Dura Mater and Dural Venous Sinuses Flashcards
What are the meninges of the brain?
membrane coverings of the brain and spinal cord
Name the 3 meninges that cover the brain (from outward to inward)?
- Dura mater - thickest
> pachymenix - Arachnoid mater
- Pia mater
> Arachnoid + pia = leptomeninges
Describe the Dura mater?
- Thick, tough collagenous membrane
- Adheres to inner surface of the skull
What are the 2 layers of the dura mater?
- Endosteal layer – acts as periosteum
> continuous with the outer periosteum of the outer cranium - Meningeal layer – meningeal dura
> continuous with spinal cord dura mater
The 2 layers of the dura separate from each other at numerous locations to form which 2 unique types of structures?
- dural partitions
> which project inward and incompletely separate parts of the brain - intracranial venous structures
What are the spaces of the dura mater?
- Epidural space – potential space between dura and calvaria
- Subdural space – potential space in the innermost dural layer: near the dural-arachnoid interface
Describe the dura mater at the foramen magnum?
- Periosteal dura layer is continuous with the outer periosteum of the outer cranium
- Meningeal dura layer is continuous with spinal cord dura mater
What are dural septa?
folds of the inner dural layer into the cranial cavity
> Dural septa partially separate different intracranial compartment
What are the 4 principal dural reflections?
- Falx cerebri – between two cerebral hemispheres
- Tentorium cerebelli – between cerebrum and cerebellum
- Falx cerebelli – small reflection that separates the two cerebellar hemispheres
- Diaphragma sellae – small reflection that covers the pituitary fossa pereforated by the infundibular stalk of the gland
Describe the falx cerebri?
Sickle shaped double layer of dura mater, lying between cerebral hemispheres
Where is the falx cerebri attached?
- anteriorly > crista galli
- posteriorly > tentorium cerebelli at internal occipital protuberance
Note: free edge parallels the corpus callosum
What are the structures contained in the falx cerebri?
- free inferior concave border > contains inferior sagittal sinus
- Upper convex margin > encloses superior sagittal sinus
Describe the falx cerebelli?
Small sickle shaped projection between the cerebellar hemispheres
> Attached to posterior parts of tentorium cerebelli
What is the corpus callosum?
a large bundle of more than 200 million myelinated nerve fibers that connect 2 brain hemispheres permitting communication between the right and the left side of the brain
> free edge of falx cerebri parrallels the corpus callosum
Describe the tentorium cerebelli?
Separates the superior part of the cerebellum and the occipital lobe of the cerebrum
The tentorium cerebelli separates the posterior fossa into?
- Superotentorial compartment - contains cerebrum
- Infratentorial compartment (posterior fossa) - contains brain stem and cerebellum
Describe the attachment points of the tentorium cerebelli?
- Posteriorly the tentorium attaches to the occipital bone
- The free edge incircles the midbrain and is called tentorial notch or tentorial incisure (clinically important)
What are the structures within the tentorium cerebelli?
External convex border encloses:
> posteriorly = transverse sinus
> anteriorly = superior petrosal sinus
Describe the diaphragma sellae?
- Circular, horizontal fold of dura mater that forms the roof of sella turcica, covering the pituitary gland
- Has a central aperture for the hypophysial stalk
Describe the venous drainage of the cranial cavity?
> Dura mater contains venous sinuses that drain the brain in edges of dural reflections
In edges of reflection the two layers separate to form channels called dural venous sinus
Cerebral veins empty into dural venous sinuses
Where are dural venous sinuses?
between the layers of the dura mater
Describe the structure of the dural sinuses?
> lined by endothelium
thick walls but devoid of muscular tissue
have no valves
What is the function of the dural venous sinuses?
to receive blood from the brain through the cerebral veins and the cerebrospinal fluid from the subarachnoid space through the arachnoid vili
Describe the course of the major dural venous sinuses?
follow the lines of attachment as well as free edges of the falx and tentorium
Name the major dural venous sinuses?
- Superior sagittal sinus - along attached edge of the falx
- Transverse sinus (left and right) – along the posterior line of attachment of the falxi and tentorium
- Straight sinus – along the line of attachment of the falx and the tentorium
- Confluence of sinuses ( torcular or torcular herophili ) - where sinuses meet near internal occipital protuberance
- Sigmoid sinus – S-shaped course that empties into internal jugular vein(IJV)
Where is the superior sagittal sinus located?
Occupies the upper fixed border of the falx cerebri
Describe the course of the superior sagittal sinus?
