Subcortical aphasia and the problem of attributing functional responsibility to parts of distributed brain processes

Variability in aphasia following subcortical hemorrhagic lesion

Background

Vascular lesion of the subcortical structures leads to aphasia. Cortical hypoperfusion has been proposed to be the etiological mechanism in aphasia following subcortical vascular lesion. Subcortical aphasia shows considerable variability in its clinical profile. Such variability has been attributed to the variable sites of cortical hypoperfusion following ischemic lesion of the subcortical structures.

Purpose

This study investigated the variability in clinical aphasic profile following subcortical hemorrhagic lesion.

Methods

We retrospectively investigated the clinical aphasic profiles of twelve patients who reported to our hospital during a period of one year with subcortical hemorrhagic lesions. All patients underwent routine neurological examination, neuroimaging (CT/MRI) investigations and linguistic assessment.

Results

Eight patients exhibited lesion to the basal ganglia and four showed thalamic lesion. All of them showed considerable variability in their aphasic profile.

Conclusion

Subcortical hemorrhagic lesion leads to variability in aphasia. Variability in aphasia may be considered as an important consequence in subcortical vascular lesion. Observations from this study were suggestive of better preservation of, and when affected, faster recovery of comprehension skills.

Subcortical aphasia and neglect in acute stroke: the role of cortical hypoperfusion

We have hypothesized that most cases of aphasia or hemispatial neglect due to acute, subcortical infarct can be accounted for by concurrent cortical hypoperfusion. To test this hypothesis, we demonstrate: (i) that pure subcortical infarctions are associated with cortical hypoperfusion in subjects with aphasia/neglect; (ii) that reversal of cortical hypoperfusion is associated with resolution of the aphasia; and (iii) that aphasia/neglect strongly predicts cortical ischaemia and/or hypoperfusion. We prospectively evaluated a consecutive series of 115 patients who presented within 24 h of onset or progression of stroke symptoms, with MRI sequences including diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI), and detailed testing for aphasia or hemispatial neglect. The association between aphasia or neglect and cortical infarct (or dense ischaemia) on DWI and cortical hypoperfusion indicated by PWI, was evaluated with chi-squared analyses. Fisher exact tests were used for analyses with small samples. Cases of DWI lesion restricted to subcortical white matter and/or grey matter structures (n = 44) were examined for the presence of aphasia or neglect, and for the presence of cortical hypoperfusion. In addition, subjects who received intervention to restore perfusion were evaluated with DWI, PWI, and cognitive tests before and after intervention. Finally, the positive predictive value of the cognitive deficits for identifying cortical abnormalities on DWI and PWI were calculated from all patients. Of the subjects with only subcortical lesions on DWI in this study (n = 44), all those who had aphasia or neglect showed concurrent cortical hypoperfusion. Among the patients who received intervention that successfully restored cortical perfusion, 100% (six out of six) showed immediate resolution of aphasia. In the 115 patients, aphasia and neglect were much more strongly associated with cortical hypoperfusion (chi(2) = 57.3 for aphasia; chi(2) = 28.7 for neglect; d.f. = 1; P < 0.000001 for each), than with cortical infarct/ischaemia on DWI (chi(2) = 8.5 for aphasia; chi(2) = 9.7 for neglect; d.f. = 1; P < 0.005 for each). Aphasia showed a much higher positive predictive value for cortical abnormality on PWI (95%) than on DWI (62%), as did neglect (100% positive predictive value for PWI versus 74% for DWI). From these data we conclude that aphasia and neglect due to acute subcortical stroke can be largely explained by cortical hypoperfusion.