Arachnoiditis is a broad term encompassing inflammation of the meninges and subarachnoid space.
Multiple etiologies are recognised including:
- intrathecal haemorrhage
- intrathecal compounds
- myelographic contrast media
- steroids (accidental intrathecal injection)
- neoplastic processes
All modalities will demonstrate similar findings, although MRI is by far the most sensitive modality. Although arachnoiditis can be present throughout the subarachnoid space, it is most easily seen in the lumbar region where the cauda equina usually floats in ample CSF. In arachnoiditis the nerve roots are irregularly thickened and clumped together, often stuck to the dura, resulting in an empty thecal sac sign.
- syringomyelia is a complication of arachnoiditis and should be sought in the cord.
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