Toward the prediction of neurological injury from tethered spinal cord: investigation of cord motion with magnetic resonance.

Experience with spinal dysraphism has taught that spinal cord tethering will eventually produce neurological deficit. The primary diagnostic and monitoring tool, magnetic resonance (MR) scanning, almost always produces images consistent with cord tethering, even in asymptomatic or improved, previously operated patients. This presents a problem in selecting appropriate candidates for prophylactic intervention. Ideally, a method of monitoring should predict functional deterioration. Real-time ultrasonography, electrophysiological tests, and phase-motion MR studies could potentially be adapted for this purpose. The authors have evaluated the latter technique in both symptomatic and asymptomatic dysraphic patients with tethering. Studies of cervical cord motion show a clear separation between results in patients with cord expansion from hydromyelia and those with pure tethering. Symptomatic patients with progressive deficit or pain have limited cervical cord motion which improves after surgical untethering. MR studies of cord motion have definite promise in the prediction of deficit from spinal cord tethering and should be further evaluated in comparison with ultrasound and electrophysiologic methods.

Effect of phenytoin on human cerebral glucose metabolism.

We used serial positron emission tomography scans with [18F]2-deoxyglucose to study the effect of phenytoin on human cerebral glucose metabolism in 10 patients with seizure disorders. Local CMRglu for each patient was measured in 10 regions of interest. EEGs were performed during each procedure to match scans for state of consciousness and exclude data from scans with ictal activity. Serial scans without a drug change were performed in six control patients. Metabolic rates were significantly lower in two cortical regions while patients were taking phenytoin. No significant changes on repeat scan were seen in the control population. Measured across all regions of interest, metabolic rates were 13% higher when patients were off phenytoin (p less than 0.02).

Neuroimaging in refractory partial seizures: comparison of PET, CT, and MRI.

We compared the results of x-ray CT, magnetic resonance imaging (MRI), and positron emission tomography (PET) using 18F 2-deoxyglucose in 36 patients with partial seizures. Seventeen patients had localized epileptic discharges on surface EEG. MRI showed an abnormality in 9, CT in 4, and PET in 13 of 14 patients who had the test. Nineteen patients had nonlocalizing EEG discharges. MRI showed an abnormality in 11, CT in 10, and PET in 8 of 12. MRI is more sensitive than CT in detecting structural lesions underlying PET hypometabolism.

Barbiturates reduce human cerebral glucose metabolism.

We studied the effect of barbiturates on local cerebral glucose metabolism by performing positron emission scans before and after withdrawal of phenobarbital or primidone. The postwithdrawal scan showed a significant increase (mean, 37%) in seven of eight cortical regions tested. Patients who had serial scans without a drug change showed a nonsignificant tendency for metabolic rates to go down on the second scan (mean decrease, 7%). Addition or deletion of a single drug other than barbiturate did not change metabolic rates on repeat scans. The depression in cerebral glucose metabolic rate due to phenobarbital, if confirmed, may have bearing on the adverse neuropsychological effects of the drug.

Positron emission tomography in generalized seizures.

We used 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) to study nine patients with clinical absence or generalized seizures. One patient had only absence seizures, two had only generalized tonic-clonic seizures, and six had both seizure types. Interictal scans in eight failed to reveal focal or lateralized hypometabolism. No apparent abnormalities were noted. Two patients had PET scans after isotope injection during hyperventilation-induced generalized spike-wave discharges. Diffusely increased metabolic rates were found in one compared with an interictal scan, and in another compared with control values. Another patient had FDG injected during absence status: EEG showed generalized spike-wave discharges (during which she was unresponsive) intermixed with slow activity accompanied by confusion. Metabolic rates were decreased, compared with the interictal scan, throughout both cortical and subcortical structures. Interictal PET did not detect specific anatomic regions responsible for absence seizure onset in any patient, but the results of the ictal scans did suggest that pathophysiologic differences exist between absence status and single absence attacks.

[18F]fluorodeoxyglucose positron emission tomography in refractory complex partial seizures.

Positron emission tomography with simultaneous electroencephalographic monitoring was performed with [18F]fluorodeoxyglucose in 20 patients with complex partial seizures who had normal computed tomographic scans. Seven patients had only unilateral epileptiform discharges on the electroencephalogram, 3 had predominantly unilateral discharges, and 10 had nonlocalized epileptiform abnormalities. Positron emission tomography showed a hypometabolic lesion in 16 of the 20 patients. Pathological changes in the hypometabolic region were found in postoperative specimens in 4 of 5 patients studied. Positron emission tomography was unaffected by the seizure frequency, state of alertness, or number of spike discharges during the scan. There was a tendency for patients to have higher overall metabolic rates when taking less medication. Seizures occurring during [18F]fluorodeoxyglucose uptake in 3 patients produced a hypermetabolic area at the interictal hypometabolic focus. Positron emission tomography sometimes showed more widespread hypometabolism than suspected on the basis of the scalp-recorded electroencephalogram. The frontal lobe showed a greater degree of hypometabolism than the temporal lobe in 3 patients. Focal lesions may be identified by positron emission tomography even if the electroencephalographic abnormality is not well localized.

Neuroradiological studies of JCV-induced astrocytomas in nonhuman primates.

Astrocytomas in nonhuman primates following JC virus inoculation provides a model which can be used to evaluate diagnostic and therapeutic techniques used in humans. The CT scan appearance of astrocytomas in nonhuman primates closely resembles that seen in humans. Our studies have shown that tumors may be detected in asymptomatic monkeys. Serial scans have shown astrocytomas to grow rapidly with breakdown of the blood-brain barrier. CT scanning has demonstrated the presence of tumor which was undetectable by gross examination at necropsy but confirmed by light microscopy. Studies are in progress to further define the radiological appearance of gliomas, to evaluate contrast-tagged anti-tumor antibodies as a diagnostic tool in evaluating gliomas by computerized tomography, and to evaluate metabolic parameters of actrocytomas by positron emission tomography.

Surgically correctable lesions detected by CT in 143 patients with chronic epilepsy.

CT findings justified surgical intervention in four young patients who had suffered from intractable epilepsy for many years. Previous non-invasive and invasive neurodiagnostic procedures with these patients had failed to show focal cerebral lesions amenable to surgical treatment. All four patients achieved significant relief from seizures after the operations.

Computerized axial tomography in syringomyelia.

The ACTA-scanner, a device for computerized axial tomography, permits cross-sectional radiographic study of the entire human body, including the spine. In the ACTA-scan, the spinal cord appears as a roundish formation surrounded by the less dense subarachnoidal cerebrospinal fluid. The spines of 18 patients with verified (nine cases) or suspected (nine cases) syringomyelia were studied by ACTA-scanning. In seven of the verified and in four of the nonverified cases, some evidence of cord cavitation was shown. The cystic part of a cervical-cord ependymoma was also demonstrated. ACTA-scanning is an easily performed, noninvasive, innocuous procedure. This technic, which complements other radiographic methods of evaluating the spinal cord, is particularly suitable for screening and follow-up study of patients with syringomyelia. The easily accomplished recognition of a possible associated hydrocephalus is an added advantage of ACTA-scanning.