(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.)
The facial nerve (CN VII) follows a tortuous path through the temporal bone and parotid gland to reach its territories on the face. This exercise explores relationships important to the management of parotid cancer.
Let's begin with the skull. To simplify the image so that we may see more, we've highlighted the bones that we will keep in the next image. At any time, feel free to add back skin (slider lower left) or rotate the image (wheel between the sliders). Remember to use rollovers to identify things.
Let's look at this partial skull with the facial nerve added. From this posteriomedial view, see the nerve enter the internal acoustic meatus and exit via the stylomastoid foramen (use rollovers to identify the styloid process and temporal bone. The axial view shows the nerve entering the internal acoustic meatus. Use <ctrl-up arrow> (<apple-up arrow> on a mac) to trace the nerve to the geniculate ganglion (the bright yellow dot). Proximal to the ganglion, the facial nerve is seen in the internal acoustic meatus along side CN VIII. Observe CN VIII terminate in the spiral ganglion, which lies in the central axis of the cochlea (visible but unlabeled). Distal to the geniculate ganglion, the facial nerve is seen traveling posteriolaterally. Unseen is an important branch, the greater petrosal nerve, which travels in a direction opposite that of the main nerve. Trace the distal portion of the nerve as it bends sharply inferiorly by using the <Ctrl-down arrow> or <apple-down arrow> keys. As you pass the middle ear, the chorda tympani and nerve to stapedius branches are given off. Observe the proximal portion of the external auditory meatus and the distal portion of the auditory tube. The middle ear lies at the angle formed by these teal-colored tunnels. If you look closely, you can observe the ear drum separating the external meatus and middle ear. Continue inferiorly to the stylomastoid foramen and observe the nerve posteriolateral to the styloid process.
Now, let's follow the external course of the facial nerve. Note that a distal portion of the nerve is also seen posterior to the ramus of the mandible. Use ctrl-p (apple-p on a mac) to add the plane back on the main image. Rotate the image in increments to 100 degrees to convince yourself that the plane includes the main trunk of the nerve and the zygomatic branch of CN VII. Posterior to the ramus of the mandible, the zygomatic branch is in the company of tributaries to the retromandibular vein. The retromandibular vein is an important landmark for radiologists and surgeons alike. Note that posterior to the vein, the facial nerve branches into superior and inferior divisions. Observe how the cervical and mandibular branches of the inferior division, and buccal branch of the superior division, course lateral to the vein. Rotate the main image incrementally to appreciate the three dimensional distribution of the CN VII relative to the styloid process, mandible and retromandibular vein.
A second important relationship for the surgeon is the posterior belly of the digastric muscle.
The parotid gland has a close relationship with the mandible, facial nerve and retromandibular vein. Click here to remove the gland and go back and forth between this and the previous link. Observe the facial nerve exit the stylomastoid foramen, posterior to the styloid process, and enter the posterior surface of the parotid gland.
Similarly, toggle back and forth between this link and its sister link. Again, observe the facial nerve exit the stylomastoid foramen, posterior to the styloid process and enter the posterior surface of the parotid gland. Note the cervical (inferior-most) and mandibular branches emerging from the inferior surface of the gland
Repeat the procedure: link vs sister link. Now all five principal branches can be seen emerging from the gland. From superior to inferior they are the zygomatic, maxillary, buccal, mandibular and cervical branches. With the gland removed, trace these back to the superior and inferior divisions of the nerve, and finally back to the trunk.
Let's add in a few nearby relations.s
©2011 Lawrence Rizzolo, Yale School of Medicine