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Abstract
Background: Magnetic source imaging (MSI) is used routinely in epilepsy presurgical evaluation and in mapping eloquent cortex for surgery. Despite increasing use, the diagnostic yield of MSI is uncertain, with reports varying from 5% to 35%. To add benefit, a diagnostic technique should influence decisions made from other tests, and that influence should yield better outcomes. We report preliminary results of an ongoing, long-term clinical study in epilepsy, where MSI changed surgical decisions.
Methods: We determined whether MSI changed the surgical decision in a prospective, blinded, crossover-controlled, single-treatment, observational case series. Sixty-nine sequential patients diagnosed with partial epilepsy of suspected neocortical origin had video-EEG and imaging. All met criteria for intracranial EEG (ICEEG). At a surgical conference, a decision was made before and after presentation of MSI. Cases where MSI altered the decision were noted.
Results: MSI gave nonredundant information in 23 patients (33%). MSI added ICEEG electrodes in 9 (13%) and changed the surgical decision in another 14 (20%). Based on MSI, 16 patients (23%) were scheduled for different ICEEG coverage. Twenty-eight have gone to ICEEG, 29 to resection, and 14 to vagal nerve stimulation, including 17 where MSI changed the decision. Additional electrodes in 4 patients covered the correct: hemisphere in 3, lobe in 3, and sublobar ictal onset zone in 1. MSI avoided contralateral electrodes in 2, who both localized on ICEEG. MSI added information to ICEEG in 1.
Conclusion: Magnetic source imaging (MSI) provided nonredundant information in 33% of patients. In those who have undergone surgery to date, MSI added useful information that changed treatment in 6 (9%), without increasing complications. MSI has benefited 21% who have gone to surgery.
Glossary
- 2nd STEP=
- changed second step;
- ADD=
- MSI decision to add electrodes;
- BiF=
- bifrontal;
- Bil → Uni=
- bilateral to unilateral;
- Change ICEEG=
- MSI changed the ICEEG decision as indicated;
- Class=
- postoperative outcome class;
- Dec → VNS=
- declined surgery and had VNS;
- Decl=
- declined ICEEG and surgery;
- Defr=
- deferred surgery, pending ICEEG;
- ECoG=
- electrocorticography;
- F=
- frontal;
- FU=
- postoperative follow-up after focal excisional surgery;
- ICEEG=
- intracranial EEG;
- ICEEG Loc=
- intracranial EEG localization;
- ICEEG → VNS=
- MSI changed decision from ICEEG to VNS;
- LAT=
- left anterior temporal lobectomy;
- LF=
- left frontal;
- LT=
- left temporal;
- LTm=
- left mesial temporal;
- LTml=
- left temporal both mesial and lateral;
- LTps=
- left temporal lateral posterior;
- MSI=
- magnetic source imaging;
- MSI Lat=
- MSI lateralization;
- MSI Lob=
- MSI lobar localization;
- MSI Loc=
- MSI sublobar localization;
- Op=
- surgical intervention;
- Pdg-Surg=
- pending excisional surgery;
- Pdg-VNS=
- pending VNS;
- RAT=
- right anterior temporal lobectomy;
- RC=
- right central;
- Red %=
- percentage reduction of seizures by surgery;
- Remis=
- spontaneous remission of seizures, no surgery;
- RF=
- right frontal focal excision;
- RFp=
- right frontopolar focal excision;
- ROp=
- right opercular;
- ROpRT=
- right opercular and right temporal regional ICEEG onset and multilobar resection;
- RTm=
- right mesial temporal;
- RTml=
- right temporal both mesial and lateral;
- T=
- temporal;
- VEEG=
- video-EEG;
- VNS=
- vagal nerve stimulation.
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