Failures in Temporal Lobe Epilepsy Surgery

To the Editor: We have read with great interest the paper by Englot et al.1 The authors' study is an effort to investigate seizure semiology in patients who “fail” temporal lobectomy for intractable epilepsy. We congratulated with the Authors for their excellent analysis of seizure types and frequency in a homogeneous series of temporal lobe epilepsy patients submitted to anterior temporal lobectomy. We agree with the Authors about the importance, to better understand causes of epilepsy surgery “failures,” to identify factors predicting seizures outcome. However more attention should be paid on referring seizure outcome to the neuropathologic substrate. In fact, an increasing role of the underlying histological type and subtype of structural lesion on seizure outcome has emerged in the latest years.2-10 Seizures prognosis of patients undergoing temporal lobe epilepsy surgery appear strictly related to the type of lesion. In our retrospective study about seizures outcome in drug resistant mesial temporal lobe epilepsy (MTLE)11 patients with MTLE and epilepsy-associated low grade tumor (ELGT), mesial temporal sclerosis (MTS), or MTS associated with focal cortical dysplasia (FCD) showed the best postsurgical seizure outcome (Engel Class I in more than 80% of cases), whereas only 63% of patients with isolated FCD achieved the same outcome. Furthermore, the analysis of seizure outcome in histopathological subtypes of FCD and of MTS showed different prognoses in the different pathological subgroups, with worse outcomes for atypical MTS, absence of granular cell pathology, and isolated FCD Type I. Our results support the thesis that pathological substrate represents a significant predictor for seizure recurrence, with rates of Engel Class I outcome12 ranging from 59% for patients with isolated FCD to 82%, 83%, and 84%, respectively, for isolated MTS, ELGT, and FCD associated with MTS. Our finding according with the recent literature2-10 suggest that different pathological subtypes are associated with different postsurgery seizure outcomes. This implies that surgical failure, that is seizure recurrence, may occur either because of incomplete resection of the epileptogenic zone or because of an underlying pathological condition predicting a worse outcome. The epilepsy surgeon should be aware of the relevance of the histopathological assessment and provide adequate specimens for a proper pathological diagnosis. Moreover, neuropathological diagnosis must follow and strictly observe an adequate international pathological protocol, with demonstrated good interobserver and intraobserver reproducibility for histopathological categories13 In our opinion, with the adoption of the more recent pathological classification systems 2-5,9 some subgroups of histological abnormalities conditioning outcomes have emerged and should be considered among the factors predictive of seizure outcome. In addition, the recognition of the different subgroups of pathological features associated with different seizure outcomes may stimulate the investigation of the specific epileptogenic mechanisms involved. This approach is also in agreement with the recent suggestions of the International League Against Epilepsy (ILAE) Commission on Classifications and Terminology14 to put more emphasis on the underlying pathological substrate in the assessment of postsurgical seizure outcome and in future epilepsy classifications. Disclosure The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.