Tomonori Ono

Is a Cortical Spike Discharge “Transferred” to the Contralateral Cortex via the Corpus Callosum?: An Intraoperative Observation of Electrocorticogram and Callosal Compound Action Potentials

Summary:  Purpose: By means of the intraoperative electrophysiologic observation, we reevaluated the “transfer” theory that a transcallosal volley invoked by a cortical spike discharge in one hemisphere directly causes its contralateral counterpart via the corpus callosum (CC).

Callosal role in generation of epileptiform discharges: quantitative analysis of EEGs recorded in patients undergoing corpus callosotomy

OBJECTIVE Corpus callosotomy tends to decrease seizure frequency and severity rather than transforming the seizure pattern from a generalized form into a lateralized or a partial one. The finding implies that bisection of the corpus callosum (CC) disrupts the epileptogenicity itself. In order to gain further insight into the possible role played by the CC in intractable generalized epilepsy, quantitative analyses of long-term EEGs were performed. METHODS Analyses were made of epileptiform discharges contained in the pre- and postoperative long-term EEGs in 7 patients who had an anterior callosotomy for intractable epilepsy. The duration, number, and amplitude of all epileptiform burst activities were measured and statistically analyzed. RESULTS After callosotomy, the total number of epileptiform burst activities, mean duration, and the total number of spike discharges decreased significantly. The two hemispheres could be divided into dominant and non-dominant ones as to the quantity of the residual epileptiform discharges. CONCLUSIONS Corpus callosotomy unevenly reduced preoperative epileptiform discharges in both hemispheres, suggesting a facilitatory role played by the callosal neurons that enables the asymmetrical epileptogenic susceptible state of the two hemispheres to develop bisynchronous and bisymmetrical epileptiform discharges. SIGNIFICANCE Corpus callosotomy decreased the quantity of the epileptiform discharges, suggesting the transhemispheric facilitation of seizure mechanisms.

Brain surface spindle cell glioma in a patient with medically intractable partial epilepsy : A variant of monomorphous angiocentric glioma?

We report a case of brain surface angiocentric glioma in a 6‐year‐old Japanese boy with medically intractable partial epilepsy. MRI showed somewhat ill‐defined high‐signal lesions on fluid‐attenuated inversion recovery and T2‐weighted imagings of the right occipitoparietal cortex. At surgery, a yellowish tumor was localized in the superficial cortex. Histologically, the tumor was predominantly composed of elongated astrocytic cells forming rings around blood vessels. Tumor cells circumferential to vessels predominanted in low cellurarity areas, whereas radial alignment with perivascular pseudorosettes was observed in more cellular regions. These perivascular pseudorosettes closely resembled those of ependymoma. The tumor cells showed variable cytoplasmic immunoreactivity with GFAP. These findings were more likely monomorphous angiocentric glioma, which was first described by Wang et al. in 2005. However, in our case the tumor had a small foci of polymorphous appearance and a comparatively high MIB‐1 labeling index (8%). Therefore, the present case may be an atypical form of monomorphous angiocentric glioma. However, no de novo anaplastic monomorphous angiocentric glioma similar to our case has yet been reported in the literature. It remains to be determined whether the behavior of monomorphous angiocentric glioma is an example of benign biological characteristics or whether it more closely resembles a low‐grade malignant tumor.

Callosotomy and subsequent surgery for children with refractory epilepsy

Callosotomy has been considered as a palliative therapy for refractory epilepsy patients with non-focal onset seizures. Residual partial seizures and unilateral epileptiform discharges on electroencephalography (EEG) are sometimes observed after callosotomy. These findings suggest that some patients may be candidates for subsequent resective surgery. Of 149 children who received a callosotomy, resective/disconnective surgery was subsequently performed in 19 patients. Most patients had generalized seizures and epileptiform discharges on EEG before callosotomy. Two-third had normal neuroimaging studies at initial presurgical evaluation. After callosotomy, ictal symptoms evolved into asymmetric features suggesting partial onset seizures. Post-callosotomy EEG showed completely lateralized or localized epileptiform discharges responsible for residual partial seizures in 16 of 19 patients. Fifteen patients underwent resective surgery of the unilateral frontal lobe, and the remaining received hemispherotomy or posterior quadrantectomy. After subsequent surgery, favorable seizure outcomes were obtained in 11 patients (57.9%). Favorable seizure outcomes may be achieved with callosotomy and subsequent surgery in selected patients who are not candidates for a conventional resective surgery at initial presurgical evaluation.

Suppressive effect of callosotomy on epileptic seizures is due to the blockade of enhancement of cortical reactivity by transcallosal volleys

The present work demonstrates that the cortical reactivity of the rat, monitored by thalamocortical responses, can be enhanced by repetitive transcallosal volleys (5-20 Hz). This effect can be completely inhibited by callosotomy. We believe that the interhemispheric epileptogenesis and the suppressive effect of callosotomy for intractable epilepsy can be explained by this facilitatory effect of the corpus callosum on the cerebral cortex.

