Thecal sac
Tubular sheath of dura mater that surrounds the spinal cord and cauda equina
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Through Spinal cord and Medication
Clinical significance
The lumbar cistern is part of the subarachnoid space. It is the space within the thecal sac which extends from below the end of the spinal cord (the conus medularis), typically at the level of the transpyloric plane (lower border of the first lumbar vertebra) down to tapering of the dura at the level of the spinous process of the second sacral vertebra (S2). The dura is pierced with a needle during a lumbar puncture (spinal tap). For epidural anesthesia an anesthetic agent is injected into the space just outside the thecal sac and diffuses through the dura to the nerve roots where they exit the thecal sac. For spinal anaesthesia in general, an injection can be given intrathecally into the subarachnoid space, or into the spinal canal. This route of administration may also be used for the delivery of drugs which will evade the blood–brain barrier.
Disruption of the dural sac may occur as a complication of a medical procedure, or as a consequence of trauma causing a cerebrospinal fluid leak, or spontaneously resulting in a spontaneous cerebrospinal fluid leak.
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.
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).