title: Resective surgery for medically refractory epilepsy using intraoperative MRI and functional neuronavigation: the Erlangen experience of 415 patients.
abstract: OBJECTIVE
  Intraoperative overestimation of resection volume in epilepsy surgery is a well-known problem that can lead to an unfavorable seizure outcome. Intraoperative MRI (iMRI) combined with neuronavigation may help surgeons avoid this pitfall and facilitate visualization and targeting of sometimes ill-defined heterogeneous lesions or epileptogenic zones and may increase the number of complete resections and improve seizure outcome.
  
  
  METHODS
  To investigate this hypothesis, the authors conducted a retrospective clinical study of consecutive surgical procedures performed during a 10-year period for epilepsy in which they used neuronavigation combined with iMRI and functional imaging (functional MRI for speech and motor areas; diffusion tensor imaging for pyramidal, speech, and visual tracts; and magnetoencephalography and electrocorticography for spike detection). Altogether, there were 415 patients (192 female and 223 male, mean age 37.2 years; 41% left-sided lesions and 84.9% temporal epileptogenic zones). The mean preoperative duration of epilepsy was 17.5 years. The most common epilepsy-associated pathologies included hippocampal sclerosis (n = 146 [35.2%]), long-term epilepsy-associated tumor (LEAT) (n = 67 [16.1%]), cavernoma (n = 45 [10.8%]), focal cortical dysplasia (n = 31 [7.5%]), and epilepsy caused by scar tissue (n = 23 [5.5%]).
  
  
  RESULTS
  In 11.8% (n = 49) of the surgeries, an intraoperative second-look surgery (SLS) after incomplete resection verified by iMRI had to be performed. Of those incomplete resections, LEATs were involved most often (40.8% of intraoperative SLSs, 29.9% of patients with LEAT). In addition, 37.5% (6 of 16) of patients in the diffuse glioma group and 12.9% of the patients with focal cortical dysplasia underwent an SLS. Moreover, iMRI provided additional advantages during implantation of grid, strip, and depth electrodes and enabled intraoperative correction of electrode position in 13.0% (3 of 23) of the cases. Altogether, an excellent seizure outcome (Engel Class I) was found in 72.7% of the patients during a mean follow-up of 36 months (range 3 months to 10.8 years). The greatest likelihood of an Engel Class I outcome was found in patients with cavernoma (83.7%), hippocampal sclerosis (78.8%), and LEAT (75.8%). Operative revisions that resulted from infection occurred in 0.3% of the patients, from hematomas in 1.6%, and from hydrocephalus in 0.8%. Severe visual field defects were found in 5.2% of the patients, aphasia in 5.7%, and hemiparesis in 2.7%, and the total mortality rate was 0%.
  
  
  CONCLUSIONS
  Neuronavigation combined with iMRI was beneficial during surgical procedures for epilepsy and led to favorable seizure outcome with few specific complications. A significantly higher resection volume associated with a higher chance of favorable seizure outcome was found, especially in lesional epilepsy involving LEAT or diffuse glioma.
authors.affiliation: Departments of 1 Neurosurgery.
authors.forename: Karl
authors.initials: K
authors.lastname: Roessler
authors.affiliation: Departments of 1 Neurosurgery.
authors.forename: Andrea
authors.initials: A
authors.lastname: Hofmann
authors.affiliation: Departments of 1 Neurosurgery.
authors.forename: Bjoern
authors.initials: B
authors.lastname: Sommer
authors.affiliation: Departments of 1 Neurosurgery.
authors.forename: Peter
authors.initials: P
authors.lastname: Grummich
authors.affiliation: Neuropathology, and.
authors.forename: Roland
authors.initials: R
authors.lastname: Coras
authors.affiliation: Neurology, Epilepsy Centre, University Hospital Erlangen; and.
authors.forename: Burkard Sebastian
authors.initials: BS
authors.lastname: Kasper
authors.affiliation: Neurology, Epilepsy Centre, University Hospital Erlangen; and.
authors.forename: Hajo M
authors.initials: HM
authors.lastname: Hamer
authors.affiliation: Neuropathology, and.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Blumcke
authors.affiliation: Neurology, Epilepsy Centre, University Hospital Erlangen; and.
authors.forename: Hermann
authors.initials: H
authors.lastname: Stefan
authors.affiliation: Department of Neurosurgery, University Hospital Marburg, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Nimsky
authors.affiliation: Departments of 1 Neurosurgery.
authors.forename: Michael
authors.initials: M
authors.lastname: Buchfelder
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D000069279:Drug Resistant Epilepsy / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000601:surgery*; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D038361:Neuronavigation / Q000379:methods*; D012189:Retrospective Studies; D055815:Young Adult
keywords: CM = cavernous malformation; DTI = diffusion tensor imaging; ECoG = electrocorticography; EZ = epileptogenic zone; FCD = focal cortical dysplasia; FOV = field of view; HS = hippocampal sclerosis; LEAT = long-term epilepsy-associated tumor; MEG = magnetoencephalography; MPRAGE = magnetization-prepared rapid-acquisition gradient echo; drug-resistant epilepsy; fMRI = functional MRI; functional MRI; iMRI = intraoperative MRI; intraoperative MRI; neuronavigation; resective epilepsy surgery; seizure outcome; surgical complications