Free gas under the diaphragm – Xray

Free gas under the diaphragm – Xray

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• Free gas under diaphragm (also known as air under the diaphragm) is a finding in the chest Xray seen in case of perforation of hollow viscus.
• When there is perforation, gas within the hollow viscus escapes into the peritoneal cavity along with other contents
• When an chest xray is taken in the upright position, gas being lighter rises up and settles under the diaphragm and is seen in the xray as a radioluscent (dark) area
• If the patient is supine when the xray is taken, the gas will settle at the region of the umbilicus and hence such a film is not useful in diagnosing hollow viscus perforation

Why is it called free gas?

• It implies that the gas is localised within the peritoneal cavity and changes position with the posture of the individual
• In other cases, as in case of gas within the retroperitoneum, the location of the gas is fixed and does not change with posture

When to suspect hollow viscus perforation:

• Patients usually presents as a case of acute abdomen
• The abdomen is tense and tender
• Board like rigidity of the abdomen may be present

Differential diagnosis for free gas under diaphragm:

• Most common cause is hollow viscus perforation. Site of perforation – ordered proximal to distal – with causes:
  • Oesophagus -rupture (Boerhaave syndrome) – rare
  • Stomach and duodenum
    • Peptic ulcer perforation – commonest
    • Malignancy eroding the wall
  • Small bowel
    • Inflammatory bowel disease (eg: Chron’s disease)
    • Primary cancers of small bowel – extremely rare
    • Tumors encroaching upon bowel from adjacent structures (eg: mesenteric tumours)
  • Large bowel
    • Diverticulitis (more seen in left side, especially sigmoid colon)
    • Malignancies
  • Injury to vagnina or anus

• Abdominal trauma as in stabs, gun shots, road traffic accidents
• After laproscopic surgery

Management:

• The diagnosis of free gas under the diaphragm necessitates emergency management.
• Along with air, the gastric/intestinal contents also leak into the peritoneal cavity and the effects can be catastrophic.
• Laparotomy has to be done immediately to localise site of leak.
• Tissue should be taken for histopathology to rule out malignancy.
• The perforation is to be repaired.
• Peritoneal lavage can be done to remove as much of the spilled contents
• There is high fatality rate for hollow viscus perforation as it may be due to a malignant process and associated complications like infections