Early blood-brain barrier dysfunction predicts neurological outcome following aneurysmal subarachnoid hemorrhage

Abstract

Background: Disease progression and delayed neurological complications are common after aneurysmal subarachnoid hemorrhage (aSAH). We explored the potential of quantitative blood-brain barrier (BBB) imaging to predict disease progression and neurological outcome.

Methods: Data were collected as part of the Co-Operative Studies of Brain Injury Depolarizations (COSBID). We analyzed retrospectively, blinded and semi-automatically magnetic resonance images from 124 aSAH patients scanned at 4 time points (24-48 h, 6-8 days, 12-15 days and 6-12 months) after the initial hemorrhage. Volume of brain with apparent pathology and/or BBB dysfunction (BBBD), subarachnoid space and lateral ventricles were measured. Neurological status on admission was assessed using the World Federation of Neurosurgical Societies and Rosen-Macdonald scores. Outcome at ≥6 months was assessed using the extended Glasgow outcome scale and disease course (progressive or non-progressive based on imaging-detected loss of normal brain tissue in consecutive scans). Logistic regression was used to define biomarkers that best predict outcomes. Receiver operating characteristic analysis was performed to assess accuracy of outcome prediction models.

Findings: In the present cohort, 63% of patients had progressive and 37% non-progressive disease course. Progressive course was associated with worse outcome at ≥6 months (sensitivity of 98% and specificity of 97%). Brain volume with BBBD was significantly larger in patients with progressive course already 24-48 h after admission (2.23 (1.23-3.17) folds, median with 95%CI), and persisted at all time points. The highest probability of a BBB-disrupted voxel to become pathological was found at a distance of ≤1 cm from the brain with apparent pathology (0·284 (0·122-0·594), p < 0·001, median with 95%CI). A multivariate logistic regression model revealed power for BBBD in combination with RMS at 24-48 h in predicting outcome (ROC area under the curve = 0·829, p < 0·001).

Interpretation: We suggest that early identification of BBBD may serve as a key predictive biomarker for neurological outcome in aSAH. FUND: Dr. Dreier was supported by grants from the Deutsche Forschungsgemeinschaft (DFG) (DFG DR 323/5-1 and DFG DR 323/10-1), the Bundesministerium für Bildung und Forschung (BMBF) Center for Stroke Research Berlin 01 EO 0801 and FP7 no 602150 CENTER-TBI. Dr. Friedman was supported by grants from Israel Science Foundation and Canada Institute for Health Research (CIHR). Dr. Friedman was supported by grants from European Union's Seventh Framework Program (FP7/2007-2013; grant #602102).

Keywords: Aneurysmal subarachnoid hemorrhage; Blood-brain barrier; Extended Glasgow outcome scale (eGOS); Lesion; Long term output; Magnetic resonance imaging (MRI).

Fig. 1

Dynamics of brain MR findings during follow-up. a. Representing MR scans during follow-up. Detected abnormal brain tissue (ABT) in red contour. BBBD enhancement maps (BBBDEM) were created by reassigning each voxel with BBBD its enhancement level. The final BBBDEM was normalized to 0–1 range (minimal to maximal enhancement level). b. Bar graph showing composition of skull-peeled volume of interest at different time point during follow-up. Normal brain tissue (NBT - white); CSF sub-arachnoid space (SAS - blue); Lateral ventricles (LV -green); ABT - red. Note the gradual reduction in NBT during follow-up. c. Box plot showing mean NBT volumes in aSAH patients over time. Note a significant decrease beginning ~2 weeks after the event (p = 0·002, Friedman). d, e. Volume of LV (D) and SAS (E) showing a significant increase at t4 (p < 0·001, Friedman). f. ABT volume significantly increased in aSAH patients at all time intervals in comparison to t1 (p < 0·02). NBT and ABT volumetric changes followed a logarithmic pattern (R²_adj = 0·82(0·76–0·99) for brain volume and R²_adj = 0·81(0·78–0·97) for ABT volume (p < 0·01); correlation between model intercept (Co) and NBT and ABT sizes were correspondently: R² = 0·96 (p = 0·02) and R² = 0·88 (p = 0·01)). Dynamic of ABT and BBBD in a subgroup with all four time points is presented in Supplementary Fig. 3. g. Brain volume with BBBD within the “abnormal” brain (ABTBBBD) significantly increased in t2 and t3 compared to t1 followed by a significant reduction at t4 (lilac color). BBBD within the NBT (brown color) was 3·2 (0·8–10·8) fold greater compared to that in healthy controls at all the investigated time intervals t1-t4 (p < 0·001). Notably, brain volume with BBBD within the NBT persisted during the first two week after the acute bleeding event and was significantly reduced only at t4 (p < 0·01). Overall, NBT brain volume with BBBD was larger compared to that measured in controls at all-time points. Control data are represented by horizontal solid (median) and dash (third and first quartiles) lines. †Significant difference (p ≤ 0·05) between time points (Friedman test followed the Bonferroni procedure). *Significant difference (p ≤ 0·05) between control and aSAH patients at a single time point (Wilcoxon rank sum test). ABT = abnormal brain tissue; aSAH = aneurysmal subarachnoid hemorrhage; BBBD = blood brain barrier damage; ABTBBBD = blood brain barrier damage measured in abnormal brain tissue volume; NBTBBBD = blood brain barrier damage measured in normal brain tissue volume; LV = lateral ventricles; NBT = normal brain tissue; SAS = subarachnoid space.

