Marc-Antoine Labeyrie

Diffusion Lesion Reversal After Thrombolysis: A MR Correlate of Early Neurological Improvement

Background and Purpose— In acute stroke, diffusion-weighted imaging (DWI) lesions are commonly considered markers of irreversible ischemia yet can occasionally reverse. However, the extent and clinical correlates of DWI reversal in thrombolyzed patients remain unclear. We assessed the extent of reversible acute DWI lesions (RADs) and their relationships with clinical outcome in patients thrombolyzed ⩽4.5 hours from onset. Methods— Data were retrospectively analyzed. RAD was defined as an acute DWI lesion not part of a 24-hour DWI lesion as determined voxelwise. Associations with an early neurological improvement (early neurological improvement=&Dgr;National Institutes of Health Stroke Scale ≥8 or National Institutes of Health Stroke Scale ⩽2 at 24 hours) or an excellent outcome (modified Rankin Scale ⩽1) were assessed in multivariate analyses. Results— One hundred seventy-six patients were included. The median (interquartile range) time to treatment from onset was 150 minutes (120–194). Eighty-nine patients (50%) exhibited visually-detectable RAD irrespective of its extent. Over the whole population, the median percentage and volume of RAD were 11% (4–36) and 2.4mL (0.5–8). Subtracting RAD from initial DWI altered perfusion-weighted imaging–DWI classification in 5 of 100 patients (shift from “no mismatch” to “mismatch” profile in all). Percent RAD was significantly greater in patients treated ⩽3 hours (P=0.049), without proximal occlusion (P=0.003), and in 24-hour recanalizers (P<0.001). Early neurological improvement was independently associated with percent RAD. This association increased with percent RAD split in quartiles in a “dose-dependent” manner (P for trend=0.01). Excellent outcome was independently associated with percent RAD (P for trend <0.001). Conclusion— DWI reversal was often sizeable in patients treated ⩽4.5 hours. It was strongly associated with, albeit not necessarily causal for, early neurological improvement.

Clot Burden Score on Admission T2*-MRI Predicts Recanalization in Acute Stroke

Background and Purpose— To propose a T2*-MR adaptation of the computed tomography angiography-clot burden score (CBS), and assess its value as predictor of 24-hour recanalization and clinical outcome in anterior circulation stroke treated by intravenous thrombolysis ⩽4.5 hours from onset. Methods— Two independent observers retrospectively analyzed pretreatment T2* images for evaluation of clot burden, using a 10-point scale T2*-CBS. Three points are subtracted for susceptibility vessel sign in the supraclinoid internal carotid artery, 2 points each for susceptibility vessel sign in the proximal and distal part of middle cerebral artery, and 1 point each for susceptibility vessel sign in middle cerebral artery branches (with a maximum of 2 points) and for susceptibility vessel sign in anterior cerebral artery. Associations with 24-hour recanalization and favorable outcome (3-month modified Rankin Scale score, ⩽2) were assessed in multivariate analyses. Results— We analyzed 184 consecutive patients (mean age, 67 years) with median (interquartile range) admission National Institutes of Health Stroke Scale score and onset-to-treatment time of 15 (9–19) and 151 (120–185) minutes, respectively. The intraclass correlation for T2*-CBS between observers was 0.97 (95% confidence interval, 0.97–0.98). In multivariate analyses, T2*-CBS >6 was significantly associated with 24-hour recanalization (adjusted odds ratio, 5.1 [1.9–13.5]; P=0.001) or with favorable outcome (adjusted odds ratio, 4.2 [1.7–10.8]; P=0.003). Conclusions— T2*-CBS, a new reproducible semiquantitative score adapted from the computed tomography angiography-CBS, is associated with 24-hour recanalization and 3-month outcome after intravenous thrombolysis. This score needs external validation and could be useful to identify poor responders to intravenous thrombolysis.

3T MRI improves the detection of transmantle sign in type 2 focal cortical dysplasia.

Type 2 focal cortical dysplasia (FCD2) is one of the main causes of refractory partial epilepsy, but often remains overlooked by MRI. This study aimed to elucidate whether 3T MRI offers better detection and characterization of FCD2 than 1.5T, using similar coils and acquisition time.

