Fat stranding

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  • pls what does this mean :Herniation of bowel loops is noted in the anterior abdominal wall .Enhancement and thickening of the overlying skin is noted. This extends to the umblicus with evidence of stranding of the fat planes. Communication is noted within the herniated bowel loops and the exterior. Fluid tracks are also enhancing post contrast. Rest of the bowel loops are within normal limits.
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Fat stranding

  1. 1. By Navdeep Singh
  2. 2.  Fat stranding refers to an abnormal increased attenuation in fat.  Abdominal fat stranding can produce various appearances. Mild inflammation may cause a subtle hazy increased attenuation of the fat (ground-glass like), increasing severity of the inflammation can produce a reticular pattern, with more well-defined linear areas of increased attenuation.  The underlying pathophysiologic process is increased edema and engorgement of lymphatics.
  3. 3.  What is the location of the fat stranding?  What other structures are involved in the process?  Are there other characteristic CT findings of the diagnostic possibilities that suggest the most likely cause?
  4. 4.  “Disproportionate” Fat stranding—that is, much greater than the degree of bowel wall thickening.  Suggests a narrower differential diagnosis: diverticulitis, epiploic appendagitis, omental infarction, and appendicitis.
  5. 5.  Diverticula are small sacculations of mucosa and submucosa through the muscularis of the colonic wall.  They develop where the nerve and blood vessel pierce the muscularis between the teniae coli and mesentery, an origin that accounts for their propensity to bleed.  predominantly in the descending and sigmoid colon but not in a rectum.
  6. 6.  Diverticulitis occurs when the neck of a diverticulum becomes occluded, resulting in inflammation, erosion, and microperforation.  Microperforation results in pericolonic inflammation that typically is more severe than the inflammation of the colon.  CT finding - disproportionate paracolic fat stranding. - comma sign - engorgement of the mesenteric vessels, which appears as the ―centipede sign‖.
  7. 7.  Axial CT image of a man with left-sided diverticulitis shows severe pericolonic fat stranding (arrowheads) that is greater than the degree of wall thickening of the descending colon (curved arrow). A ―normal‖ diverticulum (open arrow) and a ill- defined (fuzzy) diverticulum (solid straight arrow) are also seen.
  8. 8.  Appendices epiploicae are pedunculated adipose structures protruding from the external surface of the colon into the peritoneal cavity.  Normally invisible on CT scans because they blend with the surrounding fat unless they are surrounded by ascites.  Each is supplied by one or two small end arteries branching from the vasa recta longa of the colon.  Their limited blood supply, together with their pedunculated shape and excessive mobility, make appendices epiploicae prone to torsion and ischemia.
  9. 9.  Axial CT image shows normal appendices epiploicae (arrows) of the sigmoid colon, which appear as fingerlike projections of pericolic fat floating within ascites (∗).
  10. 10.  Acute torsion of an appendage results in a focal inflammatory process called epiploic appendagitis.  IMAGING - a paracolonic oval fatty mass representing the infarcted or inflamed appendix epiploica, - Well-circumscribed hyperattenuated rim that surrounds the mass and represents the inflamed visceral peritoneal lining - High-attenuation central dot representing engorged or thrombosed central vessels or central areas of hemorrhage
  11. 11.  Axial contrast- enhanced CT image shows an ovoid mass (solid arrow) of fat attenuation anterior to the wall of the descending colon. The mass is surrounded by a hyperattenuated rim (representing thickened visceral peritoneum) and contains a central high- attenuation dot (most likely representing thrombosed central vessels). Note the moderate fat stranding (arrowhead) and mild focal thickening of the adjacent colonic wall (open arrow).
  12. 12.  Segmental omental infarction typically occurs on the right, a predilection that has been attributed to an embryologic variant of the blood supply.  Risk factors include obesity and recent surgery.
  13. 13.  On CT scans, the infarcted omentum appears as a large, cakelike, high-attenuation fatty mass centered in the omentum.  Reactive bowel wall thickening may occur, but the inflammatory process in the omentum usually is disproportionately more severe.  Omental infarction and epiploic appendagitis may have similar appearances on CT scans.
  14. 14.  Axial contrast-enhanced CT image of a patient who presented with acute right upper quadrant pain shows an inhomogeneous mass (arrow) in the greater omentum, anterior to the transverse colon. Moderate adjacent wall thickening is also evident (arrowhead). Diverticulitis was a diagnostic consideration, but no diverticula were seen at CT.
