Mahesh R. Patel

EEG-triggered echo-planar functional MRI in epilepsy

We investigated whether: (1) EEG recordings could be successfully performed in an MRI imager, (2) subclinical epileptic discharges could be used to trigger ultrafast functional MRI images, (3) artifact-free functional MRI images could be obtained while the patient was having the EEG monitored, and (4) the functional MRI images so obtained would show focal signal increases in relation to epileptic discharges. We report our results in two patients who showed focally higher signal intensity, reflective of increased local blood flow, in ultrafast functional MRI timed to epileptic discharges recorded while the patients were in the imager and compared with images not associated with discharges. One patient showed a focal increase despite a clinical and EEG history of generalized discharges. This approach may have the potential to identify brain regions activated during brief focal epileptic discharges. NEUROLOGY 1996;47: 89-93

Detection of Hyperacute Primary Intraparenchymal Hemorrhage by Magnetic Resonance Imaging

BACKGROUND MRI has become increasingly used in the acute setting to manage patients with stroke. There has been concern that MRI may not be sensitive in the detection of acute intracranial hemorrhage. We assessed whether strongly susceptibility-weighted MRI would be sensitive to intraparenchymal hemorrhage in the first few hours. CASE DESCRIPTIONS In the course of our ongoing studies of MRI of acute ischemic stroke in more than 200 patients, 35 patients had MR studies within 6 hours. Six of these patients who presented with acute focal symptoms with definite time of clinical onset (2.5 to 5 hours) were found to have evidence of intraparenchymal hemorrhage. Standard T1- and T2-weighted MR scans were performed. In 5 of the patients, echo-planar imaging and gradient-echo sequences were performed to increase the sensitivity of magnetic susceptibility effects of the pulse sequences. Four of the cases were of putaminal hemorrhage and 2 were lobar hemorrhages. The hemorrhage was most evident as foci of T2* hypointensity (signal loss) and unambiguous on the more susceptibility-weighted sequences, particularly echo-planar gradient-echo images. CONCLUSIONS MRI can detect hemorrhage within 2.5 to 5 hours of onset of clinical symptoms as regions of marked signal loss due to susceptibility effects, whereas conventional MR scans of ischemic stroke may appear normal. These results demonstrate that MR susceptibility sequences may be sensitive to hyperacute hemorrhage and suggest that MR may be an adequate screen for primary intraparenchymal hemorrhage.

Preoperative Assessment of the Carotid Bifurcation Can Magnetic Resonance Angiography and Duplex Ultrasonography Replace Contrast Arteriography

BACKGROUND AND PURPOSE Noninvasive studies are used with increasing frequency to assess the carotid bifurcation before endarterectomy. Therefore, assessment of their diagnostic accuracies is essential for appropriate patient management. We prospectively evaluate two noninvasive tests, magnetic resonance angiography (MRA) and duplex ultrasonography (DU), as potential replacements for contrast arteriography (CA). METHODS A blinded comparison of three-dimensional time-of-flight (TOF) MRA, two-dimensional TOF MRA, and DU in 176 arteries was performed. CA was used as the standard of comparison. RESULTS Three-dimensional TOF MRA had a sensitivity of 94%, a specificity of 85%, and an accuracy of 88% for the identification of 70% to 99% stenosis; two-dimensional TOF MRA had a sensitivity and specificity that were approximately 10% lower than those of three-dimensional TOF MRA. DU resulted in a sensitivity of 94%, a specificity of 83%, and an accuracy of 86%. Combining data from three-dimensional TOF MRA and DU, allowing for CA only for disparate results, yielded a sensitivity of 100%, a specificity of 91%, and an accuracy of 94% among concordant noninvasive tests, with CA required in 16% of arteries. MRA accurately differentiated 17 carotid occlusions from 16 high-grade (90% to 99%) stenoses, whereas with DU two patent arteries were identified as occluded and one occluded artery was identified as patent. CONCLUSIONS Three-dimensional TOF MRA is the most accurate noninvasive test. Combined use of MRA and DU results in a marked increase in accuracy to a level that obviates the need for CA in a majority of patients.

