Disproportionate FatStranding: A HelpfulCT Sign in Patientswith Acute AbdominalPain1
LEARNINGOBJECTIVESFOR TEST 3After reading thisarticle and takingthe test, the reader
will be able to:
� Define the conceptof disproportionatefat stranding.
� List the four majordifferential diagnosessuggested when dis-proportionate fatstranding is present.
� Identify the mainclinical and radio-logic features anddifferential diagnosisof diverticulitis, ap-pendicitis, epiploicappendagitis, andomental infarction.
Jose M. Pereira, MD2 ● Claude B. Sirlin, MD ● Pedro S. Pinto, MD2
R. Brooke Jeffrey, MD ● Damien L. Stella, MD ● Giovanna Casola, MD
RadioGraphics 2004; 24:703–715 ● Published online 10.1148/rg.243035084
1From the Departments of Radiology of University of California San Diego Medical Center, 200 W Arbor Dr, San Diego, CA 92103-8756 (J.M.P.,C.B.S., P.S.P., G.C.); Stanford University, Palo Alto, Calif (R.B.J.); and Royal Melbourne Hospital, Parkville, Australia (D.L.S.). Recipient of a Cer-tificate of Merit award for an education exhibit at the 2002 RSNA scientific assembly. Received March 28, 2003; revision requested June 27 and re-ceived August 15; accepted August 15. All authors have no financial relationships to disclose. Address correspondence to C.B.S. (e-mail: [email protected]).
2Current address: Department of Radiology, Porto Medical School, Hospital S. Joao, Porto, Portugal.
IntroductionIn patients with acute abdominal pain, the findingof fat stranding adjacent to thickened bowel wallon computed tomographic (CT) scans suggests agastrointestinal origin for the patient’s pain, butthe differential diagnosis is broad. Anecdotally,we have observed that fat stranding that is “dis-proportionate”—that is, much greater than thedegree of bowel wall thickening—suggests a nar-rower differential diagnosis: diverticulitis, epiploicappendagitis, omental infarction, and appendici-tis. In this article, we introduce “disproportionatefat stranding” as a CT sign that helps in theevaluation of patients with acute abdominal pain.Typical clinical and CT features of the fourpathologic entities that characteristically manifestthis sign are described. Emphasis is placed onfindings that allow differentiation of these pro-cesses from other diseases of the mesentery andomentum, including acute and chronic condi-tions. Correct noninvasive diagnosis is important,as epiploic appendagitis and omental infarctionare typically self-limited conditions, whereas ap-pendicitis and many cases of diverticulitis requiresurgery or other intervention.
Pathophysiology and CT FindingsMost acute inflammatory diseases of the gastroin-testinal tract, including infectious, noninfectious,and ischemic disorders, are centered in the bowelwall. For these diseases, the degree of bowel wallthickening typically exceeds the degree of associ-ated fat stranding, and not uncommonly, fatstranding may be subtle despite marked muralabnormality (Fig 1).
In a few acute diseases of the gastrointestinaltract, however, the pathologic process is charac-teristically centered in the mesentery adjacent tothe bowel wall rather than in the bowel wall itself.In these diseases, the fat stranding is often dispro-portionately greater than the degree of wall thick-ening (Fig 2). Because the list of diseases thattypically manifest disproportionate fat strandingis short—diverticulitis, epiploic appendagitis,omental infarction, and appendicitis—this obser-vation is a helpful diagnostic clue to narrow anotherwise broad differential diagnosis.
DiverticulitisDiverticula are small sacculations of mucosa andsubmucosa through the muscularis of the colonicwall. They develop where the nerve and bloodvessel pierce the muscularis between the teniaecoli and mesentery, an origin that accounts for
Figures 1, 2. Disproportionate fat stranding. (1) Axial contrast material–enhanced CT image of a man withpseudomembranous colitis shows severe wall thickening in the descending colon (arrows) that is disproportionatelygreater than the degree of fat stranding (arrowheads). This pattern indicates that the pathologic process is centered inthe bowel wall, a finding characteristic of infection, pseudomembranous colitis, ischemia, and inflammatory boweldisease as the main differential diagnoses. (2) Axial nonenhanced CT image of a man with diverticulitis depicts fatstranding (arrowheads) that is disproportionately greater in severity than the degree of bowel wall thickening (arrow).This pattern indicates a predominantly pericolonic process and suggests a narrower differential diagnosis. Because ofthe presence of diverticula and the involvement of the left side of the colon, diverticulitis is the primary diagnosticconsideration.
