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Ten patients were pre-operatively evaluated in the Surgical Planning Laboratory at Brigham and Women's Hospital, Boston, MA. Their ages ranged from 3 to 18, including two females and eight males. The females included one left temporal lobectomy and one right frontal tuber removal. The males included one left subcortical tuber removal and callosotomy, one left temporal lobectomy and hippocampectomy, one right parietal lobe mass removal, one left frontoparietal focus removal, one temporal epilepsy, one hypothalamic hamartoma with gelastic seizures, one right frontal interhemispheric focus removal (Table 1). The pre-operative and post-operative diagnosis was identical in all patients. Seven remained seizure free post-operatively. One girl suffering from tuberous sclerosis still experienced seizures but different in pattern from those recorded pre-operatively. The young boy suffering from the same congenital disorder remained seizure free for two months. The girl suffering from temporal lobe epilepsy showed atypical EEG readings during the initial evaluation and still had severe seizures post-operatively. No patient exhibited new post-operative neurological deficits.
For all the cases, the 3D imaging allowed the accurate evaluation of the lesions' anatomic location and relationship with neighboring cortical functionally relevant areas. The following cases illustrate the applications of our system.
Case 1: A seven year old boy with a one-year history of focal seizures and a lesion in the parasagittal posterior frontal lobe which on the MRI seemed consistent with hamartoma or dysplasia was admitted for subdural grid and strip placement and long-term monitoring. During the initial operation, 96 electrodes were applied directly to the cortical surface, including one posterior interhemispheric strip placed directly vertically down within the interhemispheric fissure posterior to the central sulcus and another placed anteriorly (Figure 2). One frontal and one parietal grid were placed subdurally on the lateral surface of the posterior frontal and the parietal lobes respectively. The location of the electrodes was recorded on the 3D model using the LED probe (black dots). Electrographic monitoring detected that all episodes were identical and consisted of abrupt and simultaneous onset of low amplitude fast activity in electrodes F32 of the frontal grid and AI11 and AI12 of the anterior interhemispheric strip. Using these results and intra-operative navigation the lesion was removed with careful motor and sensory monitoring. The patient tolerated the procedure well and has remained seizure free since then.
Case 2: An 8 year old boy suffering from intractable seizures was examined. The MRI showed no apparent lesions. Previous EEG results suggested a left temporal origin for seizure which prompted the decision to insert subdural grids and strips on that area to refine the seizure focus area. The location of the grids and strips was recorded and used as a map during bedside stimulation. Cortical stimulation was performed through the indwelling grids and strip electrodes. A mild interference with language in the superior portion of the posterior portion of the left latero-temporal grid in a region corresponding to Broca's area. As a result, it was decided to conducted a left temporal lobectomy as well as hippocampectomy. The hippocampus was reconstructed, displayed on the 3D model and used for guidance during surgery (Figure 1). The patient tolerated the procedure well and remained seizure free post-operatively.
Case 3: A two and a half year old girl with a history of tuberous sclerosis and cardiac disrrhythmia was admitted for seizure focus removal using subdural grids and strips and 3D reconstruction and navigation. A 32-contact grid was placed over the right lateral frontal region and an 8 contact strip was placed interhemispherically on the right frontal region. During the intracranial monitoring, it was noted that the seizure onset was localized to several contacts on the grid which were in the immediate region of the cortical tuber. Using 3D reconstruction and navigation, the tuber which was lying directly beneath the electrodes and which had been identified as the zone of epileptogenicity was removed (Figure 3). Following the operation, the patient remained free of post-operative neurological deficits with an MRI which showed a nice resection cavity.
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