Evaluation of facial nerve course, posterior tympanotomy width and visibility of round window in patients with cochlear implantation by performing oblique sagittal cut computed tomographic scan temporal bone
The Egyptian Journal of Otolaryngology volume 30, pages 317–321 (2014)
Posterior tympanotomy is a well-known otologic procedure that allows surgeons access to the middle ear cavity. During posterior tympanotomy the surgeon can approach the round window niche and promontory, where a cochleostomy is carried out for cochlear implant electrode array insertion. The mastoid segment of the facial nerve and the chorda tympani nerve could be injured in cases of narrow facial recess or inadequate posterior tympanotomy. With the image reconstruction in an oblique sagittal plane and curve reconstructions, the whole tympanic and mastoid segments of the facial nerve can be visualized in just one image. It is necessary to preoperatively estimate both the facial nerve status and the anatomical relationships between the facial recess and the round window, this may reduce the risk of facial nerve injury and influence the decision on which side to implant, which approach to use and whether to enter the cochlea via cochleostomy or round window membrane route.
The aim of our study is to evaluate the facial nerve (course and anomalies), visibility of the round window membrane and the width of posterior tympanotomy before cochlear implantation by using oblique sagittal cuts CT scan temporal bone.
A prospective study; done on 18 consecutive patients with severe to profound sensorineural hearing loss who are candidates for cochlear implantation in Ain Shams University Hospitals during years 2011 & 2012. We focused on oblique sagittal cut CT scan & its role to evaluate the course of facial nerve, posterior tympanotomy width and visibility of the round window.
We tried to make a statistical correlation between CT scan and intraoperative findings. Statistically significant positive correlation between posterior tympanotomy width and 2nd genu angle, distance from facial bony canal to round window and distance from facial nerve to round window. The mean distance from facial bony canal to round window was longer in operatively viewed round window than non-viewed window (4.7 and 4.4 mm respectively) (P < 0.05). The mean distance from facial nerve to round window was longer in operatively viewed round window membrane than non-viewed window (5.9 and 5.5 mm respectively) (P < 0.05). The mean width of posterior tympanotomy was wider in operatively viewed round window niche than non-viewed window niche (3.1 and 3.0 mm respectively) (P < 0.01).
Oblique sagittal cuts CT scan temporal bone is very helpful preoperative radiological tool for evaluation of the facial nerve course and anatomical factors that may determine the field of view or the accessibility of the posterior tympanotomy for either cochleostomy or round window membrane approach. Other approaches can be used with more safety when the position of the facial nerve prevents an adequate posterior tympanotomy.
Kim CW, Oh SJ, Kim HS, Ha SH, Rho YS. Analysis of axial temporal bone computed tomography scans for performing a safe posterior tympanotomy. Eur Arch Otorhinolaryngol 2008; 265: 887–891.
Hamamoto M, Murakami G, Kataura A. Topographical relationships among the facial nerve, chorda tympani nerve and round window with special reference to the approach route for cochlear implant surgery. Clin Anat 2000; 13: 251–256.
Jeon EJ, Jun B, Song JN, Kim JE, Lee DH, Chang KH. Surgical and radiologic anatomy of a cochleostomy produced via posterior tympanotomy for cochlear implantation based on three-dimensional reconstructed temporal bone CT images. Surg Radiol Anat 2013; 35: 471–475.
Calli C, Pinar E, Oncel S, Tatar B, Tuncbilek MA. Measurements of the facial recess anatomy: implications for sparing the facial nerve and chorda tympani during posterior tympanotomy. Ear Nose Throat J 2010; 89: 490–494.
Kronenberg J, Fuchs C, Bendet E. Preoperative radiologic assessment of facial nerve in cochlear implant surgery. Eur Arch Otorhinolaryngol 1994; Suppl:353-355.
Leong AC, Jiang D, Agger A, Fitzgerald-O’Connor A. Evaluation of round window accessibility to cochlear implant insertion. Eur Arch Otorhinolaryngol 2013; 270: 1237–1242.
Chuang MT, Chiang IC, Liu GC, Lin WC. Multi-detector row CT demonstration of inner and middle ear structures. Clin Anat 2006; 19: 337–344.
Conflicts of interest
There are no conflicts of interest.
About this article
Cite this article
Hasaballah, M.S., Hamdy, T.A. Evaluation of facial nerve course, posterior tympanotomy width and visibility of round window in patients with cochlear implantation by performing oblique sagittal cut computed tomographic scan temporal bone. Egypt J Otolaryngol 30, 317–321 (2014). https://doi.org/10.4103/1012-5574.144963