Abstract
This study aimed to investigate the functional network effects of corpus callosotomy (CC), a well-recognized palliative surgical therapy for patients with Lennox-Gastaut syndrome (LGS). Specifically, we sought to gain insight into the effects of CC on LGS remission, based on brain networks in LGS by calculating network metrics and evaluating by network measures before and after surgery. Electroencephalographic recordings made during preoperative and 3-month postoperative states in 14 patients with LGS who had undergone successful CC were retrospectively analyzed. First, undirected correlation matrices were constituted for the mathematical expression of functional networks. Then, we plotted these networks to analyze the effects of CC on connectivity. In addition, conventional local and global network measures were applied to evaluate differences in network topology between preoperative and postoperative states. In the preoperative state, hubs were mainly distributed around the paramedian regions. After CC, the hubs moved from the paramedian regions to the dual-hemisphere and even the lateral regions. Thus, the general connectivity state became more homogeneous, which was verified by network plots and statistical analysis of local measures. The results of global network measures indicated a decreased clustering coefficient in the delta band, decreased characteristic path length in both the delta and gamma bands, and increased global efficiency in the gamma band. Our results showed a consistent variation in the global brain network that converted to a small-world topology with an optimal balance of functional integration and segregation of the network. Such changes were positively correlated with satisfactory surgery results, which could be interpreted as being indicative of LGS recovery process after CC. For patients with refractory LGS along with no focal epileptogenic zone findings, which were not suitable for the resective surgical therapy, our results verified that CC could work as an effective surgical treatment option.
Highlights
Lennox–Gastaut syndrome (LGS) is one of the most severe childhood-onset epilepsies [1, 2]
The patients were selected according to the following inclusion criteria: [1] preoperative epileptiform discharges were typical of EEG finding of LGS: generalized slow sharp and waves and generalized paroxysmal fast activities with slow and unorganized background; [2] brain MRI findings without definite brain lesions; [3] not a candidate for focal resection based on clinical judgment and interictal EEG recording; [4] markedly improved seizure condition after surgery
The preoperative state showed a more regular network configuration with a higher clustering coefficient, characteristic path length (CPL), and a lower efficiency in specific frequency ranges. These parameters changed substantially after Corpus callosotomy (CC) and resulted in a less synchronizable network with more of a small-world topology. This network pattern change demonstrated that CC could efficiently alter brain network topology
Summary
Lennox–Gastaut syndrome (LGS) is one of the most severe childhood-onset epilepsies [1, 2]. Epilepsy in LGS is usually medically refractory and generalized with multiple types of seizures observed. Corpus callosotomy (CC) is considered as a palliative surgical treatment for LGS when treatment with AEDs fails and if there is no evident focal pathologic brain region treatable by resective surgery [6, 7]. Accumulated evidence indicates that favorable outcomes can be achieved through CC in patients with LGS who suffer from medically intractable seizures with abundant generalized and multiregional EEG abnormalities [8, 9]. Because the corpus callosum is a critical pathway for the interhemispheric spread of epileptic activity, disconnection between cerebral hemispheres can modify seizures such that spread is slow, and thereby provide patients a warning that allows them to protect themselves. In instances where seizure expression requires bilateral synchrony, disruption of this synchrony may potentially eliminate this seizure type [6, 10]
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