What feature is indicative that this lesion has been growing only very slowly?
There is extensive bony remodelling including posterior vertebral body scalloping.
What is the differential?
Myxopapillary ependymoma and schwannoma are the most likely entities. Also to be considered are paragangliomas.
What is occurring caudal to the lesion?
Trapped CSF has accumulated high T1 material. This probably represents proteinaceous 'gunk' or less likely blood products.
What is present on the anterior surface of the conus which can help with the differential?
Enlarged flow voids, suggests a vascular tumour such as a paraganglioma.
MRI demonstrates an intradural extramedullary tumour located at the L4 level and extending two vertebral body lengths. It completely fills the canal and remodels the posterior aspect of L4 (vertebral scalloping). It is of intermediate signal on both T1 and T2 weighted images and demonstrates homogenous vivid enhancement. Inferior to the mass, trapped CSF has high T1 and T2 signal, possibly due to high protein content.