Semicircular canal anatomy: Human cadaveric temporal bone study – Nguyen Thanh Vinh

Journal of military pharmaco-medicine n 0 8-2018 118 SEMICIRCULAR CANAL ANATOMY: HUMAN CADAVERIC TEMPORAL BONE STUDY Nguyen Thanh Vinh1; Nguyen Hoang Vu2; Pham Ngoc Chat2 SUMMARY Objectives: To investigate semicircular canal anatomy of Vietnamese mature cadavers as seen in microdissection; evaluate osseous semicircular canal, membranous semicircular canal and the relationship of semicircular canal with the adjacent anatomical structures. Subjects and methods: Samples of 16 human corpse heads, 32 ears were selected belonging to Department of Anatomy, University of Medicine and Pharmacy, Hochiminh City. The semicircular canal was explored with transmastoid and cranial fossa approach. Results: 16 human corpse heads, 32 ears were selected with average age of 66.8 (40 - 83 years old). Lateral, anterior osseous and posterior membranous semicircular canal were clearly identified with cranial fossa approach. Lateral, posterior osseous and membranous semicircular canal were clearly identified with transmastoid approach. Membranous semicircular canal was situated in the outer edge of the osseous semicircular canal. Conclusions: All of these approaches can be used to clearly identify the semicircular canal anatomical structure. * Keywords: Osseous semicircular canal; Membranous semicircular canal; Cranial fossa approach; Transmastoid approach. INTRODUCTION The semicircular canal system is a component of the vestibular system, contributing significantly to the body's balance function. Anatomically, there are three semicircular canals: lateral, anterior and posterior semicircular canals. They are very small structures, in different planes, lied within the earlobe and buried deep in the temporal bones. When studying, researching or teaching, people have to depend on images printed in textbooks or models, which cause a lot of difficulties to understand clearly, especially related specialities such as anatomy, neurosurgery and ENT. In the world, many books have been written on temporal bone surgery, but the presentation of the approach to this system is still unclear and specific. In Vietnam, there have also been reports of semicircular canals, images and clinical applications in the diagnosis and treatment of the disease. In fact, when the surgeons participate in the temporal bone surgery courses, it is always difficult for them to study the anatomy of semicircular canals and requires intensive means as well as the experiences of performing surgery. In order to solve this problem, we need to have a specific approach that can help physicians and practitioners to see and understand correctly the anatomy of semicircular canal system. Therefore, we investigate: Labyrinth anatomy as seen in microdissection to evaluate osseous labyrinth, membranous labyrinth 1. ENT Hospital, Hochiminh City 2. Medicine and Pharmacy University Corresponding author: Nguyen Thanh Vinh (@gmail.com) Date received: 01/08/20181 Date accepted: 20/09/2018 Journal of military pharmaco-medicine n 0 8-2018 119 SUBJECTS AND METHODS 1. Subjects. 16 Vietnamese adult human corpse heads were selected belonging to Department of Anatomy, University of Medicine and Pharmacy, Hochiminh City. 2. Research methods. Case series report. * Selection criteria: - Vietnamese adults. - Corpse heads were selected at Department of Anatomy, University of Medicine and Pharmacy, Hochiminh City. - Normal temporal bone in anatomy. * Exclusion criteria: - Age < 18. - Having ear problems. - Interventions for ear surgery. - Congenital malformations of the head and neck. - Traumatic in head or temporal region. * Research facilities: - Temporal bone dissection instruments. - Semicircular canals microsurgical instruments. - Electric drilling machine. - Carving drill bits and sharping drill bits, sizes 4 - 0.5 mm. - Aspirtor machine, suction, syringe. - Karz Zeiss microscope. - Camera. - Computers to save images. * Microdissection with cranial fossa approach: - Cut the skull formming ovale shape, across the edge of the ear on both sides. - Cut the brain stem, revealing the entire base of the skull. - Determine the Arch convex (prominence of lateral semicircular canal). - Three straight lines are perpendicular to the petromastoid bones, 1 through the center of the convex, 1 tangent to the upper edge of the convex and 1 tangent to the lower edge of the convex. - The line is perpendicular to the three lines above, tangent to the outer edge of the Arch convex. - Use electric drill machine, 3 or 4 mm carving drill pit, drill the bone along the outer edge of the tangent line outside the Arch convex, reveal the mucosal layer of posterior atrium ceiling. - Use the microsurgical knife cut the mucosal layer of posterior atrium ceiling. - Identify short process of incus and lateral semicircular canal. - Determine