Which of the following tumors is associated with drop metastasis?

At the edges of the main tumor mass, medulloblastoma cells have a propensity to form linear chains of cells infiltrating through cerebellar coex to aggregate beneath the pia, penetrate the pia, and seed into the subarachnoid space. Dissemination through the CSF is a common complication, presenting as nodular masses elsewhere in the CNS, including metastases to the cauda equina that are sometimes termed drop metastases. Ref: Robbins 8th edition Chapter 28.