Q5 LONG ANSWER 10M ★ High-yield

Describe the cavernous sinus with its contents and connections. Add a note on cavernous sinus thrombosis and the dangerous area of the face.

Anatomy · 1st Professional — Pre-Clinical

Dural Venous Sinuses — General

The dural venous sinuses are endothelium-lined channels between the two layers of dura mater, draining blood from the brain, meninges and skull to the internal jugular vein.

They have NO valves and NO muscular wall, so blood can flow in either direction — the anatomical basis of the spread of infection
Paired — cavernous, superior and inferior petrosal, transverse, sigmoid, sphenoparietal
Unpaired — superior and inferior sagittal, straight, occipital

The Cavernous Sinus

A paired sinus on either side of the body of the sphenoid, extending from the superior orbital fissure in front to the apex of the petrous temporal bone behind
About 2 cm long and 1 cm wide; trabeculated internally, giving the "cavernous" appearance

Contents — the Classical Answer

In the lateral wall (from above down)	Passing through the sinus
Oculomotor nerve (III)	Internal carotid artery with its sympathetic plexus
Trochlear nerve (IV)	Abducent nerve (VI)
Ophthalmic division of trigeminal (V1)	—
Maxillary division of trigeminal (V2)	—

Tributaries and Connections

Receives from	Drains into
Superior and inferior ophthalmic veins	Superior petrosal sinus → transverse sinus
Superficial middle cerebral vein	Inferior petrosal sinus → internal jugular vein
Sphenoparietal sinus	Emissary veins → pterygoid venous plexus
Central vein of the retina	Intercavernous sinuses to the opposite side
Inferior cerebral veins	—

Cavernous Sinus Thrombosis

Feature	Cause
Proptosis and chemosis	Obstruction of the ophthalmic veins
Ophthalmoplegia	Involvement of III, IV and VI; VI first
Ptosis and a fixed dilated pupil	Third nerve palsy and loss of sympathetic fibres
Pain and numbness of the forehead and cheek	V1 and V2 involvement
Papilloedema and retinal haemorrhage	Obstruction of the central retinal vein
Fever, headache, rapid deterioration	Sepsis

It is frequently bilateral, because the two sinuses communicate through the intercavernous sinuses — a feature almost unique to this condition
Sources — infection of the face (the danger area), paranasal sinuses (especially sphenoid and ethmoid), orbit, teeth and middle ear

The Other Dural Venous Sinuses

Sinus	Position	Drains into
Superior sagittal	Upper border of the falx cerebri; contains arachnoid granulations	Confluence of sinuses, usually then the right transverse
Inferior sagittal	Lower free margin of the falx	Straight sinus
Straight	Junction of falx and tentorium	Confluence; usually then the left transverse
Transverse	Attached margin of the tentorium	Sigmoid sinus
Sigmoid	S-shaped, in the posterior cranial fossa	Internal jugular vein at the jugular foramen
Superior petrosal	Upper border of the petrous temporal	Transverse sinus
Inferior petrosal	Lower border of the petrous temporal	Internal jugular vein

Arachnoid granulations in the superior sagittal sinus absorb the CSF; their blockage after subarachnoid haemorrhage or meningitis causes communicating hydrocephalus

Applied Aspects

Never squeeze a boil on the upper lip or nose — the danger area of the face; the valveless connection to the cavernous sinus makes it a potentially fatal act
Caroticocavernous fistula — rupture of the internal carotid within the sinus, usually after head injury; gives pulsatile proptosis with a bruit that the patient can hear
Pituitary tumours extending laterally involve the cavernous sinus and its nerves; extending upward they compress the optic chiasma, giving bitemporal hemianopia
Emissary veins connect the sinuses with the veins of the scalp and face, and are the route by which scalp infection reaches the cranial cavity
The sinuses cannot collapse, being held open by the dura, so a torn sinus bleeds profusely and may cause air embolism in a sitting patient
Sagittal sinus thrombosis causes raised intracranial pressure, seizures and bilateral cortical infarcts; seen in dehydration, pregnancy and thrombophilia
Lateral (sigmoid) sinus thrombosis classically follows middle ear infection, and gives a picket-fence fever with a tender mastoid
The internal jugular vein is cannulated at the apex of the triangle between the two heads of sternocleidomastoid, and its pulsation is the basis of the jugular venous pressure
Extradural haemorrhage is arterial, from the middle meningeal artery, and is unrelated to the sinuses — but a fracture crossing a sinus can cause profuse venous bleeding that is far harder to control
Papilloedema arises partly because the central retinal vein drains through the cavernous sinus, so raised pressure there is transmitted to the retina
Antibiotics have transformed the prognosis of cavernous sinus thrombosis, once almost invariably fatal; anticoagulation remains debated

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