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MINISTRY OF EDUCATION AND TRAINING MINISTRY OF HEALTH MILITARY MEDICAL UNIVERSITY NGUYEN THANH VINH RESEARCH IN ANATOMY OF SEMICIRCULAR CANALS APPLY TO SURGERY Major: Biomedical Science Code : 72 01 01 ABSTRACT OF MEDICAL DOCTORAL DEGREE HA NOI – YEAR 2019 THESIS COMPLETED AT MILITARY MEDICAL UNIVERSITY Tutor of thesis: Assoc.Prof.PhD PHAM NGOC CHAT Prof.PhD LE GIA VINH Reviewer 1: Prof.PhD LE VAN CUONG Reviewer 2: PhD NGUYEN PHI LONG Reviewer 3: Assoc.Prof.PhD PHAM TUAN CANH The thesis was defended at assembly of the university on: o’clock date months year Can read for this thesis at: National library Military medical university’s library ………………………… INTRODUCTION Ear is divided into parts: external ear, middle ear and inner ear; among those, the inner ear has a much more complicated anatomic structure, especially three-semicircular canal system: anterior, lateral and posterior There has been a lot of researches about anatomy of semicircular canal system, which is described and illustrated quite thoroughly in anatomy textbooks Though, in fact, each semicircular canal lies within separate bony mass those shape is similar to that such semicircular called bony cover; the bony mass covering semicircular canals lies within a hard bony mass called inner ear covering bone, outside the inner ear covering, there are many layers of developed mastoid air cell hidden, which hardly recognized Within semicircular canal bony cover, it contains bony semicircular canals; within bony semicircular canal, it contains membrane semicircular canal The latter one is more complex than the former cause membrane semicircular canals gain a much more smaller size comparing to bony semicircular canals; there are ampullae for each canals, the common limbs and separate limbs, those drain into utricle Semicircular canals system gains a little structure, locates deeply in temporal bone, adjacent to important structures of body, for examples: utricle, saccule, facial nerve, meninges, ossicles … there are many layers of developed mastoid air cell surrounding and there is no landmark aiming to identify each canals Because of such characteristics, studying, teaching, researching as well as clinical applying in treatment of related specialties including anatomy, neurology and otorhinolaryngology face with many difficulty Therefore, identifying a bony semicircular canal without injury is already a challenge, identifying membranous semicircular canal without injury to adjacent bony semicircular canal is much more difficult as well as not damaging important neighboring structures Furthermor, to operate common diseases of ear, the surgical approach is usually near those semicircular canals; thus, it is easy to get injured In ear diseases, it is still difficult to identify affected semicircular canals and easy to pass by; or can identify but can not eliminate pathogenesis To solve such problem, we perform research about “The anatomy of semicircular canal system applying for ear surgery” with two following separate objectives: Describing anatomic characteristics of semicircular canals system in Vietnamese aldults Identifying the relation between semicircular canals and adjacent structures Essential of the thesis: In treatment, the diseases of the ear, that effect the semicircular system such as: BPPV, chronic otitis media, cholesteatoma, trauma amd temporal bone tumor …, need surgery Finding one bony semicircular canal without injuring itself is difficult, as well as identifying membrane semicircular canal and not injuring other semicircular canals or surrouding important structures such as middle cranial fossa, lateral venous sinus … is more difficult On the other hand, in surgical treatment of common diseases of the ear, the incision is usually close to the semicircular canal system so it is easy to break through them The new main scientific findings of the thesis: The thesis provides specific measurements of bony as well as membranous semicircular canal Thereby, noting the changes in morphology of bony sheath, bony and membranous semicircular canal Moreover, introducing new techniques: micro-surgical incision approaching semicircular canals and how to get inside the semicircular canals following techniques “Cleaving the section of the orange” The thesis determines the relationship between the semicircular canals and surrouding structures There are structures that directly affecting micro-surgical opening of the semicircular canals such as temporal air bone cells projecting to the semicircular canals, there are structures that affecting micro-surgical incision approaching the semicircular canals such as: lateral venous sinus, middle cranial fossa… And there are structures that help identify or avoid injuring another ones: the ossicles, section of facial nerve … These results help surgery diseases related to the semicircular canals safe, effective and less sequalea Thesis layout: The thesis has 122 pages, including: Introduction, Overview (29 pages), Subjects and methods (24 pages), Results (32 pages), Discussion (33 pages), Conclusion and Recommendation There are 47 tables, 73 images and 134 references (16 Vietnamese and 118 English references) Chapter 1: SUMMARY OF DOCUMENTS