Hemispheric asymmetry of callosal neuronal participation in bilaterally synchronous epileptiform discharges

PURPOSE Callosal compound action potentials (CCAPs) recorded from the corpus callosum can reveal callosal neuronal activity. In this study, hemisphere-specific activity of callosal neurons during bilateral synchrony was evaluated in relation to the postoperative EEG. METHODS In 19 patients undergoing callosotomy for intractable epilepsy, intraoperative electrocorticograms (ECoGs) and CCAPs were simultaneously recorded prior to callosal bisection. Hemisphere-specific CCAPs during bilateral synchrony were estimated through an averaging-based method. The degree of asymmetry in hemisphere-specific CCAPs was evaluated with a laterality index (LI), and correlated with post-callosotomy outcomes. RESULTS Despite preoperative frequency of bilateral synchrony, postoperative EEG outcomes were mostly categorized as either unilaterally lateralized discharge group or bilaterally asynchronous discharge group. The LI of the former group was significantly higher than that of the latter group. In addition, higher amplitudes of the hemisphere-specific CCAP coincided with the side on which epileptiform discharges persisted postoperatively in most patients of the unilaterally lateralized discharge group. CONCLUSIONS Electrophysiologic analysis with CCAPs revealed hemispheric asymmetry of callosal neuronal participation in bilateral synchrony. More callosal neurons fire together in the more epileptogenic hemisphere during bilateral synchrony even if preoperative EEG features are virtually symmetric. This suggests transcallosal dynamic actions on the bi-hemispheric epileptogenesis maintenance.

Factors affecting rapid growth of unruptured cerebral aneurysms during the acute stage of subarachnoid hemorrhage.

Abstract Background and purpose: Several unruptured cerebral aneurysms have been reported to grow and rupture. To determine which factors affect the growth of these aneurysms during the acute stage of subarachnoid hemorrhage (SAH), a retrospective review was performed. Methods: Between January 2000 and January 2003, 130 patients with angiographically proven ruptured cerebral aneurysms were treated at our institution. Of these patients, 32 also had simultaneous unruptured aneurysms, and the total number of the unruptured aneurysms was 40, including two neck remnants which had remained since the past clipping. Seventeen patients had 17 unruptured aneurysms and two neck remnants. The unruptured aneurysms were not treated during the acute stage of SAH but had received a complete short term follow-up. Results: The rapid growth of one unruptured aneurysm and two neck remnants was confirmed by a second angiogram performed on average40 days after the first angiogram. Several candidate factors responsible for the growth of aneurysm were selected, and the results of a statistical analysis indicate that a systolic blood pressure above 200 mmHg during the acute stage of SAH and vasospasm, confirmed by transcranial Doppler ultrasound (TCD) or neurological examination, and neck remnants, are risk factors that affect the growth. Conclusions: Short term follow-up angiography is thus important for patients with untreated unruptured cerebral aneurysms after the acute stage of SAH.

Early total corpus callosotomy in a patient with cryptogenic West syndrome.

West syndrome is a generalized epileptic syndrome of infancy, that is characterized by clinical spasms and hypsarrhythmia and usually has an onset age before two years old. Children affected by West syndrome have a high risk of severe psychomotor developmental delay. Infants with West syndrome without identification of underlying neurological disorder after adequate investigations are classified as ‘‘cryptogenic’’ and usually have better prognoses than children with ‘‘symptomatic’’ West syndrome. Early seizure cessation, particularly among cryptogenic cases, may cure the disease and allow a good neurodevelopmental outcome. Corpus callosotomy was first introduced as a palliative treatment for epilepsy in 1940 and is performed in patients whose seizures are not amenable to surgical focal resection. West syndrome is often medically intractable and has features of ‘‘generalized’’ epilepsy, but corpus callosotomy has not been discussed widely as a treatment strategy. Given the catastrophic nature of West syndrome, an early indication for total corpus callosotomy may be appropriate. Here, we describe a case that was diagnosed as cryptogenic West syndrome, in which the epileptogenic focus was defined after total corpus callosotomy.

The utility of diffusion tensor imaging tractography for post-operative evaluation of a patient with hemispherotomy performed for intractable epilepsy

Hemispherotomy is an effective treatment for patients with severe epilepsy caused by hemispheric abnormalities such as hemimegalencephaly or other dysplastic malformations. Here, we report a 5-year-old boy who experienced right-side hemiconvulsion due to left hemispheric cortical dysplasia. He presented with mild right hemiparesis that had been present since seizure onset. Ictal electroencephalogram obtained during the hemiconvulsion showed localized epileptic discharges in the left hemisphere. He underwent a left peri-insular hemispherotomy. Three months after surgery, clonic convulsions returned in the left leg and EEG-video monitoring showed localized epileptic discharges in the frontal region. Magnetic resonance images showed that the genu of corpus callosum was unsectioned and diffusion tensor imaging tractography confirmed the presence of callosal fibers in the genu of the corpus callosum. Clonic convulsion disappeared after additional section of the corpus callosum. Further studies are warranted to determine the utility of diffusion tensor imaging tractography on the assessment of subcortical fibers following disconnective epilepsy surgery.

De novo ruptured aneurysm at the site of anastomosis after superficial temporal artery-middle cerebral artery anastomosis--case report and literature review.

Extracranial (EC)–intracranial (IC) bypass surgery, most comonly superficial temporal artery (STA)–middle cerebral artery MCA) anastomosis, has been established as a surgical procedure or treating major cerebral artery occlusive disease, and the main bject of this procedure is to reduce future ischemic events [1,2]. ignificant alterations in blood-flow patterns and hypertrophic hanges in the caliber of both the EC artery and adjacent segments f the cortical arteries are common after EC-IC bypass. However, ostoperative aneurysm formation at the anastomotic site or in its lose proximity is a relatively rare complication of this procedure 1–11]. We describe a rare case of intracerebral hemorrhage from a uptured aneurysm at the anastomotic site 2 years after STA–MCA nastomosis.