Meninges, Intracranial Circulation Flashcards
what are the 2 layers of the dura mater?
the periosteal dura and the meningeal dura. The periosteal dura lines the inner surface of the skull and serves as the periosteum (endosteum).
There normally is no space between the bone of the skull and the periosteal dura, but under abnormal conditions (e.g. bleeding into this plane) a space can be created called the epidural (or extradural) space. The blood occupying this space is an epidural hematoma. The meningeal dura is fused to the periosteal dura for much of its surface, but in some regions, it separates from the periosteal dura to turn internally to form dural septa.
what are the major dural septa in the skull? (3)
meningeal dura is fused to the periosteal dura for much of its surface, but in some regions, it separates from the periosteal dura to turn internally to form dural septa. The major dural septa include the:
1. falx cerebri: between 2 cerebral hemispheres
2. falx cerebelli: between 2 cerebellar hemispheres
3. tentorium cerebelli: between cerebellum and occipital lobe
They are all composed of only meningeal dura
where are dural venous sinuses located?
between the periosteal dura and the meningeal dura in those regions where the two layers separate. Dural venous sinuses are also found within reflections of the meningeal dura.
lined with simple squamous epithelium (endothelium)
what are the major dural sinuses of the skull? (10)
- superior sagittal sinus: between periosteal and meningeal dura at root of falx cerebri
- inferior sagittal sinus: within reflection of meningeal dura at edge of falx cerebri
- occipital sinus: between periosteal and meningeal dura at root of falx cerebelli
- straight sinus: within meningeal dura at the intersection of the falx cerebri and tentorium cerebelli
- confluens of sinuses: between periosteal and meningeal dura at point where superior sagittal, occipital, and straight sinuses meet
- transverse sinus: between periosteal and meningeal dura at attachment of tentorium cerebelli
- sigmoid sinus: anterior continuation of transverse sinus, drains into jugular bulb
- cavernous sinus: between periosteal and meningeal dura forming lateral walls of pituitary fossa
- superior petrosal sinus: connecting cavernous sinus to sigmoid sinus
- inferior petrosal sinus: drains cavernous sinus into jugular bulb
dural sinuses carry venous drainage from the brain and drain into internal jugular vein
the dural sinuses carry most of the venous drainage from the brain and drain into the ______ and also communicate with veins of the face, scalp, and neck through _______
the dural sinuses carry most of the venous drainage from the brain and drain into the internal jugular vein and also communicate with veins of the face, scalp, and neck through emissary veins
note that emissary veins do not contain valves - blood can flow into or out of cranial cavity depending on pressure gradient (can be pathways for spread of infection)
T/F: the dura and arachnoid maters are fused together
FALSE - the arachnoid is pressed against the dura by the pressure of CSF
if there is bleeding into this plane, subdural hematoma can occur
describe the flow of CSF through the ventricles
- CSF produced in lateral ventricles enters third ventricle via inter-ventricular foramina (of Monro)
- CSF in 3rd ventricle passes through cerebral aqueduct (of Sylvius) in the midbrain to reach the fourth ventricle
- CSF in the 4th ventricle either continues into the central canal but mostly enters subarachnoid space through 3 openings: 2 lateral foramina (of Luschka) or 1 median foramen (of Magendie)
fill in the blank regarding the flow of CSF:
1. CSF produced in lateral ventricles enters ______ via ______
2. CSF in 3rd ventricle passes through _______ in the midbrain to reach the ________
3. CSF in the 4th ventricle either continues into the _______ but mostly enters subarachnoid space through 3 openings: 2 _______ or 1 ________
- CSF produced in lateral ventricles enters third ventricle via inter-ventricular foramina (of Monro)
- CSF in 3rd ventricle passes through cerebral aqueduct (of Sylvius) in the midbrain to reach the fourth ventricle
- CSF in the 4th ventricle either continues into the central canal but mostly enters subarachnoid space through 3 openings: 2 lateral foramina (of Luschka) or 1 median foramen (of Magendie)
CSF is resorbed into the venous system at the _________, tufts of arachnoid that come into close contact with thinned out regions of the dural wall of the superior sagittal sinus.
