Dalley, 10th Edition

Chapter 2 ■ Back

136

directly covers the roots of the spinal nerves and the spinal blood vessels. Inferior to the conus medullaris, the spinal pia continues as the lum terminale (Figs. 2.45B and 2.47). The spinal cord is suspended in the dural sac by the lum terminale and the right and left denticulate ligaments (L. denticulus , small tooth), which run longitudinally along each side of the spinal cord (Figs. 2.46, 2.49, 2.50, and 2.52). The denticulate ligaments consist of a brous sheet of pia extending midway between the posterior and anterior nerve roots from the lateral surfaces of the spinal cord. The 20–22 sawtooth-like processes attach to the inner surface of the arachnoid-lined dural sac. The most superior process of the right and left denticulate ligaments attaches to the cranial dura immediately superior to the foramen magnum, and the inferior process extends from the conus medullaris, passing between the T12 and the L1 nerve roots. SUBARACHNOID SPACE The subarachnoid space is located between the arachnoid and pia mater and is lled with CSF (Figs. 2.47, 2.48, 2.49, and 2.51). The enlargement of the subarachnoid space in the

Posterior rootlets *

Entering dural sheaths

Denticulate ligament

Anterior roots of spinal nerve

Spinal cord (covered with pia mater)

Posterior rootlets * (cut)

Reflected arachnoid and spinal dura mater

Subarachnoid space

* Collectively constituting

posterior roots of spinal nerves

Arachnoid mater

Posterior view

FIGURE 2.50. Spinal cord within its meninges. The spinal dura and arachnoid mater have been split and pinned at to expose the spinal cord and denticulate ligaments between posterior and anterior spinal nerve roots.

Bright contrast enhanced CSF within sub arachnoid space in the lumbar cistern Darker “filling defects”

Pedicle, sawn through

Anterior ramus

Body of vertebra

Posterior ramus

Intervertebral disc Lumbar spinal ganglion within intervertebral foramen

Spinal dura mater enclosing lumbar cistern

surrounded by CSF are nerve roots of the cauda equina Dural sleeve containing L4 nerve root Body of L4 vertebra L5 pedicle Dural sleeve containing

Spinal ganglion, S2 (within dural root sheath) Inferior end of spinal dural and arachnoid sacs

L5

S1

S2

*

*

S3

Posterior ramus

S4 S5 Coccygeal

Anterior ramus

L5 nerve root Dural sleeve containing S1 nerve root (C) Lumbar myelogram, oblique view

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Filum terminale externum

(B) Lumbar myelogram, anterior view

Posterior superior iliac spines (PSIS) (at level of inferior end of dural sac) *

Sacral hiatus

(A) Posterior view

FIGURE 2.51. Inferior end of spinal dural sac.A. Postlaminectomy specimen (i.e., the vertebral arches of the lumbar and sacral vertebrae have been removed) to show the inferior end of the dural sac, which encloses the lumbar cistern containing CSF and the cauda equina. The lumbar spinal ganglia lie within the IV foramina, but the sacral spinal ganglia (S1–S5) are in the sacral canal. In the lumbar region, the nerves exiting the IV foramina pass superior to the IV discs at that level; thus, herniation of the nucleus pulposus tends to impinge on nerves passing to lower levels. B and C. Myelograms of lumbar region. Contrast medium was injected into the lumbar cistern. The lateral projections indicate extensions of the subarachnoid space into the dural root sheaths around the spinal nerve roots.