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Acute Epiploic Appendagitis and Its Mimics¹

¹ From the Department of Radiology, University of Massachusetts Medical Center, Worcester, MA 01605 (A.K.S.); and the Division of Abdominal Imaging and Interventional Radiology (D.A.G., P.F.H., P.S., P.R.M.) and Department of Emergency Radiology (R.A.N.), Massachusetts General Hospital, Boston, Mass. Recipient of a Certificate of Merit award for an education exhibit at the 2004 RSNA Annual Meeting. Received February 25, 2005; revision requested March 22 and received May 2; accepted May 3. All authors have no financial relationships to disclose. Address correspondence to A.K.S. (e-mail: pallaviajay{at}hotmail.com).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 
Acute epiploic appendagitis most commonly manifests with acute lower quadrant pain. Its clinical features are similar to those of acute diverticulitis or, less commonly, acute appendicitis. The conditions that may mimic acute epiploic appendagitis at computed tomography (CT) include acute omental infarction, mesenteric panniculitis, fat-containing tumor, and primary and secondary acute inflammatory processes in the large bowel (eg, diverticulitis and appendicitis). Whereas the location of acute epiploic appendagitis is most commonly adjacent to the sigmoid colon, acute omental infarction is typically located in the right lower quadrant and often is mistaken for acute appendicitis. It is important to correctly diagnose acute epiploic appendagitis and acute omental infarction on CT images because these conditions may be mistaken for acute abdomen, and the mistake may lead to unnecessary surgery. The CT features of acute epiploic appendagitis include an oval lesion 1.5–3.5 cm in diameter, with attenuation similar to that of fat and with surrounding inflammatory changes, that abuts the anterior sigmoid colon wall. The CT features of acute omental infarction include a well-circumscribed triangular or oval heterogeneous fatty mass with a whorled pattern of concentric linear fat stranding between the anterior abdominal wall and the transverse or ascending colon. As CT increasingly is used for the evaluation of acute abdomen, radiologists are likely to see acute epiploic appendagitis and its mimics more often. Recognition of these conditions on CT images will allow appropriate management of acute abdominal pain and may help to prevent unnecessary surgery.

© RSNA, 2005

	LEARNING OBJECTIVES FOR TEST 3

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 
After reading this article and taking the test, the reader will be able to:

• Identify the CT imaging features of acute epiploic appendagitis.
  
• Describe the CT imaging features that are helpful for choosing the appropriate method of treatment.
  
• Distinguish omental infarction from acute epiploic appendagitis, sclerosing mesenteritis, and acute diverticulitis on the basis of CT images.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 
Computed tomography (CT) is used with increasing frequency for the assessment of acute abdominal pain in patients at emergency centers. The goals of CT assessment are (a) to identify the cause of acute abdominal pain, (b) to aid in the optimal management of pain by designating the patient either for medical treatment or surgery, (c) to avoid the hospital admission of those who can be treated successfully as outpatients, and, when indicated, (d) to plan percutaneous image-guided aspiration and catheter-based drainage. The value of CT at emergency medical centers is enhanced by rapid image acquisition and by the many intraabdominal pathologic entities that are amenable to CT-based diagnosis. In the study by Rosen et al (1), findings at CT obviated hospital admission for 17% of patients and changed surgical management for 40% of patients who were suspected of having acute appendicitis.

There is an extensive literature about, and a widespread awareness of, the CT imaging features of such common causes of acute abdomen as appendicitis, diverticulitis, bowel obstruction, pancreatitis, perforated peptic ulcer, abscess, pyelonephritis, and obstructive urolithiasis. However, there is less published information and less extensive knowledge about rarer causes of acute abdomen, such as acute epiploic appendagitis and acute omental infarction. These conditions often manifest with acute pain in the left or the right lower quadrant and may mimic acute abdomen. Accurate assessment of the CT features of these conditions is important for selecting the appropriate mode of management and preventing unnecessary hospital admission and surgery.

