Inverted Napoleon hat sign

Last revised by Matt A. Morgan on 7 Oct 2019

The inverted Napoleon hat sign is a radiologic sign seen on the frontal pelvic or lumbar radiograph at the level of the 5th lumbar vertebra and the sacrum.

It is seen when there is bilateral spondylolysis with marked anterolisthesis of L5 on S1 or marked exaggeration of the normal lordosis at the lumbosacral junction. Spondylolysis resulting in this degree of spondylolisthesis is more often congenital and/or traumatic in origin and less often degenerative. 

The "brim" of hat is formed by the caudal translation of the transverse processes and the "dome" of hat is formed by the body of L5. 

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Figure 1: Napoleon's hat (photo)
    Drag here to reorder.
  • Case 1
    Drag here to reorder.
  • Case 2
    Drag here to reorder.
  • Updating… Please wait.

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

     Thank you for updating your details.