Collaterals: an important determinant of prolonged ischemic penumbra versus rapid cerebral infarction?

Assessing bolus peak position in CT perfusion: High variance persisting despite age-dependency in a large cohort

PURPOSE

CT perfusion (CTP) is a valuable tool in suspected acute ischemic stroke. A substantial variability of the delay between contrast injection and bolus arrival in the brain is conceivable. We investigated the distribution of the peak positions of the concentration time curves measured in an artery (arterial input function, AIF) and - in cases with ischemia - also measured in the penumbra.

METHODS

We report on 2624 perfusion scans (52 % female, mean age 72.2 ± 14.4 years) with stroke present in 1636 cases. From the attenuation time curves of the AIF and the penumbra, we calculated the respective bolus peak positions and investigated the distribution of the peak positions. Further, we analyzed the bolus peak positions for associations with age.

RESULTS

The bolus peaked significantly later in older patients, both in the AIF and in the penumbra (all p < 0.001). In the whole cohort, we found a significant association of age with the bolus peak position of the AIF (ρ = 0.334; p < 0.001). In patients with stroke, age was also associated to the peak position of the AIF (ρ = 0.305; p < 0.001), and the penumbra (ρ = 0.246, p < 0.001). However, a substantial range of peak positions of the AIF and penumbra was noted across all age ranges.

CONCLUSIONS

This study revealed a strong age-dependency of the contrast bolus arrival in both healthy and ischemic tissue. This variability makes non-uniform sampling schemes, which have been suggested to reduce radiation dose, problematic, as they might not always optimally capture the bolus in all cases.

Deep medullary veins as an important imaging indicator of poor prognosis in acute ischemic stroke: a retrospective cohort survey

Background

The deep medullary veins (DMVs), which constitute a component of the intracerebral venous circulation system and are part of intracerebral reperfusion mechanisms, have been suggested as a novel imaging marker for cerebral white matter hypersignal and cerebral small vessel disease based on their discontinuous and reduced visual representation. However, the correlation between the number and continuity of visible DMVs and the poor prognosis of acute ischemic stroke (AIS) remains undefined. Magnetic susceptibility-weighted imaging was applied in this study to assess the distribution and structural characteristics of DMVs in patients with AIS and to investigate its relationship with the poor prognosis of those with AIS.

Methods

This retrospective study included 90 patients diagnosed with AIS in the middle cerebral artery region by the Neurology Department of Liaoning Provincial People's Hospital. Clinical, laboratory, and cranial magnetic resonance imaging data were collected. After the 3-month follow-up visit, patients were dichotomized into good (0-2 points) and poor (≥3 points) prognosis groups based on the modified Rankin Scale score, and the DMV imaging characteristics were evaluated using a 3-level visual rating scale. The association between DMV and AIS prognosis was determined through Mann-Whitney test and multivariate logistic regression analysis.

Results

In univariate analysis, factors that were statistically significant between the different prognostic groups were DMV score (P=0.007), DMV symmetry (P=0.016), infarct size (P=0.029), and admission National Institutes of Health Stroke Scale (NIHSS) score (P<0.001). DMV score had a positive correlation with NIHSS score, (rs=0.209; P=0.048). Logistic regression analysis showed that the DMV score [odds ratio (OR), 1.356; 95% confidence interval (CI): 1.114-1.650; P=0.002], NIHSS score (OR, 1.280; 95% CI: 1.117-1.466; P<0.001), and fasting glucose (OR, 1.220; 95% CI: 1.023-1.456; P=0.027) were risk factors for poor prognosis in those with AIS.

Conclusions

Discontinuity in DMV visualization was found to be associated with an unfavorable prognosis for patients AIS. The visual assessment of DMV through susceptibility-weighted imaging has the potential to predict AIS prognosis and furnish valuable insights for clinical treatment.

Collaterals Predict Outcome Regardless of Time Last Known Normal

BACKGROUND AND PURPOSE

Recent studies suggest that patients with large-vessel ischemic strokes (large-vessel occlusion [LVO]) with favorable imaging may benefit from mechanical thrombolysis even when treated outside the standard 6-hour window. However, many patients in these studies presented with unknown times of onset. We compare outcomes in thrombectomy patients treated at less than versus greater than 6 hours from last known well (LKN), and evaluate whether "unknown time of onset" alters prognosis.

METHODS

We retrospectively reviewed patients at 2 comprehensive stroke centers. Student's t and chi-square tests evaluated the association between predetermined clinical and radiographic variables, including unknown time of onset, and outcome (discharge and follow-up National Institutes of Health Stroke Scale score and modified Rankin Scale [mRS] score) for LVOs treated after greater than 6 hours versus 6 hours or less from LKN. Multivariable logistic regression was used to determine the odds of good outcome (mRS score 0-2).

RESULTS

A total of 113 patients were treated over 2 years; 31 were treated at greater than 6 hours. Those who were treated at greater than 6 hours and experienced poor outcomes were more likely to have large-artery atherosclerosis (P = .033). There was no difference in outcome for patients outside the window with known (39.1%) versus unknown (60.9%) time of onset. mRS scores at discharge were higher among those outside the window (odds ratio 3.78; 95% confidence interval 1.20-11.89) but not at follow-up. After multivariable regression, favorable collaterals alone were associated with a mRS score of 0-2.

CONCLUSIONS

When imaging is favorable, the mRS score at follow-up is comparable regardless of time LKN. Functional outcomes appear to be driven most significantly by the presence of collaterals.

Is CT-Based Perfusion and Collateral Imaging Sensitive to Time Since Stroke Onset?

Purpose

CT-based perfusion and collateral imaging is increasingly used in the assessment of patients with acute stroke. Time of stroke onset is a critical factor in determining eligibility for and benefit from thrombolysis. Animal studies predict that the volume of ischemic penumbra decreases with time. Here, we evaluate if CT is able to detect a relationship between perfusion or collateral status, as assessed by CT, and time since stroke onset.

Materials and methods

We studied 53 consecutive patients with proximal vessel occlusions, mean (SD) age of 71.3 (14.9) years, at a mean (SD) of 125.2 (55.3) minutes from onset, using whole-brain CT perfusion (CTp) imaging. Penumbra was defined using voxel-based thresholds for cerebral blood flow (CBF) and mean transit time (MTT); core was defined by cerebral blood volume (CBV). Normalized penumbra fraction was calculated as Penumbra volume/(Penumbra volume + Core volume) for both CBF and MTT (Pen_CBF and Pen_MTT, respectively). Collaterals were assessed on CT angiography (CTA). CTp ASPECTS score was applied visually, lower scores indicating larger lesions. ASPECTS ratios were calculated corresponding to penumbra fractions.

Results

Both Pen_CBF and Pen_MTT showed decremental trends with increasing time since onset (Kendall’s tau-b = −0.196, p = 0.055, and −0.187, p = 0.068, respectively). The CBF/CBV ASPECTS ratio, which showed a relationship to Pen_CBF (Kendall’s tau-b = 0.190, p = 0.070), decreased with increasing time since onset (Kendall’s tau-b = −0.265, p = 0.006). Collateral response did not relate to time (Kendall’s tau-b = −0.039, p = 0.724).

Conclusion

Even within 4.5 h since stroke onset, a decremental relationship between penumbra and time, but not between collateral status and time, may be detected using perfusion CT imaging. The trends that we demonstrate merit evaluation in larger datasets to confirm our results, which may have potential wider applications, e.g., in the setting of strokes of unknown onset time.