gms | German Medical Science

Objective: The size of craniotomies necessary for subdural grid electrode placement for invasive epilepsy diagnostics is arbitrary and subject to cultural differences. Some epilepsy surgeons’ understanding that it is necessary "to see every electrode" leads to relatively large craniotomies, while others argue for minimally invasive, patient-tailored approaches. No actual numbers on the sizes of craniotomies in the field have ever been published.

Methods: During a 3-year episode, 57 patients were implanted with subdural grid-electrodes (+/- strip electrodes) through navigated, patient-tailored approaches. The numbers of implanted electrodes were counted and the size of the craniotomies was measured in postop CTs. Patients were followed-up after 1 year for the surgical outcome. Feasibility of the originally planned operative strategy was documented.

Results: In all patients, the subdural electrodes could be implanted as planned through the tailored craniotomy. In 42 out of 57 patients an epileptogenic focus could be defined and resected. The mean craniotomy size was 26±12cm2 via which 50±13 electrodes were implanted. In all but one patient, resection of the epileptogenic focus was feasible through the same craniotomy. In temporal standard implantation procedures, even smaller craniotomies were applied.

Conclusion: The craniotomy size for subdural electrode implantation is controversial. While some favor large craniotomies, other surgeons strive for minimally invasive approaches. For the first time, we measured the actual craniotomy size for subdural grid and strip electrode implantation. Implantation as well as detection and resection of the epileptogenic focus were straightforward. We therefore advocate applying patient-tailored minimally invasive approaches – standard in modern microneurosurgery – in epilepsy surgery as well.