Dural Venous Sinuses

DURAL  VENOUS  SINUSES

• Dural venous sinuses occupy the space between endosteal and meningeal layers of dura mater, except inferior sagittal and straight sinuses which lodge within the meningeal layer only.

CHARACTERISTIC  FEATURES

• They are lined with endothelium.
  
• They are valveless.
• They collect the blood from brain, meninges, diploie, internal ear and orbit.
• They absorb CSF through the arachnoid granulations.
• They receive valveless emissary veins.

CLASSIFICATION

• Dural venous sinuses are classified into paired & unpaired groups.

Unpaired Sinuses :-

1. Superior sagittal sinus
2. Inferior sagittal sinus
3. Straight sinus
4. Occipital sinus
5. Anterior intercavernous sinus
6. Posterior intercavernous sinus
7. Basilar venous plexus

Paired Sinuses :-

1. Superior petrosal sinus
2. Inferior petrosal sinus
3. Spheno-parietal sinus
4. Petro-squamous sinus
5. Middle meningeal sinus
6. Transverse sinus
7. Sigmoid sinus
8. Cavernous sinus

 

SUPERIOR  SAGITTAL  SINUS

• It lies within the convex attached margin of falx cerebri.
• It is triangular on cross-section.

It begins at the crista galli

Passes backward and lodges in a groove on the vault of the skull

 

Reaches the internal occipital protuberance

Then it deviates to right and continuous with right transverse sinus

Interior of the Sinus :-

It presents following features -

• Openings of superior cerebral veins
• Arachnoid granulations
• Fibrous bands
• Openings of three venous lacunae on each side which collect blood from diploic and meningeal veins.

Tributaries :-

• Superior cerebral veins
• Diploic veins
• Emissary veins

Communications :-

• With the veins of scalp through parietal emissary vein.
• A vein from the nose through the patent foramen caecum.
• With the cavernous sinus through the superior anastomotic vein & superficial middle cerebral vein.

Confluence of Sinuses (Torcula Hirophili) :-

• It is the dilated posterior end of superior sagittal sinus.
• It lodges in a depression on the right side of internal occipital protuberance.
• Right transverse sinus begins from the confluence.
• A communicating vein connects the confluence with left transverse sinus.

 

INFERIOR  SAGITTAL  SINUS

• It occupies the lower free margin of falx cerebri.
• It collects blood from falx cerebri and from the medial surface of cerebrum.
• It terminates into the straight sinus.

STRAIGHT  SINUS

• It is situated within the junction of falx cerebri and tentorium cerebelli.

It begins as a continuation of inferior sagittal sinus

Passes backward and downward

Terminates into the left transverse sinus where it is connected with the confluence of sinuses.

Tributaries :-

• Inferior sagittal sinus
• Superior cerebellar veins
• Great cerebral vein of Galen

 

OCCIPITAL  SINUS

• It is the smallest sinus, situated along the attached margin of falx cerebelli.
• It begins near the margin of foramen magnum and terminates in the confluence of sinuses.

 

ANTERIOR  &  POSTERIOR  INTERCAVERNOUS  SINUSES

• Each sinus traverses respectively along the anterior and posterior attached margins of diaphragma sellae.
• They connect cavernous sinuses of both sides.
• Thus, a circular sinus is formed around the sella turcica.

 

BASILAR  VENOUS  PLEXUS

• It is a plexiform venous network.
• It lies on the clivus of the skull.
• It connects inferior petrosal sinuses of both sides.
• It communicates below with the internal vertebral venous plexus through foramen magnum.

 

SUPERIOR  PETROSAL  SINUSES

• They convey blood form the cavernous sinus to transverse sinus.
• Each sinus lodge in a groove along the upper border of petrous part of temporal bone.
• They are situated in the lateral attached border of tentorium cerebelli.

Tributaries :-

• Inferior cerebral veins
• Cerebellar veins
• Veins form tympanic cavity

INFERIOR  PETROSAL  SINUSES

• Each sinus drains the cavernous sinus into superior bulb of internal jugular vein.
• They lodge in a groove along the articulation between petrous temporal and basi-occiput.
• They leave the cranial cavity through anterior compartment of jugular foramen.
• They are the first tributaries of internal jugular veins.

Tributaries :-

• Labyrinthine veins
• Veins form medulla, pons and cerebellum

SPHENO-PARIETAL  SINUSES

• They are situated along the undersurface of posterior border of lesser wings of sphenoid bone.
• They drain into the cavernous sinuses. 

PETRO-SQUAMOUS  SINUSES

• They lodge along the petro-squamous fissure.
• They drain into transverse sinuses.
• Each sinus communicates with retro-mandibular vein.

MIDDLE  MENINGEAL  SINUSES

• They accompany middle meningeal arteries.
• They consist of frontal and parietal trunks.
• Both trunks communicate above with superior sagittal sinus.
• Frontal trunk terminates into pterygoid venous plexus or spheno-parietal or cavernous sinuses.
• Parietal trunk ends in pterygoid venous plexus.

