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DISCUSSION
A provocative finding was that adhesion formation did not
progress after day 7. Any area of mesh surface free of adhesions
then remained so thereafter. The uninvolved surface was shiny
and translucent. These observations indicate that an adhesion-resistant
intraabdominal surface develops on polypropylene mesh within
a week of installation. One might speculate that fairly short-lived
protection by mechanical separation or biochemical inhibition
could result in permanent freedom from adhesions between prosthetic
mesh and abdominal viscera. Along the same lines, the adhesiolysis
study suggests that if one were to mechanically break down adhesions
to prosthetic mesh after 7 days, they would likely not reform.
Such is not the case when visceral adhesions to injured peritoneum
are divided. Both clinical and experimental
observations indicate that subsequent to such lysis newly formed
adhesions are often more extensive than the original.12,13
Laparoscopic findings of progression of adhesions up to day
7 and a stable adhesion-resistant surface thereafter correlates
with the scanning electron microscopic findings of a mesothelial
cell coating, which is not complete until then.
That mesothelial cells prevent adhesions
is well documented.14-16
Human omental mesothelial cells in vitro produce hyaluronic acid.14
Jones and colleagues14 noted that ovarian cancer cell adherence
in multiwell plates was prevented by a confluent mesothelial
cell culture. The content of hyaluronic acid in the medium was
found to be elevated. After hyaluronidase pretreatment the blocking
of adhesions was abrogated.
Whitaker and associates15 reported that a pure culture of
mesothelial cells was able to induce fibrinolysis. Another study16
suggested that the mesothelial fibrinolytic properties are associated
with the secretion of tissue plasminogen activator. These results
likely explain the observation that once the polypropylene mesh
surface is populated with mesothelial cells it remains resistant
to new adhesions.
In a relevant study by Raftery,13 a parietal peritoneal defect
was surgically created. Sequential transmission electron microscopy
was used to study healing. On postoperative day 3 a "primitive
mesenchymal cell" appeared on the surface. On day 4 these
cells were seen to have some microvilli. By day 5 mesothelial
cells with mature microvilli were identifiable. By day 8 and
later a complete layer of mesothelial cells covered the defect.
The new mesothelium was believed to arise from subperitoneal
connective tissue, whether from primitive mesenchymal cells or
from fibroblasts was uncertain.13 These observations are in agreement
with the time course of mesothelial cell coverage of prosthetic
mesh observed in the present study.
Time of observation: sequential laparoscopy versus sacrifice
Adhesion formation is a dynamic process and sequential evaluation
over an extended period of time provides important information.
We found that peritoneoscopy could be undertaken at any chosen
interval after placement of the prosthesis, allowing repeated
in vivo observations of adhesion development. Information with
respect to angiogenesis and blood flow in the microvasculature
can be assessed nicely with the high magnification obtained at
laparoscopy. The early time course, site, and progression of
adhesion formation can be determined only with repeated in vivo
visualization. Such ongoing changes are impossible to appreciate
by single observations at sacrifice. Because variations occur
among subjects, sacrifice with a single observation time and
averaging the results is less meaningful than laparoscopic observations,
where each animal provides multiple data points.
The extent of adhesions may be underestimated at necropsy
exam. The thin transparent omental membrane once firmly incorporated
onto the mesh may be recognized as an adhesion only if previously
observed during early stages of attachment.
In conclusion, evaluation of intraabdominal adhesions to prosthetic
mesh is best accomplished by means of sequential laparoscopy
with each animal serving as its own control. Adhesions are already
present 24 hours after operation. The area involved progresses
during the first week. Segments of prosthetic mesh surface free
of adhesions at 7 days remain uninvolved thereafter. The development
of an adhesion-resistant surface coincides with formation of
a confluent mesothelial cell coating. After mechanical separation
(adhesiolysis), very few new adhesions form between abdominal
viscera and prosthetic mesh. In this model, omentum has a greater
propensity to adhere to mesh than does intestine and tends to
attach first at the mesh abdominal wall interface.
Introduction
| Methods
| Results
| Discussion | References
JACS |
