Epiploic Appendagitis: An Entity Frequently Unknown to Clinicians Diagnostic Imaging, Pitfalls, and Look-Alikes

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1 Gastrointestinal Imaging Review lmeida et al. Imaging of Epiploic ppendagitis Gastrointestinal Imaging Review Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved na Teresa lmeida 1 Lina Melão arbara Viamonte Rui Cunha José Miguel Pereira lmeida T, Melão L, Viamonte, Cunha R, Pereira JM Keywords: appendagitis, appendicitis, diverticulitis, omental infarction DOI: /JR Received November 8, 2008; accepted after revision pril 12, This article was prepared based on an educational exhibit that won the Magna Cum Laude award at the 2007 annual meeting of the European Society of Gastrointestinal and bdominal Radiology. 1 ll authors: Department of Radiology, Faculdade de Medicina da Universidade do Porto, Hospital São João, lameda Professor Hernâni Monteiro, Porto, Portugal. ddress correspondence to L. Melão (lina_melao@hotmail.com). JR 2009; 193: X/09/ merican Roentgen Ray Society Epiploic ppendagitis: n Entity Frequently Unknown to Clinicians Diagnostic Imaging, Pitfalls, and Look-likes OJECTIVE. Epiploic appendagitis is an ischemic infarction of an epiploic appendage caused by torsion or spontaneous thrombosis of the epiploic appendage central draining vein. When it occurs on the right side of the abdomen, it can mimic appendicitis and right-sided diverticulitis; whereas when it occurs on the left side of the abdomen, it is often mistaken for sigmoid diverticulitis. The purpose of this article is to review the diagnostic imaging of this entity. CONCLUSION. Epiploic appendagitis is self-limited and spontaneously resolves without surgery within 5 7 days. Therefore, it is imperative for radiologists to be familiar with this entity. E piploic appendages, also known as epiploicae appendices, are pedunculated fatty structures arranged in two separate longitudinal rows next to the anterior and posterior tenia coli over the external aspect of the colon [1 4]. Epiploic appendages extend from the cecum to the rectosigmoid junction and are covered by the peritoneum [1, 4 8]. The greatest concentration of epiploic appendages is in the cecum and sigmoid colon but spares the rectum [5, 9]. Epiploic appendages are between 1 2 cm thick, cm long, and larger on the left side of the colon than on the right side [3]. Each epiploic appendage is supplied by one or two small end arteries branching from the vasa recta longa of the colon and is drained by a tortuous vein passing through its narrow pedicle [2 4]. Their limited blood supply, together with their pedunculated shape and excessive mobility, make epiploic appendages prone to torsion and ischemic or hemorrhagic infarction [1, 2, 4, 8, 10]. Epiploic ppendagitis ppendagitis is a term denoting primary or secondary inflammation of the epiploic appendages [6]. Primary Epiploic ppendagitis Primary epiploic appendagitis is an ischemic infarction of an epiploic appendage and an uncommon cause of abdominal pain that has been recognized relatively recently [11]. Primary epiploic appendagitis is caused by epi ploic appendage torsion or spontaneous thrombosis of the epiploic appendage central draining vein resulting in vascular occlusion and focal inflammation [5 7, 12, 13]. In some cases of epiploic appendagitis, inflammation may be present without any vascular impairment [6, 14, 15]. The reported age range for primary epiploic appendagitis is years, with a peak in incidence in the fifth decade. Primary epiploic appendagitis is more common in obese patients and women [3, 4]. Primary epiploic appendagitis occurs more frequently in the sigmoid colon than in the cecum or ascending colon and is uncommon in the transverse colon [3, 5, 16]. Epiploic appendages may cause incarcerated hernia; a case has been reported of an epiploic appendagitis within an incisional hernia sac [10]. Primary epiploic appendagitis usually presents as an abrupt onset of focal abdominal pain in the lateral lower quadrants, is nonmigratory, and worsens with cough and abdominal stretching [2, 3, 11, 17]. ppetite and bowel function are usually unchanged; nausea and vomiting are rare [6, 16]. On physical examination, the patient will present with localized tenderness without significant guarding or rigidity. The patient also may have a low-grade fever [3, 18]. WC count is usually normal or slightly elevated [2]. Heavy exercise has been reported as a predisposing factor [2, 4, 6]. Primary epiploic appendagitis is difficult to diagnose clinically because of the lack of pathognomonic clinical features and can simulate a case requiring surgery [3, 4]. JR:193, November

