAN DIEGO – The percentage of anterior insula that is infarcted at the time of admission in patients with acute middle cerebral artery occlusive stroke predicted infarct growth without significant revascularization in 74 consecutive patients who underwent intra-arterial therapy.

"We believe the insula is an overlooked biomarker. ... Although we have not proven it yet, we think it may do a better job than perfusion mismatch in stratifying patients who are likely to benefit from intra-arterial therapy [IAT] from patients unlikely to benefit," said Dr. Michael H. Lev, coauthor of the study and director of emergency neuroradiology and radiology at Massachusetts General Hospital’s Institute for Heart, Vascular, and Stroke Care in Boston.

Two neuroradiologists rated the admission diffusion-weighted imaging (DWI) scans of the patients according to percent anterior and posterior insula infarction using a 4-point scale (normal, less than 50%, greater than 50%, and 100%). (The anterior insula is approximately 25% of the whole insula.) Admission DWI and follow-up MRI core infarct volumes were segmented, and infarct growth was determined. Patients were stratified into those with good (TICI [thrombolysis in cerebral infarction] grade 2-3) vs. poor (TICI grade 0-1) recanalization.

No or poor recanalization occurred in 23 (31%) patients, according to Dr. Livia Morais, who presented the findings at the annual meeting of the American Society of Neuroradiology. In this group, the percent anterior insula infarct was the only predictor of infarct growth in both univariate and multivariate analyses (Spearman Rho = 0.43, P = .04). Predictors of final infarct volume were age, anterior/posterior/total insula percent infarct, and DWI lesion volume at admission (all P less than .05).

For the 69% with good recanalization, National Institutes of Health Stroke Scale score at admission was the only predictor of infarct growth in both univariate and multivariate analyses (Spearman Rho = 0.34, P = .02). Predictors of final infarct volume were percent anterior/posterior/total insula infarct and DWI lesion volume at admission (all P less than .05).

Patients who had less than 50% anterior insula infarct had significantly lower infarct volume (P less than .0001) and infarct growth (P less than .03), compared with those who had greater than 50% anterior insula infarct involvement.

One reason the investigators are focusing on the insula is that it is seen as a region of high ischemic vulnerability. "We speculate that anterior insula infarction may be a stronger surrogate for overall stroke severity than is DWI lesion volume because the unique vascular supply of this location reflects the combined effects of not only the degree of superior division MCA occlusion, but also the quality of collateral flow from both the anterior and inferior MCA divisions, as well as other pial collateral sources," said Dr. Morais, a neuroimaging fellow at Massachusetts General Hospital’s neurovascular laboratory.

This work is part of a body of research looking to identify treatment-relevant acute imaging targets, Dr. Lev said. "We are trying to break patients up into groups with high risk-to-benefit ratios and low risk-to-benefit ratios. Those who fall in-between, if they have no other exclusion criteria, can be treated." The results of this study indicate that patients who are IAT candidates with diffusion-weighted imaging lesion volume of less than 70 mL may be stratified into those with a high likelihood of benefitting from IAT based on the percent anterior insula involvement, he said.

In previous work, Dr. Lev showed that the insula was a very good predictor of aphasia recovery after infarction (Am. J. Neuroradiol. 2010;31:1661-8). The insula was also one of several predictors of motor improvement after stroke (Neurology 2012;78:1853-9). In another study, Dr. Lev said that infarction of the right insula and peri-insular regions was associated with the development of hospital-acquired pneumonia, which he attributed to the insula’s involvement with swallowing and immune modulation.

Dr. Morais said he had no relevant financial disclosures. Dr. Lev said he has received research funding from GE Healthcare.

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