I want to take a close look at the percutaneous exit site. The exudate emanating from the electrode exit site is hypothesized to be made up of dead epithelium cells continuously accumulating because of continued cell growth from the dermis. As cells are produced, outer layer cells lose contact with the dermis and nutritional support.
Shown here is a histological cross section of the implant exit site stained with cytokeratin 903, which stains basal epithelium dark brown. The downward growth of the epithelium terminates around 3 mm below the surface. At this point fibrous encapsulation, composed of fibroblasts and collagen surround the implant in layers like those along the length of the coiled wire lead. The well in the skin is in the range of 0.67 to 0.7 mm in diameter, the same as the dimension of the lead, suggesting a stable snug fit.
Shown here is a cartoon representation of the histological data. Note, that the tight cell layer, that forms around the electrode windings, is continuous with the encapsulation tissues at the electrode entry site. The ingrowth of encapsulation tissues provide mechanical stability to accommodate some relative movement between the body tissues and, a pathogenic barrier. These are the reasons that coiled wire leads have been used successfully in percutaneous implants of electrode in the abdominal cavity, the brain, and muscle. This lead configuration opens opportunities to develop implantable devices without committing to costly implantable hardware.