Filum terminale

The filum terminale is a small thin filament of connective tissue that extends inferiorly from the apex of the conus medullaris to the sacrum.

Gross anatomy

The filum terminale is continuous with the pia mater and is described as having two sections:

  • filum terminale internum: upper three quarters of the filum; covered by the spinal dura and arachnoid meninges
  • filum terminale externum: lower quarter of the filum; fuses with the investing dura mater and continues inferiorly to attach to the dorsal coccyx

Variant anatomy

  • fatty filum terminale: can be considered as a cause of tethered cord  or may be considered a rare (<0.5%) anatomical variant in the asymptomatic patient
  • ventriculus terminalis

Related pathology