in this question all choices are some sort of neoplasms, but overall most common cause of conus medullaris is supposed to be
lumbar canal stenosis followed by spinal trauma followed by disc prolapse. and then comes neoplasias (metastasis, astrocytoma, meningioma, neurofibroma etc.)
Intradural extramedullary tumors account for approximately 20% of all spinal tumors, with intradural-intramedullary tumors accounting for less than 5% of all spinal tumors.
In the adult population, ependymomas (intradural intramedullary) are the most common intra-axial tumors of the conus medullaris and filum terminale.