(At any time you can rotate the image or add or subtract structures. Clicking the link will always bring you back to a starting point. Remember to use rollovers to see the labels for the various structures. Also, by moving the axial plane to any point in the image on the right, you can see the cross-section on the lower left. Any coloration in the right image will be shown in the cross-sections.)
Besides lesions within the brain, cranial nerves can be injured along their path within the cranial vault or in the bony tunnels of the skull. Nerves can be grouped according to the foramen by which they exit the skull or by a shared relationship with the meninges. Accordingly, disease related to these structures can affect groups of nerves. We will begin inferiorly and work our way up. Because of the difficulty to illustrate it, we will omit the hypoglossal nerve (XII).
Let's begin with a posteriomedial view of the skull's interior. For clarity the sphenoid bone and sphenoid sinus are highlighted; the occipital bone is absent. To make more sense of the image, let's add and highlight some landmarks
To highlight the petrous part of the temporal bone:
Nerves of the Posterior Cranial Fossa
Let's add the three cranial nerves that exit via the sigmoid sinus: the Glossopharyngeal (IX), Vagus (X) and Spinal Accessory (XI). Note they are superimposed near the junction of the sigmoid sinus and internal jugular vein, but distally they diverge, as they head towards their targets.
Now add the Facial (VII) and Vestibulocochlear (VIII). Both exit the internal auditory meatus.
The last nerve is the Abducens (VI). It is sandwiched between the dura and the sphenoid bone as it runs superiorly, medial to the inferior petrosal sinus. Note how the abducens nerve makes a sharp bend. Rotate the image to 145 degrees to see how this bend hugs the sphenoid bone, as the nerve leaves the wall of the posterior fossa and courses along the floor of the middle cranial fossa. It is now within the cavernous sinus and headed towards the superior oblique fissure.
To confirm the course of the Abducens, trace the nerve in the axial window (ctrl or apple plus the up or down arrow). Any increase in intracranial pressure that stretches the tentorium will pinch the nerve where it bends over this edge of the sphenoid bone. Therefore, diplopia upon lateral gaze is a non-specific sign that may result from a variety of diseases.
A posterior fossa meningioma could affect all of these nerves (and also the trigeminal nerve (CN V), which we will consider in the next section).
Nerves of the Cavernous Sinus
In this Posterior View, we keep the cavernous sinus on the left, but remove all the venous sinuses and temporal bone on the right. As a reference we add the internal carotid artery. We have already discussed the portion of CN VI that runs in the cavernous sinus.
Now add in the Trigeminal nerve (V). Rollover the nerve to identify different parts of it. Add back the cavernous sinus to see the relationship of the nerve to the sinus. Manipulate both widows to fully appreciate the course of the nerve. While CN V travels through the space cerebellopontine angle (just proximal to the trigeminal ganglion and inferior to the tentorium), it can be compressed by tumors such as an acoustic neuroma or a posterior fossa meningioma.
Now add the Trochlear nerve (IV).
Now add the Oculomotor nerve (III). Besides susceptibility to disease of the cavernous sinus, it can be compressed by an aneurysm of the posterior communicating artery.
Last add the Optic nerve (II). This nerve tract exits its own foramen just superior to the cavernous sinus.
Add back the Cavernous Sinus. The nerves are within the wall of the sinus -- not outside it, as the color coding might imply.
©2011 Lawrence Rizzolo, Yale School of Medicine