An investigation of working memory rehearsal in multiple sclerosis using fMRI.

The present study examined patterns of cerebral activation during a working memory (WM) rehearsal task in individuals diagnosed with multiple sclerosis (MS) and in healthy adults. BOLD functional magnetic resonance imaging (fMRI) was performed using a 1.5 T GE scanner to assess activation during a WM task adapted from the Sternberg paradigm (Sternberg, 1969). Participants included 8 individuals diagnosed with MS, and 5 healthy controls (HCs) matched for age and education. Task difficulty was manipulated by increasing the length of time that strings of letters were to be rehearsed. Findings revealed increased right prefrontal cortex activation and increased right temporal lobe activation in individuals diagnosed with MS compared to HCs. The potential explanations for increased right hemisphere activation in persons with MS are discussed.

BOLD fMRI activation induced by vagus nerve stimulation in seizure patients.

OBJECTIVE: To identify the cerebral activated regions associated with the vagus nerve stimulation in epilepsy patients. DESIGN: Blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI) was employed to detect areas of the brain activated by vagus nerve stimulation in five patients with documented complex partial seizures. METHODS: Functional MRI was done on a GE 1.5T Echospeed horizon scanner. Before each patient entered the scanner, the vagal nerve stimulator was set to a specific ON-OFF paradigm so that the data could be analysed using a box-car type of design. The brains were scanned both anatomically and functionally. The functional images were corrected for head motion and co-registered to the anatomical images. Maps of the activated areas were generated and analysed using the brain mapping software, SPM99. The threshold for activation was chosen as p < 0.001. RESULTS: All patients showed activation in the frontal and occipital lobes. However, activation in the thalamus was seen only in the two patients with improved seizure control. CONCLUSIONS: BOLD fMRI can detect activation associated with vagus nerve stimulation. There may be a relation between thalamic activation and a favourable clinical outcome.

Functional magnetic resonance imaging of working memory impairment after traumatic brain injury.

OBJECTIVES: To examine patterns of brain activation while performing a working memory task in persons with moderate to severe traumatic brain injury (TBI) and healthy controls. It is well established that working memory is an area of cognition that is especially vulnerable to disruption after TBI. Although much has been learned about the system of cerebral representation of working memory in healthy people, little is known about how this system is disrupted by TBI. METHODS: Functional magnetic resonance imaging (fMRI) was used to assess brain activation during a working memory task (a modified version of the paced auditory serial addition test) in nine patients with TBI and seven healthy controls. RESULTS: Patients with TBI were able to perform the task, but made significantly more errors than healthy controls. Cerebral activation in both groups was found in similar regions of the frontal, parietal, and temporal lobes, and resembled patterns of activation found in previous neuroimaging studies of working memory in healthy persons. However, compared with the healthy controls, the TBI group displayed a pattern of cerebral activation that was more regionally dispersed and more lateralised to the right hemisphere. Differences in lateralisation were particularly evident in the frontal lobes. CONCLUSIONS: Impairment of working memory in TBI seems to be associated with alterations in functional cerebral activity.

Identification of the corticospinal tracts achieved using blood-oxygen-level-dependent and diffusion functional MR imaging in patients with brain tumors.

Diffusion-weighted MR imaging was used to delineate the corticospinal tract (CST) successfully and to depict its relationship to adjacent brain tumors. The CST was defined by a method by which it seems possible to delimit the distance from the CST to the main tumor mass and to show displacement and infiltration of the tract by the neoplasia. This information cannot be gathered from routine anatomic MR imaging.

The effect of brain tumors on BOLD functional MR imaging activation in the adjacent motor cortex: implications for image-guided neurosurgery.

