The cavernous sinus is a paired dural venous sinus located within the cranial cavity. It is divided by septa into small ‘caves’ – from which it gets its name. Each cavernous sinus has a close anatomical relationship with several key structures in the head, and is arguably the most clinically important venous sinus. In this article, we shall look at the anatomy of the cavernous sinus – its location, contents and clinical relevance.
The dural venous sinuses are channels between the two layers of dura mater which are responsible for the venous drainage of the brain, skull, orbit and internal ear. The cavernous sinuses are located within the middle cranial fossa, on either side of the sella turcica of the sphenoid bone (which contains the pituitary gland). They are enclosed by the endosteal and meningeal layers of the dura mater.
The borders of the cavernous sinus are as follows:
Several important structures pass through the cavernous sinus to enter the orbit. They can be sub-classified by whether they travel through the sinus itself, or through its lateral wall:
The cavernous sinus is the only site in the body where an artery (internal carotid) passes completely through a venous structure. This is thought to allow for heat exchange between the warm arterial blood and cooler venous circulation. A useful mnemonic to remember the contents and their relation to one another is ‘O TOM CAT’, where OTOM (oculomotor nerve, trochlear nerve, ophthalmic branch, maxillary branch) refers to the lateral wall contents from superior to inferior, and CAT (internal carotid artery, abducens nerve, trochlear nerve) refers to the horizontal contents, from medial to lateral.
Each cavernous sinus receives venous drainage from:
It is important to note that the superior ophthalmic vein forms an anastomosis with the facial vein. Therefore, the ophthalmic veins represent a potential route by which infection can spread from an extracranial to an intracranial site. The cavernous sinuses empty into the superior and inferior petrosal sinuses, and ultimately, into the internal jugular vein. The left and right cavernous sinuses are connected in the midline by the anterior and posterior intercavernous sinuses. They travel through the sella turcica of the sphenoid bone.
The close anatomical relationship of the cavernous sinus with several key structures in the head makes it a clinically important venous sinus. This is highlighted by its role in the venous drainage of the brain, skull, orbit and internal ear, and by being the only site in the body where an artery passes completely through a venous structure. Furthermore, the superior ophthalmic vein forms an anastomosis with the facial vein, creating a potential route for the spread of infection from an extracranial to an intracranial site.
The contents and borders of the cavernous sinus, and the structures it relates to, are important factors to consider when diagnosing and managing any conditions affecting it. A useful way to remember these details is with the mnemonic ‘O TOM CAT’.
The cavernous sinus is an important anatomical structure located in the head and neck that is formed by the connection of several veins, arteries, and nerves. It can be sub-classified based on which structures travel through the sinus itself or its lateral wall.
Structures which travel through the sinus include the abducens nerve ( CN VI), carotid plexus (post-ganglionic sympathetic nerve fibres), and the internal carotid artery (cavernous portion). Structures that travel through the lateral wall of the cavernous sinus include the oculomotor nerve (CN III), trochlear nerve (CN IV), ophthalmic (V1) and maxillary (V2) branches of the trigeminal nerve.
The cavernous sinus is unique as it is the only area in the body where an artery passes completely through a venous structure. This allows for the exchange of heat between warmer arterial blood and cooler venous circulation.
Each cavernous sinus is also part of the dural venous sinus system, which includes several veins that drain into it. These include the ophthalmic veins (superior and inferior) that enter the cavernous sinus via the superior orbital fissure, the central vein of the retina which drains into the superior ophthalmic vein or directly into the cavernous sinus, the sphenoparietal sinus which empties into the anterior aspect of the cavernous sinus, the superficial middle cerebral vein which contributes to the venous drainage of the cerebrum, and the pterygoid plexus, located within the infratemporal fossa.
The cavernous sinuses ultimately empty into the superior and inferior petrosal sinuses and the internal jugular vein. They are connected in the midline by the anterior and posterior intercavernous sinuses, which travel through the sella turcica of the sphenoid bone.
Cavernous sinus thrombosis (CST) is the formation of a clot within the cavernous sinus. The most common cause of CST is an infection, which typically spreads from an extracranial location such as the orbit, paranasal sinuses, or the danger zone of the face. This is due to the anastomosis between the facial vein and the superior ophthalmic veins.
The common clinical features associated with CST include headache, unilateral periorbital oedema, proptosis (eye bulging), photophobia, and cranial nerve palsies. The abducens nerve (CN VI) is most often affected. Treatment is typically with antibiotic therapy, as the progression of a Cavernous Sinus Thrombosis caused by infection can rapidly lead to meningitis.
