Filum terminale
Filum terminale
Also known as: terminal filum
A slender thread of pia mater, ≈20 cm long, that extends from the apex of the conus medullaris to the dorsum of the coccyx. It anchors the lower spinal cord.
Overview
The filum terminale is the inferior continuation of the pia mater beyond the conus medullaris. It contains some glial cells and a vestigial central canal near its top. It has two parts. The filum terminale internum (≈15 cm) runs within the dural sac among the cauda equina roots to the end of the sac at S2. The filum terminale externum (≈5 cm), also called the coccygeal ligament, picks up a coat of dura as it pierces the sac and attaches to the dorsum of the first coccygeal segment.
Together with the denticulate ligaments, it stabilises the cord longitudinally within the vertebral canal.
- Location
From the conus medullaris (L1–L2) through the lumbar cistern to the dural sac (S2), then to the coccyx.
Parts & subdivisions
- Filum terminale internum (pial part)The intradural part, ≈15 cm long, running in the lumbar cistern in the midline among the cauda equina.
- Filum terminale externum (coccygeal ligament)The extradural part, ≈5 cm long, invested by dura. It anchors the dural sac and cord to the coccyx.
Function
- Anchors the inferior end of the spinal cord and dural sac to the coccyx, providing longitudinal stability.
Clinical significance
Myxopapillary ependymoma
A slow-growing ependymal tumour that characteristically arises from the filum terminale in young adults. It presents with low back pain and cauda equina symptoms.
Fatty or tight filum (tethered cord)
A thickened (>2 mm) or fat-infiltrated filum can tether the conus, and surgical section of the filum is the treatment.
Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.