Spinal Meninges Neuroscience Fundamentals > Regional Neuroscience > Regional Neuroscience
SPINAL MENINGES
GENERAL ANATOMY
Meningeal Layers
From outside to inside
Meningeal spaces
From outside to inside
• Epidural (above the dura)
- See: epidural hematoma and spinal cord compression from epidural abscess
• Subdural (below the dura)
- See: subdural hematoma
• Subarachnoid (below the arachnoid mater)
- See: subarachnoid hemorrhage
Spinal canal
Key Anatomy
• Vertebral body (anteriorly)
• Vertebral arch (posteriorly).
• Vertebral foramen within the vertebral arch.
MENINGEAL LAYERS
1 / 4 • Dura mater forms a thick ring within the spinal canal.
• The dural root sheath (aka dural root sleeve) is the dural investment that follows nerve roots into the intervertebral foramen.
• The arachnoid mater runs underneath the dura (we lose sight of it under the dural root sheath).
• The pia mater directly adheres to the spinal cord and nerve roots, and so it takes the shape of those structures.
MENINGEAL SPACES
• The epidural space forms external to the dura mater, internal to the vertebral foramen.
• The subdural space lies between the dura and arachnoid mater layers.
• The subarachnoid space lies between the arachnoid and pia mater layers.
CRANIAL VS SPINAL MENINGES 
Cranial Meninges
• Epidural is a potential space, so it's not a typical disease site unless in the setting of high pressure middle meningeal artery rupture or from traumatic defect.
• Subdural is a potential space but bridging veins (those that pass from the subarachnoid space into the dural venous sinuses) can tear, so it is a common site of hematoma.
• Subarachnoid space is an actual space and is a site of hemorrhage and infection, for example.
Spinal Meninges
• Epidural is an actual space, so it's a typical site of hematoma, infection, and neoplasia (cancer).
• Subdural is a potential space (and since no dural sinuses are here, no bridging veins are here), so it is NOT a common site of disease).
• Subarachnoid space is an actual space and is continuous with the cranium, so localized spinal disease can occur there or there can be spread of disease from the cranium.
NERVE ROOTS & SPINAL NERVE 
General Anatomy
• Ventral nerve root.
• Dorsal nerve root.
- Nerve rootlets.
- Dorsal root ganglion.
• Mixed spinal nerve.
2 / 4 • Pia mater covers: the rootlets, roots, and dorsal root ganglion.
• Vasculature runs along the pia mater (within the subarachnoid space).
Arachnoid mater
• The arachnoid mater lies external to the pia mater: notice that it does not directly wrap around the nerve roots, which leaves space between it and the pia mater for the subarachnoid space.
Dura mater
• Dura mater envelops the arachnoid mater.
- Subdural space.
- Dural root sheath.
Epidural space
• Epidural space lies between the vertebral arch and the dura mater.
Dural root sheath
• The dural root sheath is superficial and the dura mater transitions into the epineurium of the peripheral nerve.
Perineurium
• The arachnoid and pia mater, together, transition into perineurium; although intertextual variation exists regarding this point, and it often goes unmentioned in textbooks.
LUMBAR PUNCTURE
• CSF is withdrawn from the subarachnoid space within the spinal canal, at the L3/L4 level of the spinal canal (typically).
Key physiology
• 150 milliliters of cerebrospinal fluid in the nervous system.
• Cerebrospinal fluid (CSF) is produced at a rate of roughly 0.35 milliliters per minute (about 20 milliliters per hour).
• 10 to 20 milliliters of CSF are typically withdrawn in an LP.
• This fluid is replaced within an hour: within 30-60 minutes.
General landmarks for LP
3 / 4 • Palpate the highest points of the iliac crests; they may intersect the spine anywhere from L1/L2 to L4/L5.
• Generally, the LP needle can be inserted at the L3/L4 or L4/L5 interspace, which should be well below the termination of the spinal cord.
See: UpToDate's Review on the Lumbar Puncture Technique
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