Acute epiploic appendagitis is a self-limited inflammation of the appendices epiploicae, a condition that, before CT was available, was most commonly diagnosed at surgery (2). The term epiploic appendagitis was introduced in 1956 by Lynn et al (3), and the CT features of this condition were initially described in 1986 by Danielson et al (4). Unlike the literature that was published before 1980, the more recent reports about this condition are primarily based on diagnosis at cross-sectional imaging, most commonly CT and occasionally ultrasonography (US) (5–18). The relative rarity of this pathologic entity, its common omission from differential diagnoses, its unique imaging appearance, and issues of its medical management make its recognition important for emergency radiologists.

This article describes the CT findings in acute epiploic appendagitis and conditions that may mimic it. The CT features discussed are variable size and location, presence of a central focal area of high attenuation, and colonic wall thickening. The evolutionary changes that accompany this condition and the potential pitfalls for image interpretation also are described.

	Normal Epiploic Appendages

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 
Epiploic (or omental) appendages are peritoneal pouches that arise from the serosal surface of the colon, to which they are attached by a vascular stalk. They frequently arise in association with colonic diverticula. Composed of adipose tissue and blood vessels, the appendages typically have a length of 0.5–5 cm. Those located near the sigmoid colon are the largest, and they may occur in multiples of approximately 100. Epiploic appendages are not found near the rectum. The appendages are arranged in two rows: one row medial to the tenia libera, and the other lateral to the tenia omentalis. Typically, the epiploic appendages are visible on CT images only when they are inflamed and/or surrounded by fluid (Fig 1).

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Normal epiploic appendages. Axial source image (a) and coronal reconstruction (b) obtained with contrast material–enhanced CT show multiple appendices epiploicae (oval line) that arise from the sigmoid colon and are outlined by a hyperattenuating rim due to ascites.

View larger version (180K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Normal epiploic appendages. Axial source image (a) and coronal reconstruction (b) obtained with contrast material–enhanced CT show multiple appendices epiploicae (oval line) that arise from the sigmoid colon and are outlined by a hyperattenuating rim due to ascites.

	Acute Epiploic Appendagitis

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

Acute epiploic appendagitis is associated with obesity, hernia, and unaccustomed exercise. Inflammation of the epiploic appendages is self limited in the majority of patients. Rarely, acute epiploic appendagitis may result in adhesion, bowel obstruction, intussusception, intraperitoneal loose body, peritonitis, and/or abscess formation (2).

Clinical Manifestations
The condition most commonly manifests in the 4th to 5th decades of life, predominantly in men (4–8). With diagnosis based on clinical manifestations alone, acute epiploic appendagitis is mis-diagnosed in the majority of patients. Clinically, acute epiploic appendagitis manifests with acute onset of pain, most often in the left lower quadrant, and this symptom often leads to its being mistaken for acute diverticulitis. Unlike acute epiploic appendagitis, acute diverticulitis is more likely to manifest with evenly distributed lower abdominal pain and to be associated with nausea, fever, and leukocytosis (7). Although most patients with acute epiploic appendagitis do not report any change in their bowel habits, a minority experience constipation or diarrhea (19).

Most patients with acute epiploic appendagitis have a normal white blood cell count and body temperature. CT images from less than 8% of patients evaluated for exclusion of sigmoid diverticulitis or appendicitis show features of primary acute epiploic appendagitis (8–9). When acute epiploic appendagitis involves the cecum or ascending colon, it may be mistaken clinically for acute appendicitis.

Imaging Features
Before the use of CT became widespread, most cases of acute epiploic appendagitis were diagnosed at surgery. Because the clinical signs and symptoms of the condition are nonspecific, however, diagnosis at preoperative assessment was correct in only 2.5% of patients. The preoperative diagnosis could be suspected in patients who had clinical signs and symptoms of acute appendicitis and a history of appendectomy, or clinical symptoms of diverticulitis in the absence of findings at barium enema study (19). Since the introduction of cross-sectional imaging, acute epiploic appendagitis has been diagnosed most commonly on the basis of CT images. There are also reports about the imaging appearance of acute epiploic appendagitis at US and, more rarely, at magnetic resonance (MR) imaging (9,15,16,20).

