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)
- Injury to vagnina or anus
- Abdominal trauma as in stabs, gun shots, road traffic accidents
- After laproscopic surgery
- 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