Meredith A. Weinstein

Evolving focal cerebral ischemia in cats: spatial correlation of nuclear magnetic resonance imaging, cerebral blood flow, tetrazolium staining, and histopathology.

The spatial correlation of nuclear magnetic resonance imaging (NMRI) and cerebral blood flow (CBF) may improve our ability to identify ischemic brain lesions and may provide further insight into the pathophysiology of early cerebral ischemia. Eleven pentobarbital-anesthetized adult cats underwent exposure of the common carotid arteries bilaterally and the right middle cerebral artery through a transorbital approach. Baseline NMRI images were obtained with a single spin-echo, multislice technique using a 0.6-T field, 0.4-cm slice thickness, and a surface coil. Focal ischemia was produced with right middle cerebral artery occlusion and potentiated with bilateral common carotid artery ligation. Sequential NMRI studies were then performed at 1, 2, 4, 6, and 12 hours or until CBF was determined in the same cats using [14C]iodoantipyrine at either 2 (n = 2), 4 (n = 2), 6 (n = 2), or 12 (n = 1) hours after the time of occlusion. This protocol allowed temporal and spatial correlation of NMRI and CBF. Alternate 5-mm brain slices were incubated with 1% 2,3,5-triphenyltetrazolium chloride (TTC) for 45 minutes at 37-41 degrees C and frozen in liquid Freon for later autoradiographic CBF determination. Four cats were studied only with NMRI and TTC (not CBF). The correlation between areas of increased NMRI signal intensity observed in T2-weighted images (repetition time 2,000 msec, echo time 120 msec), vital staining with TTC, low CBF, and routine histology was evaluated. During the early phase (less than 6 hours), T2-weighted NMRI changes were localized to the central ischemic gray matter areas, as defined in the later CBF images, with no involvement of the white matter. By the twelfth hour the NMRI changes involved the entire ischemic area including gray and white matter. The initial visible changes seen on T2-weighted NMRI are suggestive of cellular edema, and the later changes are characteristic of vasogenic edema. The spread of NMRI changes compared with the ischemic area determined from autoradiographic CBF is consistent with the previously described biphasic evolution of ischemic injury. These data suggest that T2-weighted NMRI could be used clinically to delineate areas of acute ischemic stroke.

Hemorrhage and anticoagulation after nonseptic embolic brain infarction

Among 54 consecutive patients with acute nonseptic embolic brain infarction, there was CT evidence of hemorrhagic infarction in 1 patient (2%). None had clinical or CT evidence of massive brain hemorrhage even when anticoagulation therapy was used immediately. Seven patients (13%) had recurrent brain emboli, all within 7 days of the initial stroke. None of these patients was adequately anticoagulated at the time of recurrence. Immediate anticoagulation therapy should be employed after nonseptic embolic brain infarction if CT does not show hemorrhage and there is a persistent cardiac source of emboli.

Computed Tomography in the Detection of Juxtasellar Lesions

One thousand consecutive computed tomograms were reviewed to determine the accuracy of the procedure in the detection of juxtasellar lesions. The detection rate was compared to those of plain skull films, radionuclide studies, angiography, and pneumoencephalography. Computed tomography was slightly superior to angiography and was surpassed only by pneumoencephalography, both of which are invasive procedures which carry a definite risk. The data indicate that computed tomography is the screening method of choice in the detection of juxtasellar masses.

Basilar Artery Ectasia Demonstrated by Computed Tomography

Basilar artery eclasia was demonstrated by computed tomography (CT) in 4 cases. The course and diameter of the basilar artery as seen by CT closely approximated those aspects of the artery visualized by angiography. The clinical manifestations of basilar ectasia correlated with what brain stem structures were impinged upon by the ectatic artery.

Interval Computed Tomography in Multiple Sclerosis

Computed tomography demonstrated areas of abnormal attenuation in the white matter in 14 patients with multiple sclerosis (MS). Nine were studied two or more times. Acute MS lesions exhibit decreased or normal attenuation without contrast enhancement and increased attenuation with it. On later scans these lesions show decreased attenuation with or without contrast material. Some lesions remain decreased in attenuation and some become normal both with and without contrast material.

Digital subtraction angiography in cerebrovascular disease

Abstract not available.

Correlation between magnetic resonance imaging and surgical findings in the tethered spinal cord

Between October 1982 and August 1987, 20 patients underwent magnetic resonance imaging (MRI) and subsequent surgical release of a tethered spinal cord. The tethering was caused by a thick filum terminale in 6 patients. On MRI scans, the conus medullaris was at L4 in 2 patients, at L2 in 3 patients, and the filum terminale appeared thick in 1 patient. The spinal cord was tethered to an intradural lipoma correctly demonstrated by MRI in 6 patients. Increased epidural fat was misdiagnosed as an intradural lipoma in one patient and a lipomatous stalk was not identified in 2 other patients. Scar tissue resulting from repair of a meningocele had tethered the cord in the remaining 8 patients. On MRI scans, the conus medullaris was located between L3 and S3; in 5 of the patients, scar tissue was apparent on the MRI scan. This correlative study supports the use of MRI as the initial, and possibly the only, imaging modality when a tethered spinal cord is suspected. Improved or more recent MRI techniques will help demonstrate these anomalies better.

Computed Tomography in Diastematomyelia

The diagnosis of diastematomyelia was confirmed in 2 patients by computed tomography (CT). Abnormalities of the vertebral bodies, pedicles, lamina, and spinous processes were defined and the diastematomyelic spurs were visualized.

White and Gray Matter of the Brain Differentiated by Computed Tomography

The white and gray matter of the brain can be clearly differentiated by computed tomography (CT). The differentiation is enhanced by the administration of contrast material. Without contrast material, the mean attenuation number of the white matter was 29 units, of the gray matter, 35 units. The effective low contrast resolving power of CT scanners can be clinically evaluated by comparing their ability to differentiate the white and gray matter of the brain.

Nuclear Magnetic Resonance of the Spine: Clinical Potential and Limitation

&NA; Magnetic resonance can visualize the vertebral bodies, discs, neural structures, cerebrospinal fluid (CSF), neural foramina, and extradural structures in the sagittal, axial, and coronal planes. The normal nucleus pulposus can be differentiated from the anulus and changes associated with degeneration. Infection, trauma, and neoplastic conditions can be identified. The signal intensity of the CSF relative to extradural and neural structures can be increased to provide evaluation of the size and configuration of the contents of the thecal sac without the use of an intrathecal contrast medium. Impingement by disc, tumors, fracture segments, and expansile masses can then be accurately evaluted, It is the most accurate modality for the evaluation of the foramen magnum, Chiari malformation, syringomyelia, infection, and degeneration of intervertebral discs. It can identify paravertebral soft tissue and bony changes when plain films and computed tomographic (CT) studies are negative or equivocal. Not only can lesions be localized, but significant information regarding the nature of the process can be obtained. Using variations of the spin‐echo technique with appropriate T1 and T2‐weighted images, magnetic resonance can produce tissue contrast distinctions not possible with CT scans or conventional angiography. (Neurosurgery 15:583‐592, 1984)