What is the most likely diagnosis? Is there a differential?
This lesions most likely represents a myxopapillary ependymoma. A schwannoma is the only relatively common alternative diagnosis.
Can you find and follow the filum terminale? How do you locate it?
The filum terminale is the direct continuation of the conus and as such can be followed down. Alternatively in the thecal cul de sac it can be identified as an unpaired structure often of slightly different signal intensity or different calibre to the adjacent nerve roots.
Central intrathecal enhancing mass at the lower L3 level again shows intermediate T1 and heterogeneous increased T2 signal. This displaces the cauda equina laterally with near complete effacement of CSF space. The lesion measures 12 x 16 x 30 mm (AP x ML x SI). This is inseparable from the filum terminale which runs along its posterior border. No evidence of osseous remodelling. No mass or abnormal enhancement elsewhere within the spine.