Brain meninges

Brain meninges. Dural venous sinusesPia, arachnoid and dura mater. Dural venous sinuses.
~ 8 min

In this note, we are going to discuss the anatomy and function of the brain meninges as well as the dural venous sinuses.

Since the brain is one of the most important structures in our body, it should be well protected from various damaging factors. For this purpose, actually, only the skull is not enough, so there are additionally three meninges that cover the brain.

Pia mater and arachnoid mater

The innermost one is the pia mater. It is tightly adhered to the surface of the brain and fills all its sulci.

Pia mater
Pia mater

Also, a large number of small blood vessels that supply the brain pass within this meninx or membrane.

The next one is the arachnoid mater.

Arachnoid mater
Arachnoid mater

Between it and the pia mater is the so-called subarachnoid space, filled with cerebrospinal fluid, and also containing large blood vessels.

Subarachnoid space
Subarachnoid space

Subarachnoid space is the site of the subarachnoid hemorrhage.

Subarachnoid hemorrhage
Subarachnoid hemorrhage

In some places, subarachnoid space forms extensions called cisterns. You can see the biggest ones in the illustration (next page), and the names and locations of the others are indicated in the table.

Dura mater

And the outermost one is the dura mater.

Dura mater
Dura mater

It consists of two layers: the periosteal, which plays the role of an internal periosteum of the cranial bones. And the second layer, called the meningeal layer, is located deeper.

There are two potential spaces related to the dura mater. What is actually a potential space? Well, in healthy conditions, the two membranes of whatever space are separated only by a small amount of fluid. So the structures are adjacent to each other.

But with an injury, for example, blood can accumulate between these structures, and as a result, the distance between them increases, forming a space filled with blood.

There is a potential epidural space between the cranial bone and the periosteal layer of the dura mater, which is the site of the formation of an epidural hematoma.

Между костью и периостальным листком твердой мозговой оболочки потенциально существует эпидуральное пространство (spatium epidurale), которое является местом эпидурального кровоизлияния.

Epidural hematoma
Epidural hematoma

And between the meningeal layer of the dura mater and the arachnoid mater, there is a potential subdural space, which is the site of the formation of a subdural hematoma.

Subdural hematoma
Subdural hematoma

Dural folds / reflections

In some places, the meningeal layer of the dura mater forms reflections (also known as dural folds), which divide the intracranial space into several compartments.

The first reflection, called the falx cerebri, projects downward into the fissure between the cerebral hemispheres.

Falx cerebri
Falx cerebri

The falx cerebelli (or cerebellar falx) is similar to the previous one but separates the cerebellar hemispheres.

Falx cerebelli
Falx cerebelli

The tentorium cerebelli separates the cerebrum from the cerebellum.

Tentorium cerebelli
Tentorium cerebelli

And the diaphragma sellae or sellar diaphragm, which is a kind of protection for the pituitary gland, and it is stretched directly over the sella turcica of the sphenoid bone.

Diaphragma sellae
Diaphragma sellae

Dural venous sinuses

The periosteal and meningeal layers of the dura mater are adjacent to each other quite tightly. But in some places the distance between them increases and there are several cavities called dural venous sinuses.

These sinuses are filled with venous blood because they actually collect this blood from the veins of the brain, and then drain it into the internal jugular vein.

Internal jugular vein
Internal jugular vein

Basically, most of the sinuses drain into the confluence of sinuses, which is located at the level of the internal occipital protuberance.

Confluence of sinuses
Confluence of sinuses
Confluence of sinuses
Confluence of sinuses

It continues upwards as a superior sagittal sinus,

Superior sagittal sinus
Superior sagittal sinus
Superior sagittal sinus
Superior sagittal sinus
Superior sagittal sinus
Superior sagittal sinus

bilaterally as a paired transverse sinus,

Transverse sinus
Transverse sinus
Transverse sinus
Transverse sinus
Transverse sinus
Transverse sinus

downwards as an occipital sinus,

Occipital sinus
Occipital sinus
Occipital sinus
Occipital sinus

and forward and slightly upwards as a straight sinus.

