Paul Reading Maurice Curtis, Andrew Naylor, Richard Faull ... - ACNR

Neurophysiology ArticleFigure 3: Relation between the distribution and topography of late responses to SPES and seizure onset in a patient with bitemporal subdural strips.A: Intracranial recordings of early and delayed responses to SPES. Delayed responses were seen at contact 2 of left subtemporal strip (LT2) when stimulating through electrodes 3 and4 of same strip (LT3 and LT4) B: Subdural recording of a focal seizure onset. Note the fast activity building up at electrodes 1 and 2 of the left subtemporal strip (LT1 and 2). Electrode1 was the most distal electrode to the insertion burr hole and closest to mesial temporal structures Recording displayed in common reference to Pz.Arrow=electrical stimulation; RT=right subtemporal strip; LT=left subtemporal strip.onset and responses to SPES was seen in theareas where DR were recorded and thosewhich, when stimulated, gave rise to RR(abnormal SPES areas).Neuropathology and prediction ofoutcome:We have studied 40 consecutive patients operatedon at King’s College Hospital who had previousSPES, and have more than 12 months offollow-up. 6 A strong relationship betweenfavourable post-surgical seizure control andremoval of the abnormal SPES areas was found.Whereas around 96% of patients who had completeremoval of abnormal SPES areas enjoyeda favourable outcome, only 71% of patientswhere these areas were partially removed had afavourable outcome. The three patients whereabnormal SPES areas were not removed hadpoor outcomes (Table 3). More specifically, asimilar relation has been observed after frontallobe resections. 5 An important finding was theconsistent presence of structural abnormalitiesdemonstrated by neuropathology in theremoved abnormal SPES areas despite normalneuroimaging. 6 This means that delayed andrepetitive responses arose from structurally andfunctionally abnormal regions.SPES in childrenIn a study performed in King’s CollegeHospital and in Great Ormond Street Hospitalfor Sick Children (London UK), the utility ofSPES in the paediatric population has beenevaluated in 35 children. We identified corticalresponses to SPES that were similar or identicalto those reported in adults. 7 These results areespecially important because in children withfocal epilepsy there is a compromise betweensafety and early surgical intervention. SPESTable 2: Comparison between the topographies of DR and ictal onset zones in the 83 patients withDR and seizures during telemetry.DRIctal onset zone topographytopography Focal Regional Bilateral Indep. Diffuse Totalin out in out in outFocal 17 1 7 0 3* 0 0 28Regional 6 0 31** 2 0 0 1 40Bilateral 4*** 0 4*** 0 7 0 0 15Total 27 1 41 2 10 0 1 83Patients showing focal and regional ictal onset zones were considered as having regional ictal onset zone.Patients showing focal and regional DR were considered as having regional DRin=DR inside the ictal onset zone; out=DR seen outside ictal onset zone and not within the ictal onset zone;indep=independent* All three patients had unilateral focal DR and bilateral seizures.** Two patients had DR inside and outside the ictal onset zone*** All patients had DR inside and outside the ictal onset zonecould reduce the duration of intracranial monitoringby optimising electrode placement andby providing reliable information during theinterictal period, avoiding long waiting timefor multiple seizures to occur.Early responses and brain connectivitySince early responses appear to be normalresponses to SPES, they can be used to assessconnectivity between different corticalregions. 8-10 We have studied connectionsbetween temporal and frontal cortices in 51patients. 10 Our findings suggest that connectionsbetween temporal and ipsilateral frontalregions were relatively uncommon (seen in upto 25% of hemispheres) whereas connectionsbetween frontal and ipsilateral temporal corticeswere more common, particularly fromorbital to ipsilateral medial temporal regions(40%). Contralateral bi-temporal connectionswere rare (