Mr Angiography of the Head and Neck

A review of the basic physics and techniques for acquiring and evaluating magnetic resonance angiograms is provided, including time-of-flight and phase contrast techniques. Magnetic resonance (MR) angiography is becoming a routine method of evaluating carotid bifurcation atherosclerotic disease in both a screening and diagnostic capacity. The expanding clinical utility of MR angiography in the detection of intracranial aneurysms, characterization of arteriovenous malformations, and evaluation of intracranial atherosclerotic disease are also reviewed. Furthermore, MR angiography allows for the noninvasive diagnosis of arterial dissection. Magnetic resonance venography also allows the confirmation of the previously elusive and likely underdiagnosed entity of cerebral venous thrombosis.

Imaging Spectrum of CNS Coccidioidomycosis: Prevalence and Significance of Concurrent Brain and Spinal Disease

OBJECTIVE The purpose of this study was to evaluate the prevalence and significance of concurrent coccidioidal brain and intraspinal disease. MATERIALS AND METHODS We conducted a retrospective imaging review of 23 patients with proven coccidioidal CNS meningitis. RESULTS All patients had intracranial abnormalities, and 86% (19/22) who underwent spinal imaging had signs of intraspinal disease, including leptomeningeal enhancement (84%), arachnoiditis (63%), and cord signal abnormalities (37%); seven of 15 patients (47%) who underwent myelography had complete spinal blocks. CONCLUSION The high prevalence of concurrent brain and intraspinal coccidioidomycosis supports a low threshold for spinal imaging.

Hypothermia-treated neonates with hypoxic-ischemic encephalopathy: Optimal timing of quantitative ADC measurement to predict disease severity:

To determine the optimal time window for MR imaging with quantitative ADC measurement in neonatal HIE after hypothermia treatment, a retrospective review was performed on consecutive hypothermia-treated term neonates with HIE, with an initial and follow-up MR imaging within the first two weeks of life. Three neuroradiologists categorized each set of MR imaging as normal, mild, moderate or severe HIE based on a consensus review of the serial imaging. The lowest ADC values from the white matter, corpus callosum, and basal ganglia/thalamus were measured. The ADC values between mild-moderate and severe HIE were compared using a Student’s t-test over a range of different time windows. A total of 33 MR imaging examinations were performed on 16 neonates that included three normal, four mild, five moderate, and four severe HIE. The time window of 3–10 days showed a statistically significant decrease in ADC value in severe HIE compared to mild-moderate HIE in all three locations, respectively: white matter 0.5 ± 0.22 versus 0.83 ± 0.27 (p value 0.01), corpus callosum 0.69 ± 0.19 versus 0.91 ± 0.17 (p value 0.01), and basal ganglia/thalamus 0.63 ± 0.16 versus 0.98 ± 0.06 (p value <0.01). The range of 3–10 days is the optimal time window for MR imaging with quantitative ADC after hypothermia treatment.

Low gradient echo parenchymal signal in late infantile GM1 gangliosidosis

GM1 gangliosidosis is a rare storage disorder caused by a deficiency of lysosomal beta-galactosidase. Symptoms are nonspecific and include profound central nervous system involvement, and visceral and musculoskeletal manifestations. We report a case of late infantile GM1 gangliosidosis with magnetic resonance imaging manifestations that have not been previously described. These include regions of patchy parenchymal gradient echo signal loss, progressive atrophic changes, and magnetic resonance spectroscopy demonstrating decreased N-acetyl aspartate, and increased choline and myoinositol peaks.

Percutaneous Therapy of a Post-surgical Suboccipital Cerebrospinal Fluid Fistula with Fibrin Glue.

The successful therapy of a suboccipital cerebrospinal fluid fistula by the percutaneous introduction of fibrin glue under computed tomographic guidance is described.