Anatomy of Meninges in a Nutshell

Anatomy of Meninges

• Meninges: 3 layers of connective tissue
  • Provide support for the brain and the spinal cord
  • Pia mater:

1. 1. • Directly associated with the spinal cord / Brain
      • Cranial pia essentially the same as spinal

1. • Arachnoid:

• • • In subarachnoid space, find CSF
    • Has processes to pia mater
    • Same in brain as in spinal cord
  • Dura mater:

• • • Thickest layer
    • Has 2 layers in the cranial vault (different than in spinal cord)
  • Endocranium (aka periosteal dura)
    • Layer closer to the skull- is the periostium
    • Is firmly attached to the internal aspect of the cranial vault.
  • Meningeal layer: the layer closer to the brain (usually intimate with arachnoid)
    • These two layers are usually fused and appear as a single layer.
    • Occasionally, the layers separate to create a dural fold (reflection of the meningeal dura)
    • The meningeal layer comes away from the endocranium and folds back on itself to rejoin it.
    • These folds compartmentalize the cranial vault and give more support to the brain.

Dural folds:

• Falx Cerebri
  • Large sickle shaped fold down the midline
  • Suspended vertically on the internal aspect of the skull along sagittal suture
  • Divides brain into R / L cerebral hemispheres
• Falx Cerebelli:
  • Continuation of Falx Cerebri
  • Much smaller fold
  • Divides cerebellum into R / L hemispheres
  • Found in the posterior cranial fossa.
• Tentorium Cerebelli:
  • Stretches out perpendicularly to the Falx Cerebri
  • Divides the cranial vault into superior / inferior portions
  • Cerebral hemispheres are superior, cerebellar hemispheres are inferior.
• Diaphragma Sellae
  • Very small circular fold of Dura mater on the superior aspect of the pituitary gland
  • Encircles the pituitary gland

Dural Venous Sinuses

• When meningeal dura folds back on itself, it creates a triangular space between itself and the endocranium.
• Folding Also creates a sinus deeper in the brain where meningeal dura folded on itself.
• These have an endothelial lining similar to that of vein.
• These become filled with venous blood and are thus dural venous sinuses.
• These eventually end at the jugular foramen which is the start of the internal jugular vein.
• All venous blood from the brain will end up in the internal jugular vein.

Major Dural Venous Sinuses:

• Superior sagittal sinus- runs along the superior aspect of the falx cerebri
• Inferior sagittal sinus- runs along the inferior margin of the falx cerebri
• Straight sinus: runs in the tentorium.
• Confluence of sinuses: point in which superior sagittal sinus and straight sinus meet.
• Transverse Sinus (R/L)
  • Blood runs along the R and L transverse sinus
  • In the posterior aspect of the tentorium
  • S shaped sigmoidal sinus is a continuation of the transverse sinus
• Major Pathway:
  • Blood from anterior portion of brain→ superior sagittal sinus→
  • posteriorly to confluence→ meets blood from inferior sagittal sinusà
  • goes along transverse sinusà sigmoidal sinus→ jugular foramen with jugular bulb→ internal jugular vein.
• Pathway for the Base of the Brain
  1. Cavernous sinus:
• On the R / L side of the pituitary gland have Cavernous sinus
• drains blood from orbit and base of the brain. Blood from here has 2 options:
  • First option: superior petrosal sinus
  • Second option: inferior petrosal sinus
  • These are related to the petrous portion of the temporal bone.
• • Path: blood accumulates in cavernous sinusà use either petrosal sinusà run along temporal boneà (2 options)
• Superior uses sigmoid sinus to the jugular foramen
• Inferior goes to jugular foramen directly

Calvaria: the dome shaped cap of the skull

• No real definition for the boundaries due to it being a relative structure (more of a clinical term)
• Contains parts of frontal, parietal, and possibly occipital bone depending on the cut (flat bones of the skull)
• Structure:
  • Outer table / Inner table of compact bone
  • In between the tables, have spongy bone layer (called the Diploe)
• Called the diploe (is diploic bone)
  • Have interconnecting system of diploic veins which lack valves (thus, blood can flow in either direction)
  • Diploic veins drain into dural venous sinuses (which drain all of brain)
• This arrangement makes the skull strong, but light

Middle meningeal artery:

• Is outside the periosteal dura (is thus epidural)
• is squished between the skull and the periosteal dura
• Creates a groove in the skull where it is located
• Arose from the maxillary artery (from the external carotid)
• Supplies most of cranial dura mater
• Clinical: the anterior branch will cross the pterion internal aspect
  • This region is thinner portion of the skull
  • Fracture of the lateral skull in this area will likely lacerate this artery
  • If you don’t tear the dura, you end up with an epidural hematoma
• Epidural hematoma are usually from middle meningeal artery
• It takes a while to have neurologic symptoms from a tear here due to the blood needing to work through the space between the dura mater and the skull. It will eventually push on the brain.

• • Epidural hematomas are easily repaired.

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