BACKGROUND AND PURPOSE: Functional MR (fMR) imaging data coregistered to a neurosurgical navigation system have been proposed as guides for the resection of brain tumor in or adjacent to eloquent cortices. The purpose of this study was to compare data obtained from the side of the brain affected by tumor with the contralateral side and to determine if there are physiological limitations of fMR imaging in accurately determining the location of the primary motor cortex. METHODS: Ten patients with tumors in or directly adjacent to the motor cortex were studied with fMR imaging (finger-tapping paradigm). fMR imaging data were analyzed using multiple R values. These data were coregistered to a real-time intraoperative neurosurgical navigation system. RESULTS: Significant variability of motor cortex activation patterns was noted among individual patients. The activation volumes on the side of the tumor were significantly smaller compared with the contralateral side for all tumors not previously resected (0.66+/-0.47). This was most pronounced in glioblastomas (0.27+/-0.21). We propose that these differences were caused by a loss of autoregulation in the tumor vasculature of glioblastomas and venous effects. CONCLUSION: Notwithstanding the differences noted, the motor cortex was identified successfully in all patients. This was confirmed by intraoperative physiological identification of the motor cortex and a lack of postoperative neurologic deficit.

Functional magnetic resonance imaging aided radiation treatment planning.

Functional MRI (magnetic resonance imaging) allows one to noninvasively identify various eloquent cortices in the brain. The integration of cortical activation information into radiosurgical treatment planning may provide an alternative to prevent or minimize radiation damage to eloquent cortex. A novel approach of directly integrating the fMRI (functional magnetic resonance imaging) brain map into treatment planning is proposed. Three brain tumor patients have been studied using this method with motor and/or visual paradigms. Brain activation was demonstrated in eloquent cortex at the precentral gyrus (motor area) and medial occipital lobe (visual area). The activation maps were transferred to a treatment planning workstation, (XKnife), and 3D (three-dimensional) activation maps were generated and co-registered to a 3D CT (computed tomography) anatomical data set, which provided the calibration localizer, for treatment planning. Radiosurgery was designed based on both functional and structural information by the medical team consisting of a radiation oncologist, a neurosurgeon and a physicist. The average maximum dose for the tumor was 2113 cGy. The average maximum dose for tissue surrounding the tumor was 1600 cGy. The average dose with fMRI information to the eloquent cortex was 163.4 cGy over three patients, while without fMRI information it was 240.5 cGy. The average percentage dose reduction over three patients is 32%. The results suggest that using this method can reduce the dose to the eloquent cortex. This approach provides the physician with additional information for treatment planning and may spare the patient unnecessary radiation exposure to adjacent eloquent cortices.

Correlation between the degree of contrast enhancement and the volume of peritumoral edema in meningiomas and malignant gliomas.

Peritumoral edema and contrast enhancement of brain tumors are both thought to be due to breakdown of the blood-brain barrier (BBB); however, the exact mechanism by which these two phenomena occur and whether there is a quantitative or etiological relationship is not known. Our purpose was to determine whether the relationship between the breakdown of the BBB, defined radiologically as the degree of contrast enhancement, and the volume of surrounding edema is different for high-grade gliomas and meningiomas. We analyzed 13 meningiomas and 23 gliomas. A direct linear relationship between the degree of contrast enhancement (dC) and volume of peritumoral edema (V) with a high correlation coefficient (R = 0.66, P = 0.0006) was established for gliomas. A mathematical relationship between dC and V could not be established for meningioma. The findings for gliomas offer indirect radiological evidence that the defect in the BBB which causes edema is quantitatively and etiologically related to the defect in the BBB responsible for contrast enhancement. For meningiomas, the lack of a relationship between dC and V implies either that the mechanisms responsible for formation of edema and contrast enhancement are fundamentally different or that a physical barrier in certain meningiomas limits propagation of edema into the adjacent white matter.

Decreased BOLD functional MR activation of the motor and sensory cortices adjacent to a glioblastoma multiforme: implications for image-guided neurosurgery.

A patient with a glioblastoma multiforme and mild sensorimotor deficits had significantly less activation of the motor and sensory cortices on the side with the tumor than on the contralateral side on blood oxygen level-dependent (BOLD) functional MR images. This difference, which may be due to pressure effects or loss of vascular autoregulation, should be considered in preoperative planning in which BOLD functional MR imaging is used to identify eloquent cortices to be avoided during brain tumor surgery.

Hemorrhagic chondroid chordoma mimicking pituitary apoplexy.

