Epilepsy affects approximately 0.5% to 1% of the general population, and at some point approximately 20% of these patients develop medically intractable epilepsy despite adequate pharmaceutical treatment. It has been estimated that 2 to 3/1000 people suffer medically refractory epilepsy, which is equivalent to 17,000 new cases per year in the United States alone. More than 700,000 cases of medically refractory epilepsy exist in the United States that may be benefited from surgery. Approximately 20% to 50% of these patients may have localized epilepsy and may be good candidates for resective, disconnecting, or neuromodulation procedures. It has been shown that surgical management of these medically refractory cases significantly increases the possibility of seizure freedom, improves the postoperative quality of life, maximizes the patient’s social function, and may minimize the need for anticonvulsant medications and their associated side effects.

In most cases, consideration for surgical intervention requires identification and accurate localization of the epileptogenic focus or foci and any associated epileptogenic zones. Surface electroencephalography (EEG) cannot localize the epileptogenic foci in approximately 25% of the medically refractory cases. In these cases in which surface EEG can identify no epileptogenic foci, or in those cases in which electrophysiologic studies are disconcordant with imaging studies, invasive EEG is necessary for further investigation. Invasive EEG permits more accurate and sensitive information because it is closer to the source of cortical electrical activity; it is separated only by high electrical conductivity media (cerebrospinal fluid [CSF], brain parenchyma), and thus is characterized by a high signal/noise ratio. In addition, it can detect electrical activity from a significantly smaller cortical area than surface EEG, and has stable impedance throughout the whole recording period. Furthermore, invasive EEG may provide valuable information regarding the presence of eloquent cortical areas, and thus allow accurate cortical mapping.

The use of subdural electrodes was first described by Penfield and his coworkers in the late 1930s. The first documented case of epidural electrode recording was performed also by Penfield, Jasper, and Hebb in 1939. The use of invasive EEG monitoring started progressively increasing within the next few decades, and in the mid-1970s it became routine clinical practice for patients with medically refractory epilepsy. Epidural electrodes were initially more popular, whereas strip subdural electrodes inserted via burr holes later became more frequently used. The evolution of stereotactic surgery and the technological advancement of stereotactic hardware and software allowed the wide application of depth along with subdural electrodes for invasive EEG monitoring. Likewise, the development of more biocompatible and more flexible grid electrodes led to their wide application in the preoperative investigation of patients with medically intractable epilepsy. It has been estimated that invasive recording is nowadays used in 25% to 50% of surgical epilepsy series.

The wide clinical application of invasive monitoring in the preoperative evaluation of patients suffering from medically refractory epilepsy brings up the issue of safety of using invasive monitoring. It is generally accepted that subdural electrodes show higher complication rates than depth electrodes. Even though subdural electrode–associated complications are rare, they can occasionally become troublesome. Thorough knowledge of all the potential complications associated with the implantation of subdural electrodes, and all subdural-related safety issues, is of paramount importance for their early recognition and prompmanagement. Moreover, meticulous knowledge of all safety issues is mandatory for medicolegal purposes, and for appropriately informing all possible surgical candidates before obtaining their consent.

This article systematically reviews the pertinent literature and identifies all safety issues associated with the implantation of subdural electrodes. All the possible complications associated with their usage are reviewed, and any predisposing factors are identified, for developing efficient strategies and protocols for avoiding complications.