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Donald W Gross

Publications and source records attributed to Donald W Gross.

9 recordsLinked to original sources
PubMed2006

Diffusion tensor imaging of time-dependent axonal and myelin degradation after corpus callosotomy in epilepsy patients.

Axonal degeneration of white matter fibers is a key consequence of neuronal or axonal injury. It is characterized by a series of time-related events with initial axonal membrane collapse followed by myelin degradation being its major hallmarks. Standard imaging cannot differentiate these phenomena, which would be useful for clinical investigations of degeneration, regeneration and plasticity. Animal models suggest that diffusion tensor magnetic resonance imaging (DTI) is capable of making such distinction. The applicability of this technique in humans would permit inferences on white matter microanatomy using a non-invasive technique. The surgical bisection of the anterior 2/3 of the corpus callosum for the palliative treatment of certain types of epilepsy serves as a unique opportunity to assess this method in humans. DTI was performed on three epilepsy patients before corpus callosotomy and at two time points (1 week and 2-4 months) after surgery. Tractography was used to define voxels of interest for analysis of mean diffusivity, fractional anisotropy and eigenvalues. Diffusion anisotropy was reduced in a spatially dependent manner in the genu and body of the corpus callosum at 1 week and remained low 2-4 months after the surgery. Decreased anisotropy at 1 week was due to a reduction in parallel diffusivity (consistent with axonal fragmentation), whereas at 2-4 months, it was due to an increase in perpendicular diffusivity (consistent with myelin degradation). DTI is capable of non-invasively detecting, staging and following the microstructural degradation of white matter following axonal injury.

Adult↗
PubMed2006

Extratemporal white matter abnormalities in mesial temporal lobe epilepsy demonstrated with diffusion tensor imaging.

PURPOSE: Recent studies have demonstrated bilateral white matter abnormalities in temporal lobe epilepsy (TLE) patients with unilateral mesial temporal sclerosis (MTS). The purpose of this project was to determine whether abnormalities of water diffusion are seen in extratemporal white matter of patients with TLE and pathologically confirmed MTS and to determine whether these findings are associated with worse surgical outcome. METHODS: Eleven patients with TLE and unilateral MTS confirmed in surgical specimens and 14 controls were studied by using cerebrospinal fluid-suppressed diffusion tensor imaging (DTI) and T2 relaxometry. RESULTS: Hippocampal T2 signal for patients was significantly elevated both ipsilateral (p<0.001) and contralateral (p=0.006) to MTS. DTI demonstrated reduced fractional anisotropy of the genu of the corpus callosum (p=0.003) and external capsule (p=0.02) and elevated mean diffusivity of the genu (p=0.005), splenium (p=0.03), and external capsule (p<0.001). For both the genu and external capsule, parallel diffusion of patients was not different from that of controls (genu, p=0.81; external capsule, p=0.45), whereas perpendicular diffusion was elevated (genu, p=0.001; external capsule, p<0.001). With mean postsurgical follow-up of 18.5 months, eight of 11 patients were entirely seizure free and the remaining three had all experienced a worthwhile reduction in seizure frequency. CONCLUSIONS: Our findings suggest that although patients with TLE and MTS have extensive bilateral and extratemporal pathology, these findings may not be associated with a worse postsurgical outcome.

Adult↗
PubMed2005

Bilateral limbic diffusion abnormalities in unilateral temporal lobe epilepsy.

Diffusion tensor magnetic resonance imaging can acquire quantitative information on the microstructural integrity of white matter structures and depict brain connectivity in vivo based on the behavior of water diffusion. Diffusion tensor imaging-derived tractography has been used for virtual dissection of the fornix and cingulum in healthy subjects, but not in patients with temporal lobe epilepsy (TLE). Eight patients with medically intractable TLE and unilateral mesial temporal sclerosis and nine healthy control subjects were imaged using diffusion tensor imaging. Fiber tracking was performed to delineate the fornix and cingulum, which were quantitatively analyzed. Bilateral symmetrical reduction in fractional anisotropy was observed in the fornix of patients with TLE, together with an increase in water mobility perpendicular to the axis of the fibers. The findings in the cingulum are similar to those of the fornix with the exception of significantly increased bulk diffusivity in the latter. We observed strikingly symmetrical bilateral abnormalities of axonal integrity in the fornix and cingulum in a series of patients with unilateral mesial temporal sclerosis. Our findings suggest that TLE with unilateral mesial temporal sclerosis is associated with bilateral limbic system pathology.

