Anatomy of the Facial Nerve in the Temporal Bone with Audio скачать в хорошем качестве

Anatomy of the Facial Nerve in the Temporal Bone with Audio

This is an anatomic specimen which represents tissue volume encompassing the posterior two-thirds of one-half of a skull base. The soft tissue will slowly disappear and we are seeing the auricle and the auricle cartilage. This clearly shows the lateral plate of the tragus and medial cartilaginous pointer of the tragus and its relationship to the skull base. When examining the skull base the stylomastoid foramen can be seen very clearly at the anterior edge of the digastric groove and just anterior to it. This relationship is very important when we enter the mastoid. The stylomastoid foramen is also just posterior to the styloid process. Note that the facial nerve descends in an inferior direction, in this case by 13 mm, before turning anteriorly 6 mm to the pes anserinus. Either the cartilaginous pointer or the tympanomastoid suture seen in this view can be used as a safe guide to identify the main trunk of the facial nerve exiting the stylomastoid foramen. In cases with more difficult anatomy because of distortion from tumor or bleeding, the styloid process can be palpated and the digastric muscle can be dissected inferior. The 1 cm space between them always contains the facial nerve and at the same plane of those structures. As the temporal bone becomes transparent, the mastoid air cells become visible. Finally, all of the bone is removed giving an excellent view of the mastoid tip area divided from the medial mastoid area by the prominent digastric ridge. This digastric ridge is a key landmark for identifying the exit of the facial nerve from the temporal bone. We will now turn the specimen into the surgical position showing the facial recess and the relationship of the tympanic segment of the facial nerve to the membranous labyrinth (shown in magenta),and the relatively constant relationship of the chorda tympani nerve to the tympanic membrane. The average maximum distance between the chorda tympani nerve and the facial nerve at the facial recess is 2.5 mm. A 2 mm bur is usually used to surgically finish the facial recess work. The view now changes so that we are sighting along the actual plane of the tympanic ring. This shows that the vertical segment of the facial nerve ascends and passes through the plane defined by the tympanic ring at approximately the 6 o’clock position. This is a nice guide for take-down of the facial ridge in mastoidectomy. Using the chorda tympani nerve as a guide, is a conservative and safe way to take-down the facial ridge without risk of facial nerve injury and keeps the surgeon at least 1.5 – 2 mm away from the main trunk of the facial nerve. The final result is a more cleanable mastoid cavity without an inaccessible mastoid tip recess. By turning the specimen to the surgical position, we can see how open recesses in the posterior tympanum are readily accessible by removing bone. The chorda tympani nerve passes lateral to the long process of the incus and medial to the neck of the malleus. We now see the dura envelope of the internal auditory canal with its four compartments for the facial nerve superiorly and anteriorly, the cochlear nerve inferiorly and anteriorly, and the superior and inferior vestibular nerve posteriorly. When we take away the dural envelope, we can easily see the AICA giving a branch of the labyrinthine artery and the facial nerve going to the brain stem, which carries sensory fibers from the facial nerve. The cochlear divisions of the eighth nerve as well as the superior and inferior divisions are now seen. To download, study and manipulate this anatomy in any view search for "3-D Virtual Model of the "Visible Ear". The "Visible Ear" is a library of digital images of a human temporal bone and surrounding structures developed by Mads Sorensen, M.D. and colleagues at the Department of Otolaryngology-Head and Neck Surgery, Rigshospitalet, Copenhagen, Denmark (Sorenson et al, ORL, 2002; 64:378-381). The temporal bone and surrounding structures were serially sectioned at 25 micron thickness. Anatomical structures of interest were segmented by Dr. Sorensen and colleagues. The surface model can also be sliced open in the X, Y or Z planes and the appropriate raw histological image can be superimposed on the cleavage plane. Contributors to this model include Haobing Wang, M.A. and Saumil N. Merchant, M.D. from Massachusetts Eye and Ear Infirmary, Michael Teixido, M.D and Brian Kung, M.D from Delaware Biotechnology Institute, as well as Mads Sorenson, M.D. and his group from Copenhagen, Denmark. Model development at the Eaton-Peabody Lab at the Massachussets Eye and Ear Infirmary was supported by a core grant from the NIDCD (P30 DC05209). Movie production in Delaware was supported by NIH Grant Number 2 P20 RR016472-04 under the INBRE Program of the National Center for Research Resources.