The thecal sac contains the cerebrospinal fluid which provides nutrients and buoyancy to the spinal cord.

[1] From the skull the tube adheres to bone at the foramen magnum and extends down to the second sacral vertebra where it tapers to cover over the filum terminale.

[2] The sac has projections that follow the spinal nerves along their paths out of the vertebral canal which become the dural root sheaths.

[6] 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.

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).