Semicircular canal anatomy as seen in microdissection

Journal of military pharmaco-medicine n06-2018<br /> <br /> SEMICIRCULAR CANAL ANATOMY AS SEEN IN<br /> MICRODISSECTION<br /> Nguyen Thanh Vinh*; Tran Ngọc Anh**<br /> Nguyen Hoang Vu***; Le Gia Vinh****; Pham Ngoc Chat*****<br /> SUMMARY<br /> Objectives: To investigate semicircular canal anatomy as seen in microdissection; evaluate<br /> osseous semicircular canal, membranous semicircular canal and the relationship of semicircular<br /> canal with the adjacent anatomical structures. Subjects and methods: Samples of 9 human<br /> corpse heads, 18 ears were selected belonging to Department of Anatomy, University of Medicine<br /> and Pharmacy, Hochiminh City. The semicircular canal was explored with transmastoid and<br /> cranial fossa approach. Results: 9 human corpse heads, 18 ears were selected with average<br /> age 61.5 (53 - 70). Horizontal, superior osseous semicircular canal and posterior membranous<br /> semicircular canal was clearly identified with cranial fossa approach. Horizontal, posterior osseous<br /> and membranous semicircular canals were clearly identified with transmastoid approach.<br /> Membranous semicircular canal was situated the outer edge of the osseous semicircular canal.<br /> Conclusions: All of these approaches can be used to clearly identify the semicircular canal<br /> anatomical structure.<br /> * Keywords: Osseous semicircular canal; Membranous semicircular canal; Cranial fossa approach;<br /> Transmastoid approach.<br /> <br /> INTRODUCTION<br /> The semicircular canals system is a<br /> component of the vestibular system,<br /> contributing significantly to the body's<br /> balance function. Anatomically, there are<br /> three semicircular canals: horizontal (lateral),<br /> superior and posterior semicircular canals.<br /> They are very small structures, in different<br /> planes, lied within the earlobe and buried<br /> deep in the temporal bones. When studying,<br /> researching or teaching, people has to<br /> depend on images printed in textbooks or<br /> <br /> models, which causes a lot of difficulties<br /> to understand clearly, especially related<br /> specialties such as: anatomy, neurosurgery<br /> and ENT.<br /> In the world, there are many books<br /> have been written on temporal bone<br /> surgery, but the presentation of the<br /> approach to this system is still unclear<br /> and specific. In Vietnam, there have also<br /> been reports of semicircular canals, there<br /> are images and clinical applications in the<br /> diagnosis and treatment of the disease.<br /> <br /> * ENT Hospital, Hochiminh City<br /> ** Vietnam Military Medical University<br /> *** Medicine and Pharmacy University<br /> **** Vietnam Medical Asociation<br /> Corresponding author: Nguyen Thanh Vinh (drvinhent@gmail.com)<br /> Date received: 26/04/20181<br /> Date accepted: 29/06/2018<br /> <br /> 121<br /> <br /> Journal of military pharmaco-medicine n06-2018<br /> In fact, when participating in the temporal<br /> bone surgery courses, it is always difficult<br /> to study the anatomy of semicircular canals<br /> and requires intensive means as well as<br /> the experience of surgeons performing<br /> surgery. In order to solve this problem, we<br /> need to have a specific approach that can<br /> help physicians and practitioners to see<br /> and understand correctly the anatomy of<br /> semicircular canal system. Therefore, we<br /> investigate “Labyrinth anatomy as seen in<br /> microdissection and evaluate osseous<br /> labyrinth, membranous labyrinth and the<br /> relationship of labyrinth with the adjacent<br /> anatomical structures”.<br /> SUBJECTS AND METHODS<br /> 1. Subjects.<br /> Vietnamese adults human corpse heads<br /> were selected belonging to Department of<br /> Anatomy, University of Medicine and<br /> Pharmacy, Hochiminh City.<br /> * Selection criteria:<br /> - Vietnamese adults.<br /> - Corpse heads were selected belong<br /> to Department of Anatomy, University of<br /> Medicine and Pharmacy of Hochiminh City.<br /> - Normal temporal bone in anatomy.<br /> * Exclusion criteria:<br /> - Age < 18.<br /> - Having ear problems.<br /> - Interventions for ear surgery.<br /> - Congenital malformations of the head<br /> and neck.<br /> - Traumatic in head or temporal region.<br /> 2. Methods.<br /> Case series report.<br /> * Research location: Department of<br /> Anatomy, University of Medicine and<br /> Pharmacy, Hochiminh City.<br /> 122<br /> <br /> * Research facilities:<br /> - Temporal bone dissection instruments.<br /> - Semicircular canal microsurgery<br /> instruments.<br /> - Electric drilling machine.<br /> - Carving drill bits and sharping drill bits,<br /> sizes ranging from 4 mm to 0.5 mm.<br /> - Aspirator machine, suction, syringe.<br /> - Karz Zeiss microscope.<br /> - Camera.<br /> - Computers to save images.