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Biomedical subjects

J G Ojemann

Publications and source records attributed to J G Ojemann.

At least 19 recordsLinked to original sources
PubMed2005

Evaluating functional MRI procedures for assessing hemispheric language dominance in neurosurgical patients.

Two methods of quantifying hemispheric language dominance (HLD) in neurosurgical patients are compared: (1) an average magnitudes (AM) method, which is a calculation of the average signal intensity variation in regions of interest for each patient that were predefined in a group analysis for each task, and (2) a lateralization indices (LI) method, which is based on the number of activated pixels in regions of interest predefined in each individual patient. Four language tasks [a living/nonliving (LNL) judgment, word stem completion (WSC), semantic associate (SA) and a phonological associate (PA) task] were compared with "gold standard" measures such as the Wada test or electrocortical stimulation. Results showed that the LI method was more accurate (73% agreement with gold standard methods) than the AM method (only 40% agreement) across tasks and subjects. Furthermore, by varying the threshold used for determining laterality, the ability of functional magnetic resonance imaging (fMRI) to predict HLD was influenced for the AM method, whereas the LI method was relatively unaffected by changing the threshold. Using the LI method, the SA task was the most accurate for quantifying HLD (100% agreement with gold standard methods) with respect to the other three language tasks (80% accuracy for WSC, 65% for the LNL and 63% for phonological task). Depending on the method and the task, fMRI may be a promising tool for assessing HLD in neurosurgical patients.

Adult↗
PubMed2004

Pathophysiology of parkinsonism due to hydrocephalus.

We report a patient with hydrocephalus who developed levodopa responsive parkinsonism and severe bradyphrenia associated with shunt malfunction and revision. Magnetic resonance imaging revealed periaqueductal edema involving medial substantia nigra. [18F]dopa positron emission tomography demonstrated reduced uptake in the caudate and putamen with relative sparing of the posterior putamen. Hydrocephalus associated with shunt malfunction can cause a distinct parkinsonian syndrome with greater dysfunction of projections from the medial substantia nigra to anterior striatum than in idiopathic Parkinson's disease.

Adult↗
PubMed2003

A critical analysis of 'normal' radionucleotide shuntograms in patients subsequently requiring surgery.

BACKGROUND: Shuntograms are performed when patients present with symptoms suggestive of, but inconclusive for, shunt malfunction, without confirmatory radiological evidence. METHODS: Shuntograms over the past 3.5 years were reviewed. Patient records were reviewed for revision in proximity to a negative (normal) study. RESULTS: One hundred and fifteen out of 149 tests were negative. Thirty-four surgeries (in 31 patients) occurred subsequent to a negative shuntogram. In 18 out of 34 revisions the shunt was functional: 13 surgeries were for overdrainage, 4 were for unrelated reasons with shunt function confirmed incidentally and 1 was an exploration for cognitive deterioration. In 16 cases (13 patients) the shunt was not functional: 12 had proximal catheter occlusion in which, on subsequent review, there was no ventricular reflux present and the remaining had distal malfunctions. CONCLUSIONS: The false negative rate for shuntograms was 16 out of 115 (14%) with proximal occlusion most common. This estimate of the predictive value of a normal flow study may influence the decision to revise a shunt.

Cerebrospinal Fluid Shunts↗
PubMed2003

Functional MRI reveals an interhemispheric dissociation of frontal and temporal language regions in a patient with focal epilepsy.

We report the case of a patient with frontal lobe epilepsy in whom the Wada test failed to lateralize representation of language (fluent speech was observed after amobarbital injection on both the right and left side). Functional magnetic resonance imaging (fMRI) during a lexical processing task revealed an atypical organization of language represented by an interhemispheric dissociation of language regions with a right frontal dominance and a left temporal dominance. Consistent with the fMRI results, the patient's ability to name pictures was not reliably impaired by electrocortical stimulation (ECS) of left frontal cortex. The findings from Wada, fMRI, and ECS were confirmed by a lack of language impairment after left frontal lobectomy for seizures. This case illustrates that fMRI can precisely map cortical language networks in epileptic patients and that fMRI may be used to help interpret laterality results provided by the Wada procedure.

Adult↗
PubMed2002

Wada testing reveals frontal lateralization for the memorization of words and faces.

