Patch grafting the renal pelvis and ureteropelvic junction. A comparative study in pigs using lyophilized dura mater and free peritoneum

Robot-assisted ureteral reconstruction using a tubularized peritoneal flap: a novel technique in a chronic porcine model

OBJECTIVE

To evaluate the feasibility and functional outcomes in porcine models of a novel robotic surgical technique for the treatment of complex ureteral injuries and strictures.

MATERIALS AND METHODS

Six pigs underwent robotic ureteral reconstruction using a long tabularized peritoneal flap and followed for 6-9 weeks after the surgery. Ureteral flap vascularity, intra-renal pressure, patency of the conduct, endoscopic aspect of the flap, renal function and histopathology were evaluated.

RESULTS

All animals successfully underwent ureteral reconstruction using a tubularized peritoneal flap. Median operative time was 223 min (162-360). Flap tubularization suture took 31 min (19-47), and proximal anastomosis took 20 min (15-38). Bladder mobilization with psoas hitch and distal anastomosis took 9 min (7-12) and 23 min (13-46), respectively. On follow-up, significant shrinkage of the ureteral flap in both length and width was observed. Antegrade pyelograms confirmed dilation and tortuosity of the proximal ureter, dilation of the renal pelvis, and major and minor calyxes without any definitive strictures. Microscopically, focal urothelial lining was seen in the neoureter. Creatinine level was significantly higher at the end of the follow-up period (p = 0.003).

CONCLUSIONS

Robot-assisted ureteral reconstruction using a tubularized peritoneum flap is technically feasible and reproducible. The flap sustained abundant vascular supply after different intervals of follow-up and the peritoneal mesenchymal cells differentiated into urothelium and myofibroblasts. Further studies are needed to address the issue of functional obstruction to improve long-term renal function outcomes.

[Tissue engineering in reconstructive urology]

The term tissue engineering incorporates various techniques for the production of replacement tissues and organs. In urology tissue engineering offers many promising possibilities for the reconstruction of the urinary tract. Currently, buccal mucosa and urothelial cells are most commonly used for tissue engineering of the urinary tract. Various materials have been tested for their suitability as tissue scaffolds. The ideal scaffold, however, has not yet been found. In addition to material sciences and cell culture methods, surgical techniques play an important role in reconstructive urology for the successful implantation of tissue engineered transplants.

The feasibility of ureteral tissue engineering using autologous veins: an orthotopic animal model with long term results

Background

In an earlier study we demonstrated the feasibility to create tissue engineered venous scaffolds in vitro and in vivo. In this study we investigated the use of tissue engineered constructs for ureteral replacement in a long term orthotopic minipig model. In many different projects well functional ureretal tissue was established using tissue engineering in animals with short-time follow up (12 weeks). Therefore urothelial cells were harvested from the bladder, cultured, expanded in vitro, labelled with fluorescence and seeded onto the autologous veins, which were harvested from animals during a second surgery. Three days after cell seeding the right ureter was replaced with the cell-seeded matrices in six animals, while further 6 animals received an unseeded vein for ureteral replacement. The animals were sacrificed 12, 24, and 48 weeks after implantation. Gross examination, intravenous pyelogram (IVP), H&E staining, Trichrome Masson’s Staining, and immunohistochemistry with pancytokeratin AE1/AE3, smooth muscle alpha actin, and von Willebrand factor were performed in retrieved specimens.

Results

The IVP and gross examination demonstrated that no animals with tissue engineered ureters and all animals of the control group presented with hydronephrosis after 12 weeks. In the 24-week group, one tissue engineered and one unseeded vein revealed hydronephrosis. After 48 weeks all tissue engineered animals and none of the control group showed hydronephrosis on the treated side. Histochemistry and immunohistochemistry revealed a multilayer of urothelial cells attached to the seeded venous grafts.

Conclusions

Venous grafts may be a potential source for ureteral reconstruction. The results of so far published ureteral tissue engineering projects reveal data up to 12 weeks after implantation. Even if the animal numbers of this study are small, there is an increasing rate of hydronephrosis revealing failure of ureteral tissue engineering with autologous matrices in time points longer than 3 months after implantation. Further investigations have to prove adequate clinical outcome and appropriate functional long-term results.

