7 - The Collar sign

*Diagnostic CT signs of diaphragm injury include a defect in the continuity of the diaphragm or crus and a waist-like constriction of abdominal viscera or omentum at the site of herniation as seen on axial or reformatted CT images, the CT “collar sign”


*On CT scans, herniation of an organ or omental fat may be visible through an abrupt discontinuity in the diaphragm. A waistlike constriction (collar sign) produced by diaphragmatic compression of herniated organs may be seen. Sagittal, coronal, and 3-dimensional (3D) reformation of CT scans may improve sensitivity.

*CT collar sign.
- Fig-a: Coronal volume-rendered image shows distinct collar sign (arrow).  
- Fig-b: Sagittal volume-rendered image shows collar sign and contact of the stomach directly with the posterior chest wall (dependent viscera sign)