|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.
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. 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. The sac has projections that follow the spinal nerves along their paths out of the vertebral canal which become the dural root sheaths.
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.
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).
- "tethered cord".
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