Frame-based vs frameless placement of intrahippocampal depth electrodes in patients with refractory epilepsy: a comparative in vivo (application) study.
BACKGROUND
Despite progress in imaging technologies, documentation of unifocal electrical excitability is pivotal in patient selection for epilepsy surgery.


OBJECTIVE
To compare the application accuracy of the Vogele-Bale-Hohner system (VBH), a maxillary fixation system with an external fiducial frame permitting frameless stereotactic guidance, with that of conventional frame-based stereotaxy for placement of intrahippocampal depth electrodes (DEs) in patients with refractory epilepsy.


METHODS
Retrospective study. Comparison of two patient cohorts with DEs implanted along the occipitotemporal axis (group A, VBH; group B, frame-based stereotaxy). In vivo accuracy (lateral target localization error [TLE]), determined postoperatively by measuring the normal distance between virtual target and real electrode position at the tip and at 4cm from the tip, number of electrode contacts within the target structure, and diagnostic quality of electroencephalogram recordings were compared.


RESULTS
Seventeen DEs (A, 6 electrodes, 60 contacts; B, 11 electrodes, 90 contacts) were placed. electroencephalogram recordings via DEs supported further treatment decisions in all patients. TLE was 2.433 ± 0.977 mm (SD) (95% confidence interval [CI], 1.715-3.214 mm) (A) and 1.803 ± 0.392 mm (SD) (95% CI,1.511-2.195 mm) (B) (P = .185). Maximal error was 4 mm (A) and 3.2 mm (B). TLE 4 cm from the tip was 2.166 ± 2.188 mm (SD) (95% CI,0.438-3.916 mm) (A) and 1.372 ± 0.548 mm (SD) (95% CI,1.049-1.695 mm) (B) (P = .39). Maximal error 4 cm from the tip was 6.4 mm (A) and 2.14 mm (B). On average, 7 (A) and 5 (B) electrode contacts were placed in the target region.


CONCLUSIONS
The VBH and frame-based systems offer similar in vivo accuracy for intrahippocampal DE placement. With frame-based methods, accuracy is higher but the number of contacts per side is lower. This does not translate to clinically important differences.
Clinical Department of Neurosurgery, Innsbruck Medical University, Innsbruck, Austria. martin.ortler@i-med.ac.at
Martin
M
Ortler
Florian
F
Sohm
Wilhelm
W
Eisner
Richard
R
Bauer
Judith
J
Dobesberger
Eugen
E
Trinka
Gerlig
G
Widmann
Reto
R
Bale
D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000295:instrumentation / Q000379:methods; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006624:Hippocampus / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D038361:Neuronavigation / Q000295:instrumentation / Q000379:methods*; D012189:Retrospective Studies; D013238:Stereotaxic Techniques / Q000295:instrumentation; D055815:Young Adult