The most common sites of acute epiploic appendagitis, in order of decreasing frequency, are areas adjacent to the sigmoid colon, the descending colon, and the right hemicolon (Fig 2). The most common CT feature in acute epiploic appendagitis is an oval lesion less than 5 cm in diameter (typical diameter range, 1.5–3.5 cm) that has attenuation equivalent to that of fat, that abuts the anterior colonic wall, and that is surrounded by inflammatory changes (5) (Figs 3, 4). Thickening of the parietal peritoneum, secondary to the spread of inflammation, also may be observed. The wall of the colon may be thickened but is most often normal in thickness (5). Intestinal obstruction and abscess formation are rare. Although the presence of a central area of high attenuation due to venous thrombosis is useful for diagnosis, the absence of this feature does not preclude a diagnosis of acute epiploic appendagitis (Fig 5). Rarely, appendagitis may occur in a hernia sac (Fig 6).

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Acute epiploic appendagitis near the sigmoid colon. Axial contrast-enhanced CT images (a in a different patient than b) show inflamed epiploic appendages (arrow) that have a hyperattenuating rim and that abut the sigmoid colon.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Acute epiploic appendagitis near the sigmoid colon. Axial contrast-enhanced CT images (a in a different patient than b) show inflamed epiploic appendages (arrow) that have a hyperattenuating rim and that abut the sigmoid colon.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Acute epiploic appendagitis with a hyperattenuating center. Axial contrast-enhanced CT images (a in a different patient than b) show a lesion (arrow) that abuts the sigmoid colon and has a central focal area of hyperattenuation with surrounding inflammation.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Acute epiploic appendagitis with a hyperattenuating center. Axial contrast-enhanced CT images (a in a different patient than b) show a lesion (arrow) that abuts the sigmoid colon and has a central focal area of hyperattenuation with surrounding inflammation.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Acute epiploic appendagitis near the cecum. Axial contrast-enhanced CT images (a in a different patient than b) show lesions (arrow) with fat attenuation and surrounding inflammation that abut the cecum. (Fig 4b reprinted, with permission, from reference 5.)

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Acute epiploic appendagitis near the cecum. Axial contrast-enhanced CT images (a in a different patient than b) show lesions (arrow) with fat attenuation and surrounding inflammation that abut the cecum. (Fig 4b reprinted, with permission, from reference 5.)

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Acute epiploic appendagitis near the descending colon. Axial contrast-enhanced CT images (a in a different patient than b) show an epiploic appendage (arrow), anterior to the descending colon, that is surrounded by inflammation but that has no hyperattenuating center.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Acute epiploic appendagitis near the descending colon. Axial contrast-enhanced CT images (a in a different patient than b) show an epiploic appendage (arrow), anterior to the descending colon, that is surrounded by inflammation but that has no hyperattenuating center.

View larger version (182K): [in this window] [in a new window] [Download PPT slide]   Figure 6.  Acute epiploic appendagitis in a hernia sac. Axial contrast-enhanced CT image shows an inflamed appendix epiploica (arrow) that arose from the transverse colon in a patient with a ventral hernia that developed after gastric bypass surgery. (Reprinted, with permission, from reference 21.)

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Evolutionary changes in acute epiploic appendagitis. (a) Axial contrast-enhanced CT image acquired on the day of presentation shows a lesion with fat attenuation, a typical finding in acute epiploic appendagitis. (b) Axial contrast-enhanced CT image obtained 3 months later shows a small residual nodule with soft-tissue attenuation (arrow). (c) Axial contrast-enhanced CT image obtained in another patient at presentation shows an inflamed appendix epiploica with a hyperattenuating rim (arrow). (d) Axial contrast-enhanced CT image obtained 3 months later shows a decrease in size of the inflamed appendix epiploica (arrow), which has a fatty center and abuts the sigmoid colon.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Evolutionary changes in acute epiploic appendagitis. (a) Axial contrast-enhanced CT image acquired on the day of presentation shows a lesion with fat attenuation, a typical finding in acute epiploic appendagitis. (b) Axial contrast-enhanced CT image obtained 3 months later shows a small residual nodule with soft-tissue attenuation (arrow). (c) Axial contrast-enhanced CT image obtained in another patient at presentation shows an inflamed appendix epiploica with a hyperattenuating rim (arrow). (d) Axial contrast-enhanced CT image obtained 3 months later shows a decrease in size of the inflamed appendix epiploica (arrow), which has a fatty center and abuts the sigmoid colon.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Evolutionary changes in acute epiploic appendagitis. (a) Axial contrast-enhanced CT image acquired on the day of presentation shows a lesion with fat attenuation, a typical finding in acute epiploic appendagitis. (b) Axial contrast-enhanced CT image obtained 3 months later shows a small residual nodule with soft-tissue attenuation (arrow). (c) Axial contrast-enhanced CT image obtained in another patient at presentation shows an inflamed appendix epiploica with a hyperattenuating rim (arrow). (d) Axial contrast-enhanced CT image obtained 3 months later shows a decrease in size of the inflamed appendix epiploica (arrow), which has a fatty center and abuts the sigmoid colon.