CSF is resorbed into the venous system at the arachnoid granulations, tufts of arachnoid that come into close contact with thinned out regions of the dural wall of the superior sagittal sinus.
communicating vs non-communicating hydrocephalus
communicating: CSF is able to pass from lateral to 3rd/4th ventricles and then subarachnoid space, but reabsorption into venous system does not keep pace with production of CSF (defect in resorption or excess production) —> enlarged subarachnoid space
non-communicating: aka obstructive, CSF produced is not able to reach subarachnoid space (narrowing of cerebral aqueduct, obstruction of foramina, etc) —> enlarged lateral ventricles
the brain receives its blood supply from 4 arteries:
2 vertebral arteries: supply brain stem, cerebellum, occipital lobe
2 internal carotid arteries: supplies reminder of brain
[these 4 arteries anastomose with each other at cerebral arterial circle of Willis]
what is the basilar artery formed from?
2 vertebral arteries combine to form basilar artery (pons-medulla junction) —> divides into 2 posterior cerebral arteries (pons-midbrain junction)
2 vertebral arteries combine to form ______ artery (pons-medulla junction) —> divides into 2 ______ arteries (pons-midbrain junction)
2 vertebral arteries combine to form basilar artery (pons-medulla junction) —> divides into 2 posterior cerebral arteries (pons-midbrain junction)
after exiting from the cavernous sinus, the internal carotid artery divides into: (3)
- anterior cerebral artery
- middle cerebral artery
- posterior communicating artery
the posterior communicating arteries connect the 2 internal carotid arteries to the 2 posterior cerebral arteries (dividends of basilar artery, which is formed from 2 vertebral arteries)
what regions are supplied by the following vertebrobasilar arteries (posterior cerebral circulation)?
1. vertebral
2. anterior spinal
3. PICA
4. pontine
5. AICA
6. superior cerebellar
7. labyrinthine
8. posterior cerebral
- Vertebral - Ventral medulla
- Anterior Spinal - Ventromedial medulla and anterior spinal cord
- PICA - Cerebellum and ventrolateral medulla
- Pontine - Ventral pons
- AICA - Cerebellum and ventrolateral caudal pons
- Superior Cerebellar - Cerebellum and ventrolateral rostral pons
- Labyrinthine - Inner ear
- Posterior Cerebral - Occipital lobe and ventral midbrain
what cerebral region is supplied by the anterior vs middle cerebral arteries (branches of internal carotid)?
Anterior Cerebral - Medial side of frontal and parietal lobes
Middle Cerebral - Lateral side of frontal, parietal and temporal lobes
what type of hematoma would occur from injury to the middle meningeal artery?
middle meningeal artery (a branch of the maxillary artery), enters the cranial cavity through the foramen spinosum. Within the cranial cavity, the branches of this artery lie between the inner surface of the skull and the periosteal dura (tightly bound to the dura)
injury —> bleeding into plane between periosteal dura and the skull —> epidural hematoma
what type of hematoma would occur from injury to the cortical (“bridging”) veins?
cortex of the brain has venous drainage through cortical veins which drain into dural venous sinuses, primarily the superior sagittal sinus. These veins “bridge across the subarachnoid space to penetrate the arachnoid and then the dura to enter the sinus
The veins may tear at the site where they are anchored to the dura. This will result in venous bleeding which will separate the arachnoid from the dura —> subdural hematoma
can an epidural or subdural hematoma cross suture lines, and why?
Because the periosteal dura is very tightly attached to the bone of the skull at the suture lines, an epidural hematoma does not cross suture lines. In contrast, because arachnoid is not directly attached to the bone of the skull, a subdural hematoma easily crosses suture lines. This difference allows the clinician to distinguish between the two types of hematomas radiographically.
Subdural hematomas do not cross the midline because of the presence of the falx cerebri
what is it called when an artery that provides blood to the brain (branches of vertebral and internal carotid arteries) rupture? why does this make sense?
bound in the pia mater on the surface of the brain and are thus in the subarachnoid space —> rupture causes subarachnoid hemorrhage
arterial blood enters the subarachnoid space and mixing with the cerebrospinal fluid
what type of brain bleed occurs form injury to the following structures?
a. middle meningeal artery
b. cortical (bridging) veins
c. cerebral arteries
a. middle meningeal artery —> epidural hematoma
b. cortical (bridging) veins —> subdural hematoma
c. cerebral arteries —> subarachnoid hemorrhage
