A rare dysraphic abnormality characterized by the infiltration of fatty tissue localized in the filum terminale, with abnormal conus shape. The spinal cord is typically attenuated and the limit between its end and the fatty filum is hard to distinguish. There are no additional spinal cord malformation, but it can be associated with vertebral abnormalities, anorectal malformation or other syndromic condition. It is named transitional for its intermediate image between an isolated filum lipoma and a terminal conus region lipoma.