|
RESULTS
Single observations at sacrifice: omentectomy and abdominal
wall resection
In the absence of omentum, adhesions to the mesh were significantly
fewer with or without abdominal wall resection than if omentum
had been preserved. When the omentum was present, adhesions were
far more prevalent if the abdominal wall had been resected. The
most extensive adhesion formation to the surgical mesh developed
with the combination of abdominal wall resection and intact omentum
(range 75% to 100%) (Table 1).
Laparoscopic observations
Adhesions previously seen laparoscopically were compared with
postmortem observations in the same animals. Necropsy observations
tended to underestimate adhesion area. Details such as the presence
of adipose cells, which identified adherent omentum, were seen
with laparoscopic magnification but could not be appreciated
at autopsy. The thin clear membranous omentum once adhered to
the mesh was difficult to recognize as an adhesion by a single
observation at necropsy but was readily identified by sequential
laparoscopy.
Adhesions tended to attach first to the mesh and abdominal
wall interface, then extended to cover larger areas of the mesh
surface. It was very unusual to see adherence to the central
surface without edge involvement.
At laparoscopy 24 hours after operation one could appreciate
tissue swelling and initial growth of microvessels along the
cut edge of the muscle. Some omental adhesions were invariably
present by 24 hours. Adhesion-free areas of mesh had a shiny
translucent surface. The interstices were sealed, as evidenced
by the fact that no injected intraperitoneal air escaped through
the mesh into the subcutaneous space, judged by inspection and
palpation. In some instances a seroma was already present in
the subcutaneous space contained there by the now relatively
impermeable mesh.
Three days after placement of the prosthesis, microvessels
could be seen growing onto the surface from the cut edge of the
peritoneum. By day 7, the area involved with adhesions had increased
compared with days 1 and 3. Blood vessels growing from the wound
edges toward the center of the prosthetic patch were beginning
to anastomose with omental vessels. Blood flow in small arteries
was generally from the abdominal wall toward the adhesions, but
in some animals bidirectional flow could be seen.
By day 14 edema and inflammation had subsided. There was no
change in the extent of adhesions as compared with day 7. Microvascular
anastomoses were more extensive.
On day 28 adhesions to the mesh were identical to those found
on days 7 and 14. Strands of polypropylene were readily visible
through the now translucent omentum (Fig. 1). At this time the
adhesions had become firmly fixed to the mesh. The initial erythema
and edema had disappeared. Wound contraction was evident from
the fact that the center of the mesh folded inward toward the
abdominal cavity and the original 2.5×2.5-cm abdominal
wall defect was now diminished in size.
Table 2 summarizes the laparoscopic estimations of
mesh area involved with adhesions. The most important observation
is that those areas free of adhesions on day 7 remained so on
subsequent examinations; that is, the adhesions did not progress.
Table 2. Percent of Polypropylene Mesh Area Covered by
Adhesions Estimated by Laparoscopy after Abdominal Wall Resection
with Preservation of Omentum
|
|
|
Observation day |
|
|
|
|
|
1 |
3 |
7 |
14 |
28 |
|
|
n |
7 |
4 |
25 |
23 |
23 |
|
Mean, % (range) |
58
(5–100) |
84
(67–100) |
91
(75–100) |
90
(75-100) |
91
(75–100) |
|
Light microscopy
Histologic preparations were difficult to obtain on day 1
because of weak attachment of the prosthetic fibers to the abdominal
wall. During processing the mesh separated from the fragile adhesions
and from the abdominal wall. Adequate histologic specimens were
first obtainable on day 3, at which time the fibers of the mesh
were seen to be coated by adhesions or by scattered cells, mostly
neutrophils and fibroblasts. Macrophages were more prominent
than on day 1. The samples did not yet demonstrate significant
collagen deposition as judged by polarizing microscopy of sirius
red stained samples.11
On day 7 inflammation was still present but the population
of neutrophils had decreased. Macrophages were prominent around
the polypropylene fibers (Fig. 2). Some fibroblasts were present
but little collagen had yet infiltrated between mesh fibers.
Figure 2. Histology of the abdominal wall with polypropylene
mesh. On days 1 and 3 inflammatory cells surround mesh fibers.
On day 7 inflammation is still present but the predominant cells
are macrophages. On day 28 most of the acute inflammation has
subsided and histiocytes are now prominent. Hematoxylin and eosin
stain, original magnification ×100.
Tissues harvested on day 28 had well-formed collagen interposed
between the threads, along with macrophages and fibroblasts.
The mesh was firmly incorporated into the abdominal wall by fibrous
tissue. At the intersection of the sutured junction collagen
was more abundant than at the center of the mesh (Fig. 3).