Free peritoneal graft for repair of severe seromuscular defect of bowel: from experiment to clinical practice

BACKGROUND

Severe seromuscular tear of the bowel with impending perforation following enterolysis or trauma is not uncommon in gastrointestinal surgery. It is sometimes complicated with enterocutaneous fistula, intra-abdominal abscess or free perforation, especially of the ileus. In addition, direct serosal repair is often impossible, or complicated by lumen compromise. Serosal patch repair also reportedly is also associated with complications such as dislodgement of the sutured bowel loop, fistula formation, adhesion ileus, or volvulus. Free peritoneal graft (FPG), as in split-thickness skin graft (STSG), can be taken by underlying healthy tissue within 24 to 48 h and used for repair of such defect.

PATIENTS AND METHODS

In this study, FPG was used as an alternative to serosal patch repair or resection to cover severe defects of the colon, rectum, duodenum, or small bowel in 30 consecutive patients. All defects were over 8 x 4 cm in size and involved 30 to 80% of the circumference of the bowel wall. Each defect was deep enough to expose the thin mucosal layer, with the intestinal content visible through it. These defects could have been successfully treated by resection or repair using a serosal or mucosal patch instead of FPG. After making sure that the mucosa associated with the defect was alive and not perforated, a patch of intact peritoneum with pre-peritoneal tissue from the lateral abdominal wall (slightly smaller than the defect) was superimposed, with the edges simply sewn to the margin of the defect.

RESULTS

All patients recovered uneventfully, with no untoward effects determined, even after long-term follow-up.

CONCLUSION

We believe that FPG provides a feasible, simple, effective, economic, and safe alternative for repair of severe seromuscular defects; potentially making it widely applicable in clinical practice.

Local mechanical anisotropy in human cranial dura mater allografts

Human cranial dura mater (CDM) allograft's success as a repair biomaterial is partly due to its high mechanical strength, which facilitates its ability to form water-tight barriers and resist high in-vivo mechanical loads. Previous studies on CDM allograft mechanical behavior used large test specimens and concluded that the allograft was mechanically isotropic. However, we have quantified CDM microstructure using small angle light scattering (SALS) and found regions of well-aligned fibers displaying structural symmetry between the right and left halves (Jimenez et al., 1998). The high degree of fiber alignment in these regions suggests that they are mechanically anisotropic. However, identification of these regions using SALS requires irreversible tissue dehydration, which may affect mechanical properties. Instead, we utilized CDM structural symmetry to estimate the fiber architecture of one half of the CDM using computer graphics to flip the SALS fiber architecture map of the corresponding half about the plane of symmetry. Test specimens (20 mm x 4 mm) were selected parallel and perpendicular to the preferred fiber directions and subjected to uniaxial mechanical failure testing. CDM allografts were found to be locally anisotropic, having an ultimate tensile strength (UTS) parallel to the fibers of 12.76 +/- 1.65 MPa, and perpendicular to the fibers of 5.21 +/- 1.01 MPa (mean +/- sem). These results indicate that uniaxial mechanical tests on large samples used in previous studies tended to mask the local anisotropic nature of the smaller constituent sections. The testing methods established in this study can be used in the evaluation of new CDM processing methods and post-implant allograft mechanical integrity.

Comparative study of lyophilized human dura mater and lyophilized bovine pericardium as dural substitutes in neurosurgery

In a prospective, controlled randomized study either lyophilized bovine pericardium or lyophilized human dura mater have been used as a patch for the closure of the dura in 102 patients. The aim of this investigation was to compare both materials in terms of immunogenic response of the patients. The rate of post-operative complications was comparably low in both groups (wound infection in 1/51 patients each). In regard of workability, thickness of the material and flexibility the pericardium patches were judged to be by far superior. Neither signs of a cellular nor of an intesified humoral response could be detected in patients who received the pericardium implants. Thus, lyophilized bovine pericardium seems to be a superior alternative for the surgical repair of dural defects.