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# Filum terminale

The filum terminale is a thin strand running from the end of the [spinal cord](https://durgical.com/en/anatomy/spinal-cord/) down to the [coccyx](https://durgical.com/en/anatomy/coccyx/); it anchors the lower end of the cord.

Official name: Filum terminale internum

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## What it is

A thin strand that continues from the end of the spinal cord down to the coccyx.

## What it does

Anchors the lower end of the cord. If it is too tight from birth (tethered cord), it can stretch the cord.

## Key points

- A thickened filum (over about 2 mm) or a fatty filum that holds the conus low is the classic cause of tethered cord syndrome
- At surgery it is told apart from the nerve roots by its pale, shiny look, a small vessel running along it and no muscle response on nerve stimulation
- Cutting it (detethering) releases the cord; the sacral roots lie right beside it, so the operation is done with nerve monitoring

## Key facts

**Where**
From the conus (L1–L2): filum internum inside the dural sac to S2 (about 15 cm), filum externum below S2 (about 5 cm); about 20 cm in all

**Attaches**
Conus medullaris above; dorsum of the first coccygeal segment below (as the coccygeal ligament)

**Function**
Pial strand that anchors the lower end of the cord and dural sac

## Relations

**Above**
The tip of the [conus medullaris](https://durgical.com/en/anatomy/conus-medullaris/)

**Lateral**
The roots of the [cauda equina](https://durgical.com/en/anatomy/cauda-equina/), floating around it in the lumbar cistern

**Below**
After leaving the end of the dural sac at about S2, it runs through the sacral canal to the back of the first coccygeal segment

## How to find it

It cannot be felt. It runs from the tip of the conus (usually at L1–L2) down the middle of the cauda equina, leaves the dural sac at about S2 and ends on the back of the first coccygeal segment; for detethering it is reached through a short laminectomy low in the lumbar [spine](https://durgical.com/en/anatomy/region/spine/).

## On imaging

Axial and sagittal T1 MRI show a fatty filum as a bright strand; its thickness is measured on axial images at about L5–S1. In young infants, ultrasound shows the filum and whether the conus and roots move freely.

## Clinical notes

- Tethered cord symptoms often appear in growth spurts: back and leg pain worse on bending, leg weakness or numbness, a progressive cavus foot or scoliosis, and bladder trouble
- [Skin](https://durgical.com/en/anatomy/skin/) markers over the lower back (hairy patch, a dimple high above the gluteal cleft, haemangioma, fatty lump) suggest a hidden spinal dysraphism with a tethered cord
- Myxopapillary ependymoma is the typical tumour of the filum and conus, in young adults, causing back pain and sometimes cauda equina symptoms

## Anatomical variants

- Some fat in the filum is found on MRI in a small proportion of healthy adults; it matters only with a low conus or symptoms

## Development

The filum is the remnant of the tail end of the neural tube, left behind as the column outgrows the cord; faulty regression leaves a thick or fatty filum.

## Related conditions

- [Spina bifida (myelomeningocele)](https://durgical.com/en/conditions/spina-bifida/)

## Test yourself

Think of the answer, then tap the question to see it.

## What are the attachments of the filum terminale?

From the conus medullaris above to the back of the first coccygeal segment below, as the coccygeal ligament after leaving the dural sac at about S2.

## Which filum terminale finding is the classic cause of tethered cord syndrome?

A thickened filum (over about 2 mm) or a fatty filum that holds the conus medullaris low.

## Which tumour is typical of the filum terminale and conus?

Myxopapillary ependymoma, in young adults, causing back pain and sometimes cauda equina symptoms.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
filum terminale internum; filum terminale externum TA2 5414

**Official Spanish (DeCS)**
Filum terminal DeCS D002420

**English (TA2)**
Filum terminale internum

**Also called**
pial part of filum terminale · pial filament · dural part of filum terminale · coccygeal ligament · terminal filum · filamentum terminale · filum terminale pialis

## Related

- [Cauda equina](https://durgical.com/en/anatomy/cauda-equina/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=2459); [Neuroanatomy, Conus Medullaris](https://www.ncbi.nlm.nih.gov/books/NBK545227/).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/filum-terminale-internum/