Caterpillar sign (pyloric stenosis)

Last revised by Rohit Sharma on 28 May 2023

The caterpillar sign is a radiological sign described in pyloric stenosis.

It refers to the appearance of the stomach on an upper gastrointestinal radiographic series or plain abdominal radiograph 1,2. On these imaging modalities in a patient with pyloric stenosis, the stomach appears distended, air-filled and with wave-like contours, resembling the appearance of a caterpillar 1,2.

This sign is produced when the gastric hyperperistaltic waves come to an abrupt stop at the pylorus 1,2. It is the radiographic correlate of the visible peristaltic waves that may be appreciated clinically in the left upper quadrant and epigastrium of the abdomen 1,2.

See also

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Cases and figures

  • Figure 1: caterpillar (photo)
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  • Case 1
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