First and second year — the floor first, then every step
Read both hemidiaphragms on coronal and sagittal reformats: a discontinuity, a collar of herniated viscus, or bowel lying against the posterior ribs with no diaphragm between is the diagnosis that is missed on axial slices.
Orient first
Left-sided ruptures are diagnosed far more often than right-sided ones; the liver buffers and hides the right side.
In a ventilated patient positive pressure keeps viscera in the abdomen, so the hernia may appear only after extubation — a normal early CT does not settle it.
The diaphragm is thin and runs in the axial plane over much of its surface, which is why axial slices miss the tear.
Acquire the study
Trauma CT with thin slices and CORONAL and SAGITTAL reformats through both hemidiaphragms; read on soft-tissue and lung windows.
The manoeuvre
Follow each hemidiaphragm on coronal and sagittal reformats from front to back and look for an abrupt discontinuity or a free edge.
COLLAR SIGN: a waist-like constriction of stomach, bowel or liver where it passes through the defect.
DEPENDENT VISCERA SIGN: bowel or stomach lying directly against the posterior ribs, with no diaphragm between (on the left); on the right, the upper third of the liver against the posterior ribs.
Thickening of the crus or the diaphragm itself, and fluid or haematoma tracking through a defect.
Elevated hemidiaphragm on the scout image compared with any prior film.
What confirms it
A focal discontinuity with herniated abdominal content, the collar sign, or the dependent viscera sign.
What licenses you to exclude it
A normal CT does not exclude a small tear, especially on the right or in a ventilated patient; with a penetrating thoracoabdominal wound, laparoscopy is the reference test — say so.
The classic misread
Calling a congenital Bochdalek hernia or eventration traumatic — look for the collar and the free edge, and for any prior imaging.
Reading only axial slices.
Reporting the injury
Classification to use
AAST diaphragm injury scale (contusion, laceration by length, tissue loss) — rarely used in reports; the side, site and length of the defect and what has herniated are what is acted on.
Measurements — and how to take them
Length of the defect on the reformat that shows it best, in mm or cm.
What to report
Side, site (central tendon, posterolateral, crus), length of the defect, herniated organs, and signs of strangulation (hypoenhancing bowel wall, closed loop).
How to report it
CT: "Left hemidiaphragmatic rupture with a 5 cm posterolateral defect through which the stomach and splenic flexure herniate, showing a collar sign. The herniated stomach enhances normally."
What not to report
Do not report "elevated left hemidiaphragm" alone in a trauma patient without saying whether the diaphragm is intact on reformats.
Associated injuries to look for
Splenic, hepatic and renal injuries, lower rib fractures, pelvic fractures in blunt trauma; thoracoabdominal penetrating wounds.
What changes management
Any diaphragmatic rupture is surgical (it does not heal and herniation strangulates); strangulated herniated bowel is an emergency.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Diagnostic criteria
Diaphragm (eventration vs rupture) · Hemidiaphragm bulge versus traumatic tear
a named smooth, intact hemidiaphragmatic bulge (eventration) versus a discontinuous diaphragm with herniated viscera (rupture) — companion to chest2-diaphragm-us, not a fake “normal hemidiaphragm millimetre”
A collar sign and a dependent-viscera sign favour rupture. Eventration is smooth and chronic.
X-ray · CT · USG
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.