The paper reviewed here is ‘Insular Cortex Infarction in Acute Middle Cerebral Artery Territory Stroke. Predictor of Stroke Severity and Vascular Lesion‘ by John Fisk and colleagues. I’ve selected the paper in order to develop the model of insular cortex function on the blog although this is more of a neurology paper which however fits within the domain of the medical article reviews.
The aim of this study were to characterise the cardiovascular consequences of strokes involving the insular cortex and also to look at the imaging findings in these cases.
People with strokes who were admitted to the Beth Israel Deaconess Medical Center over a 3-year period were identified from a database retrospectively and several types of data were collected from the records providing the patient had undergone an MRI study within 48 hours. Patients with lacunar stroke were excluded. Statistical tests to be used depending on the type of data were specified and these included the Wilcoxon rank sum test and the t-test.
There were 150 people (average age 71) admitted with acute strokes. 72 of these people had strokes which involved the insular cortex as identified by diffuse-weighted imaging. There was a roughly equal division of major and minor insular cortex lesions. There were no lesions involving the insular cortex alone without the other areas of the MCA territory. 84% of cases of major insular infarction involved vascular occlusions proximal to and including M1 MCA.
An interesting finding was the correlation between the CT scan results and the MRI results. If a CT insular ribbon sign was identified then in all cases there was a major insular infarction identified on the corresponding MRI. If there was no finding on the CT scan then there was either minor or no involvement of the insular cortex found in the MRI scan.
With regards to the cardiovascular findings these could be summarised as follows
(1) Receiving acute antihypertensives – 4 people with no insular cortex involvement
(2) Minor ECG changes – No significant difference between insular infarction and non-insular infarction groups
(3) Clinically significant new arrythmia – this was a kind of interesting finding – insular infarction group v non-insular infarction group – significant difference at 0.06 level.
(4) Congestive cardiac failure – one patient – insular cortex involvement not specified
(5) Myocardial infarction – no documentation in patient group during admission
(6) 2 unexpected sudden deaths – no insular cortex involvement in one (possible pulmonary embolism) and post-CABG CVA in the other (minor L.P insular infarct)
(7) Reduced diastolic blood pressure in the the group with insular infarction – this time it was significant at the .02 level. (Reduced pulse rate however was associated with lenticulostriate involvement).
The authors comment that the Insular Cortex is a vulnerable region of the brain in terms of strokes because it doesn’t receive a collateral supply from the posterior or anterior arteries. The authors also concluded that they weren’t able to investigate the more subtle cardiovascular parameters as this was a retrospective study. I would also argue that
(1) It wasn’t clear whether the relationships above were for unilateral or bilateral involvement of the Insular Cortex
(2) If there was Insular Cortex involvement does that necessarily mean that the affected Insular Cortex doesn’t function at all? There could be residual function within the affected cortex.
(3) The other possibility is that in cases of unilateral involvement, the contralateral cortex will be able to compensate thus concealing some possible cardiovascular-related functions of the insular cortex.
(4) The Insular Cortex may function as part of a circuit which may have multiple redundant pathways meaning that loss in any part of this circuit can be compensated by the other areas. Indeed point (3) could be considered to be an example of this argument.
The study is interesting as it identifies possible Insular Cortex functions from clinical observations as well as providing some potentially useful negative findings.
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