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/epidural soft tissue mass or infiltration of the pedicle or to other vertebrae, however these features are not always present in metastatic disease, and as such ancillary signs are useful.
The exact pathogenesis is not known, although proposed mechanisms include 1:
- spontaneous avascular necrosis of the vertebral body (or Kümmell disease)
- osteonecrosis at the site of an acute insufficiency 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.