Armin Thron

Type and extent of hemispheric brain infarctions and clinical outcome in early and delayed middle cerebral artery recanalization

We evaluated the influence of time of recanalization or degree of initial leptomeningeal collateral blood flow in cardioembolic or arterio-arterial middle cerebral artery (MCA) occlusion on infarct size and clinical outcome in a series of 34 consecutive acute stroke patients with main stem (N = 31) or major branch (N = 3) occlusions using CT, initial cerebral arteriography (N = 21), repetitive close-meshed transcranial Doppler ultrasonography, and a neurologic stroke scale. We treated 15 patients with tissue plasminogen activator intravenously within the first 6 hours. The type and size of infarction depended on the location of the occluding lesions within the MCA trunk. Proximal MCA occlusion always led to infarction involving the striatum and internal capsule. Sixty-five percent of patients showed recanalization of the occluded MCA within 1 week. Following MCA recanalization, hyperperfusion was present in 38 to 44% of cases. There was a marginally significant relation between size of infarction on CT and recanalization time within the first 24 hours. The more rapidly recanalization occurred, the smaller the size of the infarct. When recanalization time was greater than 8 hours, the lesions always extended to the cortex. An additional good leptomeningeal collateral blood flow significantly reduced the size of the infarct and improved clinical outcome after 17 days and after 10 months. Early recanalization of embolic MCA occlusions within up to 8 hours, in conjunction with good transcortical collateralization, has a favorable impact on infarct size and outcome and may constitute the therapeutic window of opportunity.

Diagnostic accuracy of MRI compared to CCT in patients with brain metastases

AbstractObjectives. In patients with extracranial neoplasms, the occurrence and number of brain metastases (BM) are critical for further diagnostic approaches and therapeutic strategies and the patients prognosis. Although widely accepted, there is surprisingly little evidence in the literature that MRI is superior to CCT. Therefore, in patients with solitary BM according to diagnostic contrast-enhanced computed tomography (CCT), we investigated, what additional information could be gained by contrast-enhanced magnetic resonance imaging (MRI). Methods/Results. Among 55 patients with solitary BM according to CCT, 17 had multiple BM on MRI (31%) and 38 had solitary BM in both. Based on a presumed binomial distribution of our data, we calculated a rate of at least 19% of patients with solitary BM on CCT, in which MRI would show multiple lesions (p=0.05). The two main characteristics for BM missed by CCT were the smaller diameter, which averages 2 cm less than in BM identified with both modalities, and a preferential frontotemporal location. Conclusion. MRI is indeed superior to CCT in the diagnosis of BM the essential reasons besides detection of smaller lesions being a better soft tissue contrast, significantly stronger enhancement with paramagnetic contrast agents, the lack of bone artifacts, fewer partial volume effects, and direct imaging in three different planes. Therefore, MRI is indispensable in the diagnostic workup of patients with BM for choosing the optimum therapeutic approach, especially with regard to the decision whether to operate or to primarily irradiate the patients metastases.

Cortical activation patterns during complex motor tasks in piano players and control subjects. A functional magnetic resonance imaging study

We performed functional magnetic resonance imaging (MRI) in professional piano players and control subjects during an overtrained complex finger movement task using a blood oxygenation level dependent echo-planar gradient echo sequence. Activation clusters were seen in primary motor cortex, supplementary motor area, premotor cortex and superior parietal lobule. We found significant differences in the extent of cerebral activation between both groups with piano players having a smaller number of activated voxels. We conclude that, due to long-term motor practice a different cortical activation pattern can be visualized in piano players. For the same movements lesser neurons need to be recruited. The different volume of the activated ortical areas might therefore reflect the different effort necessary for motor performance in both groups.

Effects of Blood Estrogen Level on Cortical Activation Patterns during Cognitive Activation as Measured by Functional MRI

Modulation of the blood estrogen level as it occurs during the menstrual cycle has a strong influence on both neuropsychological and neurophysiological parameters. One of currently preferred hypotheses is that the menstrual cycle hormones modulate functional hemispheric lateralization. We examined six male and six female subjects by functional magnetic resonance imaging (fMRI) to image cortical activation patterns associated with cognitive and motor activation to determine whether these changes during the menstrual cycle can be visualized. Female subjects, who did not use oral contraceptives, were scanned twice, once during the menses and once on the 11/12 day of the menstrual cycle. A word-stem-completion task, a mental rotation task and a simple motor task were performed by all subjects. Our data provide evidence that the menstrual cycle hormones influence the overall level of cerebral hemodynamics to a much stronger degree than they influence the activation pattern itself. No differences were seen between male subjects and female subjects during the low estrogen phase. During both neuropsychological tasks blood estrogen level had a profound effect on the size but not on the lateralization or the localization of cortical activation patterns. The female brain under estrogen showed a marked increase in perfusion in cortical areas involved in both cognitive tasks, whereas the hemodynamic effects during the motor tasks were less pronounced. This might be due to differences in neuronal or endothelian receptor concentration, differences in synaptic function, or, most likely, changes in the cerebrovascular anatomy in different cortical regions.