<br /> * Microdissection with cranial fossa<br /> approach:<br /> - Cut the skull forming oval shape,<br /> across the edge of the ear on both sides.<br /> - Cut the brain stem, revealing the entire<br /> base of the skull.<br /> - Determine the Arch convex (prominence<br /> of lateral semicircular canal).<br /> - Three straight lines are perpendicular<br /> to the petromastoid bones, 1 through the<br /> center of the convex, 1 tangent to the<br /> upper edge of the convex and 1 tangent<br /> to the lower edge of the convex.<br /> - The line is perpendicular to the three<br /> lines above, tangent to the outer edge of<br /> the Arch convex.<br /> - Use electric drill machine, 3 or 4 mm<br /> carving drill pit, drill the bone along the<br /> outer edge of the tangent line outside the<br /> Arch convex, reveal the mucosal layer of<br /> posterior atrium ceiling.<br /> - Use the microsurgical knife cut the<br /> mucosal layer of posterior atrium ceiling.<br /> - Identify short process of incus and<br /> lateral semicircular canal.<br /> - Determine the superior osseous<br /> labyrinth from the Arch convex to the front<br /> of lateral osseous labyrinth.<br /> <br /> Journal of military pharmaco-medicine n06-2018<br /> - Use the 1 - 2 mm carving drill pit, drill<br /> out mastoid cells of surrounding vestibule<br /> group of the superior osseous labyrinth,<br /> exposing the entire superior osseous<br /> labyrinth.<br /> <br /> - Drill the mastoid cells around the<br /> lateral and posterior semicircular canal.<br /> <br /> - Use the 3 mm carving drill pit, drill the<br /> cranial fossa bone surrounding the superior<br /> osseous labyrinth.<br /> <br /> - Grind the edge of 3 semicircular canals.<br /> <br /> * Microdissection with transmastoid<br /> approach:<br /> - Make a postaural incision with No.15<br /> or No. 20 scalpel blade, until the temporal<br /> bone.<br /> - Detach the musculoperiosteal flap<br /> posteriorly and anteriorly to the external<br /> auditory canal.<br /> - The self-retaining retractor is utilized to<br /> pull up the flap, expose the mastoid cortex.<br /> - Using a large cutting burr (3 - 4 mm),<br /> drilling is started along the temporal line,<br /> then along the posterior wall of the external<br /> auditory canal. Finally, a third line is drilled<br /> perpendicular to the temporal line, through<br /> the mastoid tip, to create a triangle.<br /> - Continue to drill the mastoid cells to<br /> open the antrum.<br /> - Drill the tegmental mastoid cells, expose<br /> the middle cranial fossa.<br /> - Using a small cutting burr (1 - 2 mm),<br /> drill the anterior and posterior signal cells<br /> to expose the sinus and the Citelli’s angle.<br /> <br /> - Using a 0.5 - 1 mm diamond burr, drill<br /> the mastoid cells around the semicircular<br /> canal, until no mucosa left.<br /> - Identify the subarcuate artery, near the<br /> center of 3 semicircular canals.<br /> - Using a 0.5 - 1 mm diamond burr,<br /> grind the bone surface of the mastoid<br /> segment of CN VII, near posterior and<br /> lateral semicircular canal, the second<br /> genu of CN VII.<br /> * Microdissect the semicircular canals:<br /> - Through cranial fossa approach, use a<br /> 0.5 mm diamond burr to drill along the<br /> medial side of the superior semicircular<br /> canal, from the conjunction between the<br /> superior semicircular canal and the lateral<br /> semicircular canal to the conjuction between<br /> the superior semicircular canal to the<br /> posterior semicircular canal.<br /> - Drill the bony semicircular canal until<br /> the mucosa of the membranous semicircular<br /> canal can be seen; from there, continue to<br /> drill the superior semicircular canal to<br /> expose totally the membranous superior<br /> semicircular canal, from the ampulla to<br /> the crus commune.<br /> <br /> - Drill posteriorly to the tip cells, expose<br /> the bone around the digastric muscle.<br /> <br /> - Use the 0.5 - 1 mm diamond burr to<br /> drill along the medial side of the lateral<br /> semicircular canal, from the connection<br /> with the superior semicircular canal to the<br /> conjunction between the lateral semicircular<br /> canal to the posterior semicircular canal.<br /> <br /> - Drill to open the aditus, until the incus<br /> can be identified. The lateral semicircular<br /> canal can be seen.<br /> <br /> - Drill the bony lateral semicircular canal<br /> until the mucosa of the membranous<br /> lateral semicircular canal can be seen;<br /> <br /> - Continue to drill the perifacial cells,<br /> expose the third segment of facial nerve.<br /> <br /> 123<br /> <br /> Journal of military pharmaco-medicine n06-2018<br /> continue to drill carefully the bony lateral<br /> semicircular canal to expose totally the<br /> membranous lateral semicircular canal.