  15. 15.  Axial contrast- enhanced CT images (a obtained at a higher level than b) show an inhomogeneou s round, high- attenuation fatty mass (arrowheads) in the greater omentum, anterior to and exerting mass effect on the transverse colon (arrow in b).
  16. 16.  Is the most common cause of acute abdominal pain that requires surgical intervention.  The primary pathogenic event in the majority of cases is luminal obstruction caused by fecaliths and lymphoid hyperplasia.
  17. 17.  Once obstruction occurs, the continued secretion of mucus results in elevated intraluminal pressure and luminal distention, with consequent venous engorgement, arterial compromise, and tissue ischemia. Luminal bacteria multiply and invade the appendiceal wall, causing transmural inflammation.
  18. 18.  CT Findings - Direct visualization of a dilated (>6 mm in maximum diameter), fluid-filled appendix is the most specific.  Other direct signs include an abnormally thickened appendix, increased attenuation of the appendix after contrast material administration, and periappendicular fat stranding.  Secondary signs include appendicolith(s) or thickening of the cecal apex (cecal bar sign).
  19. 19.  Axial nonenhance d CT image shows a thickened appendix (white arrows) surrounded by marked fat stranding (arrowhead s). Note the high- attenuation appendicoli th (black arrow).
  20. 20.  Axial contrast- enhanced CT images (a obtained at a higher level than b) show the high-attenuation wall of the dilated fluid- filled appendix (white arrow). Surrounding fat stranding is severe (arrowheads). Note mild posterolateral wall thickening of the cecum (cecal bar sign) (solid straight black arrow) and also the arrowhead-shaped collection of contrast agent (arrowhead sign) (curved arrow) formed as contrast material funnels into the partially coapted cecal wall adjacent to the occluded appendiceal orifice. An appendicolith is also seen (open arrow).
  21. 21.  Bowel ischemia—Ischemia and infarction of the gastrointestinal tract are a heterogeneous group of disorders that have the unifying theme of hypoxia of the small bowel or colon.  more common in the geriatric population, especially in those with comorbid cardiovascular disease.  CT can accurately show ischemic bowel segments and often aids in determining the primary underlying cause
  22. 22.  CT Findings - wall thickening, which may be hypoattenuating when there is submucosal edema or hyperattenuating when there is intramural hemorrhage from a reperfusion injury.  Other findings are bowel dilatation, lack of bowel wall enhancement, mesenteric fat stranding, vascular engorgement, ascites, pneumatosis and portal venous gas.
  23. 23.  There is abnormal loop of ileum in right lower quadrant (thick arrows). Wall of affected bowel is thickened with low- density center representing submucosal edema. There is mild surrounding fat stranding (thin arrows).
  24. 24.  Filling defect in superior mesenteric vein (arrow) represents thrombus. Rim of enhancement around thrombus represents enhancing vessel wall, and fat stranding around affected vessel is due to edema.
  25. 25.  Complicated bowel obstruction, the visualization of mesenteric fat stranding, mesenteric fluid, and ascites can strongly suggest the diagnosis of partial or transmural bowel ischemia.  If two of these three findings are present, the specificity of this diagnosis is reported to be about 95%.  single best predictor of ischemia is lack of bowel wall enhancement.
  26. 26.  There is pneumato sis of right colon (arrows).
  27. 27.  May cause fat stranding that is difficult to differentiate from that seen with acute diverticulitis.  The degree of bowel wall thickening can be a helpful differential feature.  The bowel wall thickening is of soft-tissue attenuation and does not display the target sign or mural stratification signifying bowel wall edema that is seen in inflammatory processes or ischemia.
  28. 28.  Focally thickened segment of sigmoid colon, which is of soft-tissue attenuation, represents colon carcinoma with shouldering (short arrow). There is moderate fat stranding in region of carcinoma, secondary to perforation (long arrow).
  29. 29.  Ulcerative colitis primarily affects the colon (rectum and left colon), occasionally also involving the terminal ileum with backwash ileitis.  In contrast, Crohn disease usually affects the small bowel (almost always the terminal ileum) with or without colonic or anal involvement.
  30. 30.  Bowel wall thickening is the most common CT finding.  Hazy (ground-glass) fat stranding in the mesentery results in a ―misty‖ mesentery.  Ulcerative colitis – diffuse symmetric colonic thickening. - asymmetric inflammation along the mesenteric border. - halo sign, which is due to the deposition of submucosal fat that results in a low-attenuation ring in the bowel wall.  Crohn disease - eccentric and segmental - Pseudodiverticula develop on the antimesenteric border of the colon opposite regions of fibrosis and scarring. - Asymmetric Fibrofatty proliferation along the mesentric border. - Creeping fat sign
  31. 31.  Coronal reformatted image shows thickened terminal ileal wall (short arrows) and coned cecum. Small mesenteric nodes are also present in right iliac fossa (long arrows).