Adult↗
PubMed2005

Diffusion tensor imaging abnormalities in focal cortical dysplasia.

PURPOSE: Focal cortical dysplasia (FCD) is one of the most common underlying pathologic substrates in patients with medically intractable epilepsy. While magnetic resonance imaging (MRI) evidence of FCD is an important predictor of good surgical outcome, conventional MRI is not sensitive enough to detect all lesions. Previous reports of diffusion tensor imaging (DTI) abnormalities in FCD suggest the potential of DTI in the detection of FCD. The purpose of this study was to study subcortical white matter underlying small lesions of FCD using DTI. METHODS: Five patients with medically intractable epilepsy and FCD were investigated. Diffusion tensor imaging images were acquired (20 contiguous 3 mm thick axial slices) with maps of fractional anisotropy (FA), trace apparent diffusion coefficient (trace/3 ADC), and principal eigenvalues (ADC parallel and ADC perpendicular to white matter tracts) being calculated for each slice. Region of interest analysis was used to compare subcortical white matter ipsilateral and contralateral to the lesion. RESULTS: Three subjects with FCD associated with underlying white matter hyperintensities on T2 weighted MRI were observed to have increased trace/3 ADC, reduced fractional anisotropy and increased perpendicular water diffusivity which was greater than the relative increase in the parallel diffusivity. No DTI abnormalities were identified in two patients with FCD without white matter hyperintensities on conventional T2-weighted MRI. CONCLUSIONS: While DTI abnormalities in FCD with obvious white matter involvement are consistent with micro-structural degradation of the underlying subcortical white matter, DTI changes were not identified in FCD lesions with normal appearing white matter.

Adolescent↗
PubMed2005

Diffusion tensor tractography of the limbic system.

BACKGROUND AND PURPOSE: The limbic system, relevant to memory and emotion, is an interesting subject of study in healthy and diseased individuals. It consists of a network of gray matter structures interconnected by white matter fibers. Although gray matter components of this system have been studied by using MR imaging, the connecting fibers have not been analyzed to the same degree. Cerebrospinal fluid (CSF) signal intensity contamination of the fornix and cingulum, the 2 major white matter tracts of the limbic system, can alter diffusion-tensor imaging (DTI) measurements and affect tractography. We investigated the effect of CSF signal intensity suppression on fiber tracking of the limbic connections and characterized the diffusion properties of these structures in healthy volunteers. METHODS: Nine healthy individuals were scanned with standard and CSF-suppressed DTI. Tractography of the fornix and cingulum was performed for both acquisition methods. We report mean diffusivity and fractional anisotropy measurements of the crus, body, and columns of the fornix, and descending, superior, and anterior portions of the cingulum. RESULTS: Diffusion measurements were improved and tractography was facilitated by using CSF-suppressed DTI. In particular, tract volume increased, whereas decreases of the mean diffusivity and increases of diffusion anisotropy more accurately represented the underlying tissue by minimizing deleterious partial volume averaging from CSF. This was particularly true for the fornix because it is in closest contact to CSF. Diffusion measurements throughout the limbic connections were consistent in healthy volunteers. CONCLUSION: We recommend the use of CSF suppression when performing diffusion-tensor tractography of the limbic system.

Adult↗
PubMed2004

Reversible coma: a rare presentation of spontaneous intracranial hypotension.