2 lmeida et al. Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig year-old man with hepatic cirrhosis. Unenhanced CT image shows several epiploic appendices (arrowhead) outlined by ascites. rrow indicates normal central vein. Right-sided primary epiploic appendagitis is often confused with acute appendicitis or right-sided diverticulitis; whereas left-sided primary epiploic appendagitis is often confused with sigmoid diverticulitis [3, 4, 18]. In the past, diagnosis of epiploic appendagitis was often the result of an unexpected finding during an exploratory laparotomy [3]. Today, this condition is usually diagnosed by ultrasound or CT, with the latter more sensitive and specific. lthough ultrasound has the advantage of correlating the location of the lesion with the location of maximum tenderness, CT should be used to confirm the fatty nature of the lesion before making a definite diagnosis of primary epiploic appendagitis. With the increasing use of CT for assessing cases of acute abdominal pain, the diagnosis of epiploic appendagitis is now more common [18, 19]. Primary epiploic appendagitis is self-limited in the majority of patients and spontaneously resolves within 5 7 days. Rarely, acute epi ploic appendagitis may result in adhesion, bowel obstruction, intussusception, intraperitoneal loose bodies, peritonitis, or abscess formation [3, 5]. Primary epiploic appendagitis does not require surgery, and treatment is based on the patient s symptoms [4, 5, 7, 13, 15]. Misdiagnosis may lead to unwarranted surgery, medical treatment, and hospitalization [4]. Secondary Epiploic ppendagitis In secondary epiploic appendagitis, the epiploic appendage is inflamed because of another process, such as diverticulitis, appendicitis, pancreatitis, or cholecystitis. Management of secondary epiploic appendagitis is based on treatment of the primary abnormality [1, 2, 4, 7]. Imaging Findings The diagnosis of acute epiploic appendagitis primarily relies on cross-sectional CT, although ultrasound and MRI are occasionally used [11, 19]. Fig. 2 Epiploic appendagitis in 46-year-old man. and, xial contrast-enhanced CT images show severe fat stranding (arrowhead) and fatty ovoid mass (curved arrow) with hyperattenuated rim and central dot (thin straight arrow). ssociated thickening of colonic wall (open arrow) is mild. CT In CT of a healthy patient, the epiploic appendages blend in with the surrounding pericolic fat but become apparent when surrounded by ascites (Fig. 1) or inflammation [3, 5, 8]. n infarcted or inflamed epiploic appendage on CT appears as a 1 4 cm ovoid pericolic lesion with fat density surrounded by inflammatory changes and abuts the anterior colonic wall [1, 3, 5, 11, 15]. Primary epiploic appendagitis may have a lobular appearance because of two or more affected, contiguous epiploic appendages with hyperattenuated rings lying in proximity [19]. 2 3 mm hyperdense rim surrounding the ovoid mass on CT (hyperattenuating ring sign) represents the inflamed visceral peritoneal covering of the epiploic appendage and is diagnostic of primary epiploic appendagitis [13, 15]. The hyperdense rim surrounding the ovoid mass on CT corresponds to the hypoechoic halo on ultrasound [13, 15, 19] (Figs. 2 6). Thickening of the parietal peritoneum secondary to the spread of inflammation may be observed [3, 5 7]. Fat stranding is more pronounced than wall thickening because the paracolonic inflammatory changes are disproportionately more severe than the mild local reactive thickening of the adjacent colonic wall (Figs. 2 6). Wall thickening of the adjacent side of the colon is asymmetric [1, 4, 8] (Figs. 2 and 3). central, hyperattenuating, ill-defined round area ( central dot sign ) or a longitudinal linear area corresponds to engorged or thrombosed central vessels or central areas of hemorrhage or fibrosis (Figs. 2 4). lthough the presence of a central dot or linear area is useful for diagnosis, their absence does not exclude the diagnosis of acute epiploic appendagitis [4 6, 11, 19, 20]. The central dot may have high attenuation because the infarcted tissue tends to calcify. Calcification may be eggshell in shape and may become detached and appear as a peritoneal loose body in the abdominal cavity [1, 3, 16, 21]. The calcified tissue may reattach itself to a surface, such as the lower aspect of the spleen, in which case it is called a parasitized epiploic appendage [3]. The smooth surface and calcified consistency of the epiploic appendage help to distinguish it from a metastatic lesion (Fig. 7). Ultrasound t the site of maximum tenderness, a noncompressible hyperechoic small ovoid or round solid mass of adipose tissue is seen be 1244 JR:193, November 2009

3 Imaging of Epiploic ppendagitis Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 3 Primary epiploic appendagitis in 23-year-old man with clinical diagnosis of presumed colonic diverticulitis. xial contrast-enhanced CT scan shows pericolonic fatty lesion surrounded by hyperattenuating ring (thick arrow) containing central hyperattenuating area (thin arrow) corresponding to thrombosis and hemorrhagic changes and very mild thickening of colonic wall (open arrow). Fig. 6 cute epiploic appendagitis (arrow) with hyperattenuating ring sign adjacent to sigmoid colon without significant involvement of colonic wall in 52-year-old man. tween the colon and the abdominal wall in the anterior or anterolateral compartment of the abdomen [1, 6, 22] (Fig. 8). In most cases, a mass effect is seen either on the adjacent bowel or in the anterior parietal peritoneum. Changes to the colonic wall are not seen [12]. The lesion is adherent to the colonic wall, is frequently surrounded by a hypoechoic border (Fig. 8), and does not have central blood flow on Doppler ultrasound [4, 12]. The absence of a Doppler signal because of a lack of blood flow as a result of torsion in epiploic appendagitis is a useful finding to differentiate epiploic appendagitis from acute diverticulitis [12]. MRI The involved epiploic appendage is hyperintense on unenhanced T1-weighted imaging but is slightly less intense than normal peritoneal fat. Epiploic appendages show marked loss of signal on fat-suppressed T2-weighted Fig. 4 cute epiploic appendagitis with hyperattenuating center in 31-year-old woman. xial contrast-enhanced CT image shows lesion (arrow) that abuts sigmoid colon and has central focal area of hyperattenuation with surrounding inflammation. Fig. 7 CT image shows small calcified body (arrow) adjacent to normal epiploic appendices, probably residual to anterior epiploic appendagitis in 59-yearold man. images, confirming the fatty nature of the lesion [23]. In epiploic appendagitis, the thin peripheral rim and the perilesional inflammatory changes appear hypointense on T1-weighted imaging, appear hyperintense on T2-weighted imaging, and show marked enhancement on contrast-enhanced T1-weighted fat-suppressed images, whereas the central draining vein usually has low signal on both T1- weighted and T2-weighted imaging [23]. Differential Diagnosis In epiploic appendagitis, there is much more fat stranding than bowel wall thickening. In patients with acute abdominal pain, the finding of fat stranding that is disproportionate suggests a relatively narrow differential diagnosis: diverticulitis; omental infarction; appendicitis; and, less commonly, mesenteric panniculitis and primary tumors and metastases to the omentum. Fig year-old man with acute epiploic appendagitis with hyperattenuating ring sign (thick arrow) adjacent to left colon without significant involvement of colonic wall. Severe and disproportionate fat stranding (thin arrow) is seen nearby. Fig. 8 Sonogram in 22-year-old man shows hyperechoic small mass (asterisk) surrounded by hypoechoic border (arrow) corresponding to hyperattenuating ring on CT scans at site of maximum tenderness, located anteriorly between colon and abdominal wall. Diverticulitis Diverticula are herniations of the mucosa and submucosa through the muscular layers of the bowel wall in areas of bowel wall weakness (between the mesenteric and antimesenteric