Utility and safety of depth electrodes within the supratemporal plane for intracranial EEG

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OBJECTIVE

The epileptogenic zones in some patients with temporal lobe epilepsy (TLE) involve regions outside the typical extent of anterior temporal lobectomy (i.e., “temporal plus epilepsy”), including portions of the supratemporal plane (STP). Failure to identify this subset of patients and adjust the surgical plan accordingly results in suboptimum surgical outcomes. There are unique technical challenges associated with obtaining recordings from the STP. The authors sought to examine the clinical utility and safety of placing depth electrodes within the STP in patients with TLE.

METHODS

This study is a retrospective review and analysis of all cases in which patients underwent intracranial electroencephalography (iEEG) with use of at least one STP depth electrode over the 10 years from January 2006 through December 2015 at University of Iowa Hospitals and Clinics. Basic clinical information was collected, including the presence of ictal auditory symptoms, electrode coverage, monitoring results, resection extent, outcomes, and complications. Additionally, cases in which the temporal lobe was primarily or secondarily involved in seizure onset and propagation were categorized based upon how rapidly epileptic activity was observed within the STP following seizure onsets: within 1 second, between 1 and 15 seconds, after 15 seconds, and not involved.

RESULTS

Fifty-two patients underwent iEEG with STP coverage, with 1 STP electrode used in 45 (86.5%) cases and 2 STP electrodes in the other cases. There were no complications related to STP electrode placement. Of 42 cases in which the temporal lobe was primarily or secondarily involved, seizure activity was recorded from the STP in 36 cases (85.7%): in 5 cases (11.9%) within 1 second, in 5 (11.9%) between 1 and 15 seconds, and in 26 (61.9%) more than 15 seconds following seizure onset. Seizure outcomes inversely correlated with rapid ictal involvement of the STP (Engel class I achieved in 25%, 67%, and 82% of patients in the above categories, respectively). All patients without ictal STP involvement achieved seizure freedom. Only 4 (11.1%) patients with STP ictal involvement reported auditory symptoms.

CONCLUSIONS

Ictal involvement of the STP is common even in the absence of auditory symptoms and can be effectively detected by the STP electrodes. These electrodes are safe to implant and provide useful prognostic information.

ABBREVIATIONS ATL = anterior temporal lobectomy; ATO = anterior temporal operculum; EEG = electroencephalography; HG = Heschl’s gyrus; iEEG = intracranial EEG; IN = insula; PT = planum temporale; SEEG = stereo-EEG; STP = supratemporal plane; TLE = temporal lobe epilepsy.

Article Information

Correspondence Yasunori Nagahama: University of Iowa Hospitals and Clinics, Iowa City, IA. yasunori-nagahama@uiowa.edu.

INCLUDE WHEN CITING Published online September 7, 2018; DOI: 10.3171/2018.4.JNS171812.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    Intraoperative placement of HG depth electrode. A: Planning view on the frameless stereotactic system (Stealth Navigation, Medtronic) showing the entry point and the trajectory (green circles and dotted lines). B: Similar planning view showing the target and the trajectory. C and D: Intraoperative photographs showing placement of the HG depth electrode. A Stealth Navigus probe was used to select the appropriate trajectory of a guiding tube positioned over the entry point (C). An electrode-guiding cannula was advanced through the tube to the previously determined depth (D). An actual depth electrode was subsequently passed through the cannula, followed by removal of the guiding tube/cannula system. Note the unique anterolateral-to-posteromedial trajectory within the STP for placement of the HG depth electrode. Reproduced from Nagahama Y, et al: Localization of musicogenic epilepsy to Heschl’s gyrus and superior temporal plane: case report. J Neurosurg 129:157–164, 2018. Published with permission. Figure is available in color online only.

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    Preoperative and postimplantation MRI with projection of STP electrodes. A: Sagittal, coronal, and axial T1-weighted preoperative MR images with the location of one of the HG depth electrode contacts mapped (red cross) based on postoperative MRI and CT. B: Sagittal, coronal, and axial T1-weighted MR images acquired after implantation showing the location of the same contact (red cross). C: Top-down view of the right STP showing the locations of the HG (contacts 7–14) and PT (contacts 57–64) depth electrode contacts projected on the surface rendering of the STP. Note that the second deepest contact of the HG depth electrode, marked in A and B, is also marked with a red cross in C. Figure is available in color online only.

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