ICL 2.2: Dural Venous Sinuses & CNS Vascular Systems

Question 1

what are the layers of the meninges?

Answer 1

most superficial, right under the skull

1. dura mater
2. arachnoid mater
3. pia mater

deepest layer, right on top of the brain

each of these have layers within them

Question 2

what are the layers of the dura mater?

Answer 2

1. periosteal dura
2. meningeal dura

these two layers are inseparable; the only way you see them separately is at the dural reflections (this would only be the meningeal layer*)

Question 3

what is the periosteal dura?

Answer 3

the more superficial layer of the dura mater

the wallpaper right inside the cranial vault; you literally have to peel it off the bone to expose the skull

Question 4

what is the meningeal dura?

Answer 4

the deep layer of the dura mater

Question 5

which layer is under the arachnoid layer?

Answer 5

subarachnoid space

this is where the CSF is

Question 6

where is the pia mater located?

Answer 6

right on the surface of the brain

it also follows the into the sulci too

Question 7

what are the characteristics of the dura mater?

Answer 7

1. found as a two-layered thick membrane
2. periosteal layer lines the inner surface of the skull
3. meningeal layer is continuous with the periosteal layer and draws away to form dural infoldings/reflections into the sulci
4. shiny, tough and leather-like

right on its surface you’ll see branches of the middle meningeal artery which provides the dura mater with blood supply!

Question 8

is there an epidural space in the cranial cavity?

Answer 8

no

in the vertebral column there is but in the cranial cavity the dura is up close tot he bone – the dura attaches tightly to the suture lines of the skull

Question 9

what is the subdural space?

Answer 9

between the dura and arachnoid

Question 10

what is the subarachnoid space?

Answer 10

the space between the pia and arachnoid layers

it contains cerebrospinal fluid, bridging veins, trabecular cells, collagen fibrils and cranial nerves –> these vessels may be damaged from trauma or may rupture spontaneously, resulting in the spread of blood around the brain; this event is a subarachnoid hemorrhage (blood will seep into the sulci)

subarachnoid space contains cerebrospinal fluid (CSF) and vessels and is bridged by fibroblasts of various sizes and shapes that collectively form the arachnoid trabeculae

Question 11

what are the leptomeninges?

Answer 11

pia mater + arachnoid mater = leptomeninges

the inner two layers of the meninges, the arachnoid mater and the pia mater, are collectively known as the leptomeninges

meningeal infections are frequently sequestered in the subarachnoid space; hence they are within the leptomeninges

Question 12

what is the arachnoid mater?

Answer 12

a thin cellular layer attached to the overlying dura but, with the exception of the arachnoid trabeculae, is separated from the pia mater by the subarachnoid space

this layer is avascular!! it doesn’t contain any nerve fibers at all

Question 13

what is the function of the arachnoid trabeculae?

Answer 13

they reabsorb the CSF made by the ventricles of the brain

Question 14

what is the pia mater?

Answer 14

it is is located on the surface of the brain and spinal cord and closely follows all their various grooves and elevations

around the spinal cord, the pia mater contributes to the formation of the denticulate ligaments and the filum terminale internum

film terminale internum is part of the pia extension that holds the spinal column down

the denticulate ligaments are found up and down the spinal cord and they’re white fibrous looking fibers going from the spinal cord to the dura – they stabilize the spinal cord

Question 15

what is a subarachnoid hemorrhage?

Answer 15

a bleed in-between the arachnoid and pia mater layers of the meninges

clinically patients will present with a sudden horrible horrible headache or a loss of consciousness

subarachnoid space is continuous all around the brain so if there’s a bleed nothing will contain it and it’ll spread all over the brain –> compare this with an epidural hematoma that is contained between suture lines because that’s where the dura binds to the skull

however, there are also patients that walk around with a non-symptomatic aneurism that never ruptures

Question 16

what innervates the dura?

Answer 16

there are a number of nerves, specifically branches from the trigeminal nerve that innervate the dura

just understand the trigeminal nerve innervates the dura, you don’t need to know specifically which ones do it

there’s also CN 10 and the vagus nerve but it’s mostly the trigeminal nerve

Question 17

what is the falx cerebri?

Answer 17

a dural reflection that lies in the midsagittal plane to separate right and left cerebral hemispheres

Question 18

what is the falx cerebelli?

Answer 18

a dural reflection that lies in the sagittal plane to separate right and left cerebellar hemispheres

found in the posterior fossa

Question 19

what is the tentorium cerebelli?

Answer 19

a dural reflection that lies in the horizontal pane to separate the occipital lobe from the cerebellum

Question 20

what is the diaphragma sellae?

Answer 20

a dural reflection that lies in the horizontal plane, covering the sella turcica –> it wants to contain and protect the pituitary gland within!

it has a small opening for passage of the infundibular stalk of the pituitary

so this means the hypothalamus is right above the diaphragma sellae because it’s what controls the pituitary gland!

Question 21

what are the 4 dural specializations?

Answer 21

1. falx cerebri
2. falx cerebelli
3. tentorium cerebelli
4. diaphragma sellae

Question 22

what is a meningioma?