Optimizing MR Imaging Detection of Type 2 Focal Cortical Dysplasia: Best Criteria for Clinical Practice

BACKGROUND AND PURPOSE: Type 2 FCD is one of the main causes of drug-resistant partial epilepsy. Its detection by MR imaging has greatly improved surgical outcomes, but it often remains overlooked. Our objective was to determine the prevalence of typical MR imaging criteria for type 2 FCD, to provide a precise MR imaging pattern, and to optimize its detection. MATERIALS AND METHODS: We retrospectively reviewed 1.5T MR imaging of 71 consecutive patients with histologically proved type 2 FCD. The protocol included millimetric 3D T1-weighted, 2D coronal and axial T2-weighted, and 2D or 3D FLAIR images. Two experienced neuroradiologists looked for 6 criteria: cortex thickening, cortical and subcortical signal changes, blurring of the GWM interface, the “transmantle” sign, and gyral abnormalities. The frequency of each sign and their combination were assessed. We compared the delay between epilepsy onset and surgery, taking into account the time of type 2 FCD detection by MR imaging. RESULTS: Only 42 patients (59%) had positive MR imaging findings. In this group, a combination of at least 3 criteria was always found. Subcortical signal changes were constant. Three characteristic signs (cortical thickening, GWM blurring, and transmantle sign) were combined in 64% of patients, indicating that MR imaging can be highly suggestive. However, typical features of type 2 FCD were overlooked on initial imaging in 40% of patients, contributing to a delay in referral for surgical consideration (17 versus 11.5 years when initial MR imaging findings were positive). CONCLUSIONS: A combination of 3 major MR imaging signs allows type 2 FCD to be recognized in clinical practice, thereby enabling early identification of candidates for surgery.

Unexplained Early Neurological Deterioration After Intravenous Thrombolysis: Incidence, Predictors, and Associated Factors

Background and Purpose— Early neurological deterioration (END) after anterior circulation stroke is a serious clinical event strongly associated with poor outcome. Regarding specifically END occurring within 24 hours of intravenous recombinant tissue-type plasminogen activator, apart from definite causes such as symptomatic intracranial hemorrhage and malignant edema whose incidence, predictors, and clinical management are well established, little is known about END without clear mechanism (ENDunexplained). Methods— We analyzed 309 consecutive patients thrombolysed intravenously ⩽4.5 hours from onset of anterior circulation stroke. ENDunexplained was defined as a ≥4-point deterioration on 24-hour National Institutes of Health Stroke Scale, without definite mechanism on concomitant imaging. ENDunexplained and no-END patients were compared for pretreatment clinical and imaging (including magnetic resonance diffusion and diffusion/perfusion mismatch volumes) data and 24-hour post-treatment clinical (including blood pressure and glycemic changes) and imaging (24-hour recanalization) data, using univariate logistic regression. Exploratory multivariate analysis was also performed after variable reduction, with bootstrap analysis for internal validation. Results— Among 33 END patients, 23 (7% of whole sample) had ENDunexplained. ENDunexplained was associated with poor 3-month outcome (P<0.01). In univariate analysis, admission predictors of ENDunexplained included no prior use of antiplatelets (P=0.02), lower National Institutes of Health Stroke Scale score (P<0.01), higher glycemia (P=0.03), larger mismatch volume (P=0.03), and proximal occlusion (P=0.01), with consistent results from the multivariate analysis. Among factors recorded during the first 24 hours, only no recanalization was associated with ENDunexplained in multivariate analysis (P=0.02). Conclusions— ENDunexplained affected 7% of patients and accounted for most cases of END. Several predictors and associated factors were identified, with important implications regarding underlying mechanisms and potential prevention of this ominous event.