- Begins in the front at the foramen cecum where it receives a vein from the nasal cavity
- It runs backward, grooving vault of the skull and at the internal occipital protuberance it is continuous with the transverse sinus
> It communicates through small openings with 2 or 3 venous lacunae on each side
What are arachnoid villi/granulations?
small projections of the arachnoid barrier layer into the venous sinus and its major tributaries
> act a one way valves for the flow of CSF into venous blood
Describe the structures that project into the communicating lacunae of the superior sagittal sinus?
- Numerous arachnoid villi and granulations
- the diploic, emissary and meningeal veins
Which vein does the superior sagittal sinus receive?
superior cerebral veins
Describe the confluence of the sinuses?
at the internal occipital protuberance the SSS is dilated to form the confluence of the sinuses which is connected to the opposite transverse sinus and receives the occipital sinus
Where is the inferior sagittal sinus located?
Occupies the free lower margin of the falx cerebri
Describe the course of the inferior sagittal sinus?
Runs backward and joins great cerebral vein which is formed by the union of the 2 internal cerebral veins at the free margin of the tentorium cerebelli to form the straight sinus
Which veins does the inferior sagittal sinus receive?
Receives cerebral veins from the medial surface of the cerebral hemisphere
Where is the straight sinus located?
It occupies the line of junction of the falx cerebri with the tentorium cerebelli
Describe the course of the straight sinus?
- It is formed by the union of the inferior sagittal sinus with the great cerebral vein
- It ends by turning to the left (sometimes to the right) to form the transverse sinus
Where is the occipital sinus located?
It is a small sinus occupying the attached margin of the falx cerebelli
Describe the course of the occipital sinus?
- It communicates with the vertebral veins near the foramen magnum
- Superiorly it drains into the confluence of sinuses
Where is the transverse sinus located?
Each sinus occupies the attached margin of the tentorium cerebelli, grooving the occipital bone and posteroinferior angle of the parietal bone
Describe the course of the transverse sinus?
- Paired and begin at the internal occipital protuberance
- The right sinus usually continuous with the superior sagittal sinus
- The left is continuous with the straight sinus
> They end by turning downward as the sigmoid sinuses
Which veins do the transverse sinuses receive?
- the superior petrosal sinuses
- inferior cerebral
- cerebellar veins
- diploic veins
What is the location of the superior and inferior petrosal sinuses?
They are small and situated on the superior and inferior borders of the petrous part of the temporal bone on each side
Describe the drainage of the superior and inferior petrosal sinuses?
> Each superior sinus drains the cavernous sinus into the transverse sinus
Each inferior sinus drains the cavernous sinus into the internal jugular vein
Describe the course of the sigmoid sinus?
> They are a direct continuation of the transverse sinuses
Each sinus turns downward and medially and grooves mastoid part of the temporal bone
It then turns downward through the posterior part of the jugular foramen to become continuous with the superior bulb of the internal jugular vein
What are the boundaries of the cavernous sinus?
• Anterior - extends into medial end of superior orbital
fissure.
Posterior - upto apex of petrous temporal bone.
• Medial - Pitutary above and sphenoid below
Lateral - temporal lobe and
uncus
• Superior - optic chiasma
• Inferior - endosteal dura mater, greater wing of sphenoid
What are the tributaries of the cavernous sinus?
1 - Superior ophthalmic vein which communicates it with the facial V
2 - Inferior ophthalmic vein.
3 - Cerebral veins
4 - Central vein of the retina
5 - Sphenopareital sinus
Describe the drainage of the cavernous sinus?
> posteriorly into the superior and inferior petrosal sinuses
inferiorly into the pterygoid venous plexus
Describe the communication of the superior and inferior petrosal sinuses?
The 2 sinuses communicate with one another by means of the anterior and posterior intercavernous sinuses which run in the diaphragma sellae in front and behind the stalk of the hypophysis cerebri
Which structures are found within the walls of the cavernous sinus?
1 oculomotor
2 trochlear
3 V1
4 V2
Which structures are found within the cavernous sinus?
- abducens
- autonomic plexus
- internal carotid artery
- pituitary gland
- body of sphenoid bone
Describe the clinical correlations of hypophyseal enlargement and the optic chiasma?
A pituitary tumor pushes the diaphragma sellae upward and causes pressure on the optic chiasma. This results in interference with the function of the nerve fibers crossing in the chiasma ( from the inner quadrants of the retina ) and the patient presents with bitemporal hemianopsia. Further expansion of the pituitary tumor causes erosion of the body of the sphenoid bone.