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.  Evolutionary changes in acute epiploic appendagitis. (a) Axial contrast-enhanced CT image acquired on the day of presentation shows a lesion with fat attenuation, a typical finding in acute epiploic appendagitis. (b) Axial contrast-enhanced CT image obtained 3 months later shows a small residual nodule with soft-tissue attenuation (arrow). (c) Axial contrast-enhanced CT image obtained in another patient at presentation shows an inflamed appendix epiploica with a hyperattenuating rim (arrow). (d) Axial contrast-enhanced CT image obtained 3 months later shows a decrease in size of the inflamed appendix epiploica (arrow), which has a fatty center and abuts the sigmoid colon.

View larger version (172K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Acute epiploic appendagitis in the descending colon in a 34-year-old woman. (a) US image of the left lower quadrant shows an oval noncompressible lesion (arrows) with heterogeneous echotexture, located at the point of maximum tenderness. (b) Axial contrast-enhanced CT image shows the corresponding inflamed appendix epiploica (arrow) anterior to the distal descending colon.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Acute epiploic appendagitis in the descending colon in a 34-year-old woman. (a) US image of the left lower quadrant shows an oval noncompressible lesion (arrows) with heterogeneous echotexture, located at the point of maximum tenderness. (b) Axial contrast-enhanced CT image shows the corresponding inflamed appendix epiploica (arrow) anterior to the distal descending colon.

When acute epiploic appendagitis is diagnosed, it is treated conservatively with oral anti-inflammatory medication, and antibiotics are not routinely indicated. The condition is self limited, and most patients recover with conservative management in less than 10 days. In contrast, a misdiagnosis of acute epiploic appendagitis as acute diverticulitis may result in unnecessary hospital admission, antibiotic therapy, laboratory testing, and dietary restrictions.

In a study by Rao et al (10), 2% of cases diagnosed as acute diverticulitis on the basis of initial CT evaluation were later categorized as acute epiploic appendagitis. The average cost per misdiagnosed patient, calculated on the basis of the combined costs of unnecessary hospital admission, medical treatment, and laboratory testing in these patients, was $4117.

	Mimics of Acute Epiploic Appendagitis

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 
Omental Infarction
Omental infarction is a rare cause of acute abdomen. It typically simulates acute appendicitis, with clinical features that include abdominal pain of a few days’ duration, most often localized in the right lower or upper quadrant. The manifestation of right-sided pain may lead to clinical misdiagnosis of omental infarction as appendicitis or cholecystitis; thus, imaging is required to achieve an accurate diagnosis and to avoid unnecessary laparotomy and antibiotic therapy.

Unlike acute epiploic appendagitis, which predominantly affects adults (the youngest patient with this reported diagnosis was in the 2nd decade of life), omental infarction occurs in a fair number of pediatric patients (approximately 15% of cases) (22). Infarction of the omentum is less common than infarction of either the small or the large bowel because abundant collateral vessels perfuse the omentum. The most frequent cause of non–torsion-related omental infarction is venous insufficiency due to trauma or thrombosis of the omental veins (23). Factors that predispose people to omental infarction include obesity, strenuous activity, congestive heart failure, digitalis administration, recent abdominal surgery (Figs 9–11), and abdominal trauma (24–26).

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Evolutionary changes in omental infarction. (a) Axial contrast-enhanced CT image obtained after colectomy shows an acute omental infarct (arrows) in the left upper quadrant. (b) Axial contrast-enhanced CT image obtained 3 years later shows a small residual lesion (arrow) with the attenuation of fat and with well-defined margins.

