The Cavernous Sinus

Question.

A 60yr old man with widespread malignancy and sinusitis presents with severe headache, fever and proptosis. He is diagnosed with the cavernous sinus syndrome. All of the following structures are at risk of compression in this man EXCEPT which one?

a. the oculomotor nerve (CN III)
b. sympathetic fibres to the face, head and neck
c. the internal carotid artery
d. mandibular division of the trigeminal nerve (CN V3)
e. trochlear nerve

 
 

Answer.

d.

 
Explanation.

The cavernous sinuses are paired venous channels in the sphenoid bone either side of the pituitary fossa and just below the optic nerve. As well as playing a role in the drainage of venous blood from the orbits and cranium, the cavernous sinus transmits several important structures (see figure below).

First, in the lateral wall of the sinus, from superior to inferior, are found the
•     Oculomotor nerve (CN III)
•     Trochlear nerve (CN IV)
•     Ophthalmic division of the trigeminal nerve (CN V1)
•     Maxillary division of the trigeminal nerve (CN V2)

Then, through the superior sinus, horizontally from medial to lateral passes the:
•     Cavernous segment (C4) of the internal carotid artery
•     Abducens nerve (CN VI)
•     Trochlear nerve (CN IV)

This way of dividing the important structures of the cavernous sinus lead to the pneumonic O TOM CAT!

Sympathetic nerves from the superior cervical ganglion (C1 – C3) surround the cavernous segment of the internal carotid artery. The superior cervical ganglion is the most rostral extension of the sympathetic chain of ganglia and supply post-ganglionic sympathetic innervation to the face, head and neck.

Thus cavernous sinus syndrome – caused by either thrombosis or infection (often both) of the cavernous sinus – may result in compression of any or all of the listed structures. Signs of the cavernous sinus syndrome therefore include varied ophthalmoplegias, Horner’s syndrome, sensory loss over the upper face as well as chemosis and proptosis of the eye resulting from failure of venous drainage from the orbit.

Figure 2. The cavernous sinus including related structures

The cavernous sinus including related structures