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1 Division of Abdominal Imaging and Interventional Radiology, Massachusetts
General Hospital, 55 Fruit St., Boston, MA 02114.
2 Department of Emergency Radiology, Massachusetts General Hospital, Boston, MA
02114.
Received March 5, 2004;
accepted after revision April 15, 2004.
Address correspondence to A. K. Singh.
Abstract
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MATERIALS AND METHODS. Fifty patients diagnosed with acute epiploic appendagitis seen on contrast-enhanced CT were included in this study. The CT scans of the epiploic appendagitis were evaluated for the presence of colon wall thickening, a focal fatty center, inflammatory changes, location in relationship to the colon, size, and presence or absence of central high density within the fat. In 10 patients, the initial findings were compared with findings of follow-up CT performed between 3 days-21 months after the first CT.
RESULTS. The most common part of colon involved by acute epiploic appendagitis was the sigmoid colon (31/50), and the most common position was anterior to the colonic lumen (41/50). All 50 patients with acute epiploic appendagitis had a central fatty core surrounded by inflammation. Colon wall thickening was present in only two, and a central high-density focus was noted only in 27 of 50 patients. In 86% (43/50) of patients, the fatty central core was between 1.5 and 3.5 cm in length. The changes seen on follow-up CT varied, including increased density with a decrease in the size of the fatty central core, no change, complete resolution of findings, and minimal residual density.
CONCLUSION. On CT, acute epiploic appendagitis has a predictable appearance in terms of location, size, and density. The most common finding on CT is a fat-density oval lesion with surrounding inflammation on the anterior aspect of the sigmoid colon. The changes on CT are not predictable in the 2-week to 6-month window.
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Because of the benign self-limited course of this condition, it is important to recognize and understand its various manifestations. Only a few case series in literature describe the CT features of acute epiploic appendagitis [2, 4-12]. In this study, we evaluated the spectrum of CT features of acute epiploic appendagitis and determined the incidence of various imaging features associated with this condition. We also describe the evolutionary changes of acute epiploic appendagitis seen on serial follow-up CT imaging, when available.
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CT Technique
The contrast-enhanced CT was performed using a helical CT scanner (HiSpeed,
LightSpeed, GE Healthcare; Somatom, Siemens Medical Solutions). All 50
patients underwent contrast-enhanced CT after IV injection of 140 mL of
nonionic contrast material (300 mg I/mL) at a rate of 2-3 mL per second. The
CT slice thickness for the abdominal and pelvic scans was 5 mm; the pitch was
1.5. The images were available for interpretation on an Impax DS3000 SP4SU2
PACS workstation (AGFA Technical Imaging Systems).
CT Evaluation
Two board-certified radiologists who were blinded to each other's
interpretations evaluated all 52 CT scans. Two of 52 patients were excluded
from the final core group as described previously. In case of lack of
consensus between the two radiologists, a third radiologist was involved in
the final CT interpretation.
CT and Laboratory Findings
The CT scans of the epiploic appendagitis were evaluated by the
radiologists for the presence of colon wall thickening, focal fatty center,
inflammatory changes, location in relation to the colon (anterior, posterior,
cranial, caudal, medial, or lateral), size (< 1.5 cm, 1.5-3.5 cm, > 3.5
cm), and presence or absence of central high density within the fat. The
presence or absence of leukocytosis was also noted.
Follow-Up CT
The two radiologists also interpreted the follow-up CT scans available for
10 of the 50 patients. The time between the initial and follow-up CT ranged
from 3 days to 21 months. The improvement in CT features over time was
documented and correlated with the length of time between the acquisitions of
the two CT scans. The clinical characteristics in four of the 50 patients were
presented in a previous report
[8].
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The two radiologists were in agreement regarding the final diagnosis of acute appendagitis in 49 of the 52 initial cases. In three patients for whom there was lack of agreement between the other two radiologists, the interpretation of a third radiologist who was aware of the interpretations of the two radiologists was used to diagnose an acute appendagitis, omental infarct, and a chronic torsed appendix epiploica.
Location
The most common part of the colon affected by acute epiploic appendagitis
in decreasing order of frequency was the sigmoid colon (n = 31),
descending colon (n = 9), cecum (n = 6), and ascending colon
(n = 4) (Figs. 1 and
2). The most common positions
of inflammatory changes in relationship to the colonic lumen, in descending
order of frequency, were anterior (n = 41), lateral (n = 4),
inferior (n = 3), and medial (n = 2). No patients had acute
appendagitis in the hernial sac.
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Size
In five patients, the size of the fatty central core was greater than 3.5
cm. The largest fatty central core measured 5.8 cm in a 32-year-old man with
right upper quadrant pain. The size of the fatty central core was between 1.5
and 3.5 cm in 43 (86%) of the 50 patients. In the remaining two patients, the
central fatty core was less than 1.5 cm in long-axis diameter.
Morphology
A fatty central core abutting the colon wall with surrounding inflammatory
changes and a base narrower than the equator was documented on CT in all 50
patients. The fatty attenuation centers were visible in all patients on
soft-tissue window settings (width, 350 H; level, 50 H), without the use of an
attenuation coefficient in the region of interest. The CT finding of a central
high-density dot, irregular or linear focus, was noted in 27 (54%) of 50
patients (Figs. 3 and
4).