We describe a hemorrhagic chondroid chordoma involving the sella turcica with suprasellar extension. The CT and MRI appearances mimiked a hemorrhagic pituitary adenoma. Chondroid chordoma is a variant composed of elements of both chordoma and cartilaginous tissue. An uncommon bone neoplasm, located almost exclusively in the spheno-occipital region, it is usually not considered in the differential diagnosis of a tumor with acute hemorrhage in the sellar region. We discuss the clinical and radiological characteristics which may allow one to differentiate chondroid chordoma from other tumors of this area.

Focal dilation and paradoxical collapse of cortical fissures and sulci in patients with normal-pressure hydrocephalus.

OBJECT: The authors describe a subgroup of patients with shunt-proven normal-pressure hydrocephalus (NPH) who presented with focal fissural and sulcal dilation on imaging studies. The specific radiological features and methods of differentiating this condition from cortical atrophy are delineated. METHODS: Normal-pressure hydrocephalus has been described as dilation of the ventricles that is out of proportion to the sulci. Sulcal dilation has been taken as evidence of cortical atrophy and has even been used as a criterion to exclude patients from undergoing a shunting procedure. The authors describe five cases of patients with shunt-proven NPH who presented with focal dilation of cortical fissures and sulci. In three of the cases, there was a paradoxical decrease in the size of the dilated fissures and sulci that paralleled the decrease in the size of the lateral ventricles following successful shunting. CONCLUSIONS: This study demonstrates that focal fissural and sulcal dilation may represent reservoirs of cerebrospinal fluid analogous to the ventricular system. Patients should not be denied a shunting procedure solely on the basis of focally dilated fissures of sulci.

MR differential diagnosis of normal-pressure hydrocephalus and Alzheimer disease: significance of perihippocampal fissures.

PURPOSE: In the older patient with dilated ventricles, it is often difficult to differentiate normal pressure hydrocephalus (NPH) from cerebral atrophy caused by Alzheimer disease (AD). This study was undertaken to see if dilatation of the perihippocampal fissures (PHFs) could be used as a distinguishing characteristic of these two disorders. METHODS: MR images of 17 patients with AD were compared with those from an equal number of patients with NPH who improved after ventriculoperitoneal shunting. The PHFs, lateral ventricles, third ventricle, and temporal horns were graded subjectively. Objective, computer-aided volumetric measurements of the PHFs and lateral ventricles were obtained. The preshunt images of the NPH patients were evaluated. RESULTS: Significant differences between the two groups were found for the PHFs and lateral ventricles by both the subjective and objective methods, with a high degree of correlation between the two methods. CONCLUSION: The degree of dilatation of PHFs appears to be a sensitive and specific marker for differentiating AD from NPH by both subjective and objective means, with a very small overlap between the two groups. This observation may have relevance in day-to-day practice.

The perihippocampal fissures: normal anatomy and disease states.

Understanding the three-dimensional anatomy of the perihippocampal fissures (PHFs) can be helpful in making the correct diagnosis of diseases of the mesial temporal lobe. Disorders of the parenchyma and cerebrospinal fluid spaces are reflected by specific changes in the PHFs. A marker for Alzheimer disease and mesial temporal sclerosis is atrophy of the hippocampus and associated dilatation of the PHFs. This finding is best visualized on coronal magnetic resonance images but can and should be appreciated on routine computed tomographic scans. Hydrocephalus is characterized by dilatation of the temporal horn of the lateral ventricle without dilatation of the transverse fissure and its extensions. Normal-pressure hydrocephalus can usually be distinguished from Alzheimer disease on the basis of the pattern of dilatation of the PHFs. Understanding the anatomy of the PHFs often makes it possible to better characterize the extents of intra- and extraaxial tumors of the mesial temporal lobe.

Optic chiasmal compression by venous aneurysm: magnetic resonance imaging diagnosis.

The overwhelming majority of traumatic carotid cavernous fistulas present with a bruit, arterialization of conjunctival vessels, or an elevated intraocular pressure. Described herein is a patient who presented with progressive deterioration of vision, without any of the above signs. Magnetic resonance imaging demonstrated compression of the optic ch asm by a venous aneurysm arising from a carotid cavernous fistula. This entity should be considered in patients who present with progressive visual loss.