Cavernous Sinus – Simplified

Synonyms: Sinus cavernosus, Lateral sellar compartment

Definition and Extent

• Paired dural venous sinuses
• Located in the middle cranial fossa on the side of the body of sphenoid bone

Size: 2 cm long and 1 cm wide

Walls:

• Floor and Medial wall: Endosteal (Periosteal) layer of dura
• Roof and Lateral wall: Meningeal (Fibrous) layer of dura

Extent:

• Anteriorly: Upto the medial end of Superior Orbital Fissure (SOF)
• Posteriorly: Upto the apex of petrous temporal bone

Contents of Cavernous sinus

These are closely related to the floor of sinus and are separated from the interior of sinus by endothelium.

1. Internal carotid artery (ICA) surrounded by sympathetic plexus (ICA comes out of the sinus by piercing the roof)
2. Abducent nerve (CN VI) – infero-lateral to ICA

4 nerves in the lateral wall:

1. Occulomotor nerve (CN III)
2. Trochlear nerve (CN IV)
3. Ophthalmic division of Trigeminal nerve (CN V1)
4. Maxillary division of Trigeminal nerve (CN V2)

Note: Mandibular branch of trigeminal nerve (CN V3) anatomically lies posterolateral to the cavernous sinus inferior to the trigeminal or gasserian ganglion.

Relation to surrounding structures:

1. Medial: Pituitary fossa, Sphenoid sinus
2. Lateral: Temporal lobe

Mnemonic for structures inside and beside cavernous sinus: O TOM CAT (Occulomotor nerve, Trochlear nerve, Ophthalmic branch of Trigeminal nerve, Maxiallary branch of Trigeminal nerve, Carotid artery, Abducens nerve)

              O                   O (III)
              T A C           C A T (IV)
              O                   O (V1)
              M                   M (V2)

Tributaries (Incoming channels)

1. From orbit:

• Superior ophthalmic vein
• Inferior ophthalmic vein
• Central vein of retina

2. From brain:

• Superficial middle cerebral vein
• Inferior cerebral veins

3. From meninges:

• Spheno-parietal sinus
• Middle meningeal sinus (vein)

Communications (Draining channels)

1. Transverse sinus: via superior petrosal sinus
2. Internal jugular vein (IJV): via inferior petrosal sinus
3. Pterygoid venous plexus: via emissary veins (passing through foramen ovale, spinosum and lacerum)
4. Facial vein: via superior ophthalmic vein
5. Opposite cavernous sinus: via anterior and posterior inter-cavernous sinus

Note: In all communications, blood can flow in either directions.

Factors responsible for drainage of blood from cavernous sinus:

1. Expansile pulsation of Internal carotid artery (ICA) within the sinuses
2. Gravity
3. Position of head

Special features of Cavernous sinus

1. Lies between the 2 layers of dura mater
2. No muscle tissue in the wall
3. No valve, hence blood can flow in both directions
4. Cavernous/plexiform pattern interiorly
5. Internally lined by endothelium, which is continuous with the veins

Applied anatomy of Cavernous sinus

1. Cavernous Sinus Thrombosis (CST): Cavernous sinus can get infected from different septic foci as illustrated below:

2. Danger area/triangle/zone of face: The three points of triangle are the 2 corners of mouth and the bridge of nose. Infections from the face can spread in retrograde direction and cause thrombosis of the cavernous sinus via facial vein and pterygoid plexus.

3. Cavernous sinus syndrome: It is caused by various parasellar pathological condition that involves cavernous sinuses along with cranial nerves (3,4,5,6), Internal carotid artery and sympathetic plexus due to its close anatomical association and gives rise to various signs and symptoms in different combinations in different diseases.

• Ophthalmoplegia
• Chemosis (Conjunctival edema)
• Proptosis
• Ptosis
• Diplopia
• Pain (Orbital or retro-orbital)
• Ocular hypertension
• Ocular bruits
• Optic disc edema and retinal hemorrhage
• Pupillary abnormalities (non-reactive, mid dilated)
• Arterialization of conjunctival vein
• Anesthesia of CN V1

4. Tolosa-Hunt syndrome: It is a painful ophthalmoplegia caused by nonspecific inflammation (noncaseating granulomatous or non-granulomatous) of the cavernous sinus or superior orbital fissure.

5. Carotid-cavernous fistula: It is an abnormal communication (direct or indirect) between cavernous sinuses and carotid artery or its branches.