Dados do Trabalho

Título

Late seizure recurrence following surgery for type II focal cortical dysplasia: the concept of relevant epileptogenic tissue

Introdução

Epilepsy surgery for intractable seizures related to type II focal cortical dysplasia (FCD II) aims to completely control seizures. Such a favourable outcome depends upon correct localization and complete resection of the epileptogenic zone (EZ). When resection of the EZ is incomplete, most recurrences occur in the first year after operation. Seizure recurrences after several years of complete seizure freedom are thus challenging to explain.

Objetivo

To delineate the time-course of seizure relapse in patients with FCD II and seek for predictors of late recurrences.

Método

64 patients with FCD II with at least 4 years follow-up (mean 9 years) had non-invasive presurgical evaluation and surgery with sequential electrocorticographic (ECoG) recordings and stepwise resections. Median duration of epilepsy and age at surgery were 7 and 16 years, respectively. 37 (58 %) had lesions or highly epileptogenic cortex involving indispensable regions (M1, language, SMA, visual, S1). Histopathologically, 42 had FCD IIA and 22 IIB. Demographic, anatomical, surgical and histological variables related to seizure outcome at the last visit were studied. Post-operative seizure recurrence was classified as early (in 1 year) or late (more than 1 year).

Resultados

50 patients (78%) were seizure-free 1 year after surgery. 12 (24%) had late recurrences, from 1 to 7 years after surgery. Main predictor was incomplete resection of ECoG abnormalities. 4 of these 12 were reoperated and highly epileptogenic patterns were again recorded by ECoG, correlated with dysplastic abnormalities in histopathology. At last visit, 37 patients (58%) were seizure free. Variables associated with seizure freedom were complete resection of cortical tissue displaying highly epileptogenic patterns on ECoG, complete resection of the lesion and FCD IIB on histopathology (all p< 0.001). Complete resections were highly related to lesion location: only 5/37 patients with lesions in indispensable cortex were seizure free, compared to 16/27 with lesions elsewhere (p<0.001).

Conclusão

Late recurrences occur in about ¼ patients operated for FCD II due to incomplete resection of a latent part of the epileptogenic network that may become active years after apparently successful operations. This tissue, in conjunction with the EZ identified, comprise a larger cortical area we name relevant epileptogenic tissue (R.E.T.). Sequential acute ECoG recordings may have a crucial role in identifying the R.E.T.

Palavras-chave

Epilepsy surgery; Type II focal cortical dysplasia; FCD II;