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their propensity to bleed. Diverticula can befound anywhere in the colon, but they occur pre-dominantly in the descending and sigmoid colon.They do not develop in the rectum. Diverticulaalso occur in the small intestine, but they are lesscommon than those arising from the colon. AMeckel diverticulum is a congenital outpouching
derived from an unobliterated yolk stalk, and itoccurs exclusively in the distal ileum.
Diverticulitis occurs when the neck of a diver-ticulum becomes occluded, resulting in inflam-mation, erosion, and microperforation. Microper-foration results in pericolonic inflammation thattypically is more severe than the inflammation ofthe colon itself. Ninety-five percent of cases occurin the left side of the colon. Right-sided diverticu-litis accounts for 5% of cases and occurs morefrequently in Asians. Diverticulitis of the trans-verse colon or small intestine is rare.
The appearance of acute diverticulitis on CTscans parallels the pathologic features. The mostcommon CT finding is paracolic fat stranding.The fat stranding characteristically is dispropor-tionately more severe than the relatively mild,focal colonic wall thickening (Fig 3). Diverticulaare typically present. The inflammatory processcan result in accumulation of fluid in the root ofthe sigmoid mesentery, which appears on CTscans as the “comma sign” (Fig 4), and engorge-ment of the mesenteric vessels, which appears asthe “centipede sign” (Fig 5) (1).
Figure 3. Diverticulitis. Axial CT image of a manwith left-sided diverticulitis shows severe pericolonic fatstranding (arrowheads) that is greater than the degreeof wall thickening of the descending colon (curved ar-row). A “normal” diverticulum (open arrow) and a ill-defined (fuzzy) diverticulum (solid straight arrow) arealso seen.
Figure 4. Diverticulitis and the comma sign. Axialnonenhanced CT image of a 47-year-old patient withcecal diverticulitis shows thickening of the lateral conalfascia, a finding known as the reverse comma sign (ar-rowhead). Note the mild wall thickening of the cecum(small arrow) and a diverticulum (large arrow).
Figure 5. Diverticulitis and the centipede sign. Axialcontrast-enhanced CT image of a patient with diver-ticulitis shows engorgement of the vasa recta that feedsthe sigmoid colon, a finding known as the centipedesign (open arrows). Note also the mild wall thickeningof the colon (long solid arrow), diverticula (arrow-heads), and fluid at the root of the sigmoid mesentery(short solid arrow).
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Although a diagnosis of diverticulitis from CTfindings may be difficult to make when the loca-tion is atypical, the combination of diverticulaand disproportionate fat stranding suggests the
diagnosis, even in unusual locations, such as theright side of the colon, transverse colon, distalileum, and jejunum (Figs 6–9) (2–5). The mostimportant entity in the differential diagnosis toexclude is colon adenocarcinoma. However, there
Figure 6. Acute right-sided diverticulitis.(a) Axial nonenhanced CT image shows mildwall thickening of the ascending colon (solidstraight arrow) and moderate pericolonic fatstranding (open arrows). Diverticulum(curved arrow) and the reverse comma sign(arrowhead) are also present. (b) On an axialnonenhanced CT image obtained at a lowerlevel than a, the appendix appears normal(arrow), a finding that rules out appendicitis.
Figure 7. Transverse colon diverticulitis in a 62-year-old man. Axial nonenhanced (a) and contrast-enhanced (b) CT images show a fecalith within a diverticulum (solid straight arrow) surrounded by se-vere pericolonic fat stranding (arrowheads). Colonic wall thickening is mild (curved arrow) and scattereddiverticula (open arrow) are present.
