Relating MRI Changes to Motor Deficit After Ischemic Stroke by Segmentation of Functional Motor Pathways

Abstract

Background and Purpose-Infarct size on T2-weighted MRI correlates only modestly with outcome, particularly for small strokes. This may be largely because of differences in the locations of infarcts and consequently in the functional pathways that are damaged. To test this hypothesis quantitatively, we developed a "mask" of the corticospinal pathway to determine whether the extent of stroke intersection with the pathway would be more closely related to clinical motor deficit and axonal injury in the descending motor pathways than total stroke lesion volume. Methods-Eighteen patients were studied Ն1 month after first ischemic stroke that caused a motor deficit by use of brain T2-weighted imaging, MR spectroscopic (MRS) measurements of the neuronal marker compound N-acetyl aspartate in the posterior limb of the internal capsule, and motor impairment and disability measures. A corticospinal mask based on neuroanatomic landmarks was generated from a subset of the MRI data. The maximum proportion of the cross-sectional area of this mask occupied by stroke was determined for each patient after all brain images were transformed into a common stereotaxic brain space. Results-There was a significant linear relationship between the maximum proportional cross-sectional area of the corticospinal mask occupied by stroke and motor deficit (r 2 ϭ0.82, PϽ0.001), whereas the relationship between the total stroke volume and motor deficit was better described by a cubic curve (r 2 ϭ0.76, PϽ0.001). Inspection of the data plots showed that the total stroke volume discriminated poorly between smaller strokes with regard to the extent of associated motor deficit, whereas the maximum proportion of the mask cross-sectional area occupied by stroke appeared to be a more discriminatory marker of motor deficit and also N-acetyl aspartate reduction. Conclusions-Segmentation of functional motor pathways on MRI allows estimation of the extent of damage specifically to that pathway by the stroke lesion. The extent of stroke intersection with the motor pathways was more linearly related to the magnitude of motor deficit than total lesion volume and appeared to be a better discriminator between small strokes with regard to motor deficit. This emphasizes the importance of the anatomic relationship of the infarct to local structures in determining functional impairment. Prospective studies are necessary to assess whether this approach would allow improved early estimation of prognosis after stroke. (Stroke. 2000;31:672-679.)

Poststroke Cerebral Peduncular Atrophy Correlates with a Measure of Corticospinal Tract Injury in the Cerebral Hemisphere

“…The significant relationship that has been demonstrated to occur between acute ischemic lesion extent and infarction extent later in the first year after stroke onset (rs ϭ 0.68 -0.84) 1,2 suggests that the acute ischemic lesion extent could also reliably predict the amount of subsequent poststroke loss in the remote CST due to wallerian degeneration, at least in the affected cerebral peduncle. Our findings also suggest that the significant relationship between infarction extent in chronic stroke and concurrent motor findings 18,21 may be entirely due to local infarction effects and is not additionally affected by the extent of remote tissue loss.…”

“…In our sample, 24 patients had single infarctions, and 10 patients had multiple unilateral infarctions. The technique that was used to measure the maximal amount of postinfarction injury to the CST in the cerebral hemisphere was described by Pineiro et al 18 An infarction mask was initially created on each patient's scan by manually tracing each infarction within its corresponding horizontal section. The CST mask was then created by transferring to the MR image the boundaries of the CST that were indicated on the axial views from the Talairach atlas 32 at approximately the same anatomic levels as those of the infarction.…”

“…We had the opportunity to examine whether structural MR imaging of chronic supratentorial infarction could predict the extent of concurrent ipsilateral peduncular atrophy. Specifically, we assessed the extent of injury to the corticospinal tract (CST) in the cerebral hemisphere, 18 because the CST constitutes a sizable fraction of the total peduncular transaxial area (ϳ25%), 19 and, therefore, CST degeneration could substantially affect the extent of postinfarction peduncular atrophy. The patients in our study were specifically recruited for mildto-moderate chronic hemiparesis and, thus, were likely to have CST injury.…”

Absence of a proximal to distal gradient of motor deficits in the upper extremity early after stroke

“…The perception is consistent with disruption to the corticospinal system which is known to have greater input to distal cervical motoneuron pools compared to proximal cervical motoneuron pools (Palmer and Ashby, 1992;Porter and Lemon, 1993;McKiernan et al, 1998;Turton and Lemon, 1999). Indeed, the severity of motor deficits post stroke is strongly related to the degree of corticospinal system damage (Pineiro et al, 2000). Quantitative data have shown the existence of greater strength deficits in the more distal versus the more proximal upper extremity segments in a small sample of people with chronic hemiparesis (Colebatch and Gandevia, 1989).…”

“…The general severity of motor deficits post stroke is due to the extent of damage to the corticospinal system (Pineiro et al, 2000;Stinear et al, 2007). It has been thought that the proximal to distal gradient in movement deficits stems from disruption of this system, which sends more numerous projections to the distal cervical motoneuron pools (Palmer and Ashby, 1992;Porter and Lemon, 1993;McKiernan et al, 1998;Turton and Lemon, 1999).…”