Fig. 2

Different BBB dynamics in patients with progressive vs non-progressive disease course. a. Representing MR images from aSAH patients with a progressive (PC) and non-progressive (NPC) disease course. BBBD enhancement maps (BBBDEM, color bar) are superimposed. Red contour demarcates detected abnormal brain tissue (ABT) and green contour demarcates lateral ventricles (LV). BBBDEM were created by reassigning each voxel with BBBD its enhancement level. The final BBBDEM was normalized to 0–1 range (minimal to maximal enhancement level). b. Based on measurements of changes in normal brain tissue (NBT) volume over time, patients were classified as having either a “progression course” (PC), in which NBT decreased with time (t2-t4) compared to the first, acute scan (t1) (median slope: −18·75 (−48·92–9·07) ml/ln(days)), or a “non-progression course” (NPC), characterized by NBT volume change slope of 0·73 (0·06–3·58) ml/ln(days). c. Box plot showing a significant difference in ABT growth rate between PC and NPC groups: 13·99 (5·90–36·68) ml/ln(days) vs −3·50 (−6·45–2·09) ml/ln(days); p < 0·001, Wilcoxon test. d. Bar graph showing the distribution in brain volume of NBT (white), subarachnoid space (SAS, blue), LV (green) and ABT (red) over time in the two patient groups. The increase in ABT and/or enlargement of LV and SAS were associated with decrease in NBT volume. The relative contributions of ABT growth vs CSF enlargement (LV + SAS) to NBT atrophy was about 1:2 for PC and 1:4 for NPC patients. e. A significant increase in ABT volume during consecutive scans in PC patients (ABT_i/ABT₁ > 1, for i = 2÷4, p < 0·001; see also Table 2, appendix: Table 2B). In contrast, NPC patients displayed non-significant change in ABT volume during the first 2 weeks (3 scans) after the acute bleeding event and a significant decrease in ABT volume by t4 (p < 0·007; see also appendix Table 2B). f, g. Significant differences between PC and NPC groups in both SAS volume (f) and LV volume (g) were found only in the late (t4) scans (p < 0·001, Wilcoxon test; see also Table 2). Note lack of significantly differences between the groups in none of the measures (ABT, LV or SAS volume) during the acute stage. h. Significant difference between the groups in NBT volume were seen only in the late (t4) scans (p < 0·001; Table 2). In the PC group, a significant decrease in NBT was detected from ~2 weeks after the event (p < 0·01, Friedman). i, j. Volumes of BBBD in both NBT (i, NBTBBBD) and ABT (i, ABTBBBD) were persistently and significantly greater in the PC group relative to NPC group in all time points (p < 0·001, Wilcoxon test, see also Table 2). In both groups, a significant decrease in NBTBBBD was seen only by t4 (p < 0·001, Friedman), whereas ABTBBBD increased significantly between t2-t3 in PC group, and decreased significantly by t4 in NPC group (p < 0·001, Friedman). Resolution of BBBD to 95% CI values of “healthy controls” (<47·5 ml) was found only in three patients. All these three patients were in NPC group and had ABT size significantly smaller than patients with non-resolved BBBD throughout the investigation. Overall, NBTBBBD volume was larger in both groups compared to that measured in controls at all time points (Table 2). k. Overall, in 62% of aSAH patients brain volume with BBBD (NBTBBBD + ABTBBBD) increased with time (slope: 8·57(2·02–24·64) ml/ln(days)) and in 38% of patients BBBD decreased with time (slope: −8·95(−16·87–5·07) ml/ln(days)). l. Box plot showing a significant difference in BBBD growth rate between PC and NPC groups: 3·93 (−4·44–16·78) ml/ln(days) vs −4·73 (−10·74–1·32) ml/ln(days), p = 0·001, Wilcoxon test). Interestingly, while in 64% of the patients from the PC group brain volume with BBBD increased with time, in 76% of patients in the NPC group BBBD decreased with time (p = 0·022, χ2 test). m. Box plot of the distribution of BBBD in abnormal and apparently normal brain tissue, where it was measured in three regions of interest based on the distance to ABT border (in cm). BBBD voxels were not distributed equally through all regions (p < 0·001). The highest content of BBBD voxels was found within 1 cm of ABT (33·58 (23·66–41·18) % of entire BBBD volume), whereas the lowest content of BBBD voxels was located in ABT (16·98 (10·25–26·92) % of entire BBBD volume). No significant difference was found in content of BBBD between the two remaining regions (1–2 cm and > 2 cm from ABT border): 23·90 (17·17–29·27) % and 25·16 (17·34–35·01) %, correspondently. *Significant difference (p ≤ 0·05) between outcome groups (PC vs NPC), Wilcoxon sum-rank test. †Significant difference (p ≤ 0·05) between time points, Friedman test followed the Bonferroni procedure. ABT = abnormal brain tissue; aSAH = aneurysmal subarachnoid hemorrhage; ABTBBBD = blood brain barrier damage measured in abnormal brain tissue volume; NBTBBBD = blood brain barrier damage measured in normal brain tissue volume; CI = confidence interval; CSF = cerebrospinal fluid; LV = lateral ventricles; NBT = normal brain tissue; SAS = subarachnoid space.

