Filum terminale

Last revised by Arlene Campos on 12 Jan 2024

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

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; about 62.5% of filum terminale internum and the dural sac terminates at or below S1/S2 disc space while 11.3% terminates above S1 4.

  • filum terminale externum: lower quarter of the filum; fuses with the investing dura mater and continues inferiorly to attach to the dorsal coccyx; it contains all three layers of meninges, also known as coccygeal ligament 5.

  • fatty filum terminale: can be considered as a cause of tethered cord 4 or may be considered a rare (<0.5%) anatomical variant in asymptomatic patients 3

  • ventriculus terminalis

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Cases and figures

  • Figure 1: cauda equina (Gray's illustration)
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  • Figure 2: spinal cord (Gray's illustration)
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  • Case 1: fatty filum terminale
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