The fluid sign is one of the radiological features of osteoporotic fractures, and can be helpful in distinguishing them from metastatic vertebral fractures, as it is seen more often in osteoporotic fractures and is rarely seen in metastatic fractures 1. It is not as helpful as identifying a paravertebral or epidural soft tissue mass or infiltration of pedicle or to other vertebrae, however these features are not always present in metastatic disease, and as such ancillary signs are useful.
Though the exact pathogenesis is not known, although proposed mechanisms include 1:
- sponstaneous avascular necrosis of the vertebral body (or Kummel's disease)
- osteonecrosis at the site of an insufficiency acute vertebral fracture
The ‘fluid sign’ in acute vertebral collapse is deﬁned as a horizontal focal, linear, or triangular area of fluid intensity (hypointense on T1, hyperintense on T2, STIR) on a background of diffuse hyperintensity in the vertebral body because of acute collapse.
It is seen in acute vertebral compression fractures that show bone marrow oedema.