Answer 22

tumor cells that originate from the dura

it’s specifically called an extraparychymal tumor which means the tumor doesn’t arise from cells of the brain tissue, it arises from an area outside the brain tissue

these lesions will apply pressure to the surrounding brain tissue and it will compress structures around it like ventricles – this could cause a midline shift where stuff starts moving to the other side of the brain to get to lower pressure areas of the brain

Question 23

what are dural venous sinuses?

Answer 23

venous sinuses are endothelium-lined spaces that communicate with each other between the periosteal and meningeal layers of the dura

so you find the dural venous sinuses where the meningeal layer peals off from the pereosteal layer to dive into the sulci and this is where you’d find a dural venous sinus!

Question 24

what is the superior sagittal sinus?

Answer 24

a dural venous sinus; it’s the big one you should know

it runs along the superior border of the falx cerebri

it contains arachnoid granulations to drain CSF back into the venous return to the heart

it drains into the confluence of sinus which is right at the level of the internal occipital protuberance

Question 25

what is the inferior sagittal sinus?

Answer 25

a dural venous sinus that runs along the inferior border of the falx cerebri

Question 26

what is the straight sinus?

Answer 26

a dural venous sinus that connects the two sagittal sinuses with the great cerebral vein of Galen

it’s found on the roof of the tentorium cerebelli

so the inferior sagittal sinus drains into the straight sinus which then drains into the confluence of sinuses at the internal occipital protuberance – the superior sagittal sinus directly drains into the confluence

Question 27

what is the confluence of sinuses?

Answer 27

a dural venous sinus that is found along the superior border of the tentorium cerebelli and collects all venous blood flow from these sinuses

the straight sinus and the superior sagittal sinus drain into it –> then the confluence of sinuses drains into the transverse sinuses

Question 28

what is the transverse sinus?

Answer 28

a dural venous sinus that receives blood from the confluence of sinuses so it’s a left and right continuations of venous flow from the confluence of sinuses –> this then leads to the sigmoid sinuses

it runs in the transverse sulcus of the skull

Question 29

what are the sigmoid sinuses?

Answer 29

s-shaped veins which branch from the transverse sinus

they continue as the internal jugular veins and leave the skull through the jugular foramina

jugular foramen contains CN 9, 10, 11, IJV

Question 30

what are the superior petrosal sinuses?

Answer 30

dural sinuses that drain the cavernous sinus into the sigmoid sinus/internal jugular vein

the groove for the superior petrosal sinus is on the petrous portion of the temporal bone –> the superior petrosal sinus drains the cavernous sinus into the sigmoid sinus which then drains into the IJV

Question 31

what is Mekle’s cave?

Answer 31

where the trigeminal nerve can be found which is close to the foramen rotundum, foramen ovale and superior orbital fissure which is great because that’s where V1, V2, and V3 exit the skull

it’s between the periosteal layer of dura mater and the petrous portion of the temporal bone

Question 32

what is the inferior petrosal sinus?

Answer 32

it runs bilateral to the clivus and drains the cavernous sinus which is bilateral to the hypophyseal fossa

it drains the cavernous sinus directly into the IJV

Question 33

what are the cavernous sinuses?

Answer 33

bilateral venous compartments of the sella turcica

the superior and inferior petrosal sinuses drain the cavernous sinus into the IJV

Question 34

what are the contents of the cavernous sinuses?

Answer 34

1. internal carotid artery
2. CN 6 = abducens nerve

in the lateral wall of the cavernous sinus inside the dural reflection there is CN 3, 4, V1, and V2 –> these are in the wall of the cavernous sinus, not in the actual sinus itself

Question 35

what is the flow of blood in the dural sinuses? high yield!!

Answer 35

superior sagittal sinus –> confluence of sinus –> transverse sinus –> sigmoid sinus –> IJV

inferior sagital sinus –> straight sinus –> confluence of sinus –> transverse sinus –> sigmoid sinus –> IJV

cavernous sinus –> superior petrosal sinus –> transverse sinus –> sigmoid sinus –> IJV

cavernous sinus –> inferior petrosal sinus –> IJV

Question 36

what two things are the arterial supply of the CNS?

Answer 36

1. carotid arterial system

2. vertebrobasilar arterial system

Question 37

what is the carotid arterial system?

Answer 37

aka anterior circulation and it supplies most of the cerebral hemispheres

blood coming up through the internal carotid artery which goes through the carotid canal to get into the middle cranial fossa

Question 38

what is the vertebrobasilar arterial system?

Answer 38

circulation coming from the 2 vertebral arteries and the basilar artery

the vertebral artery comes off the subclavian artery and it ascends through the transverse foramen of the vertebrae and it enters the skull through the foramen magnum

it is often designated as the posterior circulation because it supplies the posterior fossa, occipital lobes, and portions of the posterior and inferior temporal lobes

Question 39

what is the path of the arterial circulation once inside the skull?