Table 1Differentiating Features of Diverticulitis and Colon Adenocarcinoma on CT Scans
Feature Diverticulitis Adenocarcinoma
Diverticula Almost always visible May or may not be presentFat stranding Disproportionate None or minimalPresence of comma or centipede sign Yes NoFluid Present at mesenteric root NoneColon wall thickening Mild, smooth, concentric Severe, irregular, eccentricTransition from normal to abnormal wall thickness Gradual Shouldering evidentLength of affected segment Long (5–10 cm) Focal (�5 cm)Lymphadenopathy None Present
Source.—References 6–8.
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are several features that help differentiate the twoconditions (6–8), as summarized in Table 1 andshown in Figures 10 and 11.
Epiploic AppendagitisAppendices epiploicae are pedunculated adiposestructures protruding from the external surface ofthe colon into the peritoneal cavity. They are ar-ranged in two separate longitudinal rows that ex-tend from the cecum to the rectosigmoid junc-tion. Approximately 50–100 in number, appendi-ces epiploicae are typically 1–2 cm thick and 2–5cm long.
Appendices epiploicae are normally invisibleon CT scans because they blend with the sur-rounding fat unless they are surrounded by ascites(Fig 12). Each is supplied by one or two smallend arteries branching from the vasa recta longaof the colon and is drained by a tortuous veinpassing through its narrow pedicle. Their limitedblood supply, together with their pedunculatedshape and excessive mobility, make appendicesepiploicae prone to torsion and ischemic or hem-orrhagic infarction (9,10).
Figure 8. Meckel diverticulitis in a 59-year-old man.Axial contrast-enhanced CT image shows a large out-pouching (Meckel diverticulum) that extends from theileal wall (arrows) with moderate wall thickening andsevere stranding of the surrounding fat (arrowheads).
Figure 9. Jejunal diverticulitis in a woman with ab-dominal pain. Contrast-enhanced CT scan shows moder-ate fat stranding of the mesentery (arrowheads), imme-diately adjacent to jejunal diverticula (thin arrows), one ofwhich is ill defined (thick arrow). Bowel wall thickeningis mild; regional mesenteric vessels are engorged.
Figures 10, 11. Colon adenocarcinoma. (10) Axial contrast-enhanced CT image shows severe wall thickening (ar-rows) of the ascending colon with no fat stranding. This disproportionate degree of thickening suggests that the pa-tient’s disease originates in the bowel wall. (11a) Axial contrast-enhanced CT image of another patient shows wallthickening (arrows) of the descending colon that is disproportionately greater than the degree of fat stranding (arrow-head). (11b) Axial contrast-enhanced CT image obtained at a lower level shows the abrupt transition from thick tonormal wall (“shouldering”) (short arrow) and the presence of lymphadenopathy (long arrow). Enlarged regionallymph nodes are more suggestive of colon cancer than of diverticulitis.
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Figures 12–14. (12) Axial CT image shows normal appendices epiploicae (arrows) of the sigmoid colon, whichappear as fingerlike projections of pericolic fat floating within ascites (�). (13) Epiploic appendagitis in a 23-year-oldman. Axial contrast-enhanced CT image shows an ovoid mass (solid arrow) of fat attenuation anterior to the wall ofthe descending colon. The mass is surrounded by a hyperattenuated rim (representing thickened visceral perito-neum) and contains a central high-attenuation dot (most likely representing thrombosed central vessels). Note themoderate fat stranding (arrowhead) and mild focal thickening of the adjacent colonic wall (open arrow). (14) Epi-ploic appendagitis in a 46-year-old man. Axial contrast-enhanced CT image shows severe fat stranding (arrowheads)and a fatty ovoid mass (curved arrow) with a hyperattenuated rim and central dot (open arrow). Associated thicken-ing of the colonic wall is mild (solid straight arrow).
Figure 15. Normal greater omentum. Axial contrast-enhanced CT image shows the normal layer of fat at-tenuation between the transverse colon and anteriorabdominal wall (arrowheads). Mesenteric lymph nodesare mildly enlarged (arrows).