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Colon Wall
The colon wall had normal thickness in most patients
(Fig. 5) and was considered
thickened in only two patients who had acute epiploic appendagitis adjacent to
sigmoid and cecal walls.
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Evolutionary Changes
In 10 patients, follow-up CT scans were available for comparison over a
period of 3 days-21 months. In six patients in whom the follow-up CT scan was
obtained within 6 months of the primary CT scan, an abnormality was detected.
The residual abnormality in these six patients ranged from no change (in two
patients in whom the second CT was performed within 2 weeks of the acute
presentation) to the following changes: decrease in size of the fatty core
with increase in the overall density (n = 1), decrease in size only
(n = 1), increase in overall density only (n = 1), and mild
residual stranding density in the mesocolon (n = 1) (in four patients
in whom the follow-up CT was performed between 2 weeks and 6 months). In the
four patients with the follow-up CT performed more than 6 months after the
first CT, no residual abnormality was noted. The CT changes between 2 weeks
and 6 months did not correlate with the time elapsed since the acute
presentation; however, all CT scans obtained 6 months after the acute
presentation showed complete resolution of the CT findings.
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Patients with epiploic appendagitis most commonly present with localized abdominal pain, more commonly on the left. The presenting clinical symptoms of epiploic appendagitis are nonspecific, leading to clinical misdiagnosis in most patients. In the study by van Breda Vriesman et al. [11], acute appendagitis was included in the clinical differential diagnosis in only two of 49 patients.
In the absence of evaluation by radiology, these patients are often diagnosed with acute diverticulitis or appendicitis. The misdiagnoses on radiology of primary epiploic appendagitis can lead to unnecessary hospitalization and treatment [13]. The clinical management of acute appendagitis includes conservative treatment with pain medication.
The differential diagnosis of an inflammatory fatty lesion on CT includes acute epiploic appendagitis, mesenteric panniculitis, acute diverticulitis, trauma, or an omental neoplasm such as a liposarcoma. Although an omental infarction can have an appearance similar to that of epiploic appendagitis, it lacks the hyperdense ring that is seen in epiploic appendagitis. The CT features of omental infarction typically consist of a right lower quadrant well-circumscribed nonenhancing oval soft-tissue mass that is located deep relative to the anterior abdominal muscles. In our series, one case of omental infarction among the initial 52 cases was misinterpreted as acute appendagitis. CT evaluation in this patient showed a mixed-density fatty mass in the right lower quadrant, which was unusually large for a torsed appendix epiploica.
To our knowledge, this study describes one of the largest series of patients with acute epiploic appendagitis in the radiology literature. The most common CT appearance of acute epiploic appendagitis, as was seen in our study, was the presence of 1.5- to 3.5-cm-diameter fat-density lesion with surrounding inflammatory changes abutting the anterior wall of the sigmoid colon. Involvement of the proximal colon is less common, although not unusual (Fig. 6). Although the presence of a central high-attenuation focus within the fat is a helpful finding in making the diagnosis, its absence does not exclude the diagnosis of acute epiploic appendagitis. The high-density central focus within the fat was noted in only 54% (27/50) of the patients in our study. The central high-density focus was believed to represent a thrombosed vessel within the inflamed appendix epiploica.
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In agreement with the study by Hiller et al. [14], we noted colon wall thickening in only a few patients in our study. This point is important in the differentiation of acute appendicitis from acute diverticulitis. The location of an acute appendix epiploica anterior to the colon is also useful in making a confident diagnosis [1].
The CT changes of acute epiploic appendagitis in our study completely resolved in all patients who underwent follow-up CT 6 months after the acute presentation. However, the CT changes of acute epiploic appendagitis were present to a variable degree in all patients in whom CT was performed within 6 months. It is important to be aware of the evolutionary follow-up CT findings of acute appendagitis because these findings may persist for several months and mimic the diagnosis of acute epiploic appendagitis in the absence of a prior comparison study or suggestive clinical history. The morphologic changes in the appearance of acute epiploic appendagitis on CT in our study are in agreement with the study by Rao et al. [15].
The weakness in this study and other more recent studies in the literature is the lack of pathologic confirmation of acute epiploic appendagitis. Because these patients are conservatively managed, pathologic confirmation of the disease is uncommon [16]. Thus, the presumed diagnosis of this condition is based primarily on the CT features of inflammation centered over the epiploic appendage rather than the colon wall, lack of inflamed colonic diverticula, and, to a lesser extent, on the clinical features such as focal abdominal pain in the absence of fever and bloody stools [12, 17]. Earlier studies of acute appendagitis in the literature report a higher incidence of pathologic confirmation at least partly because of the lack of availability or use of CT [18].
Epiploic appendagitis and omental infarctions are more commonly diagnosed today with the increasing use of cross-sectional imaging for the assessment of acute abdominal pain [19]. With the ever-increasing use of CT in the emergency department, the radiologist is more likely to see cases of acute epiploic appendagitis as the cause of acute abdominal pain. The awareness of the CT features of acute appendagitis is important because this condition is medically managed but can mimic the surgical abdomen.
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