Review: The international consensus classification of Focal Cortical Dysplasia - a critical update 2018.

The Diagnostic Methods commission of the International League against Epilepsy (ILAE) released a first international consensus classification of Focal Cortical Dysplasia (FCD) in 2011. Since that time, this FCD classification has been widely used in clinical diagnosis and research (more than 740 papers cited in Pubmed between 1/1/2012 and 7/1/2017). Herein, we review the new data that will inform and revise the FCD classification. Many recent papers described molecular-genetic characteristics in FCD type II including multiple mutations in the mTOR pathway. In addition, the electro-clinico-imaging phenotype and surgical outcomes of FCD type II (in particular type IIb) were further defined and validated. These results pave the way for the design of an integrated clinico-pathological and genetic classification system, as recently recommended by the WHO for the classification of malignant brain tumours. On the other hand, little new information was acquired on FCD types I and III. Focal cortical dysplasia type I subtypes are still lacking a comprehensive description of clinical phenotypes, reproducible imaging characteristics, and specific molecular/genetic biomarkers. Associated FCD III subtypes also became rare in published literature. Despite temporal lobe epilepsy being the most common focal epilepsy in adults, we have not identified neurophysiological, imaging, histopathological and/or genetic biomarkers to reliably classify FCD III with or without hippocampal sclerosis. In respect of pathogenesis, FCD adjacent to a non-developmental, postnatally acquired lesion is difficult to explain and perhaps does not exist. This update may help foster shared efforts towards a better understanding of FCD, potential future updates of classification and novel targeted treatments.

Remote MEG dipoles in focal cortical dysplasia at bottom of sulcus.

OBJECTIVE: To investigate whether the magnetoencephalography (MEG) single moving dipole (SMD) method could delineate the epileptic zone of focal cortical dysplasia (FCD) at the bottom of sulcus (FCDB). METHODS: We retrospectively analyzed 17 children (11 male; mean age 8.8 years, range 3-17 years) with FCD type II who underwent epilepsy surgery. We compared spatial congruence between the following: (1) MEG cluster and FCDB and (2) MEG cluster and FCD at the brain surface (FCDS). We measured the volume and depth of magnetic resonance imaging (MRI)-visible lesions to investigate whether they affect spatial congruence between MEG cluster and MRI-visible lesion. RESULTS: Eight children had FCDB and the other nine children had FCDS. The volume of MRI-visible lesions for FCDB ranged from 1,632 to 4,707 mm(3) (mean ± standard deviation [SD] 3,095 ± 1,211 mm(3) ). The depth of FCDB ranged from 19 to 33 mm (mean ± SD 26 ± 4 mm). The volume of MRI-visible lesion for FCDS ranged from 2,375 to 57,331 mm(3) (15,470 ± 18,455 mm(3) ). There was a tendency for a smaller volume of MRI-visible lesion for FCDB, relative to FCDS(p = 0.079). In FCDB, six children showed clusters of MEG dipoles and two children showed scattered MEG dipoles for interictal spikes. The spatial congruence between the MEG result and FCDB was partially overlapping in four children and discordant in another four children. In FCDS, eight children had MEG cluster and one child had MEG scatter alone. The spatial congruence between MEG result and FCDS was overlapping in eight of nine children (fully two; partially six) and discordant in one of nine children. Fifteen children (88%; FCDB eight; FCDS seven) became seizure-free after resective surgery. MEG spike dipole resection ratio in the cluster ranged from 4-100% (mean 67%) in 6 FCDB and 23-99% (mean 77%) in 8 FCDS. SIGNIFICANCE: The SMD method may drift MEG spike dipoles for FCDB. Lesionectomy can control seizures for four of eight patients in FCDB despite the remote MEG dipoles. The FCDB or FCDS partially overlapped with MEG cluster may have an extending/invisible epileptogenic zone consecutive to the MRI-visible lesion.

