Sinus and Its Types | Term Paper | Humans | Biology

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Term Paper # 1. Venous Sinuses (Dural Venous Sinuses):

Venous spaces present between two layers of duramater, lined by endothelium.

No muscle in their walls and have no valves.

Receives venous blood from:

a. Brain

b. Meninges

c. Skull bones

d. Excess of C.S.F. is poured into them.

Communicate with veins outside the skull through emissary veins – helps in keeping the pressure of blood constant in the sinuses.

Venous sinuses are 23 in number:

a. Paired-8 and

b. Unpaired – 7

a. Paired Cranial Venous Sinuses:

These are on right and left side:

1. Cavernous sinus

2. Superior petrosal sinus

3. Inferior petrosal sinus

4. Transverse sinus

5. Sigmoid sinus

6. Spheno parietal sinus

7. Petro squamous sinus

8. Middle meningeal sinus/veins.

b. Unpaired Sinuses:

They are in median position:

1. Superior sagittal sinus

2. Inferior sagittal sinus

3. Straight sinus

4. Occipital sinus

5. Basilar plexus of veins

6. Anterior inter cavernous sinus

7. Posterior inter cavernous sinus.

Term Paper # 2. Cavernous Sinus:

Situation:

Large paired venous sinus, present in the middle cranial fossa on the sides of body of sphenoid.

Size – 2 cm long and 1 cm wide.

Space is divided into multiple small spaces by means of trabeculae giving honeycomb appearance – called caverns.

Extent:

Anteriorly- It extends upto medial end of superior orbital fissure.

Posteriorly- Extends upto apex of petrous temporal bone.

Cavity is lined by endothelium.

Development:

Primitive head vein.

Floor of the sinus is formed by endosteal duramater.

Lateral wall, roof and medial wall are formed by meningeal duramater.

Relations of Cavernous Sinus:

I. Structures Outside the Sinus:

(a) Superiorly:

i. Optic tract

ii. Optic chiasma

iii. Olfactory tract

iv. Internal carotid artery

v. Anterior perforated substance.

(b) Inferiorly:

i. Foramen lacerum

ii. Junction of body and greater wing of sphenoid.

(c) Medially:

i. Hypophysis cerebri

ii. Sphenoidal air sinus in the body of sphenoid.

(d) Laterally:

Temporal lobe with uncus (cerebrum).

(e) Anteriorly:

i. Superior orbital fissure

ii. Apex of orbit.

(f) Posteriorly:

i. Apex of petrous temporal

ii. Crus cerebri of mid-brain.

II. Structures in the Lateral Wall of Sinus:

(From above downwards)

1. Oculomoter nerve (IIIrd)

2. Trochlear nerve (IVth)

3. Ophthalmic nerve with its branches (V₁)

4. Maxillary nerve (V₂)

5. Trigeminal ganglion with its dural cave project into posterior part of lateral wall of sinus.

III. Structures Passing through Centre of Sinus:

1. Internal carotid artery – with venous and sympathetic plexus.

2. Abducent nerve – infero-lateral to artery.

Structures in the lateral wall and centre of the sinus are separated from blood by endothelial lining.

Tributaries or Incoming Channels:

To cavernous sinus are:

A. From the Orbit:

i. Superior ophthalmic vein

ii. Inferior ophthalmic vein

iii. Central vein of retina.

B. From Brain:

i. Superficial middle cerebral vein

ii. Anterior branch of middle meningeal vein either directly or through spheno parietal sinus.

iii. Inferior cerebral veins

C. From Hypophysis Cerebri:

Hypophyseal veins.

D. From Skull Bones:

Diploic veins.

Draining Channels of Cavernous Sinus- (Comm­unications):

Drains its venous blood into:

1. Transverse sinus – through superior petrosal sinus.

2. Internal jugular vein – through inferior petrosal sinus.

3. Pterygoid plexus of veins – via emissary veins.

4. Facial vein via communication with superior ophthalmic vein.

5. Through basilar plexus of veins into vertebral vein.

Factors helping expulsion of blood from sinus:

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

2. Gravity.

3. Position of the head.

Circular Sinus:

It is formed by both sides of cavernous and inter cavernous sinuses.

Applied Anatomy of Cavernous Sinus:

1. Nerves related to cavernous sinus are affected during thrombosis.

Features are:

i. Pain around orbit and forehead

ii. Eyelid swelling

iii. Chemosis

iv. Proptosis

v. Pupillary dilatation

vi. Ophthalmoplegia

vii. Papilledema.

2. Fracture of middle cranial fossa involves cavernous sinus and internal carotid artery → Arterio venous anastomosis → Pulsating exophathalmia.

