AJR 2005; 184:475-480
© American Roentgen Ray Society
Distinguishing Gelatin Bioabsorbable Sponge and Postoperative Abdominal Abscess on CT
Kumaresan Sandrasegaran1,
Chandana Lall1,
Arumugam Rajesh2 and
Dean T. Maglinte1
1 Department of Radiology, Indiana University School of Medicine, 550 N
University Blvd., Indianapolis, IN 46202.
2 Department of Radiology, University Hospitals of Leicester NHS Trust,
Leicester General Hospital, Leicester, United Kingdom LE5 4PW.
Received January 20, 2004;
accepted after revision May 17, 2004.
Address correspondence to K. Sandrasegaran
(ksandras{at}iupui.edu).
Abstract
OBJECTIVE. The objective of our study was to differentiate the CT
findings of gelatin bioabsorbable sponges used as hemostatic agents from
postoperative abdominal abscess.
CONCLUSION. Gelatin absorbable sponge may mimic a postoperative
abscess on CT. Findings that may help differentiate the hemostatic agent from
abscess include linear arrangement of tightly packed gas bubbles, fixed
position of gas bubbles on subsequent examinations, shape, lack of
air–fluid level, and lack of enhancing wall.
Introduction
With the increasing number of surgical innovations, the radiologist is
often faced with postoperative CT examinations for which the findings can be
difficult to interpret. To differentiate between postoperative complications
and the expected postsurgical appearance, the radiologist must be aware of the
surgical technique. Hemostatic agents have been used for many years to help
control intraoperative bleeding. These bioabsorbable agents are intentionally
placed in the surgical field, unlike nondegradable sponges that may be left
inadvertently during surgery. In most cases, the bioabsorbable agents blend
with tissue in the surgical bed and are not differentiated from postsurgical
scar on CT scans. However, we have seen several cases in which bioabsorbable
gelatin sponge (Gelfoam, Pharmacia) used for intraoperative hemostasis was
misdiagnosed as postoperative abscess on CT. To our knowledge, the initial and
follow-up CT appearances of gelatin bioabsorbable sponge have not been
addressed in the radiology literature. We present the CT findings in 18
patients in whom this hemostatic agent was used in a variety of surgical
procedures.
Materials and Methods
A retrospective search of reports of abdominal CT examinations performed at
our institution between December 2002 and September 2003 revealed 23 patients
with suspected presence of gas-containing foreign body in the surgical field.
The surgical notes mentioned the use of gelatin absorbable sponge during
operation in 15 of these patients. In the operative reports for two patients
who had undergone liver transplantation, the use of hemostatic agents was not
mentioned. The operating surgeon confirmed that gelatin bioabsorbable sponge
was routinely used for securing hemostasis. In one patient, who was
transferred from an outside institution after undergoing hysterectomy for
cervical cancer, the operative notes were not available. However, the
admitting records made note of considerable problems with intraoperative
hemorrhage in this patient. These 18 patients formed the study group. Five
patients were excluded from the study because we were unable to obtain
supportive data for the intraoperative use of hemostatic agents.
CT studies were performed using a 4-MDCT scanner (Mx8000, Philips Imaging),
a 16-MDCT scanner (IDT, Philips Imaging), or a 2-slice scanner (CT Twin,
Philips [formerly Elscint]). Contrast medium was given orally on the initial
CT examination in 17 patients (500–750 mL of 2% diatrizoate meglumine,
Gastrografin, Bracco). Contrast medium was given IV to all patients (150 mL of
iopamidol, Isovue-300, Bracco). The effective slice width was 6.5 mm for the
2-slice scanner and 5 mm for the MDCT scanners with longitudinal
reconstructions of 3 and 2.5 mm, respectively.
The CT images were reviewed by two abdominal radiologists to confirm the
presence of low-density material at the operative bed (density, 
–100
H). The size, shape, Hounsfield density, homogeneity, presence of
air–fluid levels, and appearance of surrounding fat were recorded by the
radiologists blinded to the postoperative course of the patients. Soft-copy
images were viewed on an MxView Station (Philips Imaging). The clinical
findings in all patients were reviewed from the hospital information system.