How Sustained Is 24-Hour Diffusion-Weighted Imaging Lesion Reversal? : Serial Magnetic Resonance Imaging in a Patient Cohort Thrombolyzed Within 4.5 Hours of Stroke Onset

Background and Purpose— Here, we assessed how sustained is reversal of the acute diffusion lesion (RAD) observed 24 hours after intravenous thrombolysis, and the relationships between RAD fate and early neurological improvement. Methods— We analyzed 155 consecutive patients thrombolyzed intravenously 152 minutes (median) after stroke onset and who underwent 3 MR sessions: 1 before and 2 after treatment (median times from onset, 25.6 and 54.3 hours, respectively). Using voxel-based analysis of diffusion-weighted imaging (DWI)1, DWI2, and DWI3 lesions on coregistered image data sets, we assessed the outcome of RAD voxels (hyperintense on DWI1 but not on DWI2) as transient or sustained on DWI3, and their relationships with early neurological improvement, defined as &Dgr;National Institutes of Health Stroke Scale ≥8 or National Institutes of Health Stroke Scale ⩽1 at 24 hours. Tmax and apparent diffusion coefficient values were compared between sustained and transient RAD voxels. Results— The median (interquartile range) baseline National Institutes of Health Stroke Scale and DWI1 lesion volume were 11 (7–18) mL and 15.6 (6.0–50.9) mL, respectively. The median (interquartile range) RAD volume on DWI2 was 2.8 (1.1–6.6) mL, of which 70% was sustained on DWI3. Sixteen (10.3%) patients had sustained RAD ≥10 mL. As compared with transient RAD voxels, sustained RAD voxels had nonsignificantly higher baseline apparent diffusion coefficient values (median [interquartile range], 793 [717–887] versus 777 [705–869]×10−6 mm2·s −1, respectively; P=0.08) and significantly better perfusion (Tmax, mean±SD, 6.3±3.2 versus 7.8±4.0 s; P<0.001). At variance with transient RAD, the volume of sustained RAD was associated with early neurological improvement in multivariate analysis (odds ratio, 1.08; 95% confidence interval, [1.01–1.17], per 1-mL increase; P=0.03). Conclusions— After thrombolysis, over two-thirds of the DWI lesion reversal captured on 24-hour follow-up MR is sustained. Sustained DWI lesion reversal volume is a strong imaging correlate of early neurological improvement.

Is White Matter More Prone to Diffusion Lesion Reversal After Thrombolysis

Background and Purpose— In acute ischemic stroke, white matter (WM) is considered more resistant to infarction than gray matter (GM). To test this hypothesis, we compared the fate of WM and GM voxels belonging to the acute diffusion-weighted imaging (DWI) lesion, expecting WM voxels to be more prone to reversal after thrombolysis. Methods— Reversible acute DWI (RAD) lesion was defined voxel-wise as an acute lesion on initial DWI (DWI1) with no visible lesion on 24-hour DWI (DWI2). Only patients with RAD lesions >10 mL and >10% of DWI1 from our previously reported cohort were eligible. The core was defined as voxels hyperintense on DWI1 and DWI2. Semiautomated segmentation of DWI1, core, and RAD lesions, normalization into standard space, and WM/GM segmentation allowed calculations of WM/GM proportions in each region of interest using a voxel-counting algorithm. Results— Thirty patients were eligible (RAD lesion median volume [interquartile range], 23.3 mL [19.1–35.0 mL]; onset-to-treatment time, 134 minutes [105–185 minutes]). WM voxels fraction was greater in RAD lesions than in the core (59.4% [52.8%–68.9%] versus 49.6% [43.0%–57.5%]; P=0.011). The proportion of reversibility was greater for WM than for GM voxels (60.8% [25.5%–88.7%] versus 53.5% [21.1%–77.3%]; P=0.02). The percentage of RAD lesions increased with the proportion of WM present in the acute DWI lesion (P<0.0001; R=0.67). Conclusions— Acute DWI lesions predominantly involving WM may be more prone to reversal and, hence, to respond to therapy than their GM counterparts.

Tips and traps in brain MRI: Applications to vascular disorders

The French Society of Radiologys guide to good use of medical imaging examinations recommends MRI as the first-line examination for exploring cerebrovascular events or disorders. This paper will discuss the main traps in the images when stroke is suspected and provide the technical tips or knowledge necessary for an optimal radiological report.