Abstract
Purpose
To localize the facial nerve course in the mastoid segment and to measure its distances relative to the tympanic membrane.
Methods
This is a cross-sectional descriptive study. During 2019 in a tertiary hospital, 129 non-contrast and non-pathologic temporal CT images were studied in a tertiary hospital. Facial nerve distances were measured from the planes passing through the annulus in the axial cross-sections at superior, umbo, and inferior levels of the tympanic membrane. It was done in two different dimensions which are anteroposterior (toward the plane of the ear canal wall) and mediolateral (toward the plane of the tympanic membrane).
Results
The least mean anteroposterior distance between the facial nerve and the posterior ear canal wall was at the level of umbo (3.66 ± 0.76 mm). The nearest point of the nerve toward the tympanic membrane was the inferior level (− 0.03 ± 0.81 mm). Overall external ear canal lengths were statistically significantly lower in women rather than men. There was a reverse correlation between the age and the ear canal length.
Conclusion
Posterior canalplasty seems to be safe unless dissection does not cross the plane of annulus. In this study, the safe margin was 1.4 mm in posterior canal wall drilling. It also should be performed carefully if it extends to the inferior side of the canal. Measuring the mediolateral dimension of the nerve toward the annulus in the axial CT images seems to be practically beneficial, especially in the inferior where the ear canal wall turns and might not act as a good landmark. Paying attention to this plane may reduce the risks of nerve injury in any procedures with transcanal approaches, particularly in inferior canaloplasty.
Similar content being viewed by others
Data availability
The data have obtained from the electronic radiology database system at Amir Alam Hospital. It shows identical information including, name, gender, and age. Other required information has derived from the CT images. All data are available for further analysis.
Code availability
Statistical Package for Social Sciences (SPSS) software, version 17, was used to analyze the data.
References
Adad B, Rasgon BM, Ackerson L (1999) Relationship of the facial nerve to the tympanic annulus: a direct anatomic examination. Laryngoscope 109:1189–1192. https://doi.org/10.1097/00005537-199908000-00002
Arístegui M, Martín-Oviedo C, Aristegui I, García-Leal R, Ruiz-Juretschke F (2019) Anatomical variations of the intrapetrous portion of the facial nerve. Anat Rec 302:588–598. https://doi.org/10.1002/ar.23923
Bance M, Erb J (2003) A reliable radiologic landmark for the facial nerve in axial temporal bone computed tomography scans. Otol Head Neck Surg 128:251–256. https://doi.org/10.1067/mhn.2003.64
Dai P, Zhang T, Wang K, Song J, Qian W, Wang Z (2004) Positional relationship between the facial nerve and other structures of the temporal bone. J Laryngol Otol 118:106–111. https://doi.org/10.1258/002221504772784540
Demontiero O, Vidal C, Duque G (2012) Aging and bone loss: new insights for the clinician. Ther Adv Musculoskelet Dis 4:61–76. https://doi.org/10.1177/1759720X11430858
Li T, Lai ZC, Wang XD, Feng Y, Li YQ, Fang XD (2013) Measurement and analysis of facial nerve on fully displayed multislice computed tomographic multiplanar reconstruction image. J Craniofac Surg 24:1411–1413. https://doi.org/10.1097/SCS.0b013e3182903673
Low WK (1999) Surgical anatomy of the facial nerve in Chinese mastoids. ORL J Otorhinolaryngol Relat Spec 61:341–344. https://doi.org/10.1159/000027696
Ni Y, Sha Y, Dai P, Li H (2008) Quantitative morphology of facial nerve based on three-dimensional reconstruction of temporal bone. Otolaryngol Head Neck Surg 138:23–29. https://doi.org/10.1016/j.otohns.2007.10.011
Ren B, Bai P, Li T, Guo H, Wang B, Zhang S, Cheng K, Li Y (2015) Anatomic landmarks for localization of the vertical segment of facial nerve on multislice computed tomography multiplanar reconstruction images. J Craniofac Surg 26:2193–2195. https://doi.org/10.1097/SCS.0000000000001448
Singh P, Mittal MK, Mathur NN, Sinha M, Panesar S, Khatri G, Thukral BB (2019) Morphometric analysis of the external auditory canal by computed tomography in Indian population. Indian J Otolaryngol Head Neck Surg 71:1115–1122. https://doi.org/10.1007/s12070-017-1200-8
Zaghal ZA, Raad RA, Nassar J, Hourani-Rizk R, Bassim MK (2014) Anatomic relationship between the facial nerve and the tympanic annulus. Otol Neurotol 35:667–671. https://doi.org/10.1097/MAO.0000000000000319
Acknowledgment
This research was extracted from the thesis for the Doctorate of Medicine degree at the Medical School of Tehran University of Medical Sciences (thesis number: 23852). The ethical committee of Tehran University of Medical Sciences approved the research (number: IR.TUMS.MEDICINE.REC.1397.218). We are honored to send our special thanks to the staff of the Department of Radiology at Amir Alam Hospital.
Author information
Authors and Affiliations
Contributions
MM: data collection, data analysis, manuscript writing. MAK: data collection, data analysis, manuscript editing. SD: project development, data analysis, data interpretation, manuscript editing. AK: data interpretation, manuscript editing.
Corresponding author
Ethics declarations
Conflict of interests
There is no conflict of interest. This research was carried out without any funds and was extracted from the thesis for the Doctorate of Medicine degree at the Medical School of Tehran University of Medical Sciences (thesis number: 23852). Amir Alam Hospital selected as the study environment just for being the referral otorhinolaryngology medical center.
Ethics approval
It is allowed by the ethical committee approval of Tehran University of Medical Sciences with code of IR.TUMS.MEDICINE.REC.1397.218.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Merati, M., Kazemi, M.A., Dabiri, S. et al. Radiologic evaluation of the mastoid segment of the facial nerve tract in the intact temporal bone. Surg Radiol Anat 43, 145–151 (2021). https://doi.org/10.1007/s00276-020-02554-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00276-020-02554-z