Electroclinical, MRI and surgical outcomes in 100 epileptic patients with type II FCD

Focal cortical dysplasias (FCDs) are highly epileptogenic malformations associated with drug-resistant epilepsy, susceptible to surgical treatment. Among the different types of FCD, the type II includes two sub-groups based on the absence (IIa) or presence (IIb) of balloon cells. The aim of this retrospective study was to investigate possible differences in electroclinical presentations and surgical outcomes between the two sub-groups in 100 consecutive surgically treated patients with type II FCDs. All patients underwent a comprehensive presurgical assessment including stereo-EEG (SEEG) when necessary. No significant differences in gender, age at epilepsy onset, duration of epilepsy, age at surgery or seizure frequency were found between the two subgroups. Patients with type IIb FCD frequently showed sleep-related epilepsy. Their peculiar electrographic pattern was characterised by localised rhythmic or pseudo-rhythmic spikes or polyspikes ("brushes") enhanced during non-REM sleep and also associated with well-localised, brief, low-voltage fast activity. The incidence and frequency of short bursts of fast discharges, interrupted by activity suppression, increased during slow-wave sleep and often recurred pseudoperiodically. The occurrence of "brushes", present in 76% of the patients with type IIb FCD, was significantly associated (p<0.001) with the presence of balloon cells. We discuss the possible pathogenetic mechanisms underlying this activity. MRI diagnosis of type II FCD was made in 93% of the patients with balloon cells (BCs), suggesting that the presence of balloon cells might be, at least partially, responsible for the MRI features. Patients had very good postsurgical outcomes (83% in Engel class I) even after a long period of follow-up.