Christian Riedel

The Importance of Size Successful Recanalization by Intravenous Thrombolysis in Acute Anterior Stroke Depends on Thrombus Length

Background and Purpose— We hypothesize that in acute middle cerebral artery stroke, thrombus lengths measured in thin-slice nonenhanced CT images define a limit beyond which systemic thrombolysis will fail to recanalize occluded arteries. Methods— In 138 patients who presented with acute middle cerebral artery stroke and who were treated with intravenous thrombolysis (IVT), we measured lengths of thrombotic clots depicted as arterial hyperdensities in admission nonenhanced CT images with 2.5-mm slice width. Vascular recanalization was investigated after thrombolysis and recanalization results were related to thrombus lengths by logistic regression. Results— In 62 patients, IVT resulted in recanalization; among these patients, no thrombus length exceeded 8 mm. The median modified Rankin scale score at hospital discharge was 2. In the remaining 76 patients, thrombus lengths mostly exceeded 8 mm and IVT failed in recanalization. These patients were discharged with a median modified Rankin scale score of 5. Conclusions— This study shows that in acute middle cerebral artery stroke, IVT has nearly no potential to recanalize occluded vessels if thrombus length exceeds 8 mm.

Assessment of thrombus in acute middle cerebral artery occlusion using thin-slice nonenhanced Computed Tomography reconstructions.

Background and Purpose— We sought to evaluate how accurately length and volume of thrombotic clots occluding cerebral arteries of patients with acute ischemic stroke can be assessed from nonenhanced CT (NECT) scans reconstructed with different slice widths. Methods— NECT image data of 58 patients with acute ischemic stroke with vascular occlusion proven by CT angiography were reconstructed with slice widths of 1.25 mm, 2.5 mm, 3.75 mm, and 5 mm. Thrombus lengths and volumes were quantified based on these NECT images by detecting and segmenting intra-arterial hyperdensities. The results were compared with reference values of thrombus length and volume obtained from CT angiography images using Bland-Altman analysis and predefined levels or tolerance to find NECT slice thicknesses that allow for sufficiently accurate thrombus quantification. Results— Thrombus length can be measured with high accuracy using the hyperdense middle cerebral artery sign detected in NECT images with slice thicknesses of 1.25 mm and 2.5 mm. We found mean deviations from the reference values and limits of agreement of −0.1 mm±0.6 mm with slice widths of 1.25 mm and 0.1 mm±0.7 mm for slice widths of 2.5 mm. Thrombus length measurements in NECT images with higher slice width and all evaluated thrombus volume measurements exhibited severe dependence on the level and did not match the accuracy criteria. Conclusion— The length of the hyperdense middle cerebral artery sign as detected on thin-slice NECT reconstructions in patients with acute ischemic stroke can be used to quantify thrombotic burden accurately. Thus, it might qualify as a new diagnostic parameter in acute stroke management that indicates and quantifies the extent of vascular obliteration.

Physiological and anatomical decomposition of subthalamic neurostimulation effects in essential tremor

Postural tremor is the leading symptom in essential tremor, but in some cases intention tremor and limb ataxia emerge and can become highly disabling features. Deep brain stimulation of the thalamus or subthalamic white matter improve tremor and ataxia; however, the underlying network mechanisms are enigmatic. To elucidate the mechanisms of deep brain stimulation in essential tremor, we pursued a multimodal approach combining kinematic measures of reach-to-grasp movements, clinical assessments, physiological measures of neuronal excitability and probabilistic tractography from diffusion tensor imaging. Seven patients with essential tremor (age 62.9 ± 10.3 years, two females) received thalamic deep brain stimulation and a clinical examination of severity of limb tremor and ataxia at off stimulation, using therapeutic and supratherapeutic stimulation parameters. A reach-to-grasp task based on acoustic cues was also performed. To examine the electrical properties of target structures, we determined the chronaxie of neural elements modulated. A control group of 13 healthy subjects (age 56 ± 7.6 years, five females) underwent whole-brain diffusion tensor imaging at 3 T. Probabilistic tractography was applied in healthy subjects from seeds in cerebellum and midbrain to reconstruct the connectivity pattern of the subthalamic area. The positions of stimulation electrodes in patients were transferred into probability maps and connectivity values were correlated to clinical outcome measures. Therapeutic stimulation improved ataxia and tremor mainly during the target period of the reaching paradigm (63% reduction compared with off stimulation). Notably the acceleration (29%) and deceleration periods (41%) were improved. By contrast, supratherapeutic stimulation worsened ataxia during the deceleration period with a 55% increase of spatial variability, while maintaining near complete suppression of tremor. Chronaxie measures were in the range of rapidly-conducting myelinated fibres with significantly different values for the anti-tremor effect of therapeutic stimulation (27 s) and the pro-ataxic effect of supratherapeutic stimulation (52 s). The degree of connectivity to the dentato-thalamic tract at the stimulating electrode correlated significantly with the reduction of tremor in the therapeutic condition. Our data suggest that stimulation induced tremor reduction and induction of ataxia by supratherapeutic stimulation are mediated by different fibre systems. Probalistic tractography identified the dentato-thalamic tract as a likely target of tremor suppression. Stimulation-induced ataxia may be caused by additional recruitment of adjacent fibre systems at higher amplitudes. Stimulation with short pulse duration may help to increase the therapeutic window and focus on the anti-tremor effect.

