Interpretation of Wada memory test for lateralization of seizure focus by use of (99m)technetium-HMPAO SPECT

Probabilistic map of blood flow distribution in the brain from the internal carotid artery

Brain single photon emission computed tomographic (SPECT) images acquired after injecting Tc-99m-HMPAO into the internal carotid artery (ICA) during an intracarotid amobarbital procedure (IAP SPECT) provide anatomical information on the blood flow distribution from the ICA. In this study, probabilistic maps of the distribution of blood supply from the ICA were developed using the IAP SPECT images. Twenty-two sets of basal and IAP SPECT were collected from an existing database. IAP SPECT images were coregistered to basal SPECT images, and spatial normalization parameters used for basal SPECT images were reapplied to IAP SPECT for anatomical standardization. Pixel counts of IAP SPECT images were then normalized, and the probabilistic map of cerebral perfusion distribution (perfusion probabilistic map) for each hemisphere was determined by averaging the spatial/count-normalized IAP SPECT images. Population-based probabilistic maps representing the extent of ICA territory (extent probabilistic map) were also composed by averaging the binary images obtained by thresholding the spatially normalized IAP SPECT images. The probabilistic maps were used to quantify cerebral perfusion and reserve change after arterial bypass surgery in 10 patients with ICA stenosis. In the probabilistic maps, blood supply from the ICA was found to be most likely in the dorsolateral frontal lobe, the anterosuperior portion of the temporal lobe, and in the frontoparietal area. Of the subcortical regions, the striatum was found to be most likely to derive its blood supply from ICA. In patients with cerebral occlusive disease, improvements in basal perfusion and perfusion reserve in the bypass-grafted ICA territory were well identified and were increased by 6.2% and 4.6%, respectively, on average. The probabilistic maps developed in this study illustrate the perfusion distribution and extent of vascular territory for ICA and would be useful for objective evaluations of perfusion status in cerebrovascular disease.

The frontal lobe role in memory: a review of convergent evidence and implications for the Wada memory test

Functional imaging studies have implicated the frontal lobe in many of the memory processes often thought to be the domain of medial temporal structures. Results from fMRI studies of normal subjects have suggested that some components of memory formation, including those components tested during the Wada memory test, may involve frontal lobe regions. Specific behavioral disruptions during carotid amytal injections support a model for frontal lobe anesthesia in explaining results of the Wada memory test. Cortical stimulation data suggest that frontal lobe disruption is sufficient to cause memory disturbances. The convergence of evidence suggests frontal lobe memory may limit the predictive value of the Wada memory test in defining the risk of memory loss following temporal lobectomy.

Supratentorial ganglioglioma and epilepsy: postoperative seizure outcome

Ganglioglioma is increasingly recognized as being a cause of epilepsy. However, controversy still exists regarding the type of surgery required for optimal seizure control. To find out the factors associated with seizure outcome and to clarify treatment guidelines, a retrospective analysis of 29 epileptic patients who had pathologically proven gangliogliomas that were operated on at our institute during a 13-year period, was performed. There were 23 temporal and six extratemporal gangliogliomas, with a mean age of 16.5 years at surgery. Epilepsy was medically intractable in 14 (48.3%) patients. There were 26 temporal and six extratemporal resections including three re-operations. Three patients underwent intracranial electroencephalography (EEG) recordings (invasive monitoring). Intraoperative electrocorticography (ECoG) was performed in four patients. The mean duration of follow-up after surgery was 36.5 months. The Fisher's Exact test (two-tailed) was used to assess the association between the seizure outcome and several preoperative and operative parameters. Surgical treatment rendered most patients (75.9%, 22/29) seizure free. All three patients who underwent re-operation were seizure-free postoperatively. Eleven (47.8%) of the 23 temporal lobe gangliogliomas were associated with cortical dysplasia. Postoperative incomplete seizure control was associated with the presence of cortical dysplasia (p < 0.001). Good seizure outcome is expected in patients with gangliogliomas, despite years of medically intractable epilepsy, once the tumor is resected. Invasive monitoring/intraoperative electrocorticography is recommended for patients with suspected cortical dysplasia on MRI or for the patients with persistent epilepsy after ganglioglioma resection.

Language dominance in children as determined by magnetic source imaging and the intracarotid amobarbital procedure: a comparison

This study evaluated the validity of data derived from magnetic source imaging regarding hemispheric dominance for language in children and adolescents with intractable seizure disorder by comparison with results of the intracarotid amobarbital procedure. Functional imaging of the receptive language cortex using a whole-head neuromagnetometer was performed in 19 consecutive epilepsy patients, ages 8 to 18 years, who also underwent the intracarotid amobarbital procedure. During magnetic source imaging recordings, patients engaged in a continuous recognition memory task for words in visual and auditory modalities. This task has previously been shown to be valid for the purpose of lateralization and localization of language cortex in adult epilepsy patients who undergo the intracarotid amobarbital procedure and intraoperative language mapping allowing confirmation of magnetic source imaging findings. Results indicated that language laterality indices formed for the intracarotid amobarbital procedure and magnetic source imaging procedures were highly correlated (R = .87). In addition, clinical judgments regarding cerebral dominance for language made by independent raters using the two methods were in excellent agreement. We conclude that magnetic source imaging is a promising method for determination of cerebral dominance for language in children and adults.