Figure 16. Omental infarction. Axial con-trast-enhanced CT image of a patient whopresented with acute right upper quadrantpain shows an inhomogeneous mass (arrow)in the greater omentum, anterior to the trans-verse colon. Moderate adjacent wall thicken-ing is also evident (arrowhead). Diverticulitiswas a diagnostic consideration, but no diver-ticula were seen at CT. A barium enemastudy performed 1 month later (not shown)revealed a normal colonic lumen without di-verticula. Cholecystitis was also a consider-ation, but there was no inflammation of thefat immediately adjacent to the gallbladder,and the gallbladder appeared normal at ultra-sonography (not shown) performed immedi-ately after CT.
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Acute torsion of an appendage results in a focalinflammatory process called epiploic appendagi-tis. The condition usually manifests as localizedabdominal pain in one of the lower quadrants,since the sigmoid colon and cecum are the mainsites of involvement. Epiploic appendagitis clini-cally mimics acute appendicitis or diverticulitis.
CT findings of epiploic appendagitis are usu-ally diagnostic (11,12). Characteristic findingsinclude (a) a paracolonic oval fatty mass repre-senting the infarcted or inflamed appendix epi-ploica, (b) a well-circumscribed hyperattenuatedrim that surrounds the mass and represents theinflamed visceral peritoneal lining, and sometimes(c) a high-attenuation central dot representingengorged or thrombosed central vessels or centralareas of hemorrhage (Fig 13). Most important,the paracolonic inflammatory changes are typi-
cally disproportionately more severe than themild local reactive thickening of the adjacent co-lonic wall (Fig 14).
Noninvasive diagnosis is important becauseepiploic appendagitis is self-limiting, and the ap-propriate management is conservative (13,14).
Omental InfarctionThe greater omentum is composed of a doublelayer of peritoneum that extends inferiorly fromthe greater curvature of the stomach, turns supe-riorly on itself to drape over the transverse colon,and extends to the retroperitoneal pancreas. Theblood supply of the greater omentum travelslargely through the right and left gastroepiploicarteries.
Normally, the greater omentum appears onCT scans as a band of fatty tissue that containssmall vessels and is located just anterior to thetransverse colon (Fig 15). It has a variable thick-ness, which depends primarily on the weight ofthe individual.
Segmental omental infarction typically occurson the right (mimicking appendicitis or gallblad-der disease [15]), a predilection that has beenattributed to an embryologic variant of the bloodsupply of the right portion of the omentum,which predisposes it to venous thrombosis (16).Risk factors include obesity and recent surgery.
On CT scans, the infarcted omentum appearsas a large, cakelike, high-attenuation fatty masscentered in the omentum (17) (Figs 16–18). Themass may or may not be immediately adjacent tothe colon, depending on the anatomic location ofthe infarcted omentum relative to the colon. Re-active bowel wall thickening may occur, but theinflammatory process in the omentum usually isdisproportionately more severe.
Figure 17. Omental infarc-tion in a 60-year-old womanwith acute right upper quad-rant pain. Axial contrast-en-hanced CT images (a ob-tained at a higher level than b)show an inhomogeneousround, high-attenuation fattymass (arrowheads) in thegreater omentum, anterior toand exerting mass effect onthe transverse colon (arrow inb).
Figure 18. Omental infarction in a 60-year-old woman with acute right flank pain. Axialnonenhanced CT image shows an inhomoge-neous, ill-defined ovoid fatty mass (arrow-heads) centered in the greater omentum, dis-tant from the ascending colon wall (arrow).
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Omental infarction and epiploic appendagitismay have similar appearances on CT scans. Dis-tinguishing features have been described (18)(Table 2); nevertheless, the clinical relevance ofsuch differentiation is limited because the treat-ment for both conditions is conservative (ie, non-surgical). Some authors advocate use of the termintraabdominal focal fat infarction for cases inwhich the two entities cannot be reliably differen-tiated (18).