<br /> - Left the bony part between the bony<br /> superior semicircular canal and the lateral<br /> semicircular canal, to distinguish the border<br /> line between 2 membranous semicircular<br /> canals and the ampulla of the superior<br /> and lateral semicircular canal.<br /> - Use 0.5 - 1 mm diamond burr, drill the<br /> bony posterior semicircular canal, from<br /> the crus commune to the opening of the<br /> ampulla into the utricle. Continue to drill to<br /> expose the mucosa of the membranous<br /> posterior semicircular canal, then expose<br /> totally the posterior semicircular canal.<br /> - Use 0.5 mm diamond burr to drill the<br /> bone between the superior semicircular<br /> canal and the lateral semicircular canal.<br /> - Use 0.5 mm diamond burr, drill the<br /> crus commune of the superior semicircular<br /> canal and the lateral semicircular canal.<br /> RESULT<br /> Through observation in 9 human corps<br /> (18 ears), including 5 men and 4 women.<br /> * Age: The youngest was 53, the oldest<br /> was 71, mean age 61.5.<br /> * Gender: Males 5 cases (55.5%); females:<br /> 4 cases (44.5%).<br /> * Mastoid cells around the semicircular<br /> canals: Well-developed: 11 cases (61.1%);<br /> moderate developed: 6 cases (33.3%);<br /> underdeveloped: 1 case (5.6%).<br /> * Lateral bony semicircular canal:<br /> Very clear: 4 cases (22.2%); clear: 12 cases<br /> (66.7%); not clear: 2 cases (11.1%).<br /> 124<br /> <br /> Table 1: Relative structure.<br /> Relative structure<br /> <br /> Number<br /> of ears<br /> <br /> Ratio<br /> <br /> Tympanic segment of CN VII<br /> <br /> 18<br /> <br /> 100<br /> <br /> Mastoid segment of CN VII<br /> <br /> 18<br /> <br /> 100<br /> <br /> Second genu of CN VII<br /> <br /> 18<br /> <br /> 100<br /> <br /> Short process of incus<br /> <br /> 18<br /> <br /> 100<br /> <br /> Table 2: Bony semicircular canal.<br /> Bony<br /> semicircul<br /> ar canal<br /> <br /> Cranial fossa<br /> approach<br /> <br /> Postauricular<br /> approach<br /> <br /> Superior<br /> <br /> Very clear<br /> <br /> Quite clear<br /> <br /> Lateral<br /> <br /> Very clear<br /> <br /> Very clear<br /> <br /> Posterial<br /> <br /> Quite clear<br /> <br /> Very clear<br /> <br /> Journal of military pharmaco-medicine n06-2018<br /> Table 3: Membranous semicircular canal.<br /> Membranous<br /> Cranial fossa Postauricular<br /> semicircular canal approach<br /> approach<br /> Superior<br /> <br /> Not clear<br /> <br /> Quite clear<br /> <br /> Lateral<br /> <br /> Quite clear<br /> <br /> Very clear<br /> <br /> Posterial<br /> <br /> Very clear<br /> <br /> Very clear<br /> <br /> Table 4: Position of the membranous<br /> semicircular canal in bony semicircular canal.<br /> Semicircular<br /> canal<br /> <br /> Superior<br /> <br /> Lateral<br /> <br /> Posterior<br /> <br /> Anterior wall<br /> <br /> 0<br /> <br /> 5<br /> <br /> 1<br /> <br /> Lateral wall<br /> <br /> 16<br /> <br /> 12<br /> <br /> 15<br /> <br /> Medial wall<br /> <br /> 2<br /> <br /> 1<br /> <br /> 2<br /> <br /> Posterior wall<br /> <br /> 0<br /> <br /> 0<br /> <br /> 0<br /> <br /> * Abnormalities:<br /> - The lateral membranous semicircular<br /> canal is concave downward in 1 case.<br /> - Absence of the crus commune in 1 case.<br /> <br /> DISCUSSION<br /> 1. Bony semicircular canal.<br /> In terms of morphology, all three bony<br /> semicircular canals are in the same<br /> position as being described in books, in<br /> which the lateral bony semicircular canal<br /> had a higher rate to be seen clearly than<br /> other bony semicircular canals in both<br /> 2 approaches (cranial and postauricular);<br /> only two ears were not really visible<br /> because of the extensive development of<br /> the mastoid air cells, which surrounded<br /> the lateral bony semicircular canal, so it<br /> was difficult to see. Due to the relatively<br /> vertical position, it was more difficult to<br /> recognize superior bony semicircular canal<br /> by the postauricular approach than cranial<br /> approach. On the other hand, on the base<br /> of the skull base, it was possible to see the<br /> protrusion of the lateral bony semicircular<br /> canal, which was easier to define. If mastoid<br /> air cell is well-developed, there will be an<br /> air cell between the superior semicircular<br /> canal and the base of the skull; so it is<br /> more easily recognized due to protrusion<br /> of the lateral bony semicircular canal.<br /> Particularly, because the posterior<br /> semicircular canal was on the horizontal<br /> position and lower than the superior and<br /> lateral semicircular canal, it was buried<br /> deep inside the otic capsule and was<br /> difficult to recognize. On the other hand,<br /> in mastoid bone with a well-developed air<br /> cell, many layers of air cell covered the<br /> lateral side of the posterior semicircular<br /> canal. Thus, it is more difficult to detect<br /> posterior semicircular canal.<br /> 125<br /> <br />