DOI: 10.1148/radiol.2262011992
(Radiology 2003;226:556-557.)
© RSNA, 2003
The Hyperattenuating Ring Sign1
Adriaan C. van Breda Vriesman, MD
1 From the Department of Radiology, Westeinde Hospital, Lijnbaan 32, The Hague, the Netherlands. Received December 5, 2001; revision requested February 18, 2002; revision received March 13; accepted April 2. Address correspondence to the author (e-mail: adriaanbreda@hotmail.com).
Index terms: Appendix epiploica • Colon, CT, 75.12112 • Signs in Imaging
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APPEARANCE
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The hyperattenuating ring sign is a finding seen on computed tomographic (CT) scans of the abdomen. It consists of a thin round or oval ring of soft-tissue attenuation surrounding an area of fat attenuation adjacent to the colon (Fig 1).
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Figure 1. Hyperattenuating ring sign. Transverse CT scan of the abdomen after intravenous administration of contrast material in a 42-year-old man with a clinical diagnosis of presumed appendicitis depicts a pericolonic lesion with fat attenuation surrounded by a hyperattenuating ring (arrowhead). The ring represents thickening of the visceral peritoneal lining of an inflamed epiploic appendix.
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EXPLANATION
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A hyperattenuating ring is a characteristic finding of primary epiploic appendagitis (1,2). The ring represents thickening of the visceral peritoneum surrounding an inflamed epiploic appendix (3). At histologic examination, the visceral peritoneal lining of the diseased epiploic appendix is covered with a fibrinoleukocytic exudate (1).
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DISCUSSION
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Epiploic appendices are small lobulated masses of pericolonic fat protruding from the serosal surface of the colon. Normally they can be seen on CT scans only when outlined by peritoneal cavity fluid (Fig 2). An epiploic appendix may undergo infarction as a result of either torsion along its pedicle with compromise of the blood supply or spontaneous venous thrombosis, followed by secondary inflammatory changes (1). The condition has been termed primary epiploic appendagitis to avoid confusion with appendicitis and to discriminate primary spontaneous inflammation from secondary epiploic appendagitis caused by inflammation of adjacent organs.
The main symptom in patients with primary epiploic appendagitis is abrupt onset of focal abdominal pain in the absence of other clinically important findings. The patient usually does not appear very ill, and the white blood cell count is either normal or moderately elevated (4). These findings are nonspecific and do not allow clinical differentiation of epiploic appendagitis from other common causes of acute abdominal pain, leading to a clinical misdiagnosis in practically all cases (5). Depending on the location, primary epiploic appendagitis may simulate nearly any acute abdominal condition, but since the infarction is frequently located in the lower quadrants, where the sigmoid colon and cecum harbor the largest number of epiploic appendices (6), the presumed clinical diagnosis is colonic diverticulitis or appendicitis in most cases.
Primary epiploic appendagitis is a benign self-limiting disease, with spontaneous symptom resolution within 1 week in most patients (1–3). Misdiagnosis, therefore, may lead to unwarranted surgery or unnecessary medical treatment and hospitalization. A correct imaging diagnosis of primary epiploic appendagitis can prevent this overtreatment.
The imaging features of primary epiploic appendagitis have been described as characteristic, allowing a definite diagnosis (1–3,7). On CT scans, the finding of a 1–4-cm-diameter pericolonic mass with fat attenuation, circumscribed by a 2–3-mm-thick hyperattenuating ring, is diagnostic of primary epiploic appendagitis. The hyperattenuating ring may be subtle, but its presence has been mentioned in all cases of primary epiploic appendagitis reported in the radiology literature. Occasionally, the lesion may contain a central hyperattenuating area (Fig 3), presumably caused by thrombosed vessels and hemorrhagic necrosis (1). Additional CT findings include periappendageal fat stranding and thickening of the parietal peritoneum. Local reactive bowel wall thickening may be present, although it is typically absent.
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Figure 3. Primary epiploic appendagitis in a 51-year-old woman with a clinical diagnosis of presumed colonic diverticulitis. Nonenhanced CT scan shows a pericolonic fatty lesion surrounded by a hyperattenuating ring (arrowhead), containing a central hyperattenuating area (arrow) corresponding to thrombosis and hemorrhagic changes. In the absence of diverticula in the region of the inflammation, diverticulitis can be ruled out. With conservative treatment, symptoms resolved within 3 days.
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Ultrasonographic (US) findings in patients with primary epiploic appendagitis include a hyperechoic noncompressible ovoid or round mass adherent to the colonic wall, frequently surrounded by a hypoechoic border corresponding to the hyperattenuating ring on CT scans. Although US has the advantage of correlation of the location of the lesion and the location of maximum tenderness as identified by the patient, CT should be used to confirm the fatty nature of the mass before a definite diagnosis of primary epiploic appendagitis is assigned (7).
The differential diagnosis of primary epiploic appendagitis, based on imaging findings, is limited and includes secondary epiploic appendagitis and omental infarction (1–3). Colonic diverticulitis is a common cause of secondary epiploic appendagitis, and care should be taken to exclude findings suggesting the diagnosis of it at US or CT (eg, presence of a diverticulum close to the inflamed fat, inflammatory colonic wall thickening, abscess). In difficult cases, color Doppler US might be useful in differentiating inflammatory from ischemic lesions (8). Omental infarction may also simulate primary epiploic appendagitis, although in omental infarction, the lesion is usually larger (average diameter of 3.5–7.0 cm), cake shaped, and typically right sided (1,2). In omental infarction, CT does not depict a hyperattenuating ring surrounding the lesion, but in cases in which the presence of a hyperattenuating ring is uncertain, discrimination of primary epiploic appendagitis from omental infarction may be difficult. Because omental infarction has a benign natural history similar to that of primary epiploic appendagitis, the distinction has no practical implications (2).
Primary epiploic appendagitis may occur at any age, including childhood, with a peak incidence in the 5th decade, with a slight male preponderance (4). The onset of pain may follow physical exertion, and obesity is a presumed predisposing factor (1,2). Though uncommon, the disorder is not as rare as generally assumed. Primary epiploic appendagitis has been reported in 2.3%–7.1% of patients clinically suspected of having colonic diverticulitis and in 1.0% of patients suspected of having appendicitis (3,7).
In summary, a hyperattenuating ring is a characteristic sign of primary epiploic appendagitis. The finding enables the imaging diagnosis, thereby avoiding unnecessary treatment.
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FOOTNOTES
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A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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REFERENCES
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- Rao PM, Wittenberg J, Lawrason JN. Primary epiploic appendagitis: evolutionary changes in CT appearance. Radiology 1997; 204:713-717.[Abstract/Free Full Text]
- Carmicheal DH, Organ CH. Epiploic disorders. Arch Surg 1985; 120:1167-1172.[Abstract]
- Rao PM, Rhea JT, Wittenberg J, Warshaw AL. Misdiagnosis of primary epiploic appendagitis. Am J Surg 1998; 176:81-85.[CrossRef][Medline]
- Gharemani GG, White EM, Hoff FL, Gore RM, Miller JW, Christ ML. Appendices epiploicae of the colon: radiologic and pathologic features. RadioGraphics 1992; 12:59-77.[Abstract]
- Molla E, Ripolles T, Martinez MJ, Morote V, Rosello-Sastre E. Primary epiploic appendagitis: US and CT findings. Eur Radiol 1996; 8:435-438.
- Danse EM, Van Beers BE, Baundrez V, et al. Epiploic appendagitis: color Doppler sonographic findings. Eur Radiol 2001; 11:183-186.[CrossRef][Medline]
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