Thin-Slice Reconstructions of Nonenhanced CT Images Allow for Detection of Thrombus in Acute Stroke

Background and Purpose— The purpose of this study was to investigate whether thin-slice image reconstructions of cranial nonenhanced CT scans could be used to significantly increase sensitivity for detecting intraluminal thrombus in patients with acute ischemic stroke due to proximal occlusion of the middle cerebral artery. Methods— In a prospective case series, the raw data of nonenhanced CT scans from 54 patients presenting with acute ischemic stroke and proven vascular obliteration of the middle cerebral artery were collected along with the same data from patients not having a stroke but the same sex and age. All raw data were reconstructed with a slice thickness of 5 mm and as thin slices with a thickness of 0.625 mm. Three observers independently evaluated the 5-mm nonenhanced CT reconstructions and 5-mm maximum intensity projections of the thin slices and rated the likelihood of a clot obliterating the middle cerebral artery trunk or first-order branches using a 5-point scale. The results were evaluated in comparison with base data using receiver operating curve analysis. Interobserver agreement was measured using Cohen &kgr; for every pair of observers. Results— The area under the curve for the receiver operating curve analysis for the thick slices ranged from 0.63 to 0.67, whereas for the maximum intensity projection images of the thin slice reconstructions, receiver operating curve analysis revealed areas under the curve between 0.94 and 0.97. Interobserver agreement was higher for thin-slice (&kgr;, 0.69–0.83) versus thick-slice nonenhanced CT reconstructions (&kgr;, 0.38–0.45). Conclusions— Thin-slice reconstructions of standard cranial nonenhanced CT raw data allow for more sensitive and reliable detection of clots occluding the proximal middle cerebral artery.

The entire dural sinus tree is compressed in patients with idiopathic intracranial hypertension: a longitudinal, volumetric magnetic resonance imaging study

IntroductionThe objective of this study was to explore the volumetric alterations of dural sinuses in patients with idiopathic intracranial hypertension (IIH).MethodsStandardized cranial magnetic resonance imaging (MRI) was used in 17 patients prior to and following treatment of IIH and in seven controls. Magnetic resonance venographies (MRV) were employed for (a) judgement of circumscript dural sinus stenoses and (b) computation of sinus volumes. Cross-sectional areas (CSA) of the superior sagittal sinuses (SSS) were measured on T2-weighted images. Results of the initial MRIs were compared to those on follow-up MRIs and to results of controls.ResultsStenoses of the transverse sinuses (TS) resulting in cranial venous outflow obstruction (CVOO) were present in 15/17 (88%) patients, normalizing in 7/15 cases (47%) after treatment of IIH. CVOO was not detected in the control group. Segmentation of MRV revealed decreased dural sinus volumes in patients with IIH as compared to controls (P = 0.018). Sinus volumes increased significantly with normalization of intracranial pressure independent from disappearing of TS stenoses (P = 0.007). The CSA of the SSS were normal on the initial MRIs of patients with IIH and increased on follow-up after treatment (P < 0.001). However, volumetries displayed overlap in patients and controls.ConclusionsPatients with IIH not only exhibit bilateral stenoses of the TS as has been reported, but volume changes of their entire dural sinus system also occur. The potential etiopathological and diagnostic roles of these changes are discussed.

Subacute Stent Thrombosis in Intracranial Stenting

Background and Purpose— We sought to determine the safety of intracranial stenting with respect to subacute stent thrombosis in patients being treated with standardized antiplatelet therapy. Methods— We retrospectively evaluated the outcome of primary intracranial stenting of atherosclerotic stenoses and of stenting in coil embolization procedures in 67 patients. We focused on those cases that led to subacute stent thrombosis even though the patients had been treated with standardized antiplatelet therapy before, during, and after stent placement. Patient age ranged from 19 to 78 years. In 33 patients, stents were placed for treatment of atherosclerotic stenoses; in the remaining 34 patients, stents were placed to assist coiling of aneurysms. The patients in this study were treated between January 2003 and August 2007. Results— Of the total 67 patients initially treated successfully by intracranial stenting, 7 patients developed subacute stent thrombosis. Of these 7 patients, 3 received stent placement into the basilar artery because of an underlying stenosis; in 1 patient, a stenosis of the M1 segment of the middle cerebral artery was treated. In 3 patients, aneurysms of the anterior cerebral artery, the posterior inferior cerebellar artery, and the basilar artery were treated by stent-assisted coil embolization. In 4 of the 7 patients with subacute thrombosis, recanalization of stents by local application of recombinant tissue-type plasminogen activator was successful. Conclusions— Intracranial stenting can lead to subacute stent thrombosis, even in patients who are treated with standardized antiplatelet therapy. Such complications have been described for patients after coronary artery stenting, but to our knowledge, no one has reported on a comparable number of cases of intracranial stenting procedures. In certain clinical scenarios, local thrombolysis with recombinant tissue-type plasminogen activator is an important treatment option to deal with subacute stent thrombosis.

