Imaging visceral adhesion to polymeric mesh using pneumoperitoneal-MRI in an experimental rat model

Can magnetisation transfer magnetic resonance imaging help for the follow-up of synthetic hernia composite meshes fate? A pilot study

PURPOSE

This study aims at evaluating the non-invasive Magnetic Resonance Imaging (MRI) technic to visualize a synthetic composite hernia mesh using a rodent model and to document the integration of this device over 4 months.

METHODS

Uncoated polyethylene terephthalate mesh and synthetic composite mesh-faced on the visceral side with a chemically engineered layer of copolymer of glycolide, caprolactone, trimethylene carbonate, and lactide to minimize tissue attachment-were placed intraperitoneally in rats, facing the caecum previously scraped to promote petechial bleeding and subsequent adhesions. Meshes fate follow-up was performed 4, 10, and 16-weeks post-implantation using a rodent dedicated high field MRI. Magnetization transfer (MT) images were acquired, associated with pneumoperitonealMRI performed after intraperitoneal injection of 8 mL gas to induce mechanical stress on the abdominal wall.

RESULTS

Uncoated meshes were clearly visible using both T2-weighted and MT imaging during the whole study while composite meshes conspicuity was not so evident on T2-weighted MRI and could be improved using MT imaging. Adhesions and collagen infiltration were massive for the uncoated meshes as expected. On the contrary, composite meshes showed very limited adhesion, and, if any, occurring at the edge of the mesh, starting at the fixation points.

CONCLUSIONS

Magnetization transfer imaging allows to detect mesh integration and, associated with pneumoperitoneum, was able to probe the effective minimizing effect of the synthetic polymeric barrier on visceral attachments. However, magnetization transfer imaging could not unambiguously allow the visualization of the mesh through the polymeric barrier.

Tissue microarray technology and collagen evaluation to analyze surgical trauma performed with usual blade or ultrasonic harmonic scalpels in rats

PURPOSE

To compare wound healing performed with cold blade (CSB) and ultrasonic harmonic scalpel (UHS) in the abdominal aponeurosis of rats.

METHODS

Eighty Wistar rats divided into two groups and underwent midline incision in the linea alba with cold blade and harmonic ultrasonic scalpel. Analysis were performed in subgroups of 10 animals after 3, 7, 14 and 21 days. Macroscopically was observed the presence of hematoma, infection, wound dehiscence, fistula and adherences. Microscopically were used collagen and immunohistochemical staining methods.

RESULTS

Macroscopic, complications showed no statistical difference. Immunohistochemical analysis for MMP-9 was more intense in UHS group (p<0.05). TGF β presented its lower expression in UHS group at 14 and 21 days, with no statistical difference at 3 and 7 days (p<0.05). α-AML expression appeared higher in UHS group after 14 days and remained similar in others (p<0.05). Collagen deposition had no change in type I, and increased in type III in UHS; at 7th day the deposition was higher in CSB group; at 14th was similar in both groups (p<0.001).

CONCLUSION

UHS compared to the CSB has higher lesion area at the time of the incision; as well as it led to the delay of regeneration and scar maturation process.

Impairment of the Peritoneal Surface as a Decisive Factor for Intestinal Adhesions in Intraperitoneal Onlay Mesh Surgery - Introducing a New Rat Model

BACKGROUND

Meshes implanted intraperitoneally are known to cause adhesions potentially resulting in complications such as chronic pain, enterocutaneous fistula, or mesh infection. This study introduces a model for investigation of intestine-to-mesh adhesions and evaluates as to whether missing of visceral peritoneum is causative.

METHODS

In 18 rats, rectangular 1.5 x 2 cm patches of an uncoated polypropylene mesh (Ultrapro(®)) were sewn to the inner abdominal wall next to the cecum. Additionally, a meso-suture ensured contact between cecum and mesh. Rats were assigned to 2 groups: in 8 rats the peritoneum was left intact, in 10 the cecum was depleted from peritoneum with abrasion. Sacrifice was on day 7. Macroscopic evaluation used two adhesion scores. Specimens were evaluated microscopically, statistical analyses employed student's t-test.

RESULTS

On day 7, rats with mesh implantation combined with locally de-peritonealization by cecal abrasion mostly showed severe cecum-to-mesh agglutination (mean Lauder score 92%, mean total Hoffmann score 90%), whereas meshes of most animals without cecal abrasion only had some coverage with intraabdominal fat (33%, 24%; p = 0.0002). Histological work-up showed adequate wall ingrowth of mesh in all rats. In animals with cecal abrasion, meshes were mostly adhesive with cecal wall. However, when the peritoneum of cecum was unimpaired, abdominal wall above the mesh as well as cecum usually revealed sub-peritoneal tissue and a mono-layer cell coverage as seen in normal peritoneum.

CONCLUSION

This study introduces a model mimicking a clinical situation of e.g. hernia repair by intraperitoneally implanted meshes when mesh has contact with normal and with de-peritonealized intestine. The model might be useful for testing mesh types and coatings as well as other devices for their efficacy in adhesion prevention. The high adhesion scores of rats with local de-peritonealization compared with the low scores of animals with intact peritoneum indicate that the integrity of intestinal peritoneum is a decisive factor for adhesion formation.