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Variations in the morphology of stylomastoid foramen: a possible solution to the conundrum of unexplained cases of Bell’s palsy
, 1
Affiliations- All India Institute of Medical Science, Patna, India
open access
Abstract
Background: Stylomastoid foramen is the terminal part of facial canal and is the exit gateway for facial nerve from skull base. We hypothesized that anatomical variations of this foramen could be a risk factor for the injury of facial nerve resulting in unilateral facial nerve paralysis or Bell’s palsy. Hence the present study was conducted to study the variations in size and shape of stylomastoid foramen in dry adult human skulls.
Materials and methods: The study was conducted on 37 dry adult human skulls of unknown age and sex. High resolution images of the skulls under study were processed by ImageJ software and observations were undertaken.
Results: Total eight variations of stylomastoid foramen were observed in terms of shape. The common variants were round, oval and square (present in 83.79% skulls on right side and 81.07% skulls on left side), whereas the rare variants were triangular, rectangular, serrated, bean-shaped and irregular. It was noted that stylomastoid foramen were associated with extensions (45.95% skulls) and also adjacent foramen (18.92% skulls). Exclusively unilateral observations included bifurcation of foramen (16.22% skulls), foramen situated deep inside skull groove (5.41% skulls) and foramen interrupted by bony spur (2.7% skulls). No significant differences were observed between the mean diameters (antero-posterior and transverse) of the stylomastoid foramen.
Conclusions: The unilateral variations along with rare variations in terms of shape such as serrated, bean-shaped and irregular foramen (which were also unilateral findings) could be potential risk factors towards injury of facial nerve at the point of exit from skull base leading to Bell’s palsy.
Abstract
Background: Stylomastoid foramen is the terminal part of facial canal and is the exit gateway for facial nerve from skull base. We hypothesized that anatomical variations of this foramen could be a risk factor for the injury of facial nerve resulting in unilateral facial nerve paralysis or Bell’s palsy. Hence the present study was conducted to study the variations in size and shape of stylomastoid foramen in dry adult human skulls.
Materials and methods: The study was conducted on 37 dry adult human skulls of unknown age and sex. High resolution images of the skulls under study were processed by ImageJ software and observations were undertaken.
Results: Total eight variations of stylomastoid foramen were observed in terms of shape. The common variants were round, oval and square (present in 83.79% skulls on right side and 81.07% skulls on left side), whereas the rare variants were triangular, rectangular, serrated, bean-shaped and irregular. It was noted that stylomastoid foramen were associated with extensions (45.95% skulls) and also adjacent foramen (18.92% skulls). Exclusively unilateral observations included bifurcation of foramen (16.22% skulls), foramen situated deep inside skull groove (5.41% skulls) and foramen interrupted by bony spur (2.7% skulls). No significant differences were observed between the mean diameters (antero-posterior and transverse) of the stylomastoid foramen.
Conclusions: The unilateral variations along with rare variations in terms of shape such as serrated, bean-shaped and irregular foramen (which were also unilateral findings) could be potential risk factors towards injury of facial nerve at the point of exit from skull base leading to Bell’s palsy.
Keywords
stylomastoid foramen, variations, risk factor, injury, facial nerve, Bell’s palsy
About this articleTitle
Variations in the morphology of stylomastoid foramen: a possible solution to the conundrum of unexplained cases of Bell’s palsy
Journal
Issue
Article type
Original article
Pages
97-105
Published online
2020-02-13
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1654
Article views/downloads
1845
DOI
Pubmed
Bibliographic record
Folia Morphol 2021;80(1):97-105.
Keywords
stylomastoid foramen
variations
risk factor
injury
facial nerve
Bell’s palsy
Authors
S. K. Ghosh
R. K. Narayan
References (25)- Ahmed A. When is facial paralysis Bell palsy? Current diagnosis and treatment. Cleve Clin J Med. 2005; 72(5): 398–401, 405.
- Celik O, Eskiizmir G, Pabuscu Y, et al. The role of facial canal diameter in the pathogenesis and grade of Bell's palsy: a study by high resolution computed tomography. Braz J Otorhinolaryngol. 2017; 83(3): 261–268.
- Finsterer J. Management of peripheral facial nerve palsy. Eur Arch Otorhinolaryngol. 2008; 265(7): 743–752.