AppendicitisIn the Western world, appendicitis is the mostcommon cause of acute abdominal pain that re-quires surgical intervention. The primary patho-genic event in the majority of cases is luminal ob-struction caused by fecaliths and lymphoid hyper-plasia. Foreign bodies, parasites, and primary and
metastatic tumors are less common causes of ob-struction. Once obstruction occurs, the continuedsecretion of mucus results in elevated intralumi-nal pressure and luminal distention, with conse-quent venous engorgement, arterial compromise,and tissue ischemia. Luminal bacteria multiplyand invade the appendiceal wall, causing trans-mural inflammation. Eventually, appendiceal in-farction and microperforation occur, and the in-flammation extends to the parietal peritoneumand adjacent structures.
Direct visualization of a dilated (�6 mm inmaximum diameter), fluid-filled appendix is themost specific CT finding of appendicitis (Fig 19)(19,20). Other direct signs include an abnormallythickened appendix, increased attenuation of theappendix after contrast material administration,and periappendicular fat stranding (21,22). Sec-ondary signs include appendicolith(s) or thicken-ing of the cecal apex (cecal bar sign and the ar-rowhead sign) (Fig 20) (23–25).
Figures 19, 20. (19) Appendicitis in a 21-year-old patient. Axial nonenhanced CT image shows a thickened ap-pendix (white arrows) surrounded by marked fat stranding (arrowheads). Note the high-attenuation appendicolith(black arrow). (20) Appendicitis in a 7-year-old boy. Axial contrast-enhanced CT images (a obtained at a higher levelthan b) show the high-attenuation wall of the dilated fluid-filled appendix (white arrow). Surrounding fat stranding issevere (arrowheads). Note mild posterolateral wall thickening of the cecum (cecal bar sign) (solid straight black ar-row) and also the arrowhead-shaped collection of contrast agent (arrowhead sign) (curved arrow) formed as contrastmaterial funnels into the partially coapted cecal wall adjacent to the occluded appendiceal orifice. An appendicolith isalso seen (open arrow).
Table 2Differentiating Features of Epiploic Appendagitis and Omental Infarction on CT Scans
Feature Epiploic Appendagitis Omental Infarction
Hyperattenuated rim Present NoneCentral area of high attenuation Present NoneAnatomic location relative to the colon Always immediately adjacent Centered in the omentumLocation of pain Right lower quadrant, left
lower quadrantRight lower quadrant,
right upper quadrant
Source.—Reference 18.
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Periappendicular fat stranding is typically mildto moderate (Fig 21), but it can be severe (Fig22). The diagnosis of appendicitis from CT find-ings is straightforward if the appendix is easilyvisualized (26). However, in cases of perforatedappendicitis with peritonitis or abscess formation,the appendix may be difficult to see (27,28). Inour experience, the finding of severe fat strandingin the right lower quadrant in the absence of sub-stantial cecal or ileal thickening suggests the pos-sibility of appendicitis. A careful search for athickened or focally perforated appendix will of-ten yield the finding to confirm the diagnosis(Figs 23, 24) (29–32).
Other Causes of Fat StrandingFat stranding may arise from other acute andchronic causes that should be considered in thedifferential diagnosis. The clinical presentation—acute or chronic—is a key diagnostic feature.Acute conditions that cause fat stranding includeperitonitis; inflammation, infection, or ischemiaof the bowel; perforation of colon cancer; inflam-mation associated with pancreatitis or cholecysti-tis; trauma; and surgery. Chronic conditions thatmanifest with fat stranding include neoplasms ofthe omentum, chronic infections of the omentum,and mesenteric panniculitis.
Figures 21, 22. (21) Appendicitis in a 72-year-old man. Axial nonenhanced CT imageshows an enlarged appendix (open arrow) with an appendicolith (solid arrow), surroundedby relatively mild stranding (arrowhead) of the adjacent fat (cf Fig 22). (22) Appendicitis in a32-year-old man. Axial nonenhanced CT image shows severe fat stranding (arrowheads)surrounding the enlarged appendix (open arrow). The fat stranding is disproportionatelygreater than the degree of wall thickening (black arrow) of the adjacent cecum. An appendi-colith (solid white arrow) is also seen.
