6.22: Vertebral Canal

 

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.

Meninges (155)

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 & Spinals / Epidurals

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.