Fig. 3

Analysis of the predictive value of BBBD measurements in aSAH patients. Receiver operating characteristic (ROC) analysis showing specificity and sensitivity for prediction of aSAH course (a) and of long-term eGOS category (b). Whereas Ψ₀^Age&WFNS (blue dashed line) and Ψ₀^RMS (blue solid line) models contain only clinical data, the remaining models combine clinical data with imaging results at the different time points (t1-t4). When only clinical data was used, ROC analysis revealed a “fair” area under the curve (AUC) for the models consisting of either patient age and WFNS score (Ψ₀^Age&WFNS: AUC = 0·712 for (a) and AUC = 0·750 for (b)), or of RMS score only (Ψ₀^RMS: AUC = 0·719 for (a) and AUC = 0·757 for (b)). Prediction was improved with addition of t1 time–restricted imaging predictor, i.e. the extent of BBBD in apparently normal brain tissue (NBTBBBD₁) and in volume of ABT₁ (ABTBBBD₁) (Ψ_t1: AUC = 0·829 for (a) and AUC = 0·827 for (b)). A better yet prediction was achieved with t2 time-restricted models (Ψ_t2: correspondently: AUC = 0·905 and 0·871 for (a) and AUC = 0·855 and 0·887 for (b)). The best prediction was achieved with t4 time-restricted model (Ψ_t4: AUC = 0·979 for (a) and AUC = 0·942 for (b)). While BBBD imaging alone revealed a “fair” prediction at t₁ (AUC = 0·724(0·059) for (a)AUC = 0·726(0·061) for (b)) and a “good” prediction at t₂ (AUC = 0.867(0.062) for (a)AUC = 0·816(0·073) for (b)). ABT = abnormal brain tissue; AUC = area under the curve; aSAH = aneurysmal subarachnoid hemorrhage; ABTBBBD = blood brain barrier damage measured in abnormal brain tissue volume; NBTBBBD = blood brain barrier damage measured in normal brain tissue volume.