Subdiaphragmatic free gas

Subdiaphragmatic free gas is one of the ways of detecting presence of free intraperitoneal air (i.e. pneumoperitoneum). It is the presence of free, extraluminal air in the anterior subhepatic space. 

Plain radiograph

Subdiaphragmatic free gas is well appreciated as the air under the diaphragm and air in the lungs outline the diaphragmatic contour well.

As little as 1 mL of free gas can be detected but the patient may be needed to be kept in upright position for about 10 minutes for the air to rise.

Erect chest x-rays covering the upper abdomen are often considered the best for detecting free subdiaphragmatic gas but an erect abdominal x-ray covering the lung bases will be just as sensitive.

  • Chilaiditi syndrome
  • subdiaphragmatic abscess
  • omental fat interpositioned between the liver and diaphragm
  • subpulmonary pneumoperitoneum
  • enlarged gastric bubble
  • gas containing liver hematoma
Share article

Article information

rID: 29545
Section: Gamuts
Synonyms or Alternate Spellings:
  • sudiaphragmatic air
  • subphrenic air

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Case 1
    Drag here to reorder.
  • Drag
    Case 2
    Drag here to reorder.
  • Drag
    Case 3
    Drag here to reorder.
  • Drag
    Case 4
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.