Meninges, venous drainage of the brain and CSF Flashcards
Describe the 3 layers of the meninges and their properties for brain and spinal cord.
The brain is surrounded by three layers of connective tissue. These meninges protect the brain and contain structures, such as blood vessels and the venous sinuses.
1) DURA MATER (outermost)
- Connected to skull
- Strongest layer (non-distensible)
- Two layers, periosteal (attaches directly to skull) + meningeal, which separate to form venous sinuses (into which the cerebral veins drain)
- Includes branches of middle meningeal artery
- Dural reflections separate diff compartments within the brain:
a. Falx cerebri, which lies within the longitudinal fissure, partially separates the two cerebral hemispheres.
b. Tentorium cerebelli separates the middle cranial fossa from the posterior cranial fossa.
c. Falx cerebelli is a small dural reflection that separates the two cerebellar hemispheres and contains the occipital sinus.
d. Diaphragma sellae is a dural reflection that covers the pituitary fossa in the base of the skull.
2) ARACHNOID MATER
- Membranous
- Pressed against the inner surface of the dura through CSF pressure
- Arachnoid granulations are specialized parts of the arachnoid that protrude into the superior sagittal sinus and are responsible for the reabsorption of CSF
- Bridges over the sulci on surface of brain and the cisterns of the subarachnoid space
- Sealed bag for CSF in subarachnoid space
3) PIA MATER
- Direct connected to brain parenchyma
- Delicate
- Follows all gyri and sulci
- Separates the brain from the CSF in the subarachnoid space
- As vessels (e.g. cerebral artery branch) penetrate the brain parenchyma from the subarachnoid space, they enter through a sleeve of pia, the perivascular space, which extends until the vessel becomes a capillary
How are arachnoid and pia connected ?
Fine arachnoid trabeculae interconnect the arachnoid and pia across subarachnoid space
Explain the significance of the subarachnoid space.
- Filled with CSF
- Where the cerebral arteries and veins travel
- Arterial circle of Willis lies in a subarachnoid space
Define cistern.
Spaces filled with CSF, in subarachnoid space.
Identify the main cisterns in the subarachnoid space.
- Superior cistern
- Interpeduncular cistern
- Cisterna magna (cerebellomedullaris)
- Cisterna pontis
Identify a possible pathology affecting Circle of Willis. Which part of the circle may specifically be affected ?
Berry aneurysm (cause of subarachnoid haemorrhage)
A frequent site is where posterior communicating artery arises from the ICA
Identify the main differences in the arrangements of meningeal layers in the spinal cord c.f. the brain.
- Dura, and arachnoid mater largely distant from the spinal cord
- Different localisers: arachnoid trabeculae no longer exist, instead denticulate ligaments from pia, joining arachnoid mater (21 of them, coursing through subarachnoid space)
- Cauda equina composed of spinal roots, NOT grey mater
Why are roots long at the spinal cord end ?
Early in development: S1 root origin close to S1 vertebrae (spinal cord and vertebral column in sinc)
Later in development: Vertebral column begins to grow faster, and becomes longer at its inferior end (which means S1 root exits well below it origin in the cord)
What is the main clinical implication of the cauda equina ?
Can put needle through gap in vertebral column and sample CSF where there is no grey matter
Where is a lumbar puncture performed ?
Subarachnoid space, well below L2, usually L4/5
Veins of the brain:
- Structural features
- Anatomical location
- Drainage
- Types
- Structure: Veins of brain have thin walls and no valves
- Anatomical location: Emerge from brain and lie in the subarachnoid space
- Drainage: Drain into cranial venous sinuses
- Types: Grouped into external (quite variable) and internal cerebral veins
Describe veinous drainage of the cerebrum.
- The dural venous sinuses lie between the periosteal and meningeal layers of the dura mater.
- All the dural venous sinuses ultimately drain into the internal jugular vein (facial veins also drain to internal jugular veins)
- There are eleven venous sinuses in total.
- The straight, superior (receives the superior cerebral veins), and inferior sagittal sinuses are found in the falx cerebri of the dura mater. They converge at the confluence of sinuses, which drains into transverse sinuses
- The straight sinus is a continuation of the great cerebral vein and the inferior sagittal sinus.
- From the confluence, the transverse sinus continues bi-laterally and drain into the sigmoid sinus, which then “converges with the inferior petrosal sinuses to form the internal jugular vein”
- The cavernous sinus drains the ophthalmic veins and can be found on either side of the sella turcica. From here, the blood returns to the internal jugular vein via the superior or inferior petrosal sinuses (towards the sigmoid sinus)
Identify the main internal cerebral veins.
“Internal cerebral veins are formed by the union of the superior thalamostriate vein and the superior choroid vein”
The two internal cerebral veins, and the two basal veins then join to form Great cerebral vein (of Galen).
What does the basal vein drain ?
Part of temporal lobe
What does the thalamostriate vein drain ?
Part of thalamus and part of striatum