Mutations in tubulin genes are frequent causes of various foetal malformations of cortical development including microlissencephaly.

Complex cortical malformations associated with mutations in tubulin genes are commonly referred to as "Tubulinopathies". To further characterize the mutation frequency and phenotypes associated with tubulin mutations, we studied a cohort of 60 foetal cases. Twenty-six tubulin mutations were identified, of which TUBA1A mutations were the most prevalent (19 cases), followed by TUBB2B (6 cases) and TUBB3 (one case). Three subtypes clearly emerged. The most frequent (n = 13) was microlissencephaly with corpus callosum agenesis, severely hypoplastic brainstem and cerebellum. The cortical plate was either absent (6/13), with a 2-3 layered pattern (5/13) or less frequently thickened (2/13), often associated with neuroglial overmigration (4/13). All cases had voluminous germinal zones and ganglionic eminences. The second subtype was lissencephaly (n = 7), either classical (4/7) or associated with cerebellar hypoplasia (3/7) with corpus callosum agenesis (6/7). All foetuses with lissencephaly and cerebellar hypoplasia carried distinct TUBA1A mutations, while those with classical lissencephaly harbored recurrent mutations in TUBA1A (3 cases) or TUBB2B (1 case). The third group was polymicrogyria-like cortical dysplasia (n = 6), consisting of asymmetric multifocal or generalized polymicrogyria with inconstant corpus callosum agenesis (4/6) and hypoplastic brainstem and cerebellum (3/6). Polymicrogyria was either unlayered or 4-layered with neuronal heterotopias (5/6) and occasional focal neuroglial overmigration (2/6). Three had TUBA1A mutations and 3 TUBB2B mutations. Foetal TUBA1A tubulinopathies most often consist in microlissencephaly or classical lissencephaly with corpus callosum agenesis, but polymicrogyria may also occur. Conversely, TUBB2B mutations are responsible for either polymicrogyria (4/6) or microlissencephaly (2/6).

Post-surgical outcome for epilepsy associated with type I focal cortical dysplasia subtypes.

Focal cortical dysplasias are a well-recognized cause of medically intractable seizures. The clinical relevance of certain subgroups of the International League Against Epilepsy (ILAE) classification scheme remains to be determined. The aim of the present work is to assess the effect of the focal cortical dysplasia type Ib and Ic histologic subtypes on surgical outcome with respect to seizure frequency. This study also provides an opportunity to compare the predictive value of the ILAE and Palmini et al classification schemes with regard to the type I focal cortical dysplasias. We retrospectively reviewed 91 focal cortical dysplasia patients (55% female; median age: 19 years (interquartile range 8-34); median seizure duration: 108 months (interquartile range 36-204)) with chronic epilepsy who underwent surgery. We compared the pathological subtypes, evaluating the patients' post-surgical outcome with respect to seizure frequency according to the Engel's classification and the ILAE outcome classification. Both the ILAE classification scheme and Palmini et al classification scheme were utilized to classify the histologic subtype. Using χ(2) and Fisher's exact tests, we compared the post-surgical outcomes among these groups. Of the 91 patients, there were 50 patients with ILAE focal cortical dysplasia type Ib, 41 with ILAE focal cortical dysplasia type Ic, 63 with Palmini et al focal cortical dysplasia type IA, and 28 with Palmini et al focal cortical dysplasia type IB. After surgery, 44 patients (48%) were seizure-free. Crude analysis revealed no significant difference between patients with subtypes of ILAE focal cortical dysplasia type I or Palmini et al focal cortical dysplasia type I concerning postoperative outcome according to the Engel and ILAE scoring systems on seizure frequency. Our findings revealed no significant difference concerning surgical outcome with respect to seizure frequency for the histologic subtypes of ILAE focal cortical dysplasia type I (Ib vs Ic) or Palmini et al focal cortical dysplasia type I (IA vs IB). In isolation, the histologic subtype of focal cortical dysplasia type I does not appear predictive of postoperative outcome.