Hippocampal spindles and barques are normal intracranial electroencephalographic entities

Abstract

Objective: To assess whether hippocampal spindles and barques are markers of epileptogenicity.

Methods: Focal epilepsy patients that underwent stereo-electroencephalography implantation with at least one electrode in their hippocampus were selected (n = 75). The occurrence of spindles and barques in the hippocampus was evaluated in each patient. We created pairs of pathologic and pathology-free groups according to two sets of criteria: 1. Non-invasive diagnostic criteria (patients grouped according to focal epilepsy classification). 2. Intracranial neurophysiological criteria (patient's hippocampi grouped according to their seizure onset involvement).

Results: Hippocampal spindles and barques appear equally often in both pathologic and pathology-free groups, both for non-invasive (P_spindles = 0.73; P_barques = 0.46) and intracranial criteria (P_spindles = 0.08; P_barques = 0.26). In Engel Class I patients, spindles occurred with similar incidence both within the non-invasive (P = 0.67) and the intracranial criteria group (P = 0.20). Barques were significantly more frequent in extra-temporal lobe epilepsy defined by either non-invasive (P = 0.01) or intracranial (P = 0.01) criteria.

Conclusions: Both spindles and barques are normal entities of the hippocampal intracranial electroencephalogram. The presence of barques may also signify lack of epileptogenic properties in the hippocampus.

Significance: Understanding that hippocampal spindles and barques do not reflect epileptogenicity is critical for correct interpretation of epilepsy surgery evaluations and appropriate surgical treatment selection.

Keywords: Epilepsy surgery; Hippocampus; Intracranial EEG; Temporal lobe epilepsy; sEEG.