Postsurgical pathologies associated with intradural electrical stimulation in the central nervous system: design implications for a new clinical device

Abstract

Spinal cord stimulation has been utilized for decades in the treatment of numerous conditions such as failed back surgery and phantom limb syndromes, arachnoiditis, cancer pain, and others. The placement of the stimulating electrode array was originally subdural but, to minimize surgical complexity and reduce the risk of certain postsurgical complications, it became exclusively epidural eventually. Here we review the relevant clinical and experimental pathologic findings, including spinal cord compression, infection, hematoma formation, cerebrospinal fluid leakage, chronic fibrosis, and stimulation-induced neurotoxicity, associated with the early approaches to subdural electrical stimulation of the central nervous system, and the spinal cord in particular. These findings may help optimize the safety and efficacy of a new approach to subdural spinal cord stimulation now under development.

Figure 1

An example of one of the original surgical approaches for placement of an intradural spinal cord stimulator array, after Figure 5 of [17] and after Figure 24.3 of [15]. (Reprinted with permission of J. G. Wepsic, M.D., Thieme Medical Publishers, Inc., and The Congress of Neurological Surgeons.)

Figure 2

An example of the endodural approach to placement of a spinal cord stimulator array in a patient, after Figure 3 in [29]. (Reprinted with permission of C. Burton, M.D., and Elsevier Inc.)

Figure 3

Summary of the types of neurosurgical complications reported during the early clinical use (ca. 1970) of intradural spinal cord stimulators in patients. (a) The baseline situation is shown in which the intradural array has been implanted either immediately under the dura, within the CSF layer, or directly on the dorsal surface of the spinal cord, with its leads traversing the dura, which forms a seal around them. (b) The difficulty encountered most frequently is shown: leakage of the CSF at the point where the leads traverse the dura. (c) Spinal cord contusion. (d) Infection within the spinal canal. (e) Formation of an intradural hematoma compressing the spinal cord. (f) Chronic formation of scar tissue or mature fibrous tissue around the stimulator.

Figure 4

The electrode-bearing surface of an early prototype version of the HSCMS. The device is shown in place on an exposed section of ovine spinal cord during an acute in vivo trial. This particular device is made of a nearly transparent thin film of silicone, had nine electrodes arranged in a 3 × 3 array, and was held in place by clips attached to dural flaps.

Figure 5

Hematoma produced by possible laceration of a pial vessel underneath the electrode bearing surface of a subdural spinal cord stimulator, after the figure in [47]. (Reprinted with permission of P. J. Grillo, M.D. and The American Medical Association.)

Figure 6

Photograph of the mechanical components of a prototype of the HSCMS which will be placed in the intradural space. The electrode-bearing surface will rest directly on the dorsal aspect of the spinal cord.