Perfusion imaging of the right perisylvian neural network in acute spatial neglect

Abstract

Recent studies have suggested a tightly connected perisylvian neural network associated with spatial neglect. Here we investigated whether structural damage in one part of the network typically is accompanied with functional damage in other, structurally intact areas of this network. By combining normalized fluid-attenuated inversion-recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI) we asked whether or not lesions centering on fronto-temporal regions co-occur with abnormal perfusion in structurally intact parietal cortex. With thresholds applied to delineate behaviourally relevant malperfusion of brain tissue, the analysis of normalized time-to-peak (TTP) and maximal signal reduction (MSR) perfusion maps did not reveal significant changes outside the area of structural damage. In particular, we found no abnormal perfusion in the structurally intact inferior parietal lobule (IPL) and/or the temporo-parietal junction (TPJ). The present results obtained in three consecutively admitted neglect patients with fronto-temporal lesions indicate that structural damage in one part of the right perisylvian network associated with spatial neglect does not necessarily require dysfunction by malperfusion in other, structurally intact parts of the network to provoke spatial neglect. The neural tissue in the fronto-temporal cortex appears to have an original role in processes of spatial orienting and exploration.

Keywords: magnetic resonance imaging; parietal cortex; perfusion-weighted imaging; right perisylvian neural network; spatial neglect; superior temporal cortex.

Figure 1

Example from one patient's normalized diffusion-weighted imaging (DWI) as well as time-to-peak (TTP) and maximal signal reduction (MSR) perfusion maps.

Figure 2

(A) Overlay plots and lateral surface views of the normalized DWI/FLAIR lesions for the patient group with spatial neglect. The number of overlapping areas are illustrated by different colours coding increasing frequencies from violet (n = 1) to red (n = 3). On the lateral surface view, >33.3% indicates that with respect to our sample at least two patients had lesioned tissue in this area and >66.6% indicates that all patients had a lesion in this area. (B) Normalized DWI/FLAIR lesions for individual patients with spatial neglect. MNI z-coordinates of the transverse sections are given.

Figure 3

Patient group with spatial neglect. Overlay plots of (A) the normalized maps of TTP delays ≥ 3 s, ≥1.5 s, and ≥0 s as well as (B) the normalized maps for MSR fractions ≤ 40%, ≤70%, and ≤100%. The number of overlapping areas are illustrated by different colours coding increasing frequencies from violet (n = 1) to red (n = 3). MNI z-coordinates of the transverse sections are given.

Figure 4

Overlay plots showing the common regions of structurally intact but malperfused brain tissue for the patient group with spatial neglect. (A) The mismatch between TTP ≥ 3.0 s delay maps and DWI/FLAIR. (B) The mismatch between MSR ≤ 40% fraction maps and DWI/FLAIR. The number of overlapping areas are illustrated by different colours coding increasing frequencies from violet (n = 1) to red (n = 3). MNI z-coordinates of the transverse sections are given.