Stereotactic depth electrode investigation of the insula in the evaluation of medically intractable epilepsy

Clinical article

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Object

The authors describe their experience with stereotactic implantation of insular depth electrodes in patients with medically intractable epilepsy.

Methods

Between 2001 and 2009, 20 patients with epilepsy and suspected insular involvement during seizures underwent intracranial electrode array implantation at the authors' institution. All patients had either 1 or 2 insular depth electrodes placed as part of an intracranial array.

Results

A total of 29 insular depth electrodes were placed using a frontal oblique trajectory. Eleven patients had a single insular electrode placed and 8 patients had 2 insular electrodes placed unilaterally. One patient had bilateral insular electrodes implanted. Postoperative imaging demonstrated satisfactory placement in all but 1 instance, and there was no associated morbidity or mortality. Fourteen patients underwent a subsequent resection, involving the frontal lobe (9 patients), temporal lobe (4), or frontotemporal lobes (1), and of these, 11 currently have Engel Class I outcome. Two patients (10%) had seizures originating within the insula and another 5 patients (25%) demonstrated early specific insular involvement. Neither patient with an insular seizure focus went on to resection. All 5 of the patients with early specific insular involvement underwent an insula-sparing resective procedure with Engel Class I outcome in all cases.

Conclusions

Stereotactic placement of insular electrodes via a frontal oblique approach is a safe and efficient technique for investigating insular involvement in medically intractable epilepsy. The information obtained from insular recording can be valuable for appreciating the degree of insular contribution to seizures, allowing localization to the insula or clearer implication of other sites.

Abbreviations used in this paper: EEG = electroencephalography; FLAIR = fluid attenuated inversion recovery; PET = positron emission tomography; SEEG = stereoencephalography; SPECT = single photon emission computed tomography.

Article Information

Address correspondence to: Atman Desai, M.D., Dartmouth-Hitchcock Medical Center, Section of Neurosurgery, One Medical Center Drive, Lebanon, New Hampshire 03756. email: atman.desai@hitchcock.org.

Please include this information when citing this paper: published online October 15, 2010; DOI: 10.3171/2010.9.JNS091803.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Illustrative Case 1: insular seizure focus (Patient 19). Postimplantation reconstructed CT-MR imaging demonstrating left anterior and posterior insular depth electrode placement. A: Reconstruction in plane of posterior insular electrode. B: Reconstruction in plane of anterior insular electrode. C: Reconstruction in combined plane of insular electrodes.

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    Illustrative Case 1: insular seizure focus (Patient 19). Ictal EEG recording demonstrating localization of seizure onset to left anterior (AID, upper arrow) and posterior (PID, lower arrow) insular depth electrodes.

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    Illustrative Case 2: secondary insular involvement (Patient 2). Postimplantation reconstructed CT-MR imaging demonstrating right anterior and posterior insular depth electrode placement. A: Reconstruction in plane of posterior insular electrode. B: Reconstruction in plane of anterior insular electrode. C: Reconstruction in combined plane of insular electrodes.

  • View in gallery

    Illustrative Case 2: secondary insular involvement (Patient 2). An EEG recording demonstrating localization of seizure onset to the left posterior frontal electrode (LPFS, lower arrow) with early secondary activity within the left anterior and posterior insular electrodes (LAI, LPI, upper and middle arrows, respectively).

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    Illustrative Case 3: no insular involvement seen (Patient 14). Postimplantation reconstructed CT-MR imaging demonstrating right insular depth electrode placement, in the plane of the electrode.

  • View in gallery

    Illustrative Case 3: no insular involvement seen (Patient 14). An EEG recording demonstrating localization of seizure onset to the right anterior interhemispheric electrodes (RAI, solid arrow), with no early discharge within the right insular electrode (RID).

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