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

1. Free water clearance
2. Mastectomy left breast – Xray
3. Tympanic membrane – central perforation

1. Pseudotumor cerebri (Benign intracranial hypertension)
2. Complications of mumps
3. Risk approach in antenatal care

1. Splint placement after septal surgery
2. Rhinosporidiosis
3. Optic nerve sheath fenestration

Tracheal shift to right due to thyroid swelling

Tracheal shift to right due to thyroid swelling seen above the level of the clavicle. Tracheal compression can rarely cause stridor in this situation.

1. Tracheal shift to right on X-ray chest PA view
2. Rotated chest x-ray
3. Pleural effusion – left

Air fluid levels in intestinal obstruction

1. X-ray of knee joint showing epiphyseal plates
2. Pericardial fluid
3. Undisplaced fracture – Inferior pubic ramus