the anterior osseous labyrinth from the Arch convex to the front of lateral osseous labyrinth. - Use the 1 - 2 mm carving drill pit, drill out mastoid cells of surrounding vestibule group of the anterior osseous labyrinth, exposing the entire anterior osseous labyrinth. - Use the 3 mm carving drill pit, drill the cranial fossa bone surrounding the anterior osseous labyrinth. * Microdissection with transmastoid approach: - Make a postaural incision with no.15 or no.20 scalpel blade, until the temporal bone. - Detach the musculoperiosteal flap posteriorly and anteriorly to the external auditory canal. Journal of military pharmaco-medicine n 0 8-2018 120 - The self-retaining retractor is utilized to pull up the flap, expose the mastoid cortex. - Use a large cutting burr (3 - 4 mm), drilling is started along the temporal line, then along the posterior wall of the external auditory canal. Finally, a third line is drilled perpendicular to the temporal line, through the mastoid tip, to create a triangle. - Continue to drill the mastoid cells to open the antrum. - Drill the tegmental mastoid cells, expose the middle cranial fossa. - Use a small cutting burr (1 - 2 mm), drill the anterior and posterior sinal cells to expose the sinus and the Citelli’s angle. - Continue to drill the perifacial cells, expose the third segment of facial nerve. - Drill posteriorly to the tip cells, expose the bone around the digastric muscle. - Drill to open the aditus, until the incus can be identified. The lateral semicircular canal can be seen. - Drill the mastoid cells around the lateral and posterior semicircular canal . - Use a 0.5 - 1 mm diamond burr, drill the mastoid cells around the semicircular canal, until no mucosa left. - Grind the edge of 3 semicircular canals. - Identify the subarcuate artery, near the center of 3 semicircular canals. - Use a 0.5 - 1 mm diamond burr, grind the bone surface of the mastoid segment of CN VII, near posterior and lateral semicircular canal, the second genu of CN VII. * Microdissection of the semicircular canals: - Through cranial fossa approach, use a 0.5 mm diamond burr to drill along the medial side of the anterior semicircular canal, from the conjunction between the anterior semicircular canal and the lateral semicircular canal to the conjuction between the anterior semicircular canal to the posterior semicircular canal. - Drill the bony semicircular canal until the mucosa of the membranous semicircular canal can be seen; from there, continue to drill the anterior semicircular canal to expose totally the membranous anterior semicircular canal, from the ampulla to the crus commune. - Use the 0.5 - 1 mm diamond burr to drill along the medial side of the lateral semicircular canal, from the connection with the anterior semicircular canal to the conjuction between the lateral semicircular canal to the posterior semicircular canal. - Drill the bony lateral semicircular canal until the mucosa of the membranous lateral semicircular canal can be seen; continue to drill carefully the bony lateral semicircular canal to expose totally the membranous lateral semicircular canal. - Leave the bony part between the bony anterior semicircular canal and the lateral semicircular canal, to distiguish the border line between 2 membranous semicircular canal and the ampulla of the anterior and lateral semicircular canal. - Use 0.5 - 1 mm diamond burr, drill the bony posterior semicircular canal, from the crus commune to the opening of the ampulla into the utricle. Continue to drill to Journal of military pharmaco-medicine n 0 8-2018 121 expose the mucosa of the membranous posterior semicircular canal, then expose totally the posterior semicircular canal. - Use 0.5 mm diamond burr to drill the bone between the anterior semicircular canal and the lateral semicircular canal. - Use 0.5 mm diamond burr, drill the crus commune of the anterior semicircular canal and the lateral semicircular canal. RESULTS Through observation in 16 human corps (32 ears, in which 16 left-sided and 16 right-sided ears), including 8 men and 8 women with the mean age of 66.8 ± 12.57 (40 - 83 years old). * Position of the membranous semicircular canal in bony semicircular canal: Anterior position of semicircular canal in bony semicircular accounted for 84.4% (27 ears), lateral position was 15.6% (5 ears). Table 1: Ampulla of the membranous semicircular canal in ampulla of bony semicircular canal. Position Number of cases Ratio (%) Total bony semicircular canal 4 12.50 ¾ bony semicircular canal 28 87.50 * Relation between ampulla of anterior membranous semicircular canal and ampulla of lateral membranous semicircular canal: 100% of ampulla of anterior membranous semicircular canal was in contact to ampulla of lateral membranous semicircular canal. Table 2: Position of the subarcuate artery. Position Number of cases Ratio (%) Anterior