Meninges & Dural venous sinusesDr.Lubna Nazli

Asst.Prof RAKMHSU

Objectives

• Definition

• Meninges of the brain

• Dural folds

• Dural venous sinuses

• Emissary veins.

Meninges

Meninges are the coverings which protect the brain and spinal cord, from injuries and infections.

There are 3 layers of meninges:

• The dura mater.

• The arachnoid mater.

• The pia mater.

Meninges of the brain

Dura mater

• outermost covering

• two layers – periosteal dura - lines the cranial bones – meningeal layer - inner layer forms partitions

or dural folds that enclose dural venous sinuses.

Projections/folds of the dura mater

Falx cerebri– Falx cerebri is the sickle-shaped double layer

of the dura mater, lying between the cerebral hemispheres.

– It is attached anteriorly to the crista galli and posteriorly to the tentorium cerebelli.

– Its inferior concave border is free and contains the inferior sagittal sinus, and its upper convex margin encloses the superior sagittal sinus.

Falx cerebelli – Falx cerebelli is a small sickle-shaped

projection between the cerebellar hemispheres.

– It is attached to the posterior and inferior parts of the tentorium and contains the occipital sinus in its posterior border.

Tentorium cerebelli – Tentorium cerebelli is a crescentic fold of dura

mater that supports the occipital lobes of the cerebral hemispheres and covers the cerebellum.

– Its internal concave border is free and defines the tentorial notch, whereas its outer convex border encloses the transverse sinus posteriorly and the superior petrosal sinus anteriorly.

Diaphragma sellae – Diaphragma sellae is a circular, horizontal fold

of dura that forms the roof of the sella turcica, covering the pituitary gland.

– It has a central aperture for the hypophyseal stalk or infundibulum.

• Arachnoid mater is a filmy, transparent, spidery layer that is connected to the pia mater by trabeculation.

• It is separated from the pia mater by the subarachnoid space, which is filled with cerebrospinal fluid (CSF). It may contain blood after hemorrhage of a cerebral artery (site of formation of subarachnoid hematoma).

– Cerebrospinal fluid • is formed by vascular choroid plexuses in the

ventricles of the brain and is contained in the subarachnoid space.

• circulates through the ventricles, enters the subarachnoid space, and eventually is returned to the venous system through the arachnoid granulations.

– Arachnoid granulations • are tuft-like collections of highly folded arachnoid

that project into the superior sagittal sinus and its lateral lacunae (lateral extensions of the superior sagittal sinus).

• release CSF into the superior sagittal sinus and often produce erosion or pitting of the inner surface of the calvaria.

Pia mater

• is a delicate investment that is closely applied to the brain and dips into fissures and sulci.

• encloses blood vessels on the surface of the brain

Dural venous sinuses

• The dural venous sinuses are spaces between the endosteal and meningeal layers of the dura.

• They contain venous blood that originates from the brain or cranial cavity.

• They are no valves in the sinuses or in the veins that are connected to the sinuses.

• The majority of the venous blood in the sinus drains from the cranium via the internal jugular vein

Venous sinuses

1. superior sagittal 2. inferior sagittal3. straight 4. sphenoparietal 5. superior petrosal 6. inferior petrosal 7. transverse 8. sigmoid 9. cavernous

• Dural Venous Sinuses.

A. Sphenoparietal

B. Intercavernous

C. Sigmoid

D. Occipital

E. Confluence

F. Basilar

G. Transverse

H. Superior Petrosal

I. Inferior Petrosal

J. Cavernous

K. Superior Sagittal

Dural Venous Sinuses

A. Sup. Sag. Sinus

B. G. Cerebral V.

C. Ophthalmic Vs.

D. Facial V.

E. Cavernous Sinus

F. Inf. Pet. Sinus

G. Jugular V.

H. Sigmoid Sinus

I. Sup. Pet. Sinus

J. Transv. Sinus

K. Straight Sinus L. Inf. Sag. Sinus

• The superior sagittal sinus is found in the upper border of the falx cerebri and begins at the crista galli.

• The superior sagittal sinus receives blood from the superior cerebral vein and ends at the confluence of sinuses near the internal occipital protuberance.

• The inferior sagittal sinus is located in the lower free border of the falx cerebri between the two cerebral hemispheres.

• It begins anteriorly and ends with its junction with straight sinus.

• The straight sinus originates with the union of the great cerebral vein and inferior sagittal sinus.

• It runs posteriorly in the junction between the falx cerebelli and tentorium cerebelli to become continuous with one of the transverse sinuses (most commonly the left).

• The cavernous sinuses are found on either side of the body of the sphenoid bone in middle cranial fossae.

• They receive blood from the sphenoparietal sinuses which are located underneath the free edges of the lesser wings of the sphenoid bone.

• Blood also drains into the cavernous sinuses via the superior and inferior ophthalmic veins.

• The intercavernous sinuses provide a communication between the cavernous sinuses.

• They are located in the diaphragma sellae which covers the hypophyseal fossa and surrounds the hypophyseal stalk.

• The internal carotid artery, sympathetic nerve plexus and the abducens nerve are inside the cavernous sinuses.

• In the wall of the cavernous sinuses are the oculomotor, trochlear, ophthalmic and maxillary nerves.

• The cavernous sinuses drain posteriorly through the superior and inferior petrosal sinuses and inferiorly through the pterygoid plexus of veins.

• The Cavernous Sinuses

A. Carotid Artery

B. Trochlear Nerve

C. Maxillary Nerve

D. Abducens Nerve

E. Sphenoid Sinus

F. Pituitary Gland

G. Cavernous Sinus

H. Ophthalmic Nerve

I. Oculomotor Nerve

Cavernous Sinus

• Structures in the wall: 1. Oculomotor nerve 2. Trochlear nerve 3. Ophthalmic division of trigeminal nerve 4. Maxillary division of trigeminal nerve

• Structures within the sinus: 1. Abducens nerve 2. Internal carotid artery 3. Carotid sympathetic plexus

• The superior petrosal sinuses are located in the edge of the tentorium cerebelli on the ridge of petrous part of the temporal bone. They drain into the transverse sinuses.

• The inferior petrosal sinuses are found at the base of the petrous part of the temporal bone in the posterior cranial fossa where they empty into the internal jugular vein.

• The transverse sinuses extend laterally from the confluence of sinuses in the tentorium cerebelli.

• The transverse sinuses travel ventrally to become the sigmoid sinuses of each side.

• The sigmoid sinuses bend into an S-shaped curve and continue into the internal jugular vein through the jugular foramen.

• The occipital sinus is located in the posterior attached border of the falx cerebelli.

• It communicates superiorly with confluence of sinuses and inferiorly with the internal vertebral plexus.

Emissary veins

• The emissary veins are small veins connecting the dural venous sinuses with the veins of the scalp.

• They are valveless and, may conduct blood inward or outward in accordance with the pressure existing in the sinuses and in the external veins.

• Some are constant, others occur occasionally. • The superior ophthalmic vein is the largest vein

of this type. It connects the angular vein of the face with the cavernous sinus.

• The mastoid emissary vein unites the posterior auricular vein with the sigmoid sinus.

• The parietal emissary vein occupies the parietal foramen and connects the veins of the scalp with the superior sagittal sinus.

• The emissary vein of the foramen cecum connects the veins of the nasal cavity with the superior sagittal sinus.

• The condyloid canal, when present, transmits an emissary vein which passes between the lower end of the sigmoid sinus and veins of the suboccipital triangle of the neck.