taeniae) and high pressure gradient (caused by dehydrated stools) [8, 24]. Diverticula occur at the point where blood vessels (vasa recta) penetrate the colon wall [24]. Diverticulitis occurs when a diverticulum becomes obstructed, with subsequent focal inflammation, diverticular distention, localized ischemia, and perforation [24]. Typically, perforation of the colonic wall is confined and restricted, leading to peridiverticular and extracolonic inflammation that is more severe than the inflammation of the colon itself [8]. However, the course of the disease may be complicated by abscess formation, hemorrhage, pneumoretroperitoneum, fistula formation, and postinflammatory stenosis. JR:193, November

4 lmeida et al. Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved Diverticula can be found anywhere in the colon, but the majority are located in the distal descending and sigmoid colon; hence, most cases (95%) of diverticulitis are located in the left side of the abdomen. minority of diverticula (5%) are located on the right side of the abdomen, which for unknown reasons has a predilection for patients of sian descent. The transverse colon is rarely affected, whereas the rectum is completely spared from diverticula formation [8]. The most common CT finding of acute diverticulitis is paracolic fat stranding. Other typical CT findings include an ill-defined or blurry diverticulum in the region where the fat stranding is most pronounced (Figs. 9 and 10); mild wall thickening (usually < 5 mm), commonly more pronounced on the side of the offending diverticulum and usually affecting a large colonic segment greater than 5 cm (Figs. 9 and 10); thickened base of the sigmoid mesocolon with fluid ( comma sign ) (Figs. 9 and 10); and engorged vessels supplying the affected segment ( centipede sign ) [8]. Other findings detected by CT include pericolic abscess, small-bowel obstruction, free intraperitoneal or extraperitoneal gas, colovesical fistula, thrombosis of the mesenteric or portal veins caused by pyophlebitis, and hepatic abscess formation. In some instances, small localized collections of gas are identified adjacent to the colonic wall and indicate localized pericolic perforation [17] (Figs. 11 and 12). In cases of complicated diverticulitis, surgical management may be required. Features that help discern the differential diagnosis lthough their clinical manifestations are similar, acute epiploic appendagitis tends to occur in younger patients, whereas acute diverticulitis frequently affects older patients (> 50 years). Patients with diverticulitis are more likely to experience nausea, vomiting, fever, rebound tenderness, and more diffuse lower abdominal pain. Only a minority (7%) of patients with acute epiploic appendagitis have leukocytosis, whereas most patients with acute diverticulitis have an elevated WC count [5]. In cases of acute epiploic appendagitis, the involved colonic segment is short; however, in cases of acute diverticulitis, a lengthy segment of thickened colonic wall is a typical CT feature [8]. The classic complications of diverticulitis (extramural abscesses, sinus tract and fistula formation, bowel obstruction, perforation, and peritonitis) are rare in the setting of acute epiploic appendagitis [5, 17] (Figs. 11 and 12). Features that complicate the differential diagnosis oth epiploic appendagitis and acute diverticulitis frequently present with a sudden focal left-sided tenderness. Moreover, the two conditions can be seen simultaneously because the inflammation from an acute diverticulitis may extend to involve the epiploic appendages [4, 5, 7] (Fig. 12). Fig year-old man with diverticulitis. and, xial contrast-enhanced CT images show mild stranding of pericolonic fat (asterisk). Fuzzy (thick arrow, ) and normal diverticula (thin arrows) are seen. Fig year-old woman with diverticulitis. and, Transverse contrast-enhanced CT images show engorgement of vasa recta feeding sigmoid colon ( centipede sign, open arrow, ). Notice mild wall thickening of colon, with fuzzy (curved arrow, ) and normal (thin arrows) diverticula and fluid by side of root of sigmoid mesentery (arrowhead, ). Comma sign (thick arrow, ) and disproportionate fat stranding (asterisk, ) are also seen. Omental Infarction