Answer 39

after the internal carotid artery enters the cranium, each internal carotid artery forms an S-shaped curve, the cavernous segment, which traverses the cavernous sinus

Question 40

what are the segments of the internal carotid artery?

Answer 40

1. cervical (before carotid canal)
2. petrous (while traversing the carotid canal)
3. cavernous part (while in the cavernous sinus)

along these different parts you can develop aneurisms and you want to be able to specifically describe where they are found!

Question 41

what branches does the internal carotid artery give off once in the skull?

Answer 41

1. ophthalmic artery
2. anterior choroidal artery
3. posterior communicating artery

each internal carotid artery divides into the anterior cerebral artery and middle cerebral artery which are huge arteries that supply a lot of the brain

Question 42

what is the function of the ophthalmic artery?

Answer 42

its a branch of the internal carotid artery inside the cavernous sinus

it supplies the retina and the choroid of the eye

it gets into the orbit through the optic canal with the optic nerve

Question 43

what is the function of the anterior choroidal artery?

Answer 43

its a branch of the internal carotid artery

it supplies the ipsilateral internal capsule, a portion of the basal ganglia, and a portion of the thalamus

Question 44

what is the function of the posterior communicating artery?

Answer 44

its a branch of the internal carotid artery

it connects the internal carotid artery with the posterior cerebral artery

Question 45

what is the pathway of the posterior circulation of the brian?

Answer 45

the vertebral arteries enter the cranium through the foramen magnum and ascend on the ventrolateral surface of the medulla oblongata

the vertebral arteries on both sides would come together to form the basilar artery

Question 46

what are the major branches from the vertebral artery?

Answer 46

1. anterior spinal artery
2. posterior spinal artery
3. posterior inferior cerebellar artery

at the lower border of the pons, the vertebral arties unite to form the basilar artery –> the basilar artery then gives off these end arteries:

1. anterior inferior cerebellar artery
2. superior cerebellar artery
3. numerous median and paramedian branches

at the level of the midbrain, the basilar artery divides into the right and left posterior cerebral arteries

Question 47

what happens if you block the paramedian pontine branches?

Answer 47

they are branches of the basilar artery that go to the pons but they are all terminal arteries so there’s no collateral circulation!

so if you block any of them, you’ll have serious brainstem problems

Question 48

what is the circle of willis?

Answer 48

a ring-like series of vessels at the base of the brain, surrounding the optic chiasm and pituitary stalk

it consists of:

1. anterior communicating artery, which unites the 2 anterior cerebral arteries
2. posterior communicating arteries, which join the internal carotid arteries with the posterior cerebral arteries

Question 49

what is vascular territory that the anterior cerebral artery supplies?

Answer 49

it supplies most of the medial surface and a small area on the superior surface of the cerebral hemisphere

so if you have a sagittal cut of the brain, it supplies the whole frontal lobe

slide 13 go look

Question 50

what is vascular territory that the middle cerebral artery supplies?

Answer 50

it supplies the lateral surface of the cerebral hemisphere, and several of the deep structures within the hemisphere

so it supplies parts of the frontal, parietal and superior and middle temporal gyruses of the temporal lobe

the middle cerebral artery provides supply to two important structures = Broca and Wernicke’s on in the left hemisphere

Question 51

what is the importance of the lenticulostriate arteries?

Answer 51

branches of the middle cerebral artery that supply the basal ganglia and internal capsule

if there’s a blockage of the lateral striate arteries then there’s going to be a huge problem in the areas of the internal capsule, caudate nucleus, putamen and globus pallidus

basal ganglia = caudate, putamen and globus pallidus

the ophthalmic artery and anterior caroidal artery also supply the internal capsule

Question 52

what is the vascular territory that the posterior cerebral artery supplies?

Answer 52

it is the terminal branch of the basilar artery.

it supplies blood to the midbrain, thalamus, the occipital lobe as well as the ventral aspect of the temporal lobe

Question 53

what are watershed infarcts?

Answer 53

a watershed area is an area that receives blood from two difference territories –> so between the ACA and MCA is one watershed and between the MCA and PCA is another

watershed cerebral infarctionsoccur at the border between cerebral vascular territorieswhere the tissue is furthest from arterial supply and thus most vulnerable to reductions in perfusion

Question 54

what are atherosclerotic lesions?

Answer 54

plaque in the arteries of the brain

Question 55

what is the blood brain barrier?

Answer 55

astrocytes help create the BBB by forming tight junctions around capillaries to help regulate which things can cross the arterial wall – this protects the brain tissue

BBB consists of tight junctions between endothelial cells of CNS capillaries. The effect is to prevent entry of organisms and toxins (and some drugs) into the brain parenchyma

however, there is diffusion of fat soluble molecules (CO2, O2, etc)

Question 56

what are the veins of the brain?

Answer 56

1. superficial middle cerebral vein (courses horizontally along the lateral cerebrum)
2. superior anastomotic vein of Trolard (courses along central sulcus)
3. inferior anastomotic vein of Labbe

Question 57

what is the function of the superior anastomotic vein of Trolard?

Answer 57

links the superior sagittal sinus with the middle cerebral vein