MR Imaging Findings in Patients with Secondary Intracranial Hypertension

BACKGROUND AND PURPOSE: IH can alter the configuration of anatomic structures of the central nervous system. We determined the sensitivity and specificity of MR imaging to detect these changes in patients with secondary IH. MATERIALS AND METHODS: Patients (n = 36) with IH were prospectively investigated with MR imaging and were matched to 36 controls. MR images were evaluated for elongation and edema of the optic nerves, protrusion of the optic disc, flattening of the posterior sclera, height of the pituitary gland, and width of the optic nerve sheath. On MRV, we recorded venous sinus abnormalities and measured the luminal width of the superior ophthalmic veins. A grading score was introduced to define cranial venous outflow obstruction. RESULTS: Cranial venous outflow obstruction and ONS hydrops were the most valid signs indicating IH with a sensitivity of 94% and 92% and a specificity of 100% and 89%, respectively. Sensitivities and specificities were 56% and 97% for reduced pituitary height, 64% and 78% for flattening of the posterior sclera, 31% and 97% for widening of the superior ophthalmic veins, 33% and 100% for optic disc protrusion, 14% and 100% for optic nerve edema, and 6% and 100% for elongation of the optic nerve. At least 2 MR imaging findings could be demonstrated in each patient but in none of the controls. The number of positive MR imaging findings correlated with CSF pressure (r = 0.62, P = .01). CONCLUSIONS: The combination of cranial and orbital MR imaging and MRV can be highly sensitive and specific in the diagnosis of patients with IH.

MR Imaging of the Optic Nerve Sheath in Patients with Craniospinal Hypotension

BACKGROUND AND PURPOSE: Craniospinal hyper- or hypotension leads to morphologic changes in certain intracranial structures. We tested the hypothesis that the amount of CSF in the ONS visible in MR imaging is reduced in patients with CSH. MATERIALS AND METHODS: Nineteen patients with CSH were prospectively studied. Three readers assessed the width of the peri-optical CSF rim at 4 different anatomic positions by using coronal STIR sequences from a 3T MR imaging scanner. The height of the pituitary gland was also measured. Results were compared with normal values obtained with the same imaging technique. Qualitative signs of CSH also recorded were engorgement of venous sinuses, dural enhancement, subdural effusion, narrow ventricles, and sagging brain. RESULTS: CSF signal intensity surrounding the optic nerves was diminished in at least 2 of the 4 positions used for measurements so that decreased diameters of the ONSs were observed in all patients (sensitivity, 100%; specificity, 97%). The height of the pituitary gland was above normal limits in 12 of 19 patients (sensitivity, 63%; specificity, 97%). Frequencies of qualitative signs of CSH varied from 32% to 81%. CONCLUSIONS: The ISSON in patients with CSH is partially or fully collapsed due to reduced CSF content. In comparison with other anatomic markers, this sign showed the highest sensitivity for the diagnosis of patients with CSH in this study.

Spinal and supraspinal processing of thermal stimuli: An fMRI study

To assess and characterize responses to innocuous/noxious thermal stimuli and heat allodynia using functional spinal magnetic resonance imaging (spinal fMRI).

Intraoperative dynamic susceptibility contrast MRI (iDSC-MRI) is as reliable as preoperatively acquired perfusion mapping

DSC-MRI was applied intraoperatively during human brain tumor removal. Immediately after complete tumor resection was presumed, MRI including a dynamic susceptibility contrast T2-weighted EPI sequence was performed in 30 patients while the skull was still open using a flexible two-channel coil system at an intraoperative 1.5-Tesla MR scanner. Maps of relative regional blood flow (rCBF), blood volume (rCBV), and mean transit time (MTT) were calculated, and ratios of these maps were compared to preoperatively acquired DSC-MRI data. The extent of the resection was compared with the postoperative MRI performed 24 h after the operation. In 8 of these patients residual tumor tissue was depicted at the time of intraoperative MRI. In corresponding regions ratios for rCBV and rCBF did not differ significantly between pre- and intraoperatively acquired data (two-tailed t-test). Furthermore, we found a high correlation between ratios created from pre- and intraoperatively measured data for both rCBV and rCBF, respectively (Pearson correlation; r(2)(rCBV)=0.86, p<or=0.01; r(2)(rCBF)=0.86, p<or=0.01). DSC-MRI is a powerful tool for the differential diagnosis of brain lesions. Its use intraoperatively provides pathophysiologic information that is up-to-date, independently of an intraoperative brain shift and also independently of the known leakage phenomenon caused by surgical manipulation. It can assist in the decision to depict residual tumor burden beyond conventional imaging. Our data demonstrate that iDSC-MRI is as reliable as preoperatively acquired data.