Neuroimaging studies have suggested that specific regions of the frontal and medial temporal cortex are engaged during memory formation. Further, there is specialization across these regions such that verbal materials appear to preferentially engage the left regions while nonverbal materials primarily engage the right regions. An open question, however, has been to what extent frontal regions contribute to successful memory formation. The present study investigates this question using a reversible lesion technique known as the Wada test. Patients memorized words and unfamiliar faces while portions of their left and right hemispheres were temporarily anesthetized with sodium amytal. Subsequent memory tests revealed that faces were remembered better than words following left-hemisphere anesthesia, whereas words were remembered better than faces following right-hemisphere anesthesia. Importantly, inspection of the circulation affected by the amytal further suggests that these memory impairments did not result from direct anesthetization of the medial temporal regions. Taken in the context of the imaging findings, these results suggest that frontal regions may also contribute to memory formation in normal performance.

Adult↗
PubMed2001

Surgical treatment of Chiari I malformation: indications and approaches.

Chiari I malformation is a well-described entity characterized by hindbrain herniation through the foramen magnum. Although the exact origin of congenital Chiari I malformation is unknown, it appears to be caused by a mismatch between the volume of the posterior fossa neural elements and the posterior fossa cranial content. Several theories have been proposed to describe the resultant pathophysiology of this mismatch. It is clear, however, that abnormal cerebrospinal fluid flow and velocity play a role in the symptoms and signs associated with this disorder. The authors will review the pathophysiology, clinical presentation, and treatment options for patients with Chiari I malformation.

Adolescent↗
PubMed2001

An event-related fMRI study of overt and covert word stem completion.

In fMRI studies of language processing, it would be extremely useful to obtain high-quality images during tasks requiring spoken output. Recent studies have suggested that this may be possible, particularly if event-related fMRI methods are used. This study assesses the feasibility of acquiring interpretable images during speech by applying event-related methods to visual word stem completion, a task that has been studied extensively. On each trial, a different three-letter word stem (e.g., COU) was presented visually and subjects were required to generate a word beginning with that stem (e.g., COUSIN). In covert runs, subjects were instructed to say the word once to themselves, without moving their lips. In overt runs, subjects were instructed to say the word once aloud. Ten subjects were scanned during six overt runs and six covert runs at three presentation rates. Data were analyzed using an implementation of the general linear model making no assumptions about response shape. Images were relatively free of artifacts, and regions demonstrating task-related activation were similar to those reported in previous imaging studies. Regions active during overt task performance were similar to those active during covert task performance, with the addition of several regions commonly associated with motor aspects of speech production. Consistent with other studies, magnitude of activation was greater in the overt condition than in the covert condition, and there was a modest decrease in magnitude at the fastest presentation rate. Together, these results help to validate the use of event-related fMRI during tasks that require spoken output. Press

Adolescent↗
PubMed2000

Comparison of brain activation during word retrieval done silently and aloud using fMRI.

Using functional MRI we compared the patterns of activation in an effortful word retrieval task (stem completion) performed both silently and aloud. The silent and overt conditions showed expected differences in activation magnitude in regions such as primary motor cortex. Some regions, such as frontal operculum and dorsolateral frontal cortex, showed similar activation magnitude across conditions. Thalamus was more active on the left in both conditions and showed a symmetric drop in activity in the silent compared with the overt condition. Putamen was also more active in the overt condition and showed a larger decrease in activity on the right than on the left in the silent compared with the overt condition. Thus it appears that silent and overt performance of this task engage the thalamus and putamen in different ways.

Adolescent↗
PubMed2000

Prepontine lesions with chiari II malformation. Report of two cases.

In 2 cases of infants with the Chiari II malformation, a prepontine cyst presented in association with the hindbrain abnormalities characteristic of the Chiari II syndrome. Both infants presented with bulbar dysfunction and had poor outcome despite decompression of the cerebellar tonsillar herniation and drainage of the prepontine cysts. No such association between prepontine lesions and Chiari II has been described previously.

Arnold-Chiari Malformation↗
PubMed1999

Sagittal sinus occlusion by intraluminal dural cysts. Report of two cases.

Lesions involving the sagittal sinus typically present as masses compressing the sinus externally. The authors describe two cases of lesions entirely within the lumen of the sagittal sinus. In one of the cases, syncope was the presenting symptom and surgical resection of the cyst was performed. An entirely intraluminal cyst, consistent with a dural cyst, was resected, followed by reconstruction of the sinus and resolution of symptoms. Entirely intraluminal lesions of the sagittal sinus have rarely been reported as incidental findings. This represents the first report of symptomatic occlusion of a venous sinus by an intraluminal cyst.