Patient demographics, type of surgery, date of operation, and postsurgical
progress were recorded.
Results
The study group was composed of seven men and 11 women with mean age of
56.2 years (range, 45–84 years). The types of surgery performed in these
patients are given in Table 1.
The initial postoperative CT examinations were performed between 1 and 29 days
after surgery (mean, 9.4 days) and were performed to assess for postoperative
complications. Eleven patients underwent a total of 16 follow-up CT
examinations performed 4–156 days after surgery. Thirty-four initial and
follow-up CT examinations were reviewed.
On the initial CT examinations, the size of the gelatin sponge ranged from
1.5 to 7.4 cm (mean, 3.2 cm). The density of the sponges measured from
–104 to –458 H, with a mean of –245 H. The overall density
of gelatin sponges was between that of gas and fluid. The shape of the sponges
was variable. In eight patients, the sponge appeared predominantly polygonal,
principally as rectangular strips (Fig.
1A,
1B,
1C). In 10 patients, the sponge
was predominantly rounded (Fig.
2A,
2B). In all patients, the gas
bubbles within the sponge were tightly packed and were not dispersed randomly
(Fig. 3). No intervening fluid
or soft-tissue density was present between gas pockets. The gas pockets within
the gelatin sponge were uniform in size without discrete dominant bubbles.
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Fig. 1A. —CT images show gelatin bioabsorbable sponge. Axial CT images
of 45-year-old woman who had cystectomy and creation of Hartmann's pouch show
lower pelvis. These images, which were obtained using soft-tissue (A)
and lung (B) window settings, show gas-filled structure with stripelike
configuration (arrow), which is consistent with gelatin bioabsorbable
sponge.
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Fig. 1B. —CT images show gelatin bioabsorbable sponge. Axial CT images
of 45-year-old woman who had cystectomy and creation of Hartmann's pouch show
lower pelvis. These images, which were obtained using soft-tissue (A)
and lung (B) window settings, show gas-filled structure with stripelike
configuration (arrow), which is consistent with gelatin bioabsorbable
sponge.
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Fig. 1C. —CT images show gelatin bioabsorbable sponge. Axial CT image
of mid abdomen of 55-year-old man after undergoing orthotopic liver
transplantation shows typical linear stripelike appearance of gelatin
bioabsorbable sponge (straight arrow). High-attenuation fluid
collection (curved arrow) surrounds sponge. Patient did not have
clinical or laboratory evidence of infection. Appearances are suggestive of
intraoperative hematoma.
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Fig. 2A. —51-year-old man who underwent partial right nephrectomy for
renal carcinoma. CT images obtained using soft-tissue (A) and lung
(B) window settings show rounded gas pockets in gelatin bioabsorbable
sponge (arrow). Note that Gelfoam (Pharmacia) has Hounsfield density
between that of fat and air.
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Fig. 2B. —51-year-old man who underwent partial right nephrectomy for
renal carcinoma. CT images obtained using soft-tissue (A) and lung
(B) window settings show rounded gas pockets in gelatin bioabsorbable
sponge (arrow). Note that Gelfoam (Pharmacia) has Hounsfield density
between that of fat and air.
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Fig. 3. —47-year-old woman who underwent total abdominal hysterectomy
and bilateral salpingo-oophorectomy for infarcted myoma. CT image depicts
fluid collection with enhancing rim (curved arrow), which is
suggestive of abscess. Patient had fever, and purulent material subsequently
was aspirated from collection. On anterior aspect of abscess is a gelatin
bioabsorbable sponge (straight arrow). Unlike gas bubbles in abscess,
which are discrete and rounded (arrowhead), gas pockets within
gelatin bioabsorbable sponge are tightly packed.
