Morphology of peritoneal dialysis catheter tunnel: macroscopy and light microscopy.

There is scanty knowledge of the morphology of peritoneal dialysis catheter tunnels in humans, even though such knowledge may impact on peritoneal catheter design, implantation and postimplantation care. Past descriptions of catheter tunnels are based mainly on data from animal experiments. Based on these data, it has been assumed that epidermal spreading is inhibited by collagen fibers ingrown into the cuff. Our preliminary investigation indicated that this may not be the case in humans and led us to study catheter tunnel morphology in more detail. Eighteen catheter tunnels (2-5mm of tissue around the catheters) were removed in 17 peritoneal dialysis patients. The catheters were inserted 30 to 2013 days prior to removal (median 366 days). The catheters were removed electively or because of infectious or noninfectious complications. Contrary to the observations in animals, in only 1 case did epithelium extend to the cuff with only a minimal amount of granulation tissue present at the end of a 9 mm long sinus tract. In the remaining cases, the leading edge of the epithelium always met granulation tissue 1-14 mm from the exit, and the cuffs were found 8-33 mm from the exit. In tunnels older than 197 days, dense fibrous tissue was ingrown into the cuffs, and a dense fibrous capsule surrounded the cuff. The uninfected intercuff segment formed a pseudosheath, indistinguishable from a tendon sheath or synovial membrane. Infection in the catheter tunnel propagates through the part of the cuff adjacent to the tubing inside the capsule, suggesting that the cuff per se does not constitute a major barrier for spreading infection. This observation, by exclusion, infers that the beneficial role of an external cuff in decreasing exit infections is by providing firm anchorage of the catheter resulting in restriction of its piston like movement and thereby minimizing trauma and inward conveyance of outer sinus tract flora.