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Evolutionary changes in omental infarction. (a) Axial contrast-enhanced CT image obtained after colectomy shows an acute omental infarct (arrows) in the left upper quadrant. (b) Axial contrast-enhanced CT image obtained 3 years later shows a small residual lesion (arrow) with the attenuation of fat and with well-defined margins.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Multiple omental infarcts secondary to superior mesenteric artery obstruction. (a, b) Axial contrast-enhanced CT images (a in a different patient than b) show multiple fatty lesions (straight arrows) in the omentum and ischemic changes (curved arrow) in the small-bowel loops. (c) Sagittal CT angiographic image shows complete occlusion of the superior mesenteric artery 2 cm beyond its origin (arrow). (Reprinted, with permission, from reference 24.)

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Multiple omental infarcts secondary to superior mesenteric artery obstruction. (a, b) Axial contrast-enhanced CT images (a in a different patient than b) show multiple fatty lesions (straight arrows) in the omentum and ischemic changes (curved arrow) in the small-bowel loops. (c) Sagittal CT angiographic image shows complete occlusion of the superior mesenteric artery 2 cm beyond its origin (arrow). (Reprinted, with permission, from reference 24.)

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.  Multiple omental infarcts secondary to superior mesenteric artery obstruction. (a, b) Axial contrast-enhanced CT images (a in a different patient than b) show multiple fatty lesions (straight arrows) in the omentum and ischemic changes (curved arrow) in the small-bowel loops. (c) Sagittal CT angiographic image shows complete occlusion of the superior mesenteric artery 2 cm beyond its origin (arrow). (Reprinted, with permission, from reference 24.)

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Infected omental infarct. (a) Axial contrast-enhanced CT image obtained after pancreatectomy and splenectomy shows an omental infarct with attenuation of fat and a fluid-filled center that indicates an abscess (arrows). (b) Follow-up CT image obtained after percutaneous catheter drainage shows resolution of the abscess.

View larger version (161K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Infected omental infarct. (a) Axial contrast-enhanced CT image obtained after pancreatectomy and splenectomy shows an omental infarct with attenuation of fat and a fluid-filled center that indicates an abscess (arrows). (b) Follow-up CT image obtained after percutaneous catheter drainage shows resolution of the abscess.

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 12.  Acute omental infarction in a young woman. Axial contrast-enhanced CT image shows an oval lesion with heterogeneous attenuation (straight arrows), well separated from the colon (curved arrow), in the right lower quadrant.

View larger version (170K): [in this window] [in a new window] [Download PPT slide]   Figure 13.  Acute omental infarction in a 6-year-old girl. Axial contrast-enhanced CT image shows a 6.5-cm-diameter fatty mass with surrounding inflammation in the right lower quadrant. Because the mass is large, the diagnosis of omental infarction was favored over that of epiploic appendagitis, in which the lesion is usually less than 5 cm long.

Acute Diverticulitis
Acute diverticulitis occurs in older patients than does acute epiploic appendagitis. The two conditions are largely indistinguishable on the basis of clinical manifestations alone. In general, however, patients with acute diverticulitis are more likely to experience nausea, vomiting, fever, elevated leukocyte count, and rebound tenderness and to have more diffuse lower abdominal pain than are patients with acute epiploic appendagitis. Unlike patients with acute epiploic appendagitis, only 7% of whom are affected by leukocytosis, most patients with acute diverticulitis have an elevated white blood cell count (5,7).

The typical CT findings in cases of acute diverticulitis include colonic diverticula with inflammation or abscess in the mesocolon and with adjacent colonic wall thickening that extends more than 5 cm (Fig 14). There may be inflammation-related fat stranding, extraluminal air or fluid accumulation, or abscess formation around the colonic lumen. Pericolic sinus and fistula are uncommon complications of this pathologic condition.

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 14.  Acute cecal diverticulitis in a young woman. Axial contrast-enhanced CT image shows a central focal area with low attenuation, which represents an inflamed diverticulum (arrow), surrounded by a rim of higher attenuation due to intense inflammation. An uninflamed diverticulum also is visible posterior to the inflamed diverticulum.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 15a.  Secondary inflammation of epiploic appendages. (a) Axial contrast-enhanced CT image shows thickening of the cecal wall (areas of low attenuation inside the oval line) because of colitis, with secondary inflammation of an epiploic appendage (arrow). (b) In a different patient, axial contrast-enhanced CT image shows acute sigmoid diverticulitis (oval) with inflammation in surrounding tissues, including an epiploic appendage (arrow). (c) In a patient with a pelvic abscess, axial contrast-enhanced pelvic CT image shows areas of inflammation-related high attenuation that outline two epiploic appendages (arrows).