BACKGROUND: Spontaneous intracranial hypotension (SIH) is a well-recognized neurologic disorder that typically presents with orthostatic headaches, low cerebral spinal fluid pressures and distinct abnormalities on magnetic resonance imaging. METHODS: We present a case of a rare presentation of SIH. RESULTS: A 49-year-old man presented with a two week history of orthostatic headaches that rapidly progressed to encephalopathy and coma, requiring intubation. Neuroimaging revealed abnormalities typical of SIH; diffusely enhancing pachymeninges, subdural fluid collections, and descent of the brain. Treatment with an epidural blood patch reversed his coma within minutes. Following a second blood patch, the patient became asymptomatic. No cerebral spinal leak could be identified on magnetic resonance imaging or on a nuclear medicine technetium cerebral spinal fluid flow study. At six month follow-up, he remained symptom free. CONCLUSION: The mechanism of coma in SIH is presumed to be compression of the diencephalon from downward displacement of the brain. Although it is very unusual for patients with SIH to present with coma, it is important to recognize since the coma may be reversible with epidural blood patches.

Blood Patch, Epidural↗
PubMed2003

alpha-[11C]-Methyl-L-tryptophan PET identifies the epileptogenic tuber and correlates with interictal spike frequency.

Epilepsy surgery has been successfully performed in patients with tuberous sclerosis complex (TSC) and seizures arising from a restricted epileptogenic area. The outcome of cortical excision depends on accurate pre-surgical identification of the epileptogenic tuber. [11C] alpha-methyl-L-tryptophan (alpha-MTrp) was originally developed to measure serotonin synthesis in vivo with positron emission tomography (PET). However in pathologic conditions its uptake may also depend on the synthesis of quinolinic or kynurenic acid via the kynurenine pathway. Increased levels of serotonin and quinolinic acid have been observed in epileptogenic lesions, raising the possibility that alpha-MTrp PET may localize the epileptogenic area. The aim of this study was to correlate alpha-MTrp PET uptake with the localization of the epileptogenic area and with interictal spike frequency in patients with TSC. alpha-MTrp uptake was measured in 8 patients (2 males, mean age 29.6+/-14.9 years, range 3-50 years) with intractable partial epilepsy due to TSC. All patients underwent scalp EEG monitoring during the PET scan. In four (50%), increased uptake of alpha-MTrp occurred in the epileptogenic area alone. Two (25%) patients showed multifocal abnormalities and the remaining two (25%) did not show focal changes. PET localization was mostly seen in patients with frequent interictal abnormalities on the EEG. Furthermore, there was a significant correlation between alpha-MTrp uptake and the frequency of interictal spikes (r=0.6; P<0.05). alpha-MTrp PET is a promising diagnostic tool in the localization of the epileptogenic area in patients with TSC.

Adolescent↗
PubMed2002

The BOLD response to interictal epileptiform discharges.

We studied single-event and average BOLD responses to EEG interictal epileptic discharges (IEDs) in four patients with focal epilepsy, using continuous EEG-fMRI during 80-min sessions. The detection of activated areas was performed by comparing the BOLD signal at each voxel to a model of the expected signal. Since little is known about the BOLD response to IEDs, we modeled it with the response to brief auditory events (G. H., NeuroImage 9, 416-429). For each activated area, we then obtained the time course of the BOLD signal for the complete session and computed the actual average hemodynamic response function (HRF) to IEDs. In two of four patients, we observed clear BOLD responses to single IEDs. The average response was composed of a positive lobe peaking between 6 and 7 s in all patients and a negative undershoot in three patients. There were important variations in amplitude and shape between average HRFs across patients. The average HRF presented a wider positive lobe than the Glover model in three patients and a longer undershoot in two. There was a remarkable similarity in the shape of the HRF across areas for patients presenting multiple activation sites. There was no clear correlation between the amplitude of individual BOLD responses and the amplitude of the corresponding EEG spike. The possibility of a longer HRF could be used to improve statistical detection of activation in simultaneous EEG-fMRI. The variability in average HRFs across patients could reflect in part different pathophysiological mechanisms.

Adolescent↗