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.

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.

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

Subarachnoid space is the site of the 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.

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.

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.

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.

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

The tentorium cerebelli separates the cerebrum from the cerebellum.

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.

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.

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

It continues upwards as a superior sagittal sinus,

bilaterally as a paired transverse sinus,

downwards as an occipital sinus,

and forward and slightly upwards as a straight sinus.

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

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

The straight sinus splits into the inferior sagittal sinus

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

The superior petrosal sinus branches off from the transverse sinus,

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

These two petrosal sinuses drain into the paired 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.

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),

CN IV (trochlear nerve),

CN VI (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.

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.

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.

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