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.  Secondary inflammation of epiploic appendages. (a) Axial contrast-enhanced CT image shows thickening of the cecal wall (areas of low attenuation inside the oval line) because of colitis, with secondary inflammation of an epiploic appendage (arrow). (b) In a different patient, axial contrast-enhanced CT image shows acute sigmoid diverticulitis (oval) with inflammation in surrounding tissues, including an epiploic appendage (arrow). (c) In a patient with a pelvic abscess, axial contrast-enhanced pelvic CT image shows areas of inflammation-related high attenuation that outline two epiploic appendages (arrows).

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 15c.  Secondary inflammation of epiploic appendages. (a) Axial contrast-enhanced CT image shows thickening of the cecal wall (areas of low attenuation inside the oval line) because of colitis, with secondary inflammation of an epiploic appendage (arrow). (b) In a different patient, axial contrast-enhanced CT image shows acute sigmoid diverticulitis (oval) with inflammation in surrounding tissues, including an epiploic appendage (arrow). (c) In a patient with a pelvic abscess, axial contrast-enhanced pelvic CT image shows areas of inflammation-related high attenuation that outline two epiploic appendages (arrows).

Sclerosing mesenteritis can be categorized, on the basis of the predominant process occurring in tissue, as mesenteric panniculitis, mesenteric lipodystrophy, or retractile mesenteritis. Mesenteric panniculitis is the term used when chronic inflammation predominates, and mesenteric lipodystrophy is used when fat necrosis is the predominant process. Retractile mesenteritis is characterized by fibrosis and may be indistinguishable from neoplasia at CT (29).

The CT findings vary from a well-defined soft-tissue mass containing areas of fat attenuation to an ill-defined area of higher attenuation in the root of the small-bowel mesentery (Fig 16). In all affected patients, there is some degree of fibrosis, chronic inflammation, and fat necrosis. Unlike the characteristic situation in tumors, these processes take place around mesenteric vessels without displacing them. The fat plane around the mesenteric vessels results in a CT feature that is called the "fat ring sign." Fibrosis may lead to bowel loop narrowing and result in spiculation that may be mistaken for a neoplastic process. Calcification is uncommon (29,30).

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 16a.  Sclerosing mesenteritis. Axial contrast-enhanced CT images show variable degrees of fibrosis, fat necrosis, lymphadenopathy, and inflammation in four patients with sclerosing mesenteritis (arrows). The fat ring sign (arrowheads in a and b) signals the conservation of fat around the superior mesenteric vessels. Because the predominance of soft-tissue attenuation in c and d did not enable differentiation of the findings from malignant neoplasms such as carcinoid and desmoid tumors, a biopsy was performed. Histopathologic analysis demonstrated retractile mesenteritis in the two patients in c and d.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 16b.  Sclerosing mesenteritis. Axial contrast-enhanced CT images show variable degrees of fibrosis, fat necrosis, lymphadenopathy, and inflammation in four patients with sclerosing mesenteritis (arrows). The fat ring sign (arrowheads in a and b) signals the conservation of fat around the superior mesenteric vessels. Because the predominance of soft-tissue attenuation in c and d did not enable differentiation of the findings from malignant neoplasms such as carcinoid and desmoid tumors, a biopsy was performed. Histopathologic analysis demonstrated retractile mesenteritis in the two patients in c and d.

View larger version (192K): [in this window] [in a new window] [Download PPT slide]   Figure 16c.  Sclerosing mesenteritis. Axial contrast-enhanced CT images show variable degrees of fibrosis, fat necrosis, lymphadenopathy, and inflammation in four patients with sclerosing mesenteritis (arrows). The fat ring sign (arrowheads in a and b) signals the conservation of fat around the superior mesenteric vessels. Because the predominance of soft-tissue attenuation in c and d did not enable differentiation of the findings from malignant neoplasms such as carcinoid and desmoid tumors, a biopsy was performed. Histopathologic analysis demonstrated retractile mesenteritis in the two patients in c and d.