The inner ear is located within the petrous part of the temporal bones, covered in bone mass called the bony labyrinth The semicircular canal system is in the inner ear and consists of hollow, circular, semicircular tubes, aligned in three perpendicular planes There are three semicircular canals: anterior, posterior, lateral semicircular canal Each has two end points The end points are bigger than their diameters, which are called ampullar limb and bony limb The plane containing lateral semicircular canal creates with the transverse plane of the head an angle of 30 degree The other two semicircular canals: one is upright and one is horizontal, they are perpendicular to each-other In human beings, the plane of anterior semicircular canal of one ear is parallel to the plane of posterior semicircular canal of the other ear and vice versa The semicircular canals which have the same name of two ears (anterior and posterior) have the planes that perpendicular to each-other The semicircular canals are oriented in different planes, and two prominent points, one projects into transverse plane (utricle), the other projects into vertical plane (saccule) There are two vertical semicircular canals: posterior and anterior; one horizontal semicircular canal: lateral The vertical semicircular canals creates with the sagital plane of the head an angle of 45 degree The horizontal semicircular canal is slightly up in the front, and creates an 30 degree angle with the transverse plane of the head Each semicircular canal is arranged in different perpendicular plane Each semicircular canal is almost perpendicular to the others and is sensitive to the rotational movement in its plane The result of this different planes arrangement corresponds to any movement of the head The canals function as unified accelerometer, each stimulation to each canal acts as an angular acceleration, the information is subsequently encrypted and stimulates centripetal nerves relevant to angular momentum These canals are organized in pairs and in the same plane Any rotational motion will stimulate one canal and inhitbit the other canal in pair The pair of two horizontal semicircular canals has more complex location and function than the vertical semicircular canals In human beings, anterior semicircular canal on one side is parallel to the posterior semicircular canal on the other side For example, the right anterior one and the left posterior one create a functional pair The others two semicircular canals are located almost perpendicularly to the lateral semicircular canal The posterior semicircular canal is located just behind the lateral semicircular canal The back border of lateral semicircular canal is the midpoint of posterior semicircular canal The posterior semicircular canal is almost parallel to the posterior cranial fossa The ampulla of posterior semicircular canal, the end point of lower branch, right inside the mastoid part of the facial nerve, the upper end point of the posterior semicircular canal joints with the superior semicircular canal to form a common limb The anterior SCC creates the prominence of the middle cranial fossa, called arcuate eminence; this is an important landmark to identify the anterior SCC and the internal auditory canal through the middle cranial fossa Moreover, the lateral SCC protrudes into the medial wall of the antrum, it is also an important landmark in mastoid surgery.On morphology, the average diameter of SCCs is about mm; the average length between two crus of SCC is approximately 6.5 mm Lateral SCC connected with the utricle at both ends; crus of posterior SCC and superior SCC join to form the crus commune, while the remaining crus of these SCCs is connected with the utricle separately Thus, the SCCs open into the vestibule actually by five orifices The membranous labyrinth is suspended in the bony labyrinth by the perilymphatic space and connective tissue; membranous SCCs is a very thin walled tube (diameter 0.4 mm) in the bony SCCs; is located at the eccentricity in the bony SCCs, which is held by the connective tissue The membranous labyrinth is surrounded by perilymphatic space which is filled with perilymph, the membrane SCCs is filled with endolymph and communicated with the utricle The region of the canal is enlarged which opens into the utricle and has a dilated sac at one end called the ampullae The frontal-upper boundary of the semicircular canals is the epitympanum, the frontal-lower boundary is utricle, saccule, cochlea; the inner boundary is temporal bone, and behind is the third part of facial nerve, mastoid cells system of mastoid bone, upper is middle skull base, behind-lower is posterior skull base, lower-frontal is the internal auditory canal The middle cranial fossa relating: The superior SCC protrudes into the middle cranial fossa in most cases, this protrusion is called arcuate eminence; In a few cases, due to the development of the perilabyrinthine cells, especially on the anterior cells, the arcuate eminence will be inserted between the superior SCC and the middle cranial fossa, separating these two components, so that the arcuate eminence will be lower or not protrude into the middle cranial fossa The posterior cranial fossa relating: The bone of the