Adult↗
PubMed1998

Functional MRI studies of word-stem completion: reliability across laboratories and comparison to blood flow imaging with PET.

Functional magnetic resonance imaging (fMRI) based on blood oxygen level-dependent (BOLD) contrast has become an increasingly popular technique for mapping the brain. The relationship between BOLD-fMRI imaging and imaging of blood flow activation with positron emission tomography (PET) remains unclear. Moreover, BOLD imaging strategies and analysis procedures vary widely across laboratories. To examine the relationship between these different methods, we compared brain activation maps of a word-stem completion task obtained both using PET and using fMRI across two separate institutions (Washington University and Massachusetts General Hospital) with different acquisitions (gradient-refocused echo and asymmetric spin echo) and different analysis techniques. Overall, activation maps were highly similar across both fMRI methods and PET. A set of activated brain areas, in consistent locations in Talairach atlas space, were identified across all three studies, including visual striate and extrastriate, left prefrontal, supplementary motor area (SMA), and right cerebellar areas. Decreases in activation were also consistently observed in medial parietal, posterior insular, and medial inferior frontal areas. Some differences were noted that may be related to the silent performance of the task with fMRI. The largely consistent results suggest that comparisons can be made appropriately across imaging modalities and laboratory methods. A further implication of the consistencies, which extended to both increases and decreases in signal, is that the underlying brain physiology leading to BOLD contrast may be more similar to blood flow than originally appreciated.

Adult↗
PubMed1998

Increased functional vascular response in the region of a glioma.

Functional imaging of a language task using positron emission tomography was performed as part of the preoperative assessment of a patient with a left supplementary motor area (SMA) tumor. Positron emission tomography scans were obtained during language tasks (verb generation and word reading of visually presented nouns) that normally lead to increased blood flow in the SMA relative to a control condition (visual fixation). In the patient, the normal SMA response was an order of magnitude larger in the region of the tumor. Other regions, such as left inferior frontal cortex and right cerebellum, showed equivalent activation in the patient and normal subjects. Histopathologic study revealed an anaplastic astrocytoma. Thus, this exaggerated vascular response to local neuronal activation occurred in the setting of a proliferation of glial cells. This is consistent with models of coupling of regional CBF and neuronal activity that implicate glia as the mediator between neurons and vasculature. The concept that tumoral disruption of normal vascular responses could, in some cases, potentially enhance rather than dampen the response is proposed.

Adult↗
PubMed1997

Anatomic localization and quantitative analysis of gradient refocused echo-planar fMRI susceptibility artifacts.

Functional magnetic resonance imaging (fMRI) techniques, such as echo-planar imaging, can permit rapid, sensitive, whole-brain measurements of local blood flow-induced MR signal changes seen during cognitive paradigms. Changes in blood oxygenation due to mismatch of flow and oxygen metabolism cause dynamic variations in microscopic susceptibility effects, leading to the blood oxygenation level-dependent (BOLD) signal measured by fMRI techniques. A related static macroscopic susceptibility effect is known to cause artifacts that attenuate the MR signal, leading to "blind spots" in some regions of brain adjacent to bone and air sinuses. The anatomical location, spatial extent, and magnitude of signal loss artifact are quantitated for a common whole-brain fMRI technique. Resting gradient-echo EPI studies were obtained in four healthy volunteers. Signal loss was primarily localized to inferior frontal regions (medial orbital gyri and gyrus rectus) and to inferior lateral temporal lobe (including part of fusiform gyrus) bilaterally. Increased echo time (TE) uniformly produced larger artifacts. The orientation of acquired slices and choice of phase-encoding direction influenced the location, shape, and extent of the artifacts. Regions of the brain with severe artifact may have attenuated activation signal, with potential implications for the design and interpretation of fMRI studies targeting activations in these areas.

Adult↗
PubMed1997

Foramen magnum decompression for cervicomedullary encroachment in craniometaphyseal dysplasia: case report.

