Insular cortex involvement in mesiotemporal lobe epilepsy: a positron emission tomography study

Area of Science:

• Neuroscience
• Epileptology
• Medical Imaging

Background:

• Mesial temporal lobe epilepsy (MTLE) commonly presents with somesthetic and emotional symptoms.
• These symptoms are often linked to the hippocampo-amygdalar complex and, more recently, insular epileptic discharges.

Purpose of the Study:

• To investigate cortical insular involvement in MTLE patients.
• To examine clinical correlates of insular involvement and its relationship with postoperative outcomes.

Main Methods:

• Positron emission tomography (PET) using fluorodeoxyglucose (18F-FDG) and flumazenil (11C-FMZ) was performed on 18 MTLE patients and 18 healthy volunteers.
• Statistical parametric mapping (SPM96) and region of interest (ROI) analysis were used to assess metabolic abnormalities and benzodiazepine receptor (BZR) binding.

Main Results:

• Significant hypometabolism and decreased BZR binding were detected in the insular cortex of MTLE patients, primarily ipsilateral to the seizure focus (present in 60% of patients).
• Emotional symptoms correlated with anterior insular hypometabolism, while somesthetic symptoms correlated with posterior insular hypometabolism.
• No correlation was found between ipsilateral insular hypometabolism and postoperative outcome after anterior lobectomy.

Conclusions:

• Unilateral MTLE is associated with insular hypometabolism and benzodiazepine receptor loss.
• The anterior insular cortex is implicated in emotional symptoms, and the posterior insular cortex in somesthetic symptoms in MTLE.
• Insular hypometabolism does not appear to influence the outcome of anterior lobectomy in MTLE patients.