semicircular canal wall 32 100 Lateral semicircular canal wall 0 0 Posterior semicircular canal wall 0 0 Table 3: Anterior semicircular canal wall Number of cases Ratio (%) Middle position 2 6.2 Posterior position 25 78.10 Lateral position 2 6.2 Anterior position 3 9.5 DISCUSSION 1. Membranous semicircular canal. Membranous semicircular canal is inside the bony semicircular canal. It has been noted that membranous semicircular canal is in lateral margin of semicircular canal. In fact, we note that most of membranous semicircular canals are located on the outer edge of the bony semicircular canal. The surgeons have to open the bony semicircular canal carefully, otherwise it will damage the membranous semicircular canal. About the membranous ampulla in bony ampulla semicircular canal, it has been noted that most of membranous ampulla occupy majority of the bony ampulla semicircular canal volume (28 ears). Journal of military pharmaco-medicine n 0 8-2018 122 The remaining occupy total of the bony ampulla volume (4 ears). All of anterior membranous ampulla are in contact to lateral membranous ampulla. One of the problems that can occur after a traumatic brain injury si profound hearing loss because semicircular canal can be broken. We noted communication between perilymph and endolymph, may cause cellular damage to the hair cells. Anatomy of the subarcuate artery is in “triangle semicircular canal walls”. We studied that this artery was on anterior semicircular canal wall (100%). Posterior position of anterior semicircular canal wall was the most common site (25 ears, 78.10%), superior position (3 ears, 9.50%), lateral and middle position (2 ears, 6.2%). The presence of this variation in “triangle semicircular canal walls” is not used to detect semicircular canal system. 2. Autopsy approach. For ENT specialists, the postauricular approach is a common approach since this way is easy to learn and easy to apply to the surgery. The semicircular canal approach is to drill half of the bony semicircular canal to clearly observe membranous semicircular canal. The postauricular approach helps to access easily in the following order: Lateral semicircular canal, posterior semicircular canal and lastly anterior semicircular canal. Lateral semicircular canal is easy to approach because the direction of the microscope is straight, and the lateral semicircular canal protrudes more distal than other semicircular canal. On the other hand, anterior semicircular canal, due to the vertical position, is higher than the lateral semicircular canal and contacts with the skull bone; so this semicircular canal is partially hidden, difficult to dislocate. Moreover, the posterior semicircular canal is usually more accessible than anterior semicircular canal because it is only covered by well-developed air cells on the surface. Surgeons, after drilling these air cells, can recognize posterior semicircular canal. As membranous semicircular canal, the postauricular approach helps surgeons see anatomy structures clearly in the following order: Posterior membranous semicircular canal, lateral membranous semicircular canal and finally anterior semicircular canal. If only doing surgery to see the anatomy structures, approach type is not a big matter. However, as we did research, our autopsy approach would be more accurate than other approach. Furthermore, for our application in surgery, our autopsy approach was much more applicable in real surgery for disease treatment. Cranial approach is easier to manipulate with the anterior semicircular canal, easier to observe the lateral membranous semicircular canal than the postauricular approach. On the other hand, this approach is wider than the postauricular one, which can manipulate on all three semicircular canals. However, this approach is only used in autopsy, not applied in real surgery. Journal of military pharmaco-medicine n 0 8-2018 123 CONCLUSION Through a combination of two approaches: The postauricular approach and cranial approach for accessing to bony - membranous semicircular canal, with 16 corpses, 32 ears, we can conclude: * Postauricular approach: - Help to approach bony semicircular canal well in following order: Lateral, posterior and finally anterior. - For membranous semicircular canal, the order is posterior, lateral and anterior. * Cranial approach: - Help to approach bony semicircular canal well in following order: Anterior, lateral and posterior. - For membranous semicircular canal, the order is lateral, posterior, anterior. Therefore, all two autopsy approaches support each other, provide good access to all three bonies and membranous semicircular canal. REFERENCES 1. J.V Beek-King. Retrolabyrithine approach. Operative Techniques in Otolaryngology. 2013, vol 24, pp.169-171. 2. J Bowman. The translabyrinthine approach. 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