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Five patients in the series had clinical and CT evidence of infection at
the operative site. In four of these five patients, a drainage catheter was
placed and purulent material was aspirated. These patients showed the presence
of a well-defined low-density region, the hemostatic sponge, surrounded by
fluid (Fig. 3). One of these
five patients had a low-grade fever (up to 39.5°C), and hemorrhagic fluid
was detected at aspiration. Results for the fluid and blood cultures were
negative in this patient.
A gelatin sponge was visible on all follow-up CT scans obtained less than
38 days after surgery. The sponge was not seen on scans obtained 56, 74, and
156 days after surgery. In all patients with serial CT examinations, the
gelatin sponge was smaller on subsequent scans. This change is best
illustrated in a patient who had three CT examinations at postoperative day 6,
15, and 22 (Fig. 4A,
4B,
4C). The gas pockets in the
gelatin sponge maintained their close spatial arrangement without dispersion
on subsequent scans (Fig. 5A,
5B). This appearance was
disparate from that of abscesses in which discrete gas bubbles were seen in
different and random positions relative to each other on follow-up
examinations.
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Fig. 4A. —45-year-old woman who underwent cystectomy. Axial CT images
of lower pelvis obtained on postoperative days 5 (A), 15 (B),
and 26 (C) show gradual resorption of gelatin bioabsorbable sponge
(arrow).
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Fig. 4B. —45-year-old woman who underwent cystectomy. Axial CT images
of lower pelvis obtained on postoperative days 5 (A), 15 (B),
and 26 (C) show gradual resorption of gelatin bioabsorbable sponge
(arrow).
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Fig. 4C. —45-year-old woman who underwent cystectomy. Axial CT images
of lower pelvis obtained on postoperative days 5 (A), 15 (B),
and 26 (C) show gradual resorption of gelatin bioabsorbable sponge
(arrow).
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Fig. 5A. —52-year-old man who underwent partial left nephrectomy.
Serial CT scans show reabsorption of gelatin bioabsorbable sponge
(arrows). Despite resorption, tightly packed gas configuration is
maintained without bubbles dispersing.
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Fig. 5B. —52-year-old man who underwent partial left nephrectomy.
Serial CT scans show reabsorption of gelatin bioabsorbable sponge
(arrows). Despite resorption, tightly packed gas configuration is
maintained without bubbles dispersing.
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Discussion
Bioabsorbable hemostatic agents are commonly used to stop intraoperative
bleeding that is not controlled by cautery or suture ligation. Types of
surgery in which gelatin absorbable sponge is used in our institution include
vascular surgery, transplantation, hysterectomy, and partial nephrectomy.
Gelatin bioabsorbable sponge also has been used extensively as an
intravascular embolization agent. In this article, we deal with surgically
placed and not catheter-injected gelatin bioabsorbable sponge. The four
commonly used hemostatic agents are collagen sponges, gelatin sponge
(Gelfoam), oxidized regenerated cellulose (Surgicel, Johnson and Johnson
Medical), and microfibrillar collagen
[1].
Gelatin bioabsorbable sponge is a purified porcine skin product that is
water-insoluble. It aids in rapid hemostasis by forming an artificial clot and
by its physical property of providing a mechanical matrix for platelet
aggregation. Gelatin absorbable sponge contains numerous gas pockets that are
not displaced immediately by interstitial body fluids. The presence of a
gas-containing structure on early postoperative scans raises the possibility
of abscess. It is interesting to note that researchers of original CT studies
mentioned the presence of a gas-containing structure consistent with an
abscess in 27 of the 34 scans. In 14 cases, the possibility of hemostatic
agent was raised; such cases were the more recent studies when our
radiologists became more aware of the CT appearances of gelatin sponge.
Our results show that it is possible to differentiate between these
entities using CT. Gas pockets in gelatin sponge are packed tightly and are
not discrete. They often are lined up in a linear fashion. Air–fluid
levels, which typify abscess, usually are not seen in gelatin sponge without
coexisting infection. Rim enhancement of the gelatin sponge generally is not
seen in the absence of coexisting abscess, although rare exceptions occur. In
one of 14 patients who did not clinically exhibit any signs of infection, the
site of gelatin bioabsorbable sponge packing showed rim enhancement. The CT
examination was performed 12 days after surgery. It is not clear if the
enhancement was due to a foreign-body reaction or if there was subclinical
infection.
