Posterior extradural migration of extruded thoracic and lumbar disc fragments: role of MRI

We report three patients with a sequestrated disc fragment posterior to the thecal sac, The affected disc was lumbar in two cases and thoracic in the third. Disc fragment migration is usually limited to the anterior extra dur al space. Migration of a disc fragment behind the dural sac is seldom encou ntered. MRI appears to be the method of choice to make this diagnosis. The disc fragments gave low signal on T1- and slightly high signal on T2-weight ed images and showed rim contrast enhancement. The differential diagnosis i ncludes abscess, metastatic tumour and haematoma.