OBJECTIVE AND IMPORTANCE: Foramen magnum encroachment has been cited as a potential cause for the premature demise of patients afflicted with craniometaphyseal dysplasia (CMD). To our knowledge, the association of Chiari malformation and syringomyelia with CMD has not been previously reported. We describe our evaluation and surgical treatment of a patient presenting with CMD, foramen magnum stenosis, Chiari I malformation, and syringomyelia. CLINICAL PRESENTATION: A 15-year-old female patient with CMD presented with severe headaches and progressive myelopathy. Evaluation by computed tomography and magnetic resonance imaging revealed mild ventriculomegaly, cervicomedullary compression secondary to Chiari I malformation and foramen magnum stenosis, and C3-T10 syringomyelia. INTERVENTION: Foramen magnum decompression was performed via suboccipital craniectomy, C1-C2 laminectomy, and dural augmentation. Dysplastic bone was revealed to be extremely thick and mineralized. Removal required lengthy and extensive drilling. The postoperative course was complicated by prolonged intubation secondary to airway obstruction and a perforated duodenal ulcer. Airway obstruction was attributed to severe nasopharyngeal bony dysplasia and soft tissue edema. The use of steroids in the treatment of airway edema and delayed enteral feeding was thought to contribute to ulcer development. Nevertheless, neurological symptoms improved dramatically. CONCLUSION: Foramen magnum decompression can be used to treat life-threatening cervicomedullary compression in patients with CMD. However, caution should be used because surgical intervention may be associated with a higher incidence of complications because of lengthy procedures and the spectrum of craniofacial impairments in patients with CMD.

Adolescent↗
PubMed1997

Lack of specificity in electrophysiological identification of lower sacral roots during selective dorsal rhizotomy.

The authors investigated the efficacy of anal sphincter electromyography (EMG) in identifying the lower sacral roots during selective dorsal rhizotomy. In nine children undergoing selective dorsal rhizotomy for cerebral palsy (CP) spasticity, direct electrical stimulation of the L1-S5 dorsal and ventral roots was performed while monitoring EMG responses from the anal sphincter and lower-extremity muscles. Anal sphincter activation was seen with stimulation of lumbosacral roots at many levels. Stimulation of dorsal and ventral roots gave anal sphincter EMG responses in 100% of the dorsal and ventral roots from L-4 and caudally. Only at the L-1 level did a minority of nerve roots have anal sphincter response to stimulation. Patterns of extremity muscle and sphincter activation specific to the S3-5 roots, namely anal sphincter activation without activation of other muscle groups, were found in only five (22%) of 23 roots stimulated. The pattern of stimulation responses in the majority of S3-5 roots indicated that the pathophysiology of lower-extremity spasticity in CP may involve the anal sphincter and does not spare the lower sacral roots. Thus, this study indicates that electrophysiological mapping alone, without anatomical identification, cannot be used to identify the lower sacral roots during selective dorsal rhizotomy for CP spasticity, and it proposes a model for investigation of associated bowel and bladder symptoms.

Anal Canal↗
PubMed1997

Calcium carbonate apatite deposition in the cervical spine with associated vertebral destruction. Case report.

This 52-year-old woman developed crystal deposition disease involving the cervical vertebrae. She presented with symptomatic spinal cord compression secondary to extensive calcified lesions in the posterior elements of the cervical spine. Surgical decompression with posterior fusion was performed. Histological examination showed hardened deposits of calcium carbonate involving the soft tissue, and dissolution of the vertebral bone trabeculae. There was no inflammatory response to these deposits. One year postoperatively the patient developed severe pulmonary disease associated with the collagen-vascular disorder, scleroderma (calcinosis, Raynaud's phenomenon, esophageal hypomotility, sclerodactyly, and telangiectasia [CREST] syndrome). Calcium carbonate deposition disease represents an unusual clinical entity that is possibly associated with scleroderma or other collagen-vascular diseases, and it is distinct from ligamentum flavum calcification, calcium pyrophosphate deposition disease, and hydroxyapatite deposition disease.

Apatites↗
PubMed1997

Imaging studies of memory and attention.

Functional brain imaging studies of memory and attention with positron emission tomography and functional magnetic resonance imaging demonstrate involvement of specific regions of the normal human brain. Possible anatomical substrates for different types of memory have been identified. Different aspects of attention mechanisms, such as modulation of early visual areas, shifts of attention, and selection of response, also appear to involve specific anatomic regions revealed by imaging. Many of these studies show activation in regions clinically considered to be "silent" regions.

Attention↗