Localization of the motor hand area using transcranial magnetic stimulation and functional magnetic resonance imaging

OBJECTIVE The anatomical location of the motor area of the hand may be revealed using functional magnetic resonance imaging (fMRI). The motor cortex representation of the intrinsic hand muscles consists of a knob-like structure. This is omega- or epsilon-shaped in the axial plane and hook-shaped in the sagittal plane. As this knob lies on the surface of the brain, it can be stimulated non-invasively by transcranial magnetic stimulation (TMS). It was the aim of our study to identify the hand knob using fMRI and to reveal if the anatomical hand knob corresponds to the hand area of the motor cortex, as identified by TMS, by means of a frameless MRI-based neuronavigation system. METHODS Suprathreshold transcranial magnetic stimuli were applied over a grid on the left side of the scalp of 4 healthy volunteers. The motor evoked potentials (MEPs) were recorded from the contralateral small hand muscles, and the centers of gravity (CoG) of the MEPs were calculated. The exact anatomical localization of each point on the grid was determined using a frameless MRI-based neuronavigation system. In each subject, the hand area of the motor cortex was visualized using fMRI during sensorimotor activation achieved by clenching the right hand. RESULTS In all 4 subjects, the activated precentral site in the fMRI and the CoG of the MEP of all investigated muscles lay within the predicted anatomical area, the so-called hand knob. This knob had the form of an omega in two subjects and an epsilon in the other two subjects. CONCLUSIONS TMS is a reliable method for mapping the motor cortex. The CoG calculated from the motor output maps may be used as an accurate estimation of the location of the represented muscle in the motor cortex.

Three-dimensional visualization of the pyramidal tract in a neuronavigation system during brain tumor surgery: first experiences and technical note.

OBJECTIVETo integrate spatial three-dimensional information concerning the pyramidal tracts into a customized system for frameless neuronavigation during brain tumor surgery. METHODSFour consecutive patients with intracranial tumors in eloquent areas underwent diffusion-weighted and anatomic magnetic resonance imaging studies within 48 hours before surgery. Diffusion-weighted datasets were merged with anatomic data for navigation purposes. The pyramidal tracts were segmented and reconstructed for three-dimensional visualization. The reconstruction results, together with the fused-image dataset, were available during surgery in the environment of a customized neuronavigation system. RESULTSIn all four patients, the combination of reconstructed data and fused images was a helpful additional source of information concerning the tumor seat and topographical interaction with the pyramidal tract. In two patients, intraoperative motor cortex stimulation verified the tumor seat with regard to the precentral gyrus. CONCLUSIONDiffusion-weighted magnetic resonance imaging allows individual estimation of large fiber tracts applicable as important information in intraoperative neuronavigation and in planning brain tumor resection. A three-dimensional representation of fibers associated with the pyramidal tract during brain tumor surgery is feasible with the presented technique and is a helpful adjunct for the neurosurgeon. The main drawbacks include the length of time required for the segmentation procedure, the lack of direct intraoperative control of the pyramidal tract position, and brain shift. However, mapping of large fiber tracts and its intraoperative use for neuronavigation have the potential to increase the safety of neurosurgical procedures and to reduce surgical morbidity.

Magnetic resonance imaging of thrombosed dural sinuses.

