Thecal sac

Thecal sac, dural sac
A section of the spinal cord with the dura opened to show the interior of the thecal sac.
The spinal canal in cross-section; the outer layer of the thecal sac, the dura, is colored green and the subarachnoid space is blue.
Anatomical terminology

The thecal sac or dural sac is the membranous sheath or tube of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid which provides nutrients and buoyancy to the spinal cord.[1] Towards the head, the tube adheres to bone at the foramen magnum and extends down to the second sacral vertebra where it tapers to covering over the filum terminale. Along most of the spinal canal it is separated from the inner surface by the epidural space.[2] The sac has projections that follow the spinal nerves along their paths out of the vertebral canal which become the dural root sheaths.[3]

Clinical significance

The lumbar cistern within the thecal sac is the subarachnoid space below the end of the spinal cord and above the tapering of the thecal sac. The dura is pierced during a lumbar puncture (spinal tap), and epidural anesthesia is injected into the just outside the thecal sac and infiltrates through it.[4][5]

The a disruption of the dural sac may occur as a complication of a medical procedure, a consequence of trauma or spontaously, resulting in a cerebrospinal fluid leak.[6]

If the spinal cord is not free to move within the thecal sac due to abnormal tissue attachments, especially during growth, tethered spinal cord syndrome may occur.[7]

In a split cord malformation, some portion of the spinal cord is divided into parallel halves. The thecal sac may be divided and surround each half with a spike of cartilage or bone dividing the halves (Type I), or both halves may be present within the same sac where the dura is bound to a band of fibrous tissue (Type II).[7]

References

  1. ↑ "tethered cord".
  2. ↑ Susan Standring (7 August 2015). Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences. pp. 764–. ISBN 978-0-7020-6851-5.
  3. ↑ Moore, Keith (2018). Clinically oriented anatomy. Philadelphia: Wolters Kluwer. p. 132. ISBN 978-1-4963-4721-3.
  4. ↑ John T. Hansen (14 February 2014). Netter's Clinical Anatomy E-Book. Elsevier Health Sciences. p. 77. ISBN 978-1-4557-7063-2.
  5. ↑ Virginia F. Schneider (2013). "15. Lumbar Puncture". In Richard W. Dehn and David P. Asprey. Essential Clinical Procedures: Expert Consult - Online and Print. Elsevier Health Sciences. pp. 146–155. ISBN 1-4557-0781-3.
  6. ↑ Nafi Aygun; Gaurang Shah; Dheeraj Gandhi (5 December 2013). Pearls and Pitfalls in Head and Neck and Neuroimaging: Variants and Other Difficult Diagnoses. Cambridge University Press. p. 475. ISBN 978-1-107-47052-1.
  7. 1 2 Dias, M.; Partington, M. (2015). "Congenital Brain and Spinal Cord Malformations and Their Associated Cutaneous Markers". Pediatrics. 136 (4): e1105–e1119. doi:10.1542/peds.2015-2854. ISSN 0031-4005.

See also

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