TRANSVERSE  SINUSES

• Each transverse sinus is situated along the posterior attached margin of tentorium cerebelli.
• They lodge in a groove extending from the internal occipital protuberance to mastoid angle of parietal bone.
• Right sinus begins as a continuation of superior sagittal sinus.
• Left sinus extends as a continuation of straight sinus.
• At the mastoid angle of parietal bone, each sinus continues below as the sigmoid sinus.

Tributaries :-

• Superior petrosal sinus
• Inferior cerebral veins
• Inferior cerebellar veins
• Posterior temporal diploic vein

 

SIGMOID  SINUSES

• Each sinus begins as a continuation of transverse sinus.
• They lodge in a S-shaped groove on the mastoid part of temporal bone and jugular process of occipital bone.
• Each sinus leaves the skull through the posterior compartment of jugular foramen.
• Below continuous with the superior bulb of internal jugular vein.

Tributaries :-

• Mastoid emissary veins
• Condylar emissary vein
• Cerebellar veins
• Labyrinthine veins

CAVERNOUS  SINUSES

SITUATION

• Cavernous sinuses are situated on each side of the body of sphenoid bone.
• Extends from superior orbital fissure to the apex of petrous part of temporal bone.

FORMATION

• Each sinus is formed by separation of meningeal & endosteal layers of dura mater.
• The sinus is filled with venous blood & lined by endothelial lining.

Roof & Lateral wall

• Formed by meningeal layer of dura mater
• Continuous medially with diaphragma sellae
• Roof is pierced by oculomotor, trochlear nerves & internal carotid artery

Floor & Medial wall

• Formed by Endosteal layer of dura mater

STRUCTURES  PASSING  THROUGH  THE  SINUS

1. Internal carotid artery

• It is surrounded by a plexus of sympathetic nerves & veins
• It enters the sinus through apex of petrous part of temporal bone
• It passes forwards along the floor of the sinus, turns upwards & pierce the roof of the sinus.

2. Abducent nerve

• It enters the roof below the petro-sphenoid ligament
• It lies infero-lateral to the internal carotid artery within the sinus
• It leaves the sinus through superior orbital fissure

3. Oculomotor nerve

• It enters the sinus by piercing the roof
• Within the sinus it runs along the lateral wall
• It leaves the sinus through tendinous ring of superior orbital fissure by dividing into two rami

4. Trochlear nerve

• It enters the sinus by piercing the roof
• Within the sinus it runs along the lateral wall below the oculomotor nerve
• It leaves the sinus through superior orbital fissure outside the tendinous ring.

5. Ophthalmic nerve

• It enters the sinus by piercing the lateral wall from cavum trigeminale
• Within the sinus it runs along the lateral wall below the trochlear nerve
• It leaves the sinus through superior orbital fissure by dividing into lacrimal, frontal, nasociliary branches.

6. Maxillary nerve

• It enters the sinus by piercing the lateral wall from cavum trigeminale
• Within the sinus it runs along the lateral wall below the ophthalmic nerve
• It leaves the sinus through foramen rotundum

EXTERNAL  RELATIONS

Medially  &  Below

• Hypophysis cerebri
• Sphenoidal air sinus

Laterally

• Cavum trigeminale containing the trigeminal ganglion
• Uncus of temporal lobe of cerebrum

Above

• Optic chiasma
• Internal carotid artery- its U-shaped course within and above the sinus known as Carotid siphon

TRIBUTARIES

1. Superior ophthalmic vein
2. A branch form inferior ophthalmic vein
3. Sometimes central vein of retina
4. Superficial middle cerebral vein
5. A few inferior cerebral veins
6. Spheno-parietal sinus

COMMUNICATIONS

1. With transverse sinus via superior petrosal sinus
2. With internal jugular vein through inferior petrosal sinus
3. With pterygoid venous plexus through emissary veins
4. With facial vein via-
• Superior ophthalmic vein & angular vein
• Pterygoid venous plexus & deep facial vein
5. With opposite cavernous sinus via anterior & posterior intercavernous sinuses
6. With superior sagittal sinus through superficial middle cerebral vein

FACTORS  REGULATING  THE  BLOOD  FLOW  WITHIN  THE  SINUS

• Pulsation of internal carotid artery
• Gravity
• Change of position of the head

APPLIED  ANATOMY

Septic Thrombosis of Cavernous Sinus

Cause-

• Infection from dangerous area of face, orbit, pharynx through its communications

Manifested by-

• Ophthalmoplegia- severe pain in the eye due to involvements of 3^rd 4^th 6^th cranial nerves
• Oedema of eye lids
• Exophthalmos
• Unilateral thrombosis may be bilateral due to inter-communications

Fracture of Base of Skull

• Internal carotid artery ruptures
• Arterio-venous communication may be established between the blood of artery and cavernous sinus

Manifested by-

• Pulsating exophthalmos
• Oedema of the eye lids
• Ophthalmoplegia