Filum terminale

The filum terminale ("terminal thread") is a delicate strand of fibrous tissue, about 20 cm in length, extending inferior-ward from the apex of the conus medullaris to attach onto the coccyx.^: 453 The filum terminale acts to anchor the spinal cord and spinal meninges inferiorly.

The upper portion of the fila terminale is formed by spinal pia mater within a dilated dural sac, while the lower portion is formed by both pia and dura mater (with the outer dural layer closely adhering to the inner pial component).

Anatomy

The proximal/superior part - the filum terminale internum or pial part of terminal filum - measures 15 cm in length and extends as far as the inferior border of the second sacral vertebra (S2)^: 437 (the inferior limit sacral canal^: 437). It is composed of the vestiges of neural tissue, connective tissue, and neuroglial tissue lined by pia mater. It is contained within a tubular sheath of the dura mater and is surrounded by the nerves of the cauda equina (from which it can be easily recognized by its blueish-white color).

The inferior/distal part - the filum terminale externum, dural part of terminal filum, or coccygeal ligament - is formed as the filum terminale internum reaches the inferior extremity of the dural sac; henceforth, the filum terminale becomes invested by a layer of dura mater.

The filum terminale ultimately terminates inferiorly by attaching to the dorsum of the coccyx^{: 437, 453} at the first coccygeal segment, flaring out to blend with the coccygeal periosteum.^: 437

Relations

The filum terminale is situated centrally^: 453 amid the spinal nerve roots of the cauda equina^: 453 (but is not itself a part of the cauda equina^: 453).

The inferior-most spinal nerve, the coccygeal nerve, leaves the spinal cord at the level of the conus medullaris via respective vertebrae through their intervertebral foramina, superior to the filum terminale. However, adhering to the outer surface of the filum terminale are a few strands of nerve fibres which probably represent rudimentary second and third coccygeal nerves.

The central canal of the spinal cord extends inferiorly into the superior part of the filum terminale.^: 487

Development

The filum terminale is the vestigial remnant of the caudal portion of the spinal cord which forms a tail-like caudal eminence in the embryo.

Additional images

References

This article incorporates text in the public domain from page 750 of the 20th edition of Gray's Anatomy (1918)

• Martini, F. Timmons, M. and Tallitsch, R. Human Anatomy. 5th ed. San Francisco: Pearson/Benjamin Cummings, 2006.

External links

• MedEd at Loyola grossanatomy/dissector/practical/back/back2.html
• lesson6spinalcord&coverings at The Anatomy Lesson by Wesley Norman (Georgetown University)
• Anatomy photo:02:08-0104 at the SUNY Downstate Medical Center - "Vertebral Canal and Spinal Cord: Regions of the Spinal Cord"
• "Anatomy diagram: 03281.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2012-07-22.

1. Tethered spinal cord syndrome
2. Conus medullaris
3. Thecal sac
4. Coccyx
5. Meninges
6. Spinal cord
7. Spinal canal
8. Arachnoid mater
9. Chiari malformation
10. Cauda equina
11. Lumbar vertebrae
12. Anterior spinal artery
13. Diastematomyelia
14. Subarachnoid cisterns
15. Pia mater
16. Urination
17. Denticulate ligaments
18. List of medical roots, suffixes and prefixes
19. Index of anatomy articles
20. Anococcygeal nerve