Cerebral Duramater

 The dura mater is the outermost, thickest and toughest membrane covering the brain 

There are two layers of dura:

a. An outer or endosteal layer which serves as an internal periosteum or endosteum or endocranium for the skull bones.

b. An inner or meningeal layer which surrounds the brain. The meningeal layer is continuous with the spinal dura mater.

The two layers are fused to each other at all places, except where the cranial venous sinuses are enclosed between them.

Endosteal Layer or Endocranium:

1. The endocranium is continuous:

a. With the periosteum lining the outside of the skull or pericranium through the sutures and foramina.

b. With the periosteal lining of the orbit through the superior orbital fissure.

2. It provides sheaths for the cranial nerves, the sheaths fuse with the epineurium outside the skull. 

Over the optic nerve, the dura forms a sheath which becomes continuous with the sclera.

3. Its outer surface is adherent to the inner surface of the cranial bones by a number of fine fibrous and

vascular processes. 

The adhesion is most marked at the sutures, on the base of the skull and around the foramen magnum.

Meningeal Layer

At places, the meningeal layer of dura mater is folded on itself to form partitions which divide the cranial cavity into compartments which lodge different parts of the brain.

 The folds are:  

1. Falx cerebri, 

2. Tentorium cerebelli, 

3. Falx cerebelli, 

4. Diphragma sellae.

Falx cerebri

The falx cerebri is a large sickle-shaped fold of dura mater occupying the median longitudinal fissure

between the two cerebral hemispheres. 

It has two ends:

1. The anterior end is narrow, and is attached to the crista galli.

2. The posterior end is broad, and is attached along the median plane to the upper surface of the tentorium

cerebelli.

The falx cerebri has two margins:

1. The upper margin is convex and is attached to the lips of the sagittal sulcus.

2. The lower margin is concave and free.

The falx cerebri has right and left surfaces each of which is related to the medial surface of the corresponding cerebral hemisphere.

Three important venous sinuses are present in relation to this fold. 

1. The superior sagittal sinus lies along the upper margin; 

2. The inferior sagittal sinus along the lower margin

3. The straight sinus along the line of attachment of the falx to the tentorium cerebelli

Tentorium cerebelli

The tentorium cerebelli is a tent-shaped fold of dura mater, forming the roof of the posterior cranial fossa. 

It separates the cerebellum from the occipital lobes of the cerebrum, 

broadly divides the cranial cavity into supratentorial and infratentorial compartments. 

The infratentorial compartment, in other words, is the posterior cranial fossa containing the hindbrain and the lower part of the midbrain.

The tentorium cerebelli has 

a free margin and 

an attached margin  

The anterior free margin is U-shaped and free. 

The ends of the 'U' are attached anteriorly to the anterior clinoid processes. 

This margin bounds the tentorial notch which is occupied by the midbrain and the anterior part of the superior vermis.

The outer or attached margin is convex. 

Posterolaterally, it is attached to the lips of the transverse sulci on the occipital bone, and on the posteroinferior angle of the parietal bone.

Anterolaterally, it is attached to the superior border of the petrous temporal bone and to the posterior clinoid processes. 

Along the attached margin, there are the transverse and superior petrosal venous sinuses.

The trigeminal or Meckel's cave is a recess of dura mater present in relation to the attached margin of the

tentorium. 

It is formed by evagination of the inferior layer of the tentorium over the trigeminal impression on the petrous temporal bone. 

It contains the trigeminal ganglion.

The free and attached margins of the tentorium cerebelli cross each other near the apex of the petrous

temporal bone. 

Anterior to the point of crossing, there is a triangular area which forms the posterior part of the roof of the cavernous sinus, and is pierced by the third and fourth cranial nerves.

The tentorium cerebelli has two surfaces. 

The superior surface is convex and slopes to either side from the median plane. 

The falx cerebri is attached to this surface, in the midline; 

the straight sinus lies along the line of this attachment. 

The superior surface is related to the occipital lobes of the cerebrum. 

The inferior surface is concave and fits the convex superior surface of the cerebellum. 

The falx cerebelli is attached to its posterior part

Falx cerebelli

The falx cerebelli is a small sickle-shaped fold of dura mater projecting forwards into the posterior cerebellar notch.

The base of the sickle is attached to the posterior part of the inferior surface of the tentorium cerebelli in the median plane. 

The apex of the sickle is frequently divided into two parts which are lost on the sides of the foramen magnum.

The posterior margin is convex and is attached to the internal occipital crest. 

It encloses the occipital sinus.

The anterior margin is concave and free.

Diaphragma sellae

The diaphragma sellae is a small circular, horizontal fold of dura mater forming the roof of the hypophyseal fossa.

Anteriorly, it is attached to the tuberculum sellae.

Posteriorly, it is attached to the dorsum sellae. 

On each side, it is continuous with the dura mater of the middle cranial fossa.

The diaphragma has a central aperture through which the stalk of the hypophysis cerebri passes.

Blood Supply

The outer layer is richly vascular. 

The inner meningeal layer is more fibrous and requires little blood supply.

1. The vault or supratentorial space is supplied by the middle meningeal artery.

2. The anterior cranial fossa and the dural lining is supplied by meningeal branches of the anterior ethmoidal, posterior ethmoidal and ophthalmic arteries.

3. The middle cranial fossa is supplied by the middle meningeal, accessory meningeal, and internal carotid arteries; and by meningeal branches of the ascending pharyngeal artery.

4. The posterior cranial fossa is supplied by meningeal branches of the vertebral, occipital and ascending pharyngeal arteries.

Nerve Supply

1. The dura of the vault has only a few sensory nerves which are derived mostly from the ophthalmic division of the trigeminal nerve.

2. The dura of the floor has a rich nerve supply and is quite sensitive to pain.

a. The anterior cranial fossa is supplied mostly by the anterior ethmoidal nerve and partly by the maxillary nerve.

b. The middle cranial fossa is supplied by the maxillary nerve in its anterior half, and by branches of the mandibular nerve and from the trigeminal ganglion in its posterior half.

c. The posterior cranial fossa is supplied chiefly by recurrent branches from first, second and third cervical spinal nerves and partly by meningeal branches of the ninth and tenth cranial nerves.

Clinical Anatomy

Pain sensitive intracranial structures are:

a. The large cranial venous sinuses and their tributaries from the surface of the brain.

b. Dural arteries.

c. The dural floor of the anterior and posterior cranial fossae.

d. Arteries at the base of the brain.

Headache may be caused by:

a. Dilatation of intracranial arteries.

b. Dilatation of extracranial arteries.

c. Traction or distension of intracranial pain sensitive structures.

d. Infection and inflammation of intracranial and extracranial structures supplied by the sensory cranial and cervical nerves.

Extradural and subdural haemorrhages are both common. 

An extradural haemorrhage can be distinguished from a subdural haemorrhage because of the following differences.

a. The extradural haemorrhage is arterial due to injury to middle meningeal artery, whereas subdural haemorrhage is venous in nature.

b. Symptoms of cerebral compression are late in extradural haemorrhage.

c. In an extradural haemorrhage, paralysis first appears in the face and then spreads to the lower parts of the body.

In a subdural haemorrhage, the progress is haphazard.

d. In an extradural haemorrhage, there is no blood in the CSF; while it is a common feature of subdural haemorrhage

Watch lectures on YouTube:

Dural Folds | Falx cerebri | Tentorium cerebelli | Falx cerebelli | Diaphragma sella | Attachments |