  32. 32.  Coronal reformatted image shows mild fat stranding around abnormal thickened terminal ileum (arrows).
  33. 33.  Axial image of right lower quadrant again shows thickening of terminal ileum, with abscess formation deep in pelvis (thick arrows), with diffuse infiltration of surrounding fat (thin arrows).
  34. 34.  Acute Pancreatitis - the pancreas appears enlarged.  The pancreatic parenchyma may not enhance after IV contrast administration in the setting of pancreatic necrosis, which can be focal or diffuse.  In addition to fat stranding in the peripancreatic tissues, other secondary findings include free fluid in the paracolic gutters and pleural effusions.
  35. 35.  There is severe peripancreatic fat stranding (thick arrows). Focal area of parenchyma in pancreatic neck is not enhancing due to necrosis (thin arrows).
  36. 36.  Severe fat stranding extends from peripancreatic region to left paracolic gutter and anterior pararenal space (arrows). There is residual enhancing pancreatic parenchyma in head of pancreas (arrowheads).
  37. 37.  Acute pyelonephritis - - The nephrographic phase of contrast enhancement is superior. - Typically ill-defined wedge-shaped areas of low density are noted radiating from the papilla to the cortical surface. - These sites represent poor- or nonfunctioning parenchyma due to vasospasm, tubular obstruction, or interstitial edema. - The striated nephrogram—bands of alternating high- and low-density parallel to the axes of the tubules, characteristic of acute pyelonephritis. - Perinephric fat stranding is usually seen adjacent to the abnormal areas because of an inflammatory reaction with leukocytes forming an infection or infarction.
  38. 38.  Contrast- enhanced coronal reformatted image shows bilateral striated nephrograms and ill-defined wedged-shaped areas of low density in upper poles of both kidneys, radiatin g from papilla to cortical surface (arrows).
  39. 39.  There is moderate right hydronephrosis (long arrows) and mild perinephric fat stranding due to edema (short arrow).
  40. 40.  Dilated right ureter with mild fat stranding (arrow)
  41. 41.  Wall of gallbladder is thickened (thin arrows), and there is mild pericholecystic fat standing (thick arrows).
  42. 42.  Multiple small hyperdense foci in gallbladder represent gallstones (thin arrow). There is severe pericholecystic fat stranding (thick arrows).
  43. 43.  idiopathic fibroinflammatory disorder that affects the small-bowel mesentery.  Categorized as mesenteric panniculitis (chronic inflammation), mesenteric lipodystrophy (fat necrosis), and retractile mesenteritis (fibrosis).  sixth and seventh decades of life.  has a poorly understood association with underlying malignancy and paraneoplastic condition.
  44. 44.  CT appearance - well-defined soft-tissue mass containing areas of fat attenuation to an ill-defined area of increased attenuation in the root of the small-bowel mesentery.  the changes of sclerosing mesenteritis occur around the mesenteric vessels and do not displace them.  The CT appearance of a ―fat ring‖ sign—a thin radiolucent rim of fat between the mesenteric vessel and the mass in the mesentery.
  45. 45.  There is moderate fat stranding in mesentery above mesenteric mass (arrows).
  46. 46.  Mesenteric mass displaces loops of small bowel (thin arrows). There is dystrophic calcification (black arrow), uncom mon finding in this condition. Diffuse mild mesenteric fat stranding is also seen (thick arrows).
  47. 47.  Involves terminal ileum and cecum (90% )  The disease causes circumferential thickening of the bowel wall, with adjacent mild fat stranding and lymphadenopathy.  In advanced ileocecal disease, small-bowel loops may become adherent in the right iliac fossa.
  48. 48.  Peritoneal tuberculosis may affect the peritoneal cavity, mesentery, and omentum.  The most frequent form (90% of cases) is the ―wet‖ type with ascites or pockets of loculated fluid.  The ―dry‖ type is characterized by fat stranding in the mesentery, dense adhesions, and adenopathy.
  49. 49.  There is extensive fat stranding of greater omentum (long arrows). Peritoneum is thickened and hyperenhancing (short arrows), and pockets of fluid are present (arrowheads)
  50. 50.  There is moderate ascites (long arrow) and enhancement of thickened peritoneum (short arrows).

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