Focal Seizures Located in the Eloquent Cortex

Currently, this is the main indication for MST. In children, as in adults, the MST can be performed as a stand-alone procedure or can be combined with cortical resection or lesionectomy.20–22 In one of the largest series, Shimizu and Machara23 presented their experience with 31 children who underwent MST. The procedure was performed along with resective surgeries (lobectomy, corticectomy, or lesionectomy) in 25 patients and as a stand-alone procedure in the remaining 6 patients. Of 25 patients who were followed for more than 1 year, 10 of them had Engel Class I or II outcome, but no details were provided as to whether these patients had MST alone or combined with cortical resection. No mortality or morbidity was encountered during surgery or postoperatively. Later, Blount et al20 described their series of 30 consecutive children who underwent MST. The procedure was performed as a stand-alone therapy (4 patients) or in conjunction with cortical excisions (26 patients). Twenty-three children underwent invasive monitoring with subdural grid electrodes, and intraoperative electrocorticography was performed in the remaining 7 children. The mean follow-up period for the group was 3.5 years (minimum 30 months in all cases). All 20 patients in whom MST was performed in the primary motor cortex experienced transient hemiparesis lasting up to 6 weeks. No patient suffered a permanent motor deficit in the long-term follow-up period. In the 26 patients who underwent cortical resections followed by MST, 12 children (46%) were seizure free (Engel Class I) after surgery. Eleven patients (42%; Engel Classes II and III) continued to suffer seizures but the improvement in seizures was still acceptable. In the 23 patients in whom subdural grids were placed to capture the ictal onset zone by invasive video-electro-encephalography (VEEG), MST area consisted of a mean of 37% of the surgically treated area under the grid. It is difficult to assess the effectiveness of MST as a distinct surgical procedure because the majority of published series include patients in whom MST is combined with lesionectomy or cortical resection. The use of MST as a stand-alone therapy has been described by Schramm et al,24 Smith,25 Lui et al,26 and Whisler et al.27 These series addressed both adult and pediatric populations. Schramm obtained 45% and 50% good results according to Engel’s and Spencer’s classifications, respectively. Seizure-free outcome was 5% in Schramm’s series, 37.5% in Smith’s series, and 63% in Whisler’s series. Téllez-Zenteno et al28 published a meta-analysis of several series of patients with MST, both pure and combined with resective surgery. The mean follow-up period was 5 years in this study. They concluded that MST has the lowest rate of long-term, seizure-free outcome (16%) among all epilepsy surgical procedures. Previously, Spencer et al29 reported their meta-analysis from six series and reviewed the data covering 211 patients collected from six different centers. Fifty-five patients in this study underwent pure MST, and 156 patients had MST and resection combined procedures. The overall seizure outcome was similar in the patients with partial seizures whether the patient had pure MST or MST with cortical resection. However, the patients with generalized seizures had better outcome if the MST was combined with cortical resections. Unfortunately, this study did not specify the postsurgical follow-up period for outcome analysis. This report and others concluded that MST could be considered an effective surgical treatment alternative for uncontrolled seizures arising in eloquent brain areas.22,25,30–34

Landau-Kleffner Syndrome

Landau-Kleffner Syndrome (LKS) has been considered as another main indication for MST in children.3 This rare syndrome consists of an acquired epileptic aphasia or verbal auditory agnosia that may start abruptly or gradually and occurs in children with previously normal developmental history. A well-defined electrophysiological profile underlying this condition consists of frequent epileptiform discharges when awake, and generalized slow spike-wave discharges over the perisylvian region during slow wave sleep.35 Anti-epileptic drugs can improve clinical seizures but EEG findings can be frequently resistant to treatment.36

The MST technique was initially applied to the LKS patients by Morrell et al,3 and they reported their experience with 14 patients. Seven recovered age-appropriate speech ability and no longer needed speech therapy or special education classes. Another four had marked improvement in their speech but still required speech therapy. Three children had no changes in their preoperative conditions. Sawhney et al34 reported improvement in all three of their patients with LKS who underwent MST. Neville et al37 reported one case that had marked postoperative improvement in reading, vocabulary, sign language, and nonverbal subtests. Nass et al38 described their experience in seven patients with atypical forms of LKS and reported mild improvement in receptive language functions. Irving et al.39 reported five children with this condition who underwent MST and reported improvement in their language skills. Although none of them improved to an age-appropriate level, seizures and behavior disturbances were immediately improved in all cases. Castillo et al35 reported one case with significant linguistic improvement after a 2-year follow-up.

In summary, MST application in LKS can result in improvements in communication skills and behavior after surgery. However, improvement in speech takes a considerably longer period of time.40,41 Use of MST for severe autistic regression in childhood epilepsy is not always associated with improvement in cognitive and behavioral function. At best, gains observed are temporary, and further studies are needed to prove its worth in this condition.38

Syndrome of Malignant Rolandic-Sylvian Epilepsy

This nonlesional syndrome described by Otsubo et al42 relates to children who have intractable rolandic partial seizures that progress to secondary generalization, fronto-centrotemporal spikes on EEG, localized spike sources in the rolandic-sylvian regions on magnetoencephalography (MEG), and neurocognitive problems. Resective surgery is required in nonfunctional cortex and as an additional management strategy. MSTs are also recommended throughout the eloquent cortex. The series included seven patients and reported that the combination of techniques could reduce or eliminate seizure activity, avoiding postoperative permanent motor deficits or further language deficits.