Brain tumors can be associated with epilepsy, and some tumors are more likely to be associated with seizures than others. Brain tumors may cause seizures by applying mechanical pressure on adjacent tissue or by releasing excitatory neurotransmitters like glutamate.
Treating Brain Tumor-related Epilepsy
The first line of treatment for brain tumor-related epilepsy is anti-epilepsy medications, but these are associated with side-effects and refractoriness (meaning seizures are not controlled). The next step is usually resection of the tumor, and the decision of how much brain tissue to resect is based on the tumor margin as seen in the MRI. However, not everyone who undergoes gross resection of the tumor experiences seizure freedom. What could explain this?
Using Intracannial EEG Monitoring During Brain Tumor Surgery
The tissue surrounding the tumoral tissue is known as the peritumoral tissue and is being investigated as an active contributor of seizures instead of a passive bystander. The authors of a recent paper wanted to characterize the electrical properties of the tumor and the adjacent tissue. The rationale was that an extensive mapping of more than just the tumor could give us information about the spatial relationship between the tumor and the seizure-producing region.
The authors used intracranial EEG monitoring . In this technique, electrodes are placed directly on the exposed surface of the brain (as opposed to placing them on the skull as is done in conventional EEG). By looking at interictal spikes – a measure of how prone to seizures the brain tissue is – the authors found that the seizure-onset zone was located quite far away from the margin of the tumor. This is information that a MRI scan wouldn’t have given.
In this study, complete removal of the seizure initiation zone resulted in better outcome for seizures. Hence, although intracranial EEG needs to be done under anesthesia and is more time-consuming, the results of this study force us to rethink conventional methods for resection in tumor-related epilepsy and to incorporate intracranial EEG to the management plan.