In addition to the obvious intradural mass, what other intradural abnormalities are visible?
Much of the cauda equina is thickened and enhancing and a further enhancing nodule is present filling the thecal cul de sac.
What other abnormality is present (not within the spinal canal) which helps with the differential diagnosis?
There are numerous enlarged retro-peritoneal lymph nodes.
What is the most likely diagnosis?
Lymphoma is most likely given the presence of enlarged lymph nodes. Other primary malignancies with lymphatic and CSF spread can be considered but are less likely. Although a CNS tumour (e.g. ependymoma, medulloblastoma) could have similar appearances, it would not explain the lymph node enlargement.
A fusiform mass involves the cauda equina with a further nodule more inferiorly filling the thecal cul de sac. Much of the cauda equina and exiting nerve roots are thickened and enhancing. These regions are isointense on T1 and T2 weighted images with homogeneous and vivid contrast enhancement. No evidence of cyst formation. No evidence of haemorrhage. Bone marrow appears normal. Conus appears normal.