3. Cavernous sinus thrombosis – due to infection from orbit, face, para nasal air sinuses, middle ear infections.

Septae dividing the sinus into many compartments retards blood circulation within the sinus.

Roof of the sinus is crossed by:

1. Oculomotor nerve (III)

2. Trochlear nerve (IV).

Roof is pierced by:

1. Internal carotid artery

2. Oculomotor nerve

3. Trochlear nerve.

Structures passing within the sinus:

I. Internal carotid artery and

II. Abducent nerve (VIth C.N.).

2. Superior Sagittal Sinus:

It is found along the mid-line.

Situated within the upper border of the falx cerebri.

Shape:

Triangular in cross-section, narrow anteriorly but broader posteriorly.

Direction of Blood Flow:

Backwards towards internal occipital protuberance.

Termination:

At internal occipital protuberance, it joins the confluence of sinuses and becomes the right transverse sinus.

Arachnoid Villi and Granulations:

These are tortuous processes formed from the arachnoid mater. It invaginates into the superior sagittal sinus. The arachnoid villi are covered by specialized mesothelial cells called meningocytes. They filter the cerebro spinal fluid into the superior sagittal sinus. Collection of arachnoid villi constitutes arachnoid granulations – found only in adults.

Tributaries:

1. A pair of parietal emissary veins from the scalp.

2. Superior cerebral veins.

3. Meningeal veins.

4. Emissary vein from nose passing through foramen caecum.

3. Inferior Sagittal Sinus:

Situated within lower border of falx cerebri.

It terminates by forming the straight sinus by joining the great cerebral vein, at the junction between falx cerebri and tentorium cerebelli.

Tributaries:

1. Great cerebral vein,

2. Meningeal veins, and

3. Cerebral veins.

4. Straight Sinus:

Situated along the junction of falx cerebri and tentorium cerebrelli.

It is formed by the union of inferior sagittal sinus and great cerebral vein.

Terminates at the confluence of sinuses by becoming the left transverse sinus.

Tributaries:

1. Inferior sagittal sinus

2. Great cerebral vein

3. Cerebellar veins.

5. Occipital Sinus:

Situated along the attached margin of the falx cerebelli within the posterior cranial fossa.

Formation:

Right and left marginal sinuses along the posterior border of the foramen magnum unite to form the occipital sinus.

Termination:

Confluence of sinuses.

6. Transverse Sinus:

Right transverse sinus is the continuation of the superior sagittal sinus and left transverse sinus is formed from the straight sinus.

Course:

Passes within the transverse sulcus along the posterior attached border of the tentorium cerebelli.

Terminates:

By becoming sigmoid sinus together forms the lateral sinus.

Tributaries:

a. Superior petrosal sinus

b. Inferior cerebral veins

c. Inferior cerebellar veins

d. Inferior anastomotic vein.

7. Sigmoid Sinus:

It is the continuation of the transverse sinus at mastoid angle.

It runs within the sigmoid groove of temporal and occipital bones and enters the posterior compartment of the jugular foramen.

Terminates:

By becoming the internal jugular vein.

Tributaries:

a. Labyrinthine veins

b. Cerebellar veins

c. Condylar emissary vein

d. Mastoid emissary vein.

Applied Anatomy:

1. Infections from middle ear and mastoid antrum may spread into sigmoid sinus and causes thrombosis.

2. Extra cranial infections from scalp, nose or occipital venous plexus may go to intra cranial sinuses and infects them causing serious problems like thrombosis, meningitis, encephalitis etc.

The Emissary Veins:

These are small veins connecting extra cranial veins with intra cranial dural venous sinuses. They do not have valves.

For example:

1. Emissary vein of foramen caecum – communi­cates the veins of nose with superior sagittal sinus. This vein carries extra cranial nasal infections intra cranially.

2. Mastoid emissary veins – communicates scalp veins with superior sagittal sinus.

3. Mastoid emissary vein – communicates posterior auricular vein and sigmoid sinus.

4. Emissary veins passing through foramen ovale, foramen vesalius and foramen lacerum are communicating the cavernous sinus with the pterygoid venous plexus.

5. Ophthalmic vein connects the facial vein and cavernous sinus.

6. Sigmoid sinus is connected with internal jugular vein by an emissary vein passing through hypoglossal canal.

7. Suboccipital plexus of veins and sigmoid sinus are connected by an emissary vein passing through posterior condylar canal.

Importance:

Emissary veins convey extra cranial infections intra cranially, e.g., infection from dangerous area of face enters the cavernous sinus through emissary communications. This leads to meningitis or encephalitis.