L13: Meningeal layers, dural folds, dural venous sinuses Flashcards
What are the meninges?
3 membranous layers that surround and protect the spinal cord
(innermost to outermost)
-pia mater (microscopic layer stuck to brain tissue, goes in gyri and sulci)
Subarachnoid space: full of cerebrospinal fluid
-arachnoid mater (translucent, soft, doesn’t extend into sulci/lateral fissure, but does extend into the longitudinal fissure)
Potential subdural space
-dura mater (tough, membranous layer, close to arachnoid
What are gyri and sulci?
Sulci= grooves Gyri= bumps
Name the two deep grooves in the brain:
Longitudinal fissure: deep groove separating the right and left hemispheres
Lateral fissure
What is found in the subarachnoid space?
- cerebrospinal fluid
- blood vessels (cerebral arteries/veins)
What is the leptomeninges?
Both the pia mater and arachnoid mater
meningitis is the infection of the leptomeninges
What arteries lie on outermost part of dura?
Meningeal arteries (b/w dura mater and inner table of skull)
What is the composition of the dura?
2 layers around the brain
-periosteal (same as periosteum)
-meningeal (adajcent to arachnoid)
These are closely adhered appearing as a single layer
Where does the separation of the dura layers occur?
-dural folds
-dural venous sinuses (filled with venous blood)
Meningeal layer peels away from the periosteal dura, and it can stretch away to form a fold/partition, and space created is a dural venous sinus
e.g. dural fold in the longitudinal fissure
What are 2 important dural folds?
Falx cerebri: (vertical plane in midline, separating the two hemispheres)
Attaches to anterior cranial fossa, posteriorly ir sits on top of the horizantal dural fold (tentorium cerebelli)
Tentorium cerebelli: horizantal, meningeal layer pulled away from lateral aspect of periosteum
What is found in the tentorial notch?
Brain stem, connecting spinal cord to brain
What is the function of dural folds?
Help stabilise the brain and act as rigid dividers.
BUT
A rise in pressure inside the skull, the brain gets squashed, so parts of brain herniate into areas of the brain they shouldn’t be in, or through the foramen magnum
Are all of the dural venous sinuses connected with each other?
Yes, and receive blood from the cerebral veins (draining the brain)
What do the dural venous sinuses continue as, as they exit the skull?
Internal jugular vein
Name some dural venous sinuses:
- superior sagittal sinus
- inferior sagittal sinus
- straight sinus (connects inferior sagittal sinus to the superior sagittal sinus at the confluence of the sinuses)
- paired transverse sinuses extended laterally from the confluence and twists until it reached the jugular foramen where it then becomes the internal jugular vein
- where the transverse sinus twists in an S shape it becomes the sigmoid sinus
- cavernous sinus
What is the cavernous sinus?
Found in middle cranial fossa, either side of body of the sphenoid.
Two cavernous sinuses have connections running between the two of them
Connect to other sinuses via petrosal sinuses (superior: connects to transverse and inferior:connects to sigmoid)
What are important connections b/w dural venous sinuses and other venous structures?
Cerebral veins via bridging veins (intracranially)
Scalp veins via emissary veins (extracranially): have to pass through bone
What is the course of a bridging vein?
From subarachnoid space to the wall of dural venous sinus
- traverses subarachnoid space
- where it feeds into the dural venous sinus is the weakest part of the bridging vein: if it ruptures= subdural haemorrhage
How can infection travel intracranially when you injure your head?
Emissary veins (involve intracranial structures) -especially with a deep cut
What is intracranial haemorrhage?
When head trauma leads to bleeding in ‘spaces’ between meningeal layers
What are the 3 types of intracranial haemorrhage?
Extradural, subdural, subarachnoid
you can also get intracerebral haemorrhage: bleeding within the brain tissue itself
Why is intracranial bleed dangerous?
Increase in pressure in skull: damage to brain tissue, brainstem and cranial nerves
What is an extradural haemorrhage?
Usually middle meningeal artery in impacts to lateral side of head, below the pterion
- lentiform shape (bleed b/w periosteal layer and innder table of bone)
- blood appears white on CT
What is a lucid interval?
Someone with a head injury becomes unconscious, then wakes up and appears fine for around an hour.
However after this they rapidly deteriorate
-indicative of an extradural haemorrhage
What is a subdural haemorrhage?
Usually venous bleed from venous bridging veins
- between the dura and arachnoid
- trauma to head
- in elderly can more easily occur: cortical shrinkage putting tension on the bridging vein
- fills subdural space in that hemisphere (cresent shape)
- headache
- less rapid deteriation
What is a subarachnoid haemorrhage?
Bleeding in subarachnoid space, where rich network of cerebral veins/arteries lie
- arterial bleed secondary to trauma/spontaneous rupture of blood vessel (aneurysm: usually in circle of willis)
- blood is highly irritant to meninges so causes a significant headache
- blood mixes with cerebrospinal fluid: lumbar puncture can detect this
- sudden and often fatal
How do you image a subarachnoid haemorrhage?
CT scan (longer time left before CT, less chance of the CT picking up evidence of a bleed) -lumbar-puncture if CT isn't conclusive: sample haemoglobin degredation products, longer time since the bleed, higher the chances that the blood has started to break down
