The cavernous sinus is located on either side of the pituitary fossa and body of the sphenoid bone. It is most easily thought of as existing between the endosteal and meningeal layers of the dura although some additional complexity is present ⁵. It spans from the apex of the orbit to the apex of the petrous temporal bone. Unlike other dural venous sinuses, it is divided by numerous fibrous septa into a series of small caves, which is where its name is derived from. The normal lateral wall should be either straight or concave.

Boundaries

roof: fold of dura mater attached to the anterior and middle clinoid processes
anterior wall: medial end of the superior orbital fissure
posterior wall: petrous apex
medial wall: endosteum overlying the body of the sphenoid bone
lateral wall: dura mater from the ridge of the roof to the floor of the middle cranial fossa
floor: endosteum overlying the base of the greater wing of the sphenoid bone

Relations

superiorly: middle cerebral artery, optic chiasm
anteriorly: apex of the orbit
posteriorly: cerebral peduncle
medially: pituitary fossa, pituitary gland
laterally: temporal lobe (medial surface), Meckel's cave (posteroinferiorly)
inferiorly: sphenoid sinus

Dural anatomy

The lateral wall of the cavernous sinus is primarily formed by the continuation of the meningeal layer of the dura, flowing medially up from the floor of the middle cranial fossa, over the cavernous sinus, to the clinoid processes before forming the diaphragma sella. From here, the meningeal layer passes downwards to surround the pituitary gland, thus forming the medial wall of the cavernous sinus. In contrast, the floor of the cavernous sinus is formed by the endosteal layer of the meninges (actually just periosteum) that covers the sphenoid bone and passes medially across the midline below the pituitary gland, separated from the aforementioned meningeal layer by the intercavernous sinus ⁵.

The nerves in the lateral wall of the cavernous sinus are surrounded by thin connective tissue and thus, the lateral wall of the cavernous sinus has two layers; a thick meningeal layer and a much thinner translucent layer surrounding the cranial nerves ^5,6. This thin layer is variably described as being meningeal in origin ⁶, or continuous with the endosteal layer ⁵.

Vascular connections

It receives venous blood from:

inferior and superior ophthalmic veins
intercavernous sinus
sphenoparietal sinus
superficial middle cerebral vein
occasionally
- central retinal vein
- a frontal tributary of the middle meningeal vein

Drainage of the cavernous sinus is via:

superior petrosal sinus to the transverse sinus
inferior petrosal sinus directly to the jugular bulb
venous plexus on the internal carotid artery (ICA) to the clival (basilar) venous plexuses
emissary veins passing through the
- foramen Vesalii
- foramen ovale: communicates between the cavernous sinus and pterygoid venous plexus
- foramen lacerum

Depending on relative pressures the superior ophthalmic veins either drain to or from the cavernous sinus.

Additionally, the cavernous sinuses connect to each other via the intercavernous sinuses.

These can be remembered with the mnemonic O TOM CAT.

Nerves

The cavernous sinus transmits multiple cranial nerves to the superior orbital fissure and foramen rotundum. These are:

in the lateral wall from superior to inferior
- oculomotor nerve (CN III)
- trochlear nerve (CN IV)
- trigeminal nerve (CN V)
  - ophthalmic division
  - maxillary division: within the very inferolateral aspect of the cavernous sinus wall or even outside the sinus rather than truly within it ⁴
traversing the sinus
- abducens nerve (CN VI): inferolateral to the internal carotid artery

Artery

The internal carotid artery enters the posterior inferior aspect of the sinus and bends upon itself as the carotid siphon (cavernous segment - C4). Two branches arise from this segment: meningohypophyseal trunk and inferolateral trunk.

The artery is surrounded by a plexus of sympathetic nerves from the superior cervical ganglion.