Background and Purpose Magnetic resonance imaging should have the potential to replace angiography in the diagnosis of dural sinus thrombosis. Concerning time-dependent signal changes of the thrombus, we intended to develop a standardized examination protocol for routine use in suspected dural sinus thrombosis. Methods The time-dependent signal changes of thrombosed dural sinuses were studied in 23 consecutive patients by multiplanar spin-echo and flow-sensitive sequences. Signal intensities and thrombus homogeneity were graded and related to the time after clinical onset and the results of the magnetic resonance angiography. Results Four stages of the thrombus evolution could be observed. The acute thrombosis (days 1 to 5) appeared strongly hypointense in T2-weighted images and isointense in spin density- and T1-weighted images. In the subacute stage (up to day 15) the thrombus signal was strongly hyperintense in T1- and T2-weighted images. The third stage began in the third week after clinical onset. The thrombus signal was decreased in all sequences and showed an increasing inhomogeneity. The fourth (late) stage was characterized by either the restitution of blood flow or the persistence of a residual thrombus. Conclusions Each stage requires a different diagnostic approach. With the combined use of spin-echo and gradient-echo sequences, it is possible to make the diagnosis of acute thrombosis; in the second stage, multiplanar spin-echo sequences are sufficient. Diagnosis of dural sinus thrombosis can be established accurately with magnetic resonance imaging in the first two stages. However, the diagnosis of the later stages is difficult because of inhomogeneous signs of recanalization and flow phenomena. Therefore, a suspected older dural sinus thrombus still requires intra-arterial angiography as the primary diagnostic tool.

Clinical significance of intracranial developmental venous anomalies

OBJECTIVES Venous angiomas, or developmental venous anomalies (DVAs), represent the most often occurring cerebral vascular malformation. The clinical significance of a DVA is, however, at present unclear. METHODS A retrospective analysis was carried out on two series of consecutive cranial MRIs performed between January 1990 and August 1996 in a university department of neuroradiology and in a large radiological private practice. The medical records of all patients in whom a DVA was diagnosed were screened to identify the specific complaint which necessitated the imaging procedure. RESULTS A total of 67 patients with DVA could be identified. In 12 patients an associated cavernoma was found. The main reason for performing the MRI was the evaluation of seizures or of headaches. In all patients with DVA in whom an intracerebral haemorrhage was diagnosed an associated cavernoma was present at the site of the haemorrhage. None of the 67 patients showed an association between the complaints that led to the MRI and the location of the DVA. CONCLUSIONS DVAs do not seem to be associated with a specific clinical presentation. In a significant percentage of cases, however, coexisting cavernomas are found which have a defined bleeding potential and should be treated independently of the DVA. This study supports the hypothesis that DVAs are a congenital abnormality of venous drainage without clinical significance.

Detectability of cerebral hemisphere ischaemic infarcts by CT within 6 h of stroke

To determine how early and how reliably ischaemic brain infarcts can be detected on CT within 6 h of the onset of cerebral hemisphere strokes, 44 such studies were interpreted by an experienced neuroradiologist blinded to clinical signs, but aware that the cohort was a stroke population. He was asked to detect and localise an area of parenchymal low density and/or focal brain swelling. A follow-up study showing the definite infarct served as a reference in each case. In 38 patients areas of slightly low density were seen, and in 36 follow-up CT confirmed infarcts in the locations indicated. In 2 patients the reading was false positive. In 6 patients no low density focus could be detected. In these 8 patients examined by CT within 180 min of the stroke, no low density could be identified, even in retrospect with the knowledge of the findings on follow-up. Thus, 42 readings (95%) were true positive or true negative; 2 were false positive; and none was a false negative. CT within 6 h of the onset of symptoms has a mean sensitivity of 82% (36/44) for ischaemic cerebral hemisphere infarcts. By contrast, its sensitivity to ischaemic parenchymal low density is low during the initial 2 h. The early development of hemispheric infarcts can be detected reliably if the radiologist is familiar with the signs.

Spinal vascular malformations

Spinal vascular malformations are rare diseases that consist of true inborn cavernomas and arteriovenous malformations (including perimedullary fistulae, glomerular and juvenile AVMs) and presumably acquired dural arteriovenous fistulae. This review article gives an overview of the imaging features both on MRI and angiography, the differential diagnoses, the clinical symptomatology and the potential therapeutic approaches to these diseases. It is concluded that MRI is the diagnostic modality of first choice in suspected spinal vascular malformation and should be complemented by selective spinal angiography. Treatment in symptomatic patients offers an improvement in the prognosis, but should be performed in specialized centers. Patients with spinal cord cavernomas and perimedullary fistulae type I are surgical candidates. Dural arteriovenous fistulae can either be operated upon or can be treated by an endovascular approach, the former being a simple, quick and secure approach to obliterate the fistula, while the latter is technically demanding. In spinal arteriovenous malformations, the endovascular approach is the method of first choice; in selected cases, a combined therapy might be sensible.