Straight sinus
Straight sinus
Straight sinus
Straight sinus

Each transverse sinus, in turn, continues as a sigmoid sinus, which leaves the skull through the jugular foramen

Sigmoid sinus
Sigmoid sinus
Sigmoid sinus
Sigmoid sinus
Sigmoid sinus
Sigmoid sinus

and drains into the internal jugular vein. This provides a connection with large systemic veins.

Internal jugular vein
Internal jugular vein
Internal jugular vein
Internal jugular vein

The straight sinus splits into the inferior sagittal sinus

Inferior sagittal sinus
Inferior sagittal sinus
Inferior sagittal sinus
Inferior sagittal sinus

and the great cerebral vein (or vein of Galen).

Great cerebral vein
Great cerebral vein
Great cerebral vein
Great cerebral vein

The superior petrosal sinus branches off from the transverse sinus,

Superior petrosal sinus
Superior petrosal sinus
Superior petrosal sinus
Superior petrosal sinus
Superior petrosal sinus
Superior petrosal sinus

and just below, the inferior petrosal sinus branches off from the sigmoid sinus.

Inferior petrosal sinus
Inferior petrosal sinus
Inferior petrosal sinus
Inferior petrosal sinus
Inferior petrosal sinus
Inferior petrosal sinus

These two petrosal sinuses drain into the paired cavernous sinus.

Cavernous sinus
Cavernous sinus
Cavernous sinus
Cavernous sinus

It is located on either side of the sella turcica and both cavernous sinuses (left and right) are connected by the so-called intercavernous sinuses.

Intercavernous sinus
Intercavernous sinus

The cavernous sinuses collect blood from the veins of the orbit and the veins of the face, so infection from these areas can somehow get into the cavernous sinus and cause inflammation.

And this is dangerous.

Because the CN III (oculomotor nerve),

Oculomotor nerve
Oculomotor nerve

CN IV (trochlear nerve),

Trochlear nerve
Trochlear nerve

CN VI (abducens nerve),

Abducens nerve
Abducens nerve

and the two branches of the CN V (ophthalmic nerve and maxillary nerve), pass within the cavernous sinus and when the sinus is inflamed, they can be compressed and this actually causes certain symptoms.

Maxillary nerve
Maxillary nerve
Ophthalmic nerve
Ophthalmic nerve

But what is the most dangerous thing: the internal carotid artery, which supplies the brain with arterial blood, also passes through the cavernous sinus. And if there is an infection in the sinus, it can easily get into the internal carotid artery and actually cause inflammation of the entire brain or its meninges.

Internal carotid artery
Internal carotid artery

Eventually, the sinuses drain blood into the internal jugular vein, and then it is heading towards the heart.

Another important point, the arachnoid mater forms a sort of projections through the dura mater into the dural sinuses. These projections are called arachnoid granulations, also known as Pacchionian granulations, and their largest cluster is located in the area of the superior sagittal sinus. And these arachnoid granulations allow cerebrospinal fluid to pass from the subarachnoid space into the venous system.

Arachnoid granulations
Arachnoid granulations
Golosary

Brain meninges

pia mater
pia mater
arachnoid mater
arachnoidea mater
subarachnoid space
spatium subarachnoideum
cisterns
cisternae
dura mater
dura mater
periosteal layer
lamina periostalis
meningeal layer
lamina meningealis
epidural space
spatium epidurale
subdural space
spatium subdurale
falx cerebri
falx cerebri
falx cerebelli
falx cerebelli
tentorium cerebelli
tentorium cerebelli
diaphragma sellae
diaphragma sellae
dural venous sinuses
sinus durae matris
internal jugular vein
vena jugularis interna
confluence of sinuses
confluens sinuum
superior sagittal sinus
sinus sagittalis superior
transverse sinus
sinus transversus
occipital sinus
sinus occipitalis
straight sinus
sinus rectus
sigmoid sinus
sinus sigmoideus
inferior sagittal sinus
sinus sagittalis inferior
great cerebral vein
vena cerebri magna
superior petrosal sinus
sinus petrosus superior
inferior petrosal sinus
sinus petrosus inferior
cavernous sinus
sinus cavernosus
intercavernous sinuses
sinus intercavernosus
arachnoid granulations
granulationes arachnoideae
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