Middle Cerebral Artery Infarcts Encompassing the Insula Are More Prone to Growth

Abstract

Background and Purpose-Based on previous observations that infarcts encompassing the insula were linked to unfavorable clinical outcome, we hypothesized that insular damage was directly associated with worsened infarction in ischemic but potentially viable neighboring brain tissue. Methods-Using acute diffusion-and perfusion-weighted MRI within the first 12 hours of symptom onset and a follow-up MRI on day 5 or later, we calculated the percentage of mismatch lost (PML) in 61 consecutive patients with ischemic stroke within the middle cerebral artery territory. PML denoted the percentage of mismatch tissue between diffusion-weighted imaging and mean transit time maps that eventually underwent infarction. We explored the relationship between PML and insular location using a regression model. Results-The median PML was 17.7% (interquartile range, 3.5% to 54.2%) in insular and 2.5% (0.0% to 12.7%) in noninsular infarcts (PϽ0.01 Key Words: cerebral infarct Ⅲ diffusion-weighted imaging Ⅲ heart-brain relationships Ⅲ insula Ⅲ MRI Ⅲ neurocardiology Ⅲ sympathetic nervous system T he insula, or the island of Reil, is an invaginated portion of the cortex that is completely enclosed within the sylvian fissure. Although the first description of the insula dates back 200 years ago, 1 insular infarcts and their clinicanatomic features have not been studied in depth. This is partly because insular infarcts are only occasionally exclusively limited to the insula 2,3 ; more frequently, they occur as a part of large middle cerebral artery (MCA) territory infarcts. 3 Despite the infrequency of solitary insular infarction, infarcts that encompass the insula are associated with higher stroke severity and poorer clinical outcome compared with infarcts sparing the insula. [3][4][5][6] The exact means by which insular infarcts are associated with unfavorable outcome is not known. At first glance, the large size of infarcts due to proximal MCA occlusions that accompany insular infarcts may be a reason for unfavorable outcome. However, alternative approaches may also be worthy of consideration. The insula is a functional integration site for autonomic responses and therefore, unlike most other brain regions, it has a unique ability to provoke systemic responses. 7 Autonomic responses such as alterations in blood glucose, blood pressure, myocardial contractility, and body temperature can in turn contribute to adverse tissue outcome in cerebral ischemia. 4,8 -10 In the current study, we sought to test the hypothesis that insular damage is a risk factor for increased conversion of ischemic but potentially viable neighboring tissues into infarction in patients with MCA stroke. Methods Study PopulationThe current study was a retrospective analysis of a prospective, ongoing, National Institutes of Health-funded study evaluating the use of diffusion-weighted imaging (DWI) and perfusion-weighted imaging in predicting tissue risk of infarction in acute stroke. The study enrolled consecutive patients who were admitted within the first 12 hours of s...

Percentage Insula Ribbon Infarction of >50% Identifies Patients Likely to Have Poor Clinical Outcome Despite Small DWI Infarct Volume

“…[5][6][7]10,11 Of note, diffusion and perfusion MR imaging have been used to demonstrate that infarctions of the insula are associated with an increased percentage of mismatch loss (conversion of potentially viable neighboring penumbra into infarction). 5,7 Fink et al 6 dichotomized patients with insula infarcts into "major" (equal to or more than two-thirds on 1 section or Ͼ50% on Ն2 sections) versus smaller "minor" insula lesions and found major insula infarct involvement to be associated with larger MCA territory infarcts and higher NIHSS scores, indicating more severe clinical deficits. In another study, Christensen et al 10 showed significantly worse mRS scores at 3 months in patients with right-sided insula infarcts compared with those with left-sided infarcts or no insula involvement.…”

“…Prior studies have suggested that prox-imal MCA infarcts that involve the insula are associated with infarct growth and unfavorable clinical outcome. [5][6][7] This association is understandable from knowledge of the vascular supply of the insula, which comprises almost exclusively superior and inferior division M2 branches. An infarct from a proximal MCA occlusion that spares the insula may be indicative of good MCA collateral flow, whereas an infarct from a proximal MCA occlusion with insula involvement may be a sign of insufficient MCA collateral flow.…”

Cortical lateralization and cardiac autonomic control. Insights from insular stroke and epilepsy

“…Therefore, insula is often involved in MCA ischemic stroke. However, strictly insular strokes represent a rare occurrence [6,7].…”

Cerebral regions preserved by successful endovascular recanalization of acute M1 segment occlusions: a voxel based analysis

“…27 It is likely that the vascular supply to the insula reflects the confluence of bulk flow through the MCA divisions, clot location and collateral flow. 28,29 Moreover, topographic studies have shown that the insula has higher vulnerability for infarction following hypoperfusion (i.e. reduced blood flow).…”