Figure 3. Distribution of collagen on day 28 shown
by polarizing microscopy. The density of collagen is maximal
at the muscle-mesh interface, seen as white to light gray. Arrows
point to the muscle wall prosthesis intersection. The holes left
behind by the individual mesh fibers after histologic preparation
are marked with asterisks. Picrosirius red stain, original magnification
×40.
Adhesions always involved omentum and sometimes intestine.
The bumpy adhesion-free surface seen at laparoscopy proved on
histology to represent mesh fibers surrounded by histiocytes
and fibrous tissue. The surface of the prosthesis facing the
abdominal cavity demonstrated a layer consistent with mesothelial
cells.
Scanning electron microscopy
On day 1 after operation, the polypropylene threads of the
mesh were bare, as seen at low magnification scanning electron
microscopy. Most of the polypropylene was directly exposed, with
no tissue coverage. Omentum was attached to the mesh-abdominal
wall interface with an abundant framework of fibrin. Fibroblasts
were present in small numbers. Leukocytes were apparent in the
spaces between the polypropylene threads. Few cells were attached
to the mesh fiber surfaces at this time. Mesothelial cells were
not yet identifiable.
On day 3 most of the surface of the polypropylene mesh was
covered by a thin layer of tissue. Fibroblasts had increased
since day 1, mostly in the crevices between mesh fibers. The
fibrin framework was more dense, and it extended onto the areas
free of adhesions. Still no mesothelial cells could be seen.
By day 5 the entire surface of the mesh was covered and mesothelial
cells had appeared (Figs. 4 and 5). Their characteristic microvilli
were relatively sparse.
Figure 4. Scanning electron microscopy of an adhesion-free
surface at low magnification on days 1, 3, and 5. On day 1 after
operation, the mesh fibers are readily seen with few attached
cells. The fibers are partially covered on day 3. On day 5 they
are completely coated with a cellular layer (original magnification
×30).
Figure 5. Scanning electron microscopy of the prosthesis
surface on days 7 and 28 after implantation. On day 7 the surface
of the mesh shows elevations corresponding to the polypropylene
fibers (original magnification ×25). Detail of this adhesion-free
area demonstrates the surface to be completely carpeted with
mesothelial cells (original magnification ×1,500). Depressions
are seen on the surface corresponding to the interstices of the
mesh (original magnification ×15). The surface on day 28
is covered with mesothelial cells as on day 7 (original magnification
×1,200).
By day 7 there were no bare polypropylene fibers. Leukocyte
infiltration had subsided. The surface of the mesh was covered
with a confluent carpet of mesothelial cells with abundant microvilli
(Fig. 5). The surface on day 14 was similar to that seen on day
7.
On day 28 the abdominal surface of the mesh and the holes
around the mesh fibers were covered by mesothelial cells (Fig.
5). Microvilli were more dense than on day 7. Macrophages were
seen adjacent to omental adhesions.
Adhesiolysis
One week after mesh installation at least 75% of the surface
was covered by adhesions. After mechanically separating the adhesions
from the mesh subsequent exams demonstrated only a few small,
newly formed adhesions. In 19 observations after day 21, no new
adhesions developed (Table 3).
Table 3. Percent of Mesh Area Covered by Adhesions after
Adhesiolysis
|
|
Day |
7 |
14 |
21 |
28 |
100 |
280 |
|
|
1 |
73% (3) |
7% (2) |
0% (0) |
6% (1) |
0% (0) |
0% (0) |
|
2 |
100% (3) |
25% (1) |
0% (0) |
0% (0) |
0% (0) |
0% (0) |
|
3 |
94% (3) |
– |
0% (0) |
0% (0) |
– |
– |
|
4 |
94% (3) |
– |
0% (0) |
0% (0) |
0% (0) |
0% (0) |
|
5 |
92% (2) |
0% (0) |
14% (1) |
0% (0) |
0% (0) |
0% (0) |
|
6 |
98% (2) |
0% (0) |
4% (1) |
0% (0) |
6% (–) |
6% (–) |
|
Mean |
92% |
4% |
3% |
1% |
1% |
1% |
|
Lysis was performed whenever adhesions were found. The percentages
represent the area of adhesions before lysis. Of the 21 exams
performed after the initial seventh day adhesiolysis, 17 showed
no further adhesions. Adhesiolysis scores are in parentheses:
0, no adhesions; 1, freed with inflation or scope tip; 2, required
grasper blunt dissection; and 3, required sharp dissection.
Introduction
| Methods
| Results | Discussion
| References
JACS |
