Anterior boundary: bodies of vertebrae, discs and posterior longitudinal ligament (146)
Posterior: vertebral lamina, ligamentum flavum, with pedicles to sides.
Canal: intervertebral foramina at sides, contains meninges and cord & nerve roots.
- bones separated from meninges by the epidural space (loose c.t., fat and veins) (159)
- this extends laterally to meet nerve roots and their dural sheaths in the intervertebral foramina
Epidural veins form anterior and posterior internal venous plexi.
- Basivertebral veins (paired) supply the plexus, draining active red marrow of vertebral bodies.
- efferents = intervertebral veins ¨ intervertebral foramina & through flava
- ¨ external vertebral plexus (159) ¨ segmental veins
- during coughing, these veins provide a bypass for extra blood return rather than through IVC and diaphragm, (pelvic and abdominal blood can squirt up here to posterior intercostals and to SVC.
- Communication with pelvic viscera veins, renal veins, intercostals, azygous (hence breast and bronchus), inferior thyroid veins (via brachiocephalics); largely valveless
- Hence spread of Ca from prostate, kidney, breast, bronchus and thyroid.
Dura (aka theca): to S2, attached at margins to: post long lig, foramen magnum & tectorial membrane.
- rest of course lies free, apart from fibrous bands to post long lig in places, esp caudally.
- pierced segmentally by exiting spinal nerves, prolonged as a sheath over these.
Arachnoid: supported by inner dura, potential space only.
- sends lace-like processes to pia over cord (fading to a delicate membrane over cauda equina).
Pia: invests CNS, clothing cord and lining anterior median sulcus.
- prolonged over nerve roots, blends with their epineurium.
- Extends as filum terminale below apex of conus medullaris at bottom of L1; this descends in middle of cauda equina to S2, then pierces theca to attach to back of coccyx.
- Denticulate ligaments on either side of pia extend laterally through arachnoid ¨ dura between successive nerve roots (21 on each side from foramen ¨ L1, have a toothy appearance)
Spinal subarachnoid space: large, accommodates 50% of CSF volume, communicates with subdural space of posterior cranial fossa..
- some CSF is able to percolate away along meningeal sheaths of spinal nerves
Lumbar puncture: insert at L3-4 or L4-5 interspace.
Spinal: inject into subarachnoid space, straight on to nerve roots
Epidural: inject into epidural space, infiltrates through sheaths to nerve roots.
- alternative approach is through sacral hiatus.