The greater omentum consists of a fourlayered fold of peritoneum that covers the colon and small bowel in the peritoneal cavity, acting as a barrier to generalized spread of intraperitoneal infection or tumor. It contains fat and vascular structures (Fig. 13). Omental infarctions are rare because abundant collateral vessels perfuse the omentum [25]. The cause of omental infarction is unclear but may be similar in pathophysiology to the cause of primary epiploic appendagitis [9]. Omental infarction occurs when there is an interruption of arterial blood supply to the omentum, possibly because of omental torsion, venous insufficiency due to trauma, or spontaneous thrombosis of the omental veins [5, 26]. Right-sided epiploic vessels are involved in 90% of the cases and are thought to be caused 1246 JR:193, November 2009

5 Imaging of Epiploic ppendagitis Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig year-old man with intraabdominal abscess. Contrast-enhanced CT image shows intraabdominal fluid air collection (arrow). Diverticulitis was proven at surgery. by the omentum being longer and more mobile on the right side [21]. Precipitating factors include obesity, recent abdominal surgery, strenuous activity, congestive heart failure, digitalis administration, and abdominal trauma [5, 12, 27]. However, most cases of omental infarction are idiopathic [16] (Fig. 13). Omental infarctions are usually localized to the right upper and lower quadrants and clinically mimic cholecystitis and appendicitis, respectively [16, 26, 28]. few cases of left-sided omental infarction have also been described [28]. Omental infarction more commonly affects elderly obese patients, with a slight predilection for men [16]. Omental infarction usually presents with acute abdominal pain with normal or mildly elevated WC count. Other presenting symptoms include nausea, vomiting, anorexia, diarrhea, and fever [21]. CT findings of omental infarction range from a subtle, focal, hazy soft-tissue infiltration of the omentum [25, 29] to a solitary large, cakelike, nonenhancing, heterogeneous, and high-attenuating fatty mass centered in the great omentum [8, 13, 21] (Figs ). Omental infarctions are usually located in the right upper or lower quadrants, deep in relation to the abdominal wall, anterior to the transverse colon, or anteromedial to the ascending colon. Colonic involvement depends on the anatomic location of the infarcted omentum relative to the colon [8, 11, 13, 26] (Figs ). Reactive bowel wall thickening may occur, although the inflammatory process in the omentum is usually disproportionately more severe [8, 21, 26]. Omental torsion is implicated as a cause of omental infarction when a whirled pattern of concentric linear strands is seen on CT [21]. In most cases of omental infarction, the process is self-limited, but surgery may be indicated if symptoms persist or an associated abscess develops [27]. Features that help discern the differential diagnosis Unlike acute epiploic appendagitis, which predominantly affects adults (> 20 years), omental infarction can occur in pediatric patients (15% of cases) [5]. On CT, omental infarction lacks the hyperattenuating ring and central dot seen in epiploic appendagitis [2, 5, 21, 28]. The focal lesion in acute epiploic appendagitis is often less than 5 cm long, may have a lobular appearance, and is frequently found adjacent to the sigmoid colon. The lesion in omental infarction is larger than that of epiploic appendagitis (averaging a diameter of up to 7 cm), cakelike, centered in the omentum, and commonly located medial to the cecum or the ascending colon [4 6, 19, 21]. The pain in acute epiploic appendagitis is typically in the inferior abdomen, whereas the pain in omental infarction is more common in the right side of the abdomen. Features that complicate the differential diagnosis The CT findings in both epiploic appendagitis and omental infarction may C D Fig year-old man with left-side diverticulitis. D, Contrast-enhanced CT images ( and C) with magnified images ( and D) show intraabdominal free air in large quantities (asterisk, and C). Severe fat stranding, comma sign (curved arrow, and ), and diverticula (thin arrows, and ) are seen. Note intraabdominal fluid air collection (open arrow, C and D) and secondary epiploic appendagitis (solid arrow, C and D). Fig. 13 Normal greater omentum in 63-year-old woman. xial contrast-enhanced CT image shows normal layer of fat attenuation between transverse colon and anterior abdominal wall (arrow). overlap and the two entities cannot be differentiated. Nevertheless, the clinical relevance of such differentiation is limited because both conditions are self-limited and tend to resolve spontaneously [4, 28]. Treatment is conservative unless the infarcted omentum becomes infected [2]. ecause they have the same common denominator of spontaneous fatty tissue JR:193, November

6 lmeida et al. Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved necrosis, epiploic appendagitis and omental infarction have recently been proposed to be regrouped under the same new term, intraabdominal focal fat infarction or Fig. 14 cute omental infarction in 68-year-old woman. C, Ultrasound images show hyperechoic, nonmobile mass (arrows, and C) located between anterior wall and colon. D, xial contrast-enhanced CT image shows oval lesion with heterogeneous attenuation (arrow) separated from colon in right lower quadrant. Fig. 15 Omental infarction in 71-year-old man. CT image shows heterogeneous, cakelike fatty mass centered in omentum located in right upper quadrant anterior to and continuous with ascending colon (arrow). Reactive bowel wall thickening (arrowhead) is seen. C Fig. 16 Omental infarction in 65-year-old man. CT image shows solitary heterogeneous and highattenuation fatty mass centered in omentum (arrow) located deep in relation to rectus abdominis muscle and anterior to transverse colon. IFFI, to stress that the differentiation is not clinically important and that the management of the two entities is conservative [9, 30]. D ppendicitis In the Western world, appendicitis is the most common cause of acute abdominal pain that requires surgical intervention [31, 32]. The cause in the majority of cases is obstruction of the lumen of the appendix secondary to fecaliths, lymphoid hyperplasia, foreign bodies, parasites, and tumors [33]. fter mechanical obstruction, the continued secretion of mucus results in luminal distention, venous engorgement, arterial compromise, and tissue ischemia. Luminal bacteria multiply and invade the appendiceal wall, causing transmural inflammation. ppendiceal infarction, microperforation, and extension of inflammation to the parietal peritoneum and adjacent structures are possible sequelae of appendicitis [8, 31, 33]. ppendicitis can affect all ages, although it is relatively rare at extremes of age, with the greatest incidence in the second decade of life [32, 33]. ppendicitis usually presents as a periumbilical pain of less than 5 days in duration and migrates to the right lower quadrant, associated with peritoneal irritation, anorexia, nausea, vomiting, diarrhea, and temperature greater than 37.5 C [34]. The WC count may be elevated, but this is not seen in all cases of appendicitis. cute appendicitis presents on CT images as a thick fluid-filled appendix (> 6 mm outer-to-outer wall), with intramural gas, appendiceal wall thickening (wall thickness 3 mm), and a stratified appearance that may hyperenhance after contrast material administration [31, 35]. Endoluminal appendicoliths are present in one third of patients with appendicitis; their presence increases the likelihood of appendiceal perforation [31, 33]. Occasionally, an appendicolith may be identified in an otherwise normal-appearing appendix [27]. Other associated CT signs of appendicitis are adjacent bowel wall thickening, cecal apical thickening ( cecal bar and arrowhead signs), adjacent fat stranding, right lateral conal thickening, the presence of an abscess, and lymphadenopathy [8, 31, 32, 34] (Figs. 18 and 19). Periappendicular fat stranding is typically mild to moderate, but the diagnosis of appendicitis is strongly implicated when severe fat stranding is found in the absence of substantial cecal or ileal thickening. careful search for a thickened or focally perforated appendix will often confirm the diagnosis of appendicitis [8]. Features that help discern the differential diagnosis ppendicitis affects all ages, 1248 JR:193, November 2009

