Head and Neck Anatomy: Cranial Venous Sinuses

These are venous spaces, the walls of which are formed by dura mater.
They have an inner lining of endothelium.
There is no muscle in their walls.
They have no valves.
Venous sinuses receive venous blood from the brain, the meninges, and bones of the skull
Cerebrospinal ﬂuid is poured into some of them.
Cranial venous sinuses communicate with veins outside the skull through emissary veins.
These communications help to keep the pressure of blood in the sinuses constant
There are 23 venous sinuses, of which 8 are paired and 7 are unpaired.

Paired Sinuses

There is one sinus each on right and left side.

1. Cavernous sinus.

2. Superior petrosal sinus

3. Inferior petrosal sinus.

4. Transverse sinus

5. Sigmoid sinus.

6. Sphenoparietal sinus.

7. Petrosquamous sinus.

8. Middle meningeal sinus/veins.

Unpaired Sinuses

These are median in position.

1. Superior sagittal sinus.

2. Inferior sagittal sinus.

3. Straight sinus.

4. Occipital sinus.

5. Anterior intercavernous sinus.

6. Posterior intercavernous sinus.

7. Basilar plexus of veins.

Cavernous Sinus

Introduction

Each cavernous sinus is a large venous space situated in the middle cranial fossa,
on either side of the body of the sphenoid bone.
Its interior is divided into a number of spaces or caverns by trabeculae.
The trabeculae are much less conspicuous in the living than in the dead.
The ﬂoor and medial wall of the sinus is formed by the endosteal dura mater.
The lateral wall, and roof are formed by the meningeal dura mater.
Anteriorly, the sinus extends up to the medial end of the superior orbital ﬁssure and
posteriorly, up to the apex of the petrous temporal bone.
It is about 2 cm long, and 1 cm wide.

Relations

Structures outside the sinus:

1. Superiorly: Optic tract, optic chiasma, olfactory tract, internal carotid artery and anterior perforated

substance.

2. Inferiorly: Foramen lacerum and the junction of the body and greater wing of the sphenoid bone

3. Medially; Hypophysis cerebri and sphenoidal air sinus.

4. Laterally: Temporal lobe with uncus.

5. Below laterally: Mandibular nerve

6. Anteriorly; Superior orbital ﬁssure and the apex of the orbit.

7. Posteriorly; Apex of the petrous temporal and the crus cerebri of the midbrain.

Structures with in the Lateral Wall

From above downwards

1. Oculomotor nerve: In the anterior part of the sinus, it divides into superior and inferior divisions which leave the sinus by passing through the superiororbital ﬁssure.

2. Trochlear nerve: In the anterior part of the sinus, it crosses superﬁcial to the oculomotor nerve, and enters the orbit through the superior orbital ﬁssure.

3. Ophthalmic nerve: In the anterior part of the sinus, it divides into the lacrimal, frontal and nasociliary nerves.

4. Maxillary Nerve: It leaves the sinus by passing through the foramen rotundum on its way to the pterygopalatine fossa.

5. Trigeminal ganglion: The ganglion and its dural cave project into the posterior part of the lateral wall of the sinus.

Structures passing through the medial aspect of the sinus:

a. lnternal carotid artery with the venous and sympathetic plexus around it.

b. Abducent nerve, inferolateral to the internal carotid artery.

The structures in the lateral wall and on the medial aspect of the sinus are separated from blood by the endothelial lining.

Tributaries or Incoming Channels

From the orbit

1. The superior ophthalmic vein.

2. A branch of the inferior ophthalmic vein or sometimes the vein itself.

3. The central vein of the retina may drain either into the superior ophthalmic vein or into the cavernous

sinus

From the Brain

1. Superﬁcial middle cerebral vein.

2. Inferior cerebral veins from the temporal lobe

From the Meninges

1. Sphenoparietal sinus.

2. The frontal trunk of the middle meningeal vein may drain either into the pterygoid plexus through the

foramen ovale or into the sphenoparietal or cavernous sinus.

Draining Channels or Communications

The cavernous sinus drains:

1. Into the transverse sinus through the superior petrosal sinus.

2. Into the internal jugular vein through the inferior petrosal sinus and through a plexus around the

internal carotid artery.

3. Into the pterygoid plexus of veins through the emissary veins passing through the foramen ovale,

the foramen lacerum and the emissary sphenoidal foramen.

4. Into the facial vein through the superior ophthalmic vein.

5. The right and left cavernous sinuses communicate with each other through the anterior and posterior

intercavernous sinuses and through the basilar plexus of veins

All these communications are valveless, and blood can ﬂow through them in either direction.

Factors helping expulsion of blood from the Sinus

1. Expansile pulsations of the internal carotid artery within the sinus.

2. Gravity.

3. Position of the head.

Clinical Anatomy

1. Thrombosis of the cavernous sinus may be caused by sepsis in the dangerous area of the face, in nasal

cavities, and in paranasal air sinuses. This gives rise to the following symptoms.

a. Nervous symptoms:

- Severe pain in the eye and forehead in the area of distribution of ophthalmic nerve.

- Involvement of the third, fourth and sixth cranial nerves resulting in paralysis of the muscles supplied.

b. Venous symptoms: Marked oedema of eyelids, cornea and root of the nose, with exophthalmos due to

congestion of the orbital veins.

