Diffusion- and perfusion-weighted magnetic resonance imaging in patients with acute ischemic stroke: can diffusion/perfusion mismatch predict outcome?

Introduction: Stroke is the third leading cause of death, and is
the leading cause of disabilities worldwide. Although stroke may
result from localized cerebral ischemia, intracerebral hemorrhage,
subarachnoid hemorrhage or venous sinus thrombosis, ischemic stroke
is the most frequently cause of the total cases. In ischemic
stroke, occlusion of the MCA or its branches accounts for more than
3/4 of infarcts and two thirds of all first strokes. The main
mechanisms causing ischemic strokes are embolism and arterial
thromboembolism. No matter what the mechanism an ischemic stroke
is, they eventually lead to a focal reduction of perfusion in the
brain. In the hyperacute stage the recognition of the ischemia
using both clinical assessment and routine neuroimaging technique
implies some uncertainties, which in turn makes it difficult to
predict the outcome, either to improve or to reverse spontaneously,
to persist or worsen. The concept of diffusion/perfusion mismatch
attracted great attention since it may represent the tissue at risk
or at least an index of penumbra. Our interest was to investigate
whether the hemodynamic parameters had correlation with clinical
severity and if they were useful for prediction of outcome in the
mismatch region. Since diffusion/perfusion mismatch was recognized
as a simple and feasible means to identify the ischemic penumbra,
we evaluated the hemodynamic parameters in acute stroke patients
and compared these parameter to the stroke scale NIHSS and to the
outcome score MRS to investigate our hypothesis. Materials and
Methods: 35 acute stroke patients (male:female=20:15, age:
61.3±15.2 years) who met the study inclusion and exclusion criteria
were selected. Significant cerebrovascular risk factors were
recorded in 27 patients. The NIHSS assessment was immediately
performed at the patients’ admission by a neurologist. Functional
outcome was measured on the day of hospital discharge following
MRS. Routine MRI sequences and DWI and PWI (dynamic susceptibility
contrast-enhanced [DSC] imaging) were employed in our patients
study. The perfusion maps were processed with MEDx and the
parameters were obtained by identifying ROIs on both ischemic core
and mismatch region, and the normal mirror region. Relative values
of the hemodynamic perfusion parameters were used in the
evaluation. Statistic treatment was used to test the significance
of the result. Results: The NIHSS score ranged from 0 to 19
(10.2±4.4) and the outcome MRS scale ranged from 0 to 6 (mean:
3.23). Between the good outcome group (MRS 0 to 3) and the poor
outcome group (MRS 4 to 6), time to scan, type of treatment, DW/PW
volume ratio, and age and female/male ratio did not show
significant differences. In ischemic core: rCBF showed a remarkable
decrease in all patients on average by 59.3±33.7% (range: 23.2 -
97.4%). rCBV decreased in 29 patients by 41.7±23.7% (range 19.6 -
55.6%), while 6 patients showed an increase of rCBV by 60.4±57.1%
(range 0.7 -139%). The mean rCBV change of the entire group was
26.3±52.5%. MTT, TTP and T0 prolonged for 4.7 (SD=15.1), 2.8
(SD=12.9) and 0.5 (SD=10.4) seconds, respectively. In mismatch
region: rCBF decreased in 15 patients by 26.2±19.9% (range:
5.3-58.4%) and increased in 20 patients by 35±23.2% (range:
6.8–74.4%). The change of the rCBF of the whole patients group was
5.8±38.4%. rCBV decreased in 7 patients by 14.7±16.5% (range:
0.8-44.5%) and increased in 28 patients by 39.5±36% (range:
2.2-91.1%). The mean change of the rCBV of the whole group was
19.9±31.2%. The mean value of MTT, TTP and T0 prolonged for 2.7
(SD=8.5), 3.2 (SD=5.2) and 1.3 (SD=4.2) seconds respectively. In
both core and mismatch region, rCBF showed statistically
significant regression to MRS. The more the rCBF decreased the
higher the MRS (poor outcome) was. Also, the MTT delay in the core
region was significantly related to MRS. TTP delay, in both core
and mismatch region, was related to both NIHSS and MRS
significantly. No statistic significance was found comparing CBV
and T0 in relation with NIHSS or MRS. Conclusion: The hemodynamic
parameters derived from perfusion MR imaging may be helpful adjunct
to predict the outcome and severity in acute stroke patients. In
mismatch region, the rCBF and TTP are predictive for the stroke
outcome.