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axr

plain abdominal X-ray (AXR)

introduction

  • plain AXR is generally avoided unless there is a specific indication which outweighs the radiation risks given the radiation dose is equivalent to ~ 20 chest XRays
  • when looking for small bowel obstruction, an erect and supine film is requested, but these are only 50-60% sensitive
  • when looking for possible perforated viscus, an erect CXR should also be requested to look for free gas under the diaphragm

normal small bowel

  • rule of threes:
    • wall thickness < 3mm
    • valvulae conniventes < 3mm thick
    • small bowel diameter < 3cm
    • less than 3 air-fluid levels per AXR

signs of small bowel obstruction

  • multiple air fluid levels on erect AXR
  • absence of colonic distention
  • stepladder appearance of small bowel loops at different heights
  • string of pearls indicating trapped air in valvulae conniventes

signs of large bowel obstruction

  • dilated colon (>6cm), especially caecum (> 9cm)
    • NB. dilation more than 3cm more than these upper limits starts to increase risk of perforation
  • air fluid levels on erect AXR, esp. distal to hepatic flexure
  • 25% have small bowel dilatation due to reflux of gas through ileocaecal valve
  • NB. non-mechanical causes include toxic megacolon and paralytic ileus

calcifications on AXR

  • 20% of gallstones are visible on AXR due to calcification
  • calcified wall of gallbladder porcelain gallbladder indicates chronic inflammation and a high risk of neoplasia, hence are usually resected
  • pancreatic calcifications are pathognomonic of chronic pancreatitis
    • NB. adenocarcinoma of pancreas almost never calcifies, although other unusual tumours may calcify
  • calcifications are commonly seen in the arterial tree (eg. aorta, iliac, renal, splenic arteries)
  • 80% of ureteric calculi are radio-opaque but CT KUB is a much more sensitive test than plain AXR to detect these, however, plain AXR is useful to monitor progress of larger ureteric stones
  • 10% of patients with appendicitis have a calcified faecolith (appendicolith) in the RIF, and this increases risk of early rupture.
  • hepatic or splenic calcifications:
  • calcification of adrenal glands:
    • old haematoma
    • old infection
    • NB. calcification is unusual in adrenal tumours
  • calcification throughout abdominal wall:
  • calcification in the pelvic region
    • calcifications within the pelvic veins (phleboliths) are common and of no importance but can be mistaken for ureteric calculi
    • arterial wall calcification in iliac arteries
    • ureteric calculus at VUJ
    • bladder stones
    • calcified material within dermoid cysts (eg. teeth)
    • fetus in pregnant patients
axr.txt · Last modified: 2013/08/15 12:42 (external edit)