Epidural cylinder electrodes for presurgical evaluation of intractable epilepsy: technical note

This is a technical report describing a different technique for the insertion of epidural electrodes in the preoperative evaluation of epilepsy surgery. Our experience in 67 cases using this technique is analyzed.

Cylinder electrodes with multiple recording nodes spaced 1 cm apart along a Silastic core are placed into the epidural space under general anesthesia through single or multiple burr holes. We reviewed the data on 67 cases of medically intractable epilepsy requiring intracranial monitoring that had epidural cylinder electrodes placed. The electrodes were placed bilaterally or contralateral to subdural grids in 64 of the 67 cases. Continuous monitoring was performed from 1 to 3 weeks.

This method was most useful when used bilaterally or contralateral to subdural grids. Definitive surgery was rendered in 48 of 67 cases. After monitoring, all electrodes were removed at bedside or upon return to the operating room for definitive surgery. There were no mortalities, infections, cerebrospinal fluid leaks, neurologic deficits, or electrode malfunctions. Two patients (2/67, 3%) did develop subdural hematomas early in our series after dural injury near the pterion; however, these patients did not sustain permanent deficit.

Epidural cylinders are another option for preoperative monitoring, useful for determining lobe or laterality of seizure genesis. They offer an alternate method to EPEs in cases where epidural recording is desirable. The cylinder electrodes are easy to place and can be removed without a return to the operating theater. The electrodes' minimal mass effect allows them to be safely placed bilaterally or contralateral to subdural grids. The epidural cylinders can monitor cortex with a greater density of nodes and can access regions not amenable to EPEs.