View larger version (178K): [in this window] [in a new window] [Download PPT slide]   Figure 16d.  Sclerosing mesenteritis. Axial contrast-enhanced CT images show variable degrees of fibrosis, fat necrosis, lymphadenopathy, and inflammation in four patients with sclerosing mesenteritis (arrows). The fat ring sign (arrowheads in a and b) signals the conservation of fat around the superior mesenteric vessels. Because the predominance of soft-tissue attenuation in c and d did not enable differentiation of the findings from malignant neoplasms such as carcinoid and desmoid tumors, a biopsy was performed. Histopathologic analysis demonstrated retractile mesenteritis in the two patients in c and d.

Primary Tumors and Metastases to the Mesocolon
The other possible causes of a CT finding of fatty mass or masslike lesion in the abdomen include fat-containing tumors such as liposarcoma, as well as exophytic angiomyolipoma and dermoid and omental metastases (Fig 17). Ill-defined lesion margins, multiplicity of lesions, a lesion epicenter in the omentum, and a history of primary neoplasm are useful for diagnosing omental metastasis.

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.  Fatty neoplasms in four patients. (a) Well-differentiated liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation fatty mass (straight arrows) that abuts the gallbladder (curved arrow). (b) Postoperative recurrence of liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation retroperitoneal liposarcoma (arrows) that abuts the cecum. (c) Tuberous sclerosis with angiomyolipoma. Axial contrast-enhanced CT image shows exophytic angiomyolipoma (straight arrows) that arises from the lower pole of the right kidney (curved arrow) and abuts the hepatic flexure of the colon. (d) Postoperative recurrence of cecal carcinoma. Axial contrast-enhanced CT image shows fat strands (arrows) lateral to the ileocolonic anastomosis site, which is marked by a bowel suture.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.  Fatty neoplasms in four patients. (a) Well-differentiated liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation fatty mass (straight arrows) that abuts the gallbladder (curved arrow). (b) Postoperative recurrence of liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation retroperitoneal liposarcoma (arrows) that abuts the cecum. (c) Tuberous sclerosis with angiomyolipoma. Axial contrast-enhanced CT image shows exophytic angiomyolipoma (straight arrows) that arises from the lower pole of the right kidney (curved arrow) and abuts the hepatic flexure of the colon. (d) Postoperative recurrence of cecal carcinoma. Axial contrast-enhanced CT image shows fat strands (arrows) lateral to the ileocolonic anastomosis site, which is marked by a bowel suture.

View larger version (184K): [in this window] [in a new window] [Download PPT slide]   Figure 17c.  Fatty neoplasms in four patients. (a) Well-differentiated liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation fatty mass (straight arrows) that abuts the gallbladder (curved arrow). (b) Postoperative recurrence of liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation retroperitoneal liposarcoma (arrows) that abuts the cecum. (c) Tuberous sclerosis with angiomyolipoma. Axial contrast-enhanced CT image shows exophytic angiomyolipoma (straight arrows) that arises from the lower pole of the right kidney (curved arrow) and abuts the hepatic flexure of the colon. (d) Postoperative recurrence of cecal carcinoma. Axial contrast-enhanced CT image shows fat strands (arrows) lateral to the ileocolonic anastomosis site, which is marked by a bowel suture.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 17d.  Fatty neoplasms in four patients. (a) Well-differentiated liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation fatty mass (straight arrows) that abuts the gallbladder (curved arrow). (b) Postoperative recurrence of liposarcoma. Axial contrast-enhanced CT image shows a mixed-attenuation retroperitoneal liposarcoma (arrows) that abuts the cecum. (c) Tuberous sclerosis with angiomyolipoma. Axial contrast-enhanced CT image shows exophytic angiomyolipoma (straight arrows) that arises from the lower pole of the right kidney (curved arrow) and abuts the hepatic flexure of the colon. (d) Postoperative recurrence of cecal carcinoma. Axial contrast-enhanced CT image shows fat strands (arrows) lateral to the ileocolonic anastomosis site, which is marked by a bowel suture.

	Conclusions

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

	References

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Normal Epiploic Appendages Acute Epiploic Appendagitis Mimics of Acute Epiploic... Conclusions References

 

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