7 Imaging of Epiploic ppendagitis Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 17 Omental infarction in 51-year-old man. Transverse contrast-enhanced CT image shows inhomogeneous, ill-defined ovoid-shaped fatty mass (thin arrow) centered in greater omentum distant from descending colon wall (thick arrow). unlike acute epiploic appendagitis, which predominantly affects adults (> 20 years). ppendicitis has a more typical clinical presentation with periumbilical pain migrating to the right lower quadrant and is associated with anorexia and nausea. Patients with acute epiploic appendagitis usually do not present with significant guarding or rigidity on physical examination. Most patients with acute appendicitis have an elevated WC count, whereas only a minority of patients with acute epiploic appendagitis have leukocytosis. definitive CT diagnosis of appendicitis can be made with the identification of an abnormal appendix or a calcified appendicolith Fig year-old man with appendicitis., xial contrast-enhanced CT image shows dilated appendix with abnormally enhanced wall (arrow). and C, Longitudinal () and transverse (C) ultrasound images show enlarged (12 mm) appendix (arrow, C) that is noncompressible with hyperreflective adjacent fat (asterisk, C) suggesting local inflammation. Line in indicates thickness of appendix. D, CT scan after IV and oral contrast administration in a different patient (41-year-old man) with appendicitis shows thickened appendiceal wall with wall enhancement (arrow) and fat stranding. Note enlargement of right vesical wall (arrowhead) caused by inflammatory process. Fig year-old man with appendicitis. and, Transverse unenhanced CT images show thickened appendix (short arrow) surrounded by marked fat stranding (asterisk). Note high-density appendicolith (long arrow, ). in association with pericecal inflammation [33]. Doppler ultrasound shows increased blood flow in contrast to absent blood flow in epiploic appendagitis [4, 12, 20]. Features that complicate the differential diagnosis Classic presentation of acute appendicitis occurs in only 50 60% of patients, and the diagnosis may be missed or delayed in cases without the classic presentation [33]. In cases of perforated appendicitis, with peritonitis and abscess formation, the appendix may be difficult to see on imaging studies [8]. In early or mild appendicitis, the appendix may remain normal in size [35], and inflammatory stranding of the periappendicular fat may be the only finding. Mesenteric Panniculitis Mesenteric panniculitis is a subgroup of sclerosing mesenteritis, consisting of nonspecific chronic inflammation and fibrosis of the fatty tissue of the bowel mesentery. Depending on the predominant tissue type in the mesenteric lesion, sclerosing mesenteritis can be categorized into three subgroups: mesenter C D JR:193, November

8 lmeida et al. Fig. 20 Mesenteric panniculitis in 57-year-old woman. and, xial contrast-enhanced CT scans for colon cancer follow-up show soft-tissue nodules corresponding to enlarged lymph nodes within inflamed mesenteric fat (arrowheads). Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved ic panniculitis if inflammation pre dominates over fibrosis, mesenteric lipodystrophy if fat necrosis is the predominant process, and retractile mesenteritis if fibrosis and retraction predominate [5, 36, 37]. Retractile mesenteritis is considered the final, more invasive stage of mesenteric panniculitis complicated by fibrosis and retraction [36]. Progression from mesenteric panniculitis to retractile mesenteritis is difficult to predict but fortunately is rare [29]. In most patients, the condition consists of a mixture of chronic inflammation, fat necrosis, and fibrosis [8]. Most cases of mesenteric panniculitis occur in middle or late adulthood (mean age, ~ 60 years), with a slight male predominance [5, 37]. Mesenteric panniculitis may be entirely asymptomatic, but clinical manifestations may be related to the inflammation or its mass effect and include acute abdominal pain, fever, nausea, vomiting, diarrhea, and weight loss [5, 36, 37]. Mesenteric panniculitis can be found in 0.6% of all patients undergoing abdominal CT for various indications. The pathogenesis is uncertain but can be associated with autoimmune