2. A communication between the cavernous sinus and the internal carotid artery may be produced

by head injury. When this happens the eyeball protrudes and pulsates with each heart beat. It is called the

pulsating exophthalmos.

Superior Sagittal Sinus

The superior sagittal sinus occupies the upper convex, attached margin of the falx cerebri

It begins anteriorly at the crista galli by the union of tiny meningeal veins.

Here it communicates with the veins of the frontal sinus, and occasionally with the veins of the nose,

through the foramen caecum.

As the sinus runs upwards and backwards, it becomes progressively larger in size.

It is triangular on cross- section.

It ends near the internal occipital protuberance by turning to one side, usually the right, and becomes

continuous with the right transverse sinus

It generally communicates with the opposite sinus.

The junction of all these sinuses is called the conﬂuence of sinuses.

The interior of the sinus shows:

a. Openings of the superior cerebral veins.

b. Openings of venous lacunae, usually three on each side.

c. Arachnoid villi and granulations projecting into the lacunae as well as into the sinus

d. Numerous ﬁbrous bands crossing the inferior angle of the sinus.

Tributaries

The superior sagittal sinus receives these tributaries.

a. Superior cerebral veins which never open into the venous lacunae.

b. Parietal emissary veins.

c. Venous lacunae, usually three on each side which ﬁrst, receive the diploic and meningeal veins,

and then open into the sinus.

d. Occasionally, a vein from the nose opens into the sinus when the foramen caecum is patent.

Clinical Anatomy:

1. Thrombosis of the superior sagittal sinus maybe caused by spread of infection from the nose,

scalp and diploe.

This gives rise to:

a. A considerable rise in intracranial tension due to defective absorption of CSF.

b. Delirium and sometimes convulsions due to congestion of the superior cerebral veins.

c. Paraplegia of the upper motor neuron type due to bilateral involvement of the paracentral lobules

of cerebrum where the lower limbs and perineum are represented.

Inferior Sagittal Sinus

The inferior sagittal sinus, a small channel lies in the posterior two-thirds of the lower, concave free margin of the falx cerebri.

It ends by joining the great cerebral vein to form the straight sinus

Straight Sinus

The straight sinus lies in the median plane within the junction of falx cerebri and the

tentorium cerebelli.

It is formed anteriorly by the union of the inferior sagittal sinus with the great cerebral vein, and

ends at the internal occipital protuberance by continuing as the transverse sinus usually left In

addition to the veins forming it, it also receives a few of the superior cerebellar veins.

At the termination of the great cerebral vein into the sinus, there exists a ball valve mechanism,

formed by a sinusoidal plexus of blood vessels, which regulates the secretion of CSF.

Transverse Sinus

The transverse sinuses are large sinuses.

The right sinus usually larger than the left, is situated in the posterior part of the attached margin of the

tentorium cerebelli.

The right transverse sinus is usually a continuation of the superior sagittal sinus, and the left sinus a continuation of the straight sinus.

Each sinus extends from the internal occipital protuberance to the posteroinferior angle of the parietal

bone at the base of mastoid process where it bends downwards and becomes the sigmoid sinus.

Its tributaries are:

1. Superior petrosal sinus

2. Inferior cerebral veins

3. Inferior cerebellar veins

4. Diploic (posterior temporal) vein

5. Inferior anastomotic vein.

Sigmoid Sinus

Each sinus right or left is the direct continuation of the transverse sinus.

It is S-shaped: hence the name.

It extends from the posteroinferior angle of the parietal bone to the posterior part of the jugular

foramen where it becomes the superior bulb of the internal jugular vein.

It grooves the mastoid part of the temporal bone, where it is separated anteriorly from the mastoid

antrum and mastoid air cells by only a thin plate of bone.

Its tributaries are:

1. The mastoid and condylar emissary veins.

2. Cerebellar veins.

3. The internal auditory vein.

Clinical Anatomy

1. Thrombosis of the sigmoid sinus is always secondary to infection in the middle ear or otitis media, or in the mastoid process called mastoiditis.

2. During operations on the mastoid process, one should be careful about the sigmoid sinus, so that it is not exposed.

3. Spread of infection or thrombosis from the sigmoid and transverse sinuses to the superior sagittal sinus may cause impaired CSF drainage into the latter and may, therefore, lead to the development of hydrocephalus. Such a hydrocephalus associated with sinus thrombosis following ear infection is known as otitic hydrocephalus.

Other Sinuses

1. The occipital sinus is small, and lies in the attached margin of the falx cerebelli.

2. The sphenoparietal sinuses, right and left lie along the posterior free margin of the lesser wing of the sphenoid bone, and drain into the anterior part of the cavernous sinus.

3. The superior petrosal sinuses lie in the anterior part of the attached margin of the tentorium cerebelli along the upper border of the petrous temporal bone.

4. The inferior petrosal sinuses right and left lie in the corresponding petro-occipital ﬁssure, and drain the cavernous sinus into the superior bulb of the internal jugular vein.

5. The basilar plexus of veins lies over the clivus of the skull.

6. The middle meningeal veins form two main trurks, one frontal or anterior and one parietal or posterior, which accompany the two branches of the middle meningeal artery.

7.The anterior and posterior intercavernous sinuses connect the cavernous sinuses.