plain abdominal X-ray (AXR)

see also:

• radiology
• the chest X-ray (CXR)
• the patient with acute abdominal pain in the ED

• 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

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

• 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

• 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

• 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:
  • small punctate calcifications in the liver and spleen may indicate past histoplasmosis infection
  • spiculated, sunburst calcification in the liver is diagnostic of haemangioma
  • other causes of calcifications in the liver:
    • PH granulomatous disease
    • old trauma
    • metastatic disease (eg. colorectal cancer (bowel cancer)
    • primary hepatocellular carcinoma
    • atypical tuberculosis (TB), Pneumocystis (carinii) jirovecii pneumonia (PCP), echinococcosis (hydatids)
  • other causes of calcifications in the spleen:
    • PH granulomatous disease
    • old trauma
    • metastatic disease (eg. colorectal cancer (bowel cancer)
    • benign primary lesions such as benign cysts, haemangiomata
• calcification of adrenal glands:
  • old haematoma
  • old infection
  • NB. calcification is unusual in adrenal tumours
• calcification throughout abdominal wall:
  • generalised calcification states (eg. hypercalcaemia)
  • abdo. wall infarction (eg. nematodes)
  • muscle inflammation (eg. dermatomyositis)
• 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