What are the most likely diagnoses?
Myxopapillary ependymoma, CSF metastatic seeding form an intracranial primary (e.g. ependymoma, medullobalastoma, GBM) or systemic metastatic disease, or schwannoma.
Which do you favour and why?
The location and appearance of the inferior nodule suggests CSF seeding rather than a schwannoma. The larger nodule is in a typical location for a myxopapillary ependymoma. Schwannomas tend to be solitary except when associated with NF2, in which case usually they are numerous and usually seen in younger patients. CSF seeding as a presenting complaint, without a known malignancy, is quite uncommon. As such a myxopapillary ependymoma with a drop metastasis should be favoured, especially as the signal characteristics are typical.
Which tumours are known to seed the CSF?
CNS primaries include high grade gliomas (e.g. glioblastoma), ependymoma, myxopapillary ependymoma, medulloblastoma and PNET, pineal tumours (eg. germinoma, pineoblastoma), and choroid plexus neoplasms. Non-CNS tumours which are recognised as metastasising to the leptomeninges include solid tumours (e.g. lung cancer, breast cancer), melanoma, and haemopoietic neoplasms (lymphoma and leukaemia)
There are in fact two, both intradural, extramedullary. The larger of the two (yellow arrow) is located just below the conus. The smaller (blue arrow) is in the thecal cul de sac.