Figures 23, 24. (23) Appendicitis with perforation and abscess. Axial contrast-enhanced CT image showsfocal disruption of the wall (black arrow) of the appendix. The disruption manifests as a focal interruption ofthe otherwise continuous mucosal enhancement (white arrow). An abscess (�) surrounds the appendix. Notealso an appendicolith and mild bowel thickening. (24) Perforated appendix with peritonitis. Axial contrast-en-hanced CT scan shows enhancement and disruption (arrow) of the appendiceal wall. Inflamed bowel wall andsevere fat stranding are also present (arrowheads).
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Acute Causes of Fat StrandingAcute peritonitis of any cause may manifest withfat stranding or ascites. The fat stranding is usu-ally diffuse or multifocal, which permits it to bedifferentiated from the stranding caused by un-complicated cases of diverticulitis, epiploic ap-pendagitis, omental infarction, and appendicitis.
Inflammation, infection, or ischemia of bowelmay manifest with fat stranding, but these entitiestypically cause circumferential thickening of thebowel wall that is more severe than the degree ofassociated fat stranding (Fig 25).
Acute perforation of the colon associated withcolon cancer may cause fat stranding that is diffi-cult to differentiate from that seen in cases of di-verticulitis. Bowel wall thickening may be a help-ful feature, as the mural thickening seen in malig-nant perforation of the colon tends to be moresevere and more focal than that associated withdiverticulitis. Other helpful clues are shouldering,whether the wall thickening is concentric or not,adjacent lymphadenopathy, and metastases(Table 1). In some cases, however, differentiationbetween colon cancer and diverticulitis is not pos-sible with CT alone (Fig 26).
In pancreatitis or cholecystitis, fat stranding ischaracteristically most severe immediately adja-
Figure 25. Crohn disease involving the ter-minal ileum and cecum. Axial CT imageshows circumferential wall thickening of thececum and terminal ileum (arrow) and fibro-fatty proliferation (“creeping fat”) (arrow-heads). Note lack of substantial fat stranding.
Figure 26. Diverticulitis that caused large bowel obstruction in a 22-year-old man.(a) Axial CT scan shows marked focal wall thickening of the sigmoid colon with abruptshouldering (arrows), mild fat stranding (arrowheads), and the comma sign. (b) Axial CTscan obtained at a lower level shows diverticula (arrow). CT findings were considered inde-terminate for differentiating diverticulitis and colon cancer. Endoscopic biopsy was per-formed, and a pathologic diagnosis of diverticulitis was made. There was no evidence of ma-lignancy.
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cent to the inflamed organ (Fig 27), and this loca-tion is atypical compared with those associatedwith the other causes of fat stranding. Moreover,other signs of pancreatitis or cholecystitis are usu-ally present.
Although trauma can cause fat stranding,trauma to the omentum or mesentery alone isuncommon. Usually, a history of trauma is avail-able and other CT findings of injury (eg, hemo-peritoneum, mesenteric hematoma or interloopfluid, and parenchymal laceration) are present,which allow a straightforward diagnosis.
Focal fat stranding in and adjacent to the sur-gical bed is extremely common after recent ab-dominal surgery. If the stranding is focal and suf-ficiently severe, differentiation from omental in-farction may be impossible, especially becausesurgery is a known risk factor for omental infarc-tion. However, differentiation is usually not clini-cally important, as management of omental in-farction is conservative.
Chronic Causes of Fat StrandingPrimary omental tumors and metastases cancause fat stranding (Fig 28); however, involve-ment of the omentum with tumor often results ina more nodular appearance than does omentalinfarction. Patient history is helpful in the differ-ential diagnosis.
Chronic infection of the omentum, particularlytuberculosis, may appear similar to omental in-farction on CT scans (Fig 29). However, the find-ings of intraabdominal lymph nodes, particularlylow-attenuation nodes, and bowel wall thicken-ing, particularly in the ileocecal region, shouldsuggest the diagnosis (33). A history of tuberculo-sis, positive tuberculin skin test, and characteristicchest radiographic findings would be additionalclues but may not be present.
