RID34410 inverted Napoleon hat sign

synonym Napoleon hat sign bow sign

definition Anterior body of L5 vertebra is anteriorly displaced over top of sacrum. Transverse processes resemble the brim, superimposition of L5 and sacrum resemble dome. Indicates spondylolisthesis at the lumbosacral junction.

comment http://radiology.rsna.org/cgi/content/full/243/2/603