Gelatin sponge usually is cut in geometric shapes to be placed against the
bleeding surface during surgery; its shape may help differentiate it from an
abscess. Follow-up CT examinations can reveal useful information. The gas
bubbles in gelatin bioabsorbable sponge maintain their spatial position, which
would be unusual in an abscess. CT performed for up to 38 days after surgery
shows the sponge as a predominantly gas-containing structure. Over time, blood
and interstitial fluid penetrate the sponge and a more homogeneous appearance
of soft-tissue rather than gas-containing structure is seen.
The presence of gelatin sponge does not preclude an abscess, and the two
can coexist. As seen in some of our cases, a well-defined geometric-shaped
gas-containing structure within a fluid collection may be seen. Other CT
findings of abscess such as scattered discrete large gas bubbles, rim
enhancement, and air–fluid levels may be seen in this collection.
Surgical sponges are made of materials such as cellulose that do not become
oxidized. They are nonabsorbable and must be removed from the surgical field
[2]. In contrast, gelatin
sponges are absorbed eventually and are left intentionally in the surgical
field after surgery to continue to function as a hemostatic agent. The
mechanism of absorption is not clear. Macrophages have been implicated in the
absorption of other bioabsorbable hemostatic agents
[3]. Of the eight patients for
whom we had serial CT examinations, gelatin bioabsorbable sponge was seen as
an identifiable structure on CT for up to 38 days after surgery. Our review
shows that eventually gelatin sponges become resorbed at a reasonably rapid
pace after the first week of surgery.
The use of hemostatic gelatin sponge is not without complications. The
incidence of infection, which may be due to presence of a foreign body or
superinfection of hemorrhage, is increased. In our series, 22.2% of the
patients had superadded infection. Foreign-body granulomas can occur with
excess use of gelatin sponges, particularly in the cranial cavity
[4–6].
Neurologic dysfunction including quadriparesis may be caused by the use of
these agents in the spinal canal
[7]. Toxic shock syndrome has
been reported after nasal surgery in which bioabsorbable gelatin sponges were
used [8,
9].
A literature review reveals sparse information about the CT appearances of
these hemostatic agents. Two groups have reviewed the CT examinations of a
total of six patients [10,
11] who had hemostasis
achieved with the use of oxidized cellulose (Surgicel) during neurologic and
abdominal surgery. Like our findings, their findings suggest that linear
arrangement of gas bubbles that maintain their position on subsequent scans
should raise the possibility of hemostatic agents in contradistinction from
abscess. It is probable that the CT findings seen with gelatin absorbable
sponges are common to other hemostatic bioabsorbable agents. In a case report,
researchers suggested the use of indium-labeled WBC scanning to differentiate
a sterile mediastinal air collection associated with the use of a gelatin
bioabsorbable sponge from abscess in a patient after aortic surgery
[12]. However, careful
evaluation of the CT findings can help differentiate gelatin sponge from
abscess in most cases. We believe that such an analysis and a review of
operative notes or consultation with the referring surgical team could prevent
unnecessary antibiotic therapy or drainage catheter placement.
We are aware of the limitations of our study. The study was retrospective
and depended on postoperative CT examinations reporting a foreign body
containing gas. Many patients with the appropriate CT examinations probably
were not included in this series. It is our experience that the gelatin sponge
frequently is mistaken for abscess. Indeed, in many patients, the CT images
from a second or third examination raised the possibility of gelatin sponge
when the finding had been overlooked or misinterpreted on the initial CT
examination. Consequently, the number of patients in this series was modest.
Only a proportion of patients in our series had serial CT examinations to
assess the natural history of gelatin sponge; it would not have been ethical
to perform additional examinations without clinical need. Nevertheless, we
were able to describe the CT features of gelatin absorbable sponge and
determine criteria that may help in differentiation from postoperative
abscess.
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Abstract
Introduction