disease, a paraneoplastic process, trauma, previous surgery, drug-induced disease, infection, and thrombosis of mesenteric vessels [37]. Mesenteric panniculitis mainly involves the mesentery of the small bowel, especially at its root [25, 37, 38]. The CT findings of mesenteric panniculitis include a focal area of increased attenuation within the mesenteric fat surrounded by a thin pseudocapsule that is usually oriented to the left side [5, 37, 38]. Mesenteric panniculitis surrounds the mesenteric vessels and shows some regional mass effect by local displacement of small-bowel loops. The small soft-tissue nodules associated with mesenteric panniculitis are thought to correspond to lymph nodes scattered within the mesenteric mass, usually less than 5 mm in diameter [8, 26]. The fat-ring sign appears as low-density fat that surrounds vessels and nodules within the mesenteric mass Fig. 21 Well-differentiated liposarcoma in 61-yearold man. and, Contrast-enhanced CT scan () and ultrasound image () show well-circumscribed fatty mass (thick arrow) with enhancing capsule and internal septa that displaces mesenteric vessels (thin arrow, ). Fig. 22 Peritoneal carcinomatosis in 52-year-old man. and, xial contrast-enhanced CT scans show omental caking (asterisks, ), omental nodules (arrows), and small-volume ascites from gastric carcinoma. and represents preservation of normal fat density because of unaffected noninflamed fat [25, 26, 37, 38] (Fig. 20). The fat-ring sign is suggestive of mesenteric panniculitis but is nonspecific because it can be found in other entities such lymphoma [26]. reas of fibrosis within the inflammation appear as linear bands of soft-tissue attenuation, resulting in spiculation that may be mistaken for a neoplastic process [5]. Calcification is uncommon and may be related to the fat necrosis [36]. The major complications of mesenteric panniculitis are related to the progressive fibrosis that may lead to shortening of the mesentery, compression of the mesenteric vessels, and bowel-loop narrowing [5, 37]. Some features can help discern the differential diagnosis. Mesenteric panniculitis is not an acute abdominal condition and appears as a larger lesion. It is most commonly located in the root of the small-bowel mesentery that does not abut the colonic wall. cute epiploic appendagitis, as the name im 1250 JR:193, November 2009

9 Imaging of Epiploic ppendagitis Downloaded from by on 05/12/18 from IP address Copyright RRS. For personal use only; all rights reserved plies, is an acute disease seen as a small focal lesion anterior or anteromedial to the colon, abuts the colon wall, and does not involve the small-bowel mesentery [5]. Primary Tumors and Metastases There are many other possible causes for a CT finding of a fatty mass or masslike lesion in the abdomen, such as liposarcoma (Fig. 21), dermoid and carcinoid tumor, lipoma, and omental metastases (Fig. 22). Omental metastases can present as soft-tissue implants on peritoneal surfaces. Omental cake is the replacement of the omental fat by tumor infiltration and on CT appears as a thick, confluent soft-tissue mass closely adherent to the ventral surface of the transverse colon in the mid abdomen [25]. The presence of ill-defined lesion margins, numerous lesions, a lesion centered in the omentum, and a history of primary neoplasm are useful for diagnosing omental metastasis [5] (Fig. 22). In patients with known malignancy, the diagnosis of acute epiploic appendagitis should only be made if there is a presentation with acute abdominal pain and no CT evidence of peritoneal metastatic disease elsewhere [2]. Conclusion Epiploic appendagitis is self-limiting, and the appropriate management is conservative. In our experience, many clinicians are not familiar with this entity, and the radiologist can provide guidance for supportive management. Therefore, a noninvasive diagnosis of this relatively rare cause of acute abdomen is important for selecting the appropriate mode of management and preventing unnecessary hospital admission and surgery. References 1. linder E, Ledbetter S, Rybicki F. Primary epi ploic appendagitis. Emerg Radiol 2002; 9: Sandrasegaran K, Maglinte DD, Rajesh, kisik FM. 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