- Fuller G, Morgan C. Bell's palsy syndrome: mimics and chameleons. Pract Neurol. 2016; 16(6): 439–444.
- Ho ML, Juliano A, Eisenberg RL, et al. Anatomy and pathology of the facial nerve. Am J Roentgenol. 2015; 204(6): W612–W619.
- Holland NJ, Weiner GM. Recent developments in Bell's palsy. BMJ. 2004; 329(7465): 553–557.
- Kawiak W, Dudkowska A, Adach B. Diagnostic difficulties in etiology of the lesion of peripheral neuron of the facial nerve during the growth of sialoma. Ann Univ Mariae Curie Sklodowska Med. 1993; 48: 125–128.
- Kefalidis G, Riga M, Argyropoulou P, et al. Is the width of the labyrinthine portion of the fallopian tube implicated in the pathophysiology of Bell's palsy?: a prospective clinical study using computed tomography. Laryngoscope. 2010; 120(6): 1203–1207.
- Mortazavi MM, Latif B, Verma K, et al. The fallopian canal: a comprehensive review and proposal of a new classification. Childs Nerv Syst. 2014; 30(3): 387–395.
- Murakami S, Mizobuchi M, Nakashiro Y, et al. Bells palsy and herpes simplex virus: identification of viral DNA in endoneural fluid and muscle. Ann Intern Med. 1996; 124: 27–30.
- Nakashima S, Sando I, Takahashi H, et al. Computer-aided 3-D reconstruction and measurement of the facial canal and facial nerve. I. Cross-sectional area and diameter: preliminary report. Laryngoscope. 1993; 103(10): 1150–1156.
- Patel DK, Levin KH. Bell palsy: Clinical examination and management. Cleve Clin J Med. 2015; 82(7): 419–426.
- Peitersen E. Bell's palsy: the spontaneous course of 2,500 peripheral facial nerve palsies of different etiologies. Acta Otolaryngol Suppl. 2002(549): 4–30.
- Phillips CD, Bubash LA. The facial nerve: anatomy and common pathology. Semin Ultrasound CT MR. 2002; 23(3): 202–217.
- Powell HC, Myers RR, Costello ML, et al. Endoneurial fluid pressure in wallerian degeneration. Ann Neurol. 1979; 5(6): 550–557.
- Salib RJ, Tziambazis E, McDermott AL, et al. The crucial role of imaging in detection of facial nerve haemangiomas. J Laryngol Otol. 2001; 115(6): 510–513.
- Sharma N, Varshney R. Morphometry of stylomastoid foramen and its clinical application in facial nerve block. Saudi J Anaesth. 2015; 9(1): 60–63.
- Shin KJ, Gil YC, Lee JY, et al. Three-dimensional study of the facial canal using microcomputed tomography for improved anatomical comprehension. Anat Rec (Hoboken). 2014; 297(10): 1808–1816.
- Standring S. Gray’s Anatomy: The anatomical basis of clinical practice. 41st Ed. Elsevier Health Sciences, Oxford, UK 2015: 1592.
- Tüccar E, Tekdemir I, Aslan A, et al. Radiological anatomy of the intratemporal course of facial nerve. Clin Anat. 2000; 13(2): 83–87, doi: 10.1002/(SICI)1098-2353(2000)13:2<83::AID-CA2>3.0.CO;2-Y.
- Upile T, Jerjes W, Nouraei SA, et al. The stylomastoid artery as an anatomical landmark to the facial nerve during parotid surgery: a clinico-anatomic study. World J Surg Oncol. 2009; 7: 71.
- Vianna M, Adams M, Schachern P, et al. Differences in the diameter of facial nerve and facial canal in bell's palsy--a 3-dimensional temporal bone study. Otol Neurotol. 2014; 35(3): 514–518.
- Wang H, Northrop C, Burgess B, et al. Three-dimensional virtual model of the human temporal bone: a stand-alone, downloadable teaching tool. Otol Neurotol. 2006; 27(4): 452–457.
- Yetiser S, Kazkayas M, Altınok D, et al. Magnetic resonance imaging of the intratemporal facial nerve in idiopathic peripheral facial palsy. Clin Imag. 2003; 27(2): 77–81.
- Zhang W, Xu L, Luo T, et al. The etiology of Bell's palsy: a review. J Neurol. 2020; 267(7): 1896–1905.
