The gastric bubble is a radiolucent rounded area generally nestled under the left hemidiaphragm representing gas in the fundus of the stomach.
On a lateral radiograph, the gastric bubble is usually located between the abdominal wall and spine. It can be seen on chest or abdominal plain films. It is seen on approximately 70% of normal chest radiographs.
An important differential is pneumoperitoneum, which is usually easily distinguishable as a thin radiolucent crescent under the hemidiaphragm.
In situs inversus, the normal gastric bubble is located under the right hemidiaphragm.
- a left-sided pleural effusion or subpulmonic effusion may cause increased distance between lower lobe air and gastric bubble
- in splenomegaly, the gastric bubble may be displaced towards the midline, however, the significance of this finding has been debated
- gastric volvulus may result in an altered appearance of the gastric bubble
- small studies have linked gastric bubble shapes to the presence of gastroesophageal reflux, however, this is not a well-established relationship
- in a tension gastrothorax there is an absence of the gastric bubble, a key differentiating point between it and a left-sided tension pneumothorax