Abdominal XRay

Aka: Abdominal XRay, Abdominal Radiograph

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II. Imaging: General

  1. Lateral fat stripes (Flank Fat Stripe)
    1. Fat stripes are vertical dark bands found lateral to the ascending and descending colon
    2. Only 1-2 cm normally separates the fat stripe from colon (ascending on right, descending on left)
      1. Free fluid, when present will increase that distance to >2 cm or more
  2. Bowel Appearance on XRay
    1. Bowel lumen is visible due to bowel gas
      1. Bowel lumen without air is of fluid density and is not visible
      2. Bowel wall is of fluid density and is not normally visible
        1. Intraabdominal free air abnormally highlights the bowel wall
    2. Small Bowel
      1. Small Bowel is located centrally
      2. Valvulae conniventes (circular folds, plicae circulares)
        1. Folds (of fluid density) within the Small Bowel
        2. Folds cross entire width of Small Bowel (contrast with Large Bowel haustra)
    3. Large Bowel (Colon)
      1. Large Bowel is located peripherally, surrounding the Small Bowel
      2. Haustra
        1. Folds that do not cross the entire bowel width

III. Imaging: Approach (Mnemonic: Free ABDO)

  1. Free Fluid
    1. Lateral fat stripe (Flank Fat Stripe) distance from colon >2 cm suggests paracolic gutter free fluid
    2. XRay cannot distinguish between Ascites and blood (similar radiographic densities)
  2. Air
    1. Intraluminal air
      1. Air fluid levels (e.g. Small Bowel Obstruction)
        1. Black air overlying a horizontal fluid density line (air-fluid level)
      2. Dilated bowel loops wider than discriminatory values (e.g. ileus, Small Bowel Obstruction, Volvulus)
        1. Small Bowel diameter >3 cm
        2. Large Bowel diameter >6 cm
        3. Cecum diameter >9 cm
    2. Extraluminal air
      1. See Extraluminal Air Below
      2. Intraperitoneal Free Air (pneumoperitoneum)
      3. Retroperitoneal Free Air
      4. Pneumatosis Intestinalis (gas within the intestinal wall)
      5. Pneumobilia (air in the biliary tree)
      6. Hepatic portal venous gas (HPVG, air in Portal System)
      7. Abscess
  3. Bowel Wall Thickening
    1. Findings
      1. Narrowed bowel lumen
      2. Thickened folds (haustra of the Large Bowel, valvulae conniventes of the Small Bowel)
      3. Large Bowel indentations (thumb printing)
      4. Bowel loop appear to separate from one another (due to bowel wall thickening)
    2. Causes
      1. Inflammatory Bowel Disease
      2. Bowel ischemia
  4. Densities (or calcifications)
    1. Bones (e.g. Lumbar Spine, hips and Pelvis, lower ribs)
    2. Gallstones
    3. Appendicolith (may be seen in up to 10% of Acute Appendicitis)
    4. Renal stones or Ureteral Stones
    5. Aortic wall calcification
    6. Pancreatic calcifications (associated with Chronic Pancreatitis)
  5. Organ outline abnormalities or distorted contour (peri-organ fat typically helps define their normal margins)
    1. Liver
    2. Spleen
    3. Kidney
    4. Bladder

IV. Causes: Extraluminal Air

  1. Intraperitoneal Free Air (pneumoperitoneum)
    1. Suggests bowel perforation (e.g. ruptured Peptic Ulcer, Diverticulitis, SBO)
    2. Intraperitoneal air may be best seen in right sub-diaphragmatic space on upright Chest XRay
      1. On the right, free air collects between the diaphragm and the well-defined liver edge
      2. In contrast, in the left subdiaphragm, the normal gastric bubble may obscure free air
    3. Rigler's Sign (double-wall sign)
      1. Bowel wall (not normally visible) is highlighted between intraluminal gas and extraluminal gas
      2. Best seen on supine abdominal view
    4. False Positives
      1. Recent intraabdominal surgery
        1. Extraluminal gas steadily decreases with reabsorption over a 10 day course
      2. Chilaiditi's Sign
        1. Uncommon variant causes a False Positive appearance of free air under the diaphragm
        2. In Chilaiditi's syndrome, colon becomes interposed between liver and diaphragm
  2. Retroperitoneal Free Air
    1. Look for air outlining the margins of the Kidney
    2. Iliopsoas Muscle may also be outlined and demonstrate dark air streaks within the Muscle body
  3. Pneumatosis Intestinalis (gas within the intestinal wall)
    1. Bowel wall is streaked with black
    2. Ominous finding suggesting bowel ischemia, infarction or gangrene
  4. Pneumobilia (air in the biliary tree)
    1. Dark branchining structures within the hilum of the liver
    2. May be seen with Emphysematous Cholangitis, as well as recent ERCP
  5. Hepatic portal venous gas (HPVG, air in Portal System)
    1. Ominous finding of dark branching structure from the liver hilum toward the bowel
    2. Concerning for abdominal catastrophe (e.g. bowel infarction, infection)
  6. Abscess
    1. Black air overlying a horizontal fluid density line (air-fluid level) in a contained extraluminal space
    2. Unlike intraluminal air, abscesses lack haustra of the Large Bowel and valvulae conniventes of the Small Bowel
    3. Unlike air which transits the bowel with serial xrays, an abscess remains fixed in position on serial exam

V. References

  1. Ouellette and Tetreault (2015) Clinical Radiology, Medmaster, Miami, p. 26-36

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