In such cases, remesothelialization still occurs, but the mesothelial cells cover the adhesion as well as the normal tissue surfaces, forming adhesive bands and other types of connections between opposing serosal tissue surfaces. Angiogenesis then occurs as the hypoxic tissue in the adhesion sends signals (such as vascular endothelial growth factor) in an attempt to reestablish a supply of oxygen and nutrients to the injured and devascularized tissues. Subsequently, as the tissue remodels, there is a propensity for the adhesion to become more vascular and denser.
Understanding this process is important because the products currently available for reducing adhesions act as barriers during this critical period of remesothelialization, keeping peritoneal surfaces apart and minimizing the potential development of a fibrinous mass that bridges tissue surfaces. If an adhesion does not form during the 3–5-day period of remesothelialization, it is theorized that there will not be any adhesion development — unless there's new injury to the tissue surfaces.
Once an adhesion forms, however, it has acquired a particular “adhesion phenotype” — different from that of normal peritoneum — that appears to be irreversible. This is likely why it is so difficult to prevent adhesion reformation after adhesiolysis. Rates of adhesion reformation — even in the best of surgical hands — run between 80% and 90%, compared with a 50% chance of de novo adhesion development after surgery (at new sites of injury).
The identification of an adhesion phenotype came originally from comparisons of normal peritoneal and adhesion tissues harvested from the same patient, and were later confirmed in cell culture studies in which normal peritoneal fibroblasts were subjected to hypoxia (2% O2 conditions). Fibroblasts cultured under hypoxic conditions were subsequently found to have developed particular molecular biologic characterizations that are different from those of normal peritoneal fibroblasts.
When exposed to normal amounts of oxygen again, the fibroblasts did not go back to being normal fibroblasts — they continued to manifest the adhesion phenotype (J. Am Assoc. Gynecol. Laparosc. 2004;11:307–14). These findings have been confirmed in animal and human studies, and such relationships have also been identified in other peritoneal tissue types such as mesothelial cells and macrophages.
Further research on the pathogenesis of adhesions and the molecular biologic differences between normal peritoneum and adhesions may allow identification of which patients, and which sites within a patient, are most at risk for adhesion development, as well as the discovery of new ways to reduce the development of postoperative adhesions and their clinical sequelae.
It is possible that a future generation of barrier products not only will work as a barrier separating surfaces prior to remesothelialization, but will also have local biologic effects — delivering adhesion-reducing drugs or biologics, for instance, to specific localized tissue sites. A personalized approach to adhesion prevention also might be possible, with particular factors deemed to increase adhesion risk in individual patients (a deficiency of plasminogen activator, for instance) being corrected.
In the meantime, as we've learned more about the pathophysiological state under which adhesions develop, we have found that adhesion development may occur faster than we had thought. In one recent rodent study, we identified postoperative tissue attachments as early as 2 hours after cecal abrasion. We noted considerable local edema and vessel dilatation within 2 hours of injury, angiogenesis and fibrin deposition at 8 hours, and cell proliferation at 24 hours (Fertil. Steril. 2010;93:2734–7). And interestingly, recent studies in mice have shown that laparoscopic insufflation per se can induce peritoneal adhesions, with the adhesions increasing proportionally with both increasing duration of insufflation and an increase in intraperitoneal pressure.
Prevention in Practice
During the past decade a variety of surgical adjuvants — from procoagulants and fibrinolytic agents to anti-inflammatory drugs and antibiotics — have been investigated for use in reducing the occurrence, extent, and severity of adhesions. Unfortunately, most approaches seemingly have been futile. Some products have shown trends toward efficacy in animal or early human studies and need further investigation.
The three synthetic products that are approved by the Food and Drug Administration—Gynecare Interceed, Seprafilm, and Adept — can help reduce postoperative adhesions after gynecologic procedures, and should be considered as potentially useful surgical adjuvants. A meta-analysis of studies of Gynecare Interceed, for instance, found that approximately twice as many operative sites were adhesion free after use of the barrier than after surgery alone (J. Reprod. Med. 1999;44:325–31).
Gynecare Interceed (Johnson & Johnson) and Seprafilm (Genzyme) are approved for use only at laparotomy, while Adept (Baxter International), an icodextrin solution that disperses throughout the abdominopelvic cavity, is approved for use only in laparoscopic surgery.