Localization of musicogenic epilepsy to Heschl's gyrus and superior temporal plane: case report

Abstract

Musicogenic epilepsy (ME) is an extremely rare form of the disorder that is provoked by listening to or playing music, and it has been localized to the temporal lobe. The number of reported cases of ME in which intracranial electroencephalography (iEEG) has been used for seizure focus localization is extremely small, especially with coverage of the superior temporal plane (STP) and specifically, Heschl's gyrus (HG). The authors describe the case of a 17-year-old boy with a history of medically intractable ME who underwent iEEG monitoring that involved significant frontotemporal coverage as well as coverage of the STP with an HG depth electrode anteriorly and a planum temporale depth electrode posteriorly. Five seizures occurred during the monitoring period, and a seizure onset zone was localized to HG and the STP. The patient subsequently underwent right temporal neocortical resection, involving the STP and including HG, with preservation of the mesial temporal structures. The patient remains seizure free 1 year postoperatively. To the authors' knowledge, this is the first reported case of ME in which the seizure focus has been localized to HG and the STP with iEEG monitoring. The authors review the literature on iEEG findings in ME, explain their approach to HG depth electrode placement, and discuss the utility of STP depth electrodes in temporal lobe epilepsy.

Keywords: AED = antiepileptic drug; ATL = anterior temporal lobectomy; EEG = electroencephalography; HG = Heschl’s gyrus; Heschl’s gyrus depth electrode; ME = musicogenic epilepsy; PT = planum temporale; STG = superior temporal gyrus; STP = superior temporal plane; iEEG = intracranial EEG; intracranial electroencephalography; medically refractory epilepsy; musicogenic epilepsy; superior temporal plane.

FIG. 1.

Intraoperative photograph demonstrating exposure and intracranial electrode placement. A right frontotemporoparietal craniotomy (A) allowed proper exposure for placement of grid, strip, and depth electrodes (B), including the HG depth electrode. The sylvian fissure is marked with a dashed line. The HG depth electrode and the PT depth electrode are marked with X symbols anteriorly and posteriorly, respectively, at their entry points at the cortical surface. Ant = anterior; inf = inferior; post = posterior; sup = superior. Figure is available in color online only.

FIG. 2.

Intraoperative placement of HG depth electrode. A: The planning view on the frameless stereotactic system (Stealth Navigation, Medtronic) showing the entry point and the trajectory (green circles and dotted lines B: The similar planning view showing the target and the trajectory. C and D: Intraoperative photographs showing placement of 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 HG depth electrode. Figure is available in color online only.

FIG. 3.

Invasive EEG results showing significant spikes along the HG depth electrode at the onset of a typical seizure. The most significant (largest in amplitude) spikes were consistently noted along the HG depth electrode at the seizure onset (marked with a dashed rectangular area), followed by spikes of smaller amplitudes along the PT depth electrode. Spikes noted with the frontotemporal grid electrode over the lateral temporal cortex and centered around the entry points of the HG and PT depth electrodes were delayed in some cases by 1–2 msec, and were smaller in amplitude at seizure onset. No significant spikes were noted in the mesial temporal lobe with amygdala or posterior hippocampus depth electrodes or with a parahippocampal strip electrode. Neither an inferior orbital depth electrode nor an insula depth electrode was involved.

FIG. 4.

The location of each contact of the HG depth electrode. The location of each contact (numbered from 109 posteromedially to 120 anterolaterally) is shown on the axial image on the left and on the coronal images on the right. The electrode contacts that showed significant spikes during the seizure onsets were marked with a dashed line (from contact 114 medially through contact 119 laterally).

FIG. 5.

Intraoperative photograph demonstrating resection of seizure focus. A: Right frontotemporoparietal craniotomy (same image as Fig. 1A). The box corresponds to the approximate area shown in panel B. Gross anatomical landmarks (primary motor area and sylvian fissure) are indicated by dashed lines. B: An expanded view showing the extent of resection visible in this view (a solid white line) along with the HG depth electrode anteriorly and the PT depth electrode posteriorly that were kept in place during resection (entry points are marked by X symbols). Figure is available in color online only.

FIG. 6.

Reconstructed brain images with electrode contacts, showing the locations of the most significantly involved contacts during seizure onset and propagation, the extent of resection, and the HG and PT depth electrodes relative to the STP. The surface views were created by the FreeSurfer software based on preoperative and postoperative imaging studies. The lateral (upper panel) and ventral (lower panel) views show electrode contacts (large white circles), areas most significantly involved in seizure onset and propagation (dotted lines), the mapped primary motor area (dashed line), the extent of resection (solid line), and the entry points for the HG and PT depth electrodes (X symbols). The top-down view of the right STP (center panel) shows the locations of the HG and PT depth electrode contacts (small white circles).