Perfusion imaging and stroke: A more sensitive measure of the brain bases of cognitive deficits

We provide evidence that the use of perfusion imaging reveals the neuroanatomical basis for a behaviourally demonstrated cognitive deficit that is not revealed via standard neuroradiological imaging techniques.

We present a case study of a 52-year-old female stroke survivor (16 years post onset) whose speech was fluent and grammatical with some word-finding difficulties that were typically overcome with common circumlocution strategies. Based on standardised measures, the patient's clinical diagnosis was anomie aphasia. In addition to word-finding deficits, it was discovered that this patient also demonstrated difficulties in reading; while able to eventually read and understand text, there was extreme difficulty in completing such tasks. A series of experimental findings exploring this reading deficit are presented. This patient's lesion, as revealed via structural brain imaging, did not involve a brain region typically implicated in reading dysfunction. This behaviour-lesion inconsistency was explored via perfusion MRI technology as a means of assessing whether other neural regions not directly implicated in the structural scans (such as the angular gyros) could in fact show some level of dysfunction.

Analysis of the patient's overall reading time demonstrated that as compared to a matched control, this patient took significantly more time in reading paragraphs both silently and aloud. In addition, the patient produced more errors (fillers, pauses, elongations) than the matched control during the reading paragraphs aloud and story-retelling conditions. There were no differences exhibited between the patient and control with respect to content accuracy produced during these conditions.

Structural images demonstrate damage to the left basal ganglia and surrounding white matter with sparing of the left insular cortex. Collection of perfusion images (pulsed arterial spin labelling) clearly demonstrates hypoperfusion in the seemingly intact brain regions of the left angular gyros and the left supramarginal gyrus.

This paper presents evidence from a detailed case study that the use of perfusion imaging successfully reveals the neural basis for a reading deficit in a stroke survivor that is not revealed via standard "structural" neuroradiological imaging techniques. We argue for more standardised use of perfusion imaging, in that it reveals a brain basis for "functional lesions", which less sensitive neuroimaging measures often fail to capture.