Mesenteric panniculitis is a rare idiopathicdisorder characterized by a chronic nonspecific
Figure 27. Pancreatitis in a 45-year-old woman.Axial contrast-enhanced CT image shows marked fatstranding (arrows) adjacent to an enlarged pancreasand fluid in the anterior pararenal space (arrowheads),findings that are characteristic of pancreatitis.
Figure 28. Carcinomatous peritonitis in a patientwith large bowel obstruction. Axial contrast-enhancedCT image shows mild wall thickening (white arrow) ofthe transverse colon adjacent to an area of heteroge-neous attenuation in the greater omentum (arrow-heads). Enlarged mesenteric lymph nodes (black ar-row) are also seen.
Figure 29. Mesenteric tu-berculosis. (a) Contrast-en-hanced CT scan shows thicken-ing of the anterior wall of thetransverse colon (arrow) adja-cent to a focal area of heteroge-neous attenuation in the greateromentum (arrowheads). Ap-pearance is similar to that ofomental infarction (cf Figs 16–18), but here the mesentericmass has a nodular pattern notseen in omental infarction.(b) Contrast-enhanced CTscan shows enlarged periportalnodes (arrow).
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inflammation involving the adipose tissue of thebowel mesentery (34). It has a poorly understoodassociation with underlying malignancy, whichsuggests that, at least in some patients, it may be aparaneoplastic condition. On CT scans, pannicu-litis characteristically manifests as a solitary well-defined mass of inhomogeneous fatty tissue at theroot of the jejunal mesentery. Because it extendsalong the root of the jejunal mesentery, panniculi-tis typically has a leftward orientation (Fig 30a).The fatty mass engulfs superior mesenteric vesselswithout vascular narrowing. Bowel loops are of-ten displaced but not invaded. Well-defined, soft-tissue nodules less than 5 mm in diameter are of-ten scattered throughout the mass. A distinctive,hypoattenuated fatty halo typically surrounds thenodules and vessels (Fig 30b) and helps differen-tiate panniculitis from lymphoma and other ma-lignant causes of mesenteric adenopathy. A hy-perattenuating stripe partially surrounding themass is also suggestive of panniculitis (Fig 31).The characteristic location and appearance ofpanniculitis, and the asymptomatic or chronicpresentation of patients with this disease permitthe diagnosis.
SummaryThe observation of disproportionate fat strandingis a helpful CT sign in patients with acute ab-dominal pain. Anecdotally, we observed that thepresence of fat stranding that is more severe than
expected for the degree of bowel wall thickeningsuggests that the pathologic process is centered inthe mesentery. This sign helps narrow the differ-ential diagnosis of gastrointestinal disorders tofour main entities: diverticulitis, epiploic ap-pendagitis, omental infarction, and appendicitis.The characteristic CT findings of each of theseentities often lead to a final diagnosis. Other enti-ties, although less common, include acute andchronic processes of the mesentery and bowelwall and should also be considered.
Figure 30. Mesenteric panniculitis in a 54-year-old man with colon cancer. (a) Axial contrast-enhanced CT imageshows a solitary well-defined mass in the left side of the mesentery (arrowheads in a, open arrows in b) that hashigher attenuation than that of retroperitoneal fat. Note the fatty halo surrounding the soft-tissue nodules and vessels(arrows). (b) Axial contrast-enhanced CT image obtained at a lower level shows irregular thickening of the proximalascending colon (arrowheads) at the site of the patient’s colon cancer and small regional nodes (solid arrow). As illus-trated by this case, mesenteric panniculitis has a poorly understood association with underlying malignancy. It doesnot represent a metastatic process, however; malignant cells are not present within the inflamed tissue.
Figure 31. Mesenteric panniculitis. Axial contrast-enhanced CT image shows a well-defined fatty inho-mogeneous mass (solid arrows) with a hyperattenuat-ing peripheral rim (arrowheads). Note the fatty halosurrounding the mesenteric vessels and nodes (openarrow).
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This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician’s Recognition Award. To obtaincredit, see accompanying test at http://www.rsna.org/education/rg_cme.html.