posterior cranial fossa can be continued or separated to the posterior SCC, depend on the infralabyrinthine cell; if there are numerous infralabyrinthine cells, it will be separated the posterior cranial fossa from the posterior SCC If there are few infralabyrinthine cells, the posterior SCC will contact directly with the posterior cranial fossa The posterior boundary of the mastoid bone is the sigmoid sinus (also known as external sinus); the sigmoid sinus is located below the posterior cranial fossa, usually protrude into the mastoid bone and divide the posterior cranial fossa into the presinus and postsinus areas The sigmoid sinus is less related to the SCCs system, but the protrusion of the sigmoid sinus directly affects the approach to the SCCs, especially the posterior SCC The facial nerve relating: The second segment runs from the geniculate ganglion posteriorly, has a length of 10-12, directs horizontally; is called the tympanic segment Also called the atrium Then, the tympanic segment turns laterally at a 70º angle and inferiorly at a 10º angle, next to the ampulla of the lateral SCC and superior to the oval window, then curves inferiorly to become the second genu of the facial nerve At the second genu, the facial nerve turns at a 125º angle and close to the lateral SCC, in some cases, the Fallopian canal is overlying deeply the lateral SCC Then, it runs vertically to become the third segment (the mastoid segment of the facial nerve); directs to the stylomastoid foramen The third segment runs from the second genu, closes to the lateral SCC and superior to posterior SCC, become the medial wall of the facial recess; there is no another structures inferior to the posterior SCC The perilabyrinthine cells relating: The superior prelabyrinthine cell tracts: superior to the ampulla of the superior and lateral SCCs, inferior to the geniculate ganglion and Fallopian canal Then, they extend medially through the superior SCC to the superlabyrinthine cells located on the internal auditory canal, they are the superior prelabyrinthine cells The translabyrinthine or intralabyrinthine cells: These air cells derived from the antrum, located in a "triangle" formed from three SCCs It traverses the subarcuate cell tract and the subarcuate artery, through the vestibule to the medial surface of the superior SCC before reaching the supralabyrinthine cells and the suprameatal cells They can pass through the entire temporal bone in about 2-3% of cases, but on the surface of the antrum, the intralabyrinthine cells are often seen between the SCCs The supralabyrinthine cells: these air cells are the prolongation of the periantral air cells, extending along the middle cranial fossa, superior to the superior SCC and the crus commune between the superior and posterior SCCs, and terminating superior to the internal auditory canal as the suprameatal cells The microsurgery pathways to approach the SCCs include: The microsurgery through temporal bone: drill the temporal bone to expose lateral sinus and the dural of the middle cranial fossa;open the antrum to expose the lateral SCC Identify the short process ocf the incus lateral to the lateral SCC Identify the length of the third segment of VII CN, reserve the buttress Open the aditus and attic, exopose the preattic The microsurgery through the cranial fossa: Open the skull by 4x5 cm, two third anterior to the outer ear canal and one third posterior to the outer ear canal After lifting the dural, open the anterior SCC anterior to the arcuate eminence The microsurgery through the perilabyrinthine: drill all the air cells, expose the inferior border of the posterior SCC, open the labyrinthine from the lateral SCC, then open the posterior SCC and the anterior SCC, exopose totally the bony cover of the SCCs, the bony SCCs and the membranous SCCs Application in treatment of BPPV by opening the bony SCCs and the membranous SCCs Application in cover the dehiscence of the bony SCC in patients with COM with cholesteatoma which cause erosion of the SCCS and cause dizziness, or in dehiscence of the SCCs after trauma or congenital 11 Chapter 3: RESULT OF STUDY In our research there is 32 ears of 16, involved males and females, mean age is 67,69 ± 13,04; 16 right ears 16 left ear + Morphology of semicircular canals Table 3.4: Morphology of semicircular canals (n = 32) Morphology Cases Percentage % Clear 13 40,60 Not clear 19 59,40 + Position of subarcuate artery Table 3.6: Position of subarcuate artery (n = 32) Cases Percentage  Anterior SCC’s wall 32 100 Lateral SCC’s wall 00 Posterior SCC’s wall 00 Position 3.1 Descriptive anatomy of membrane SCCs + Position of membrane SCCs in bony SCCs Table 3.8: Position of membrane SCCs in bony SCCs (n = 32) Position Cases Percentage % Middle 00 Superior wall 27 84,40 Lateral wall 15,60 Medial wall 00 Posterior wall 00 12 + Ampulla of membrane SCCs in ampulla of bony SCCs Table 3.9: Ampulla of membrane SCCs in ampulla of bony SCCs (n= 32) Position Cases Percentage % Involved all 12,50 Involved partial 28 87,50 + Relation of ampulla of anterior and lateral membrane SCC Table 3.10: Relation of ampulla of anterior and lateral membrane SCCs (n=32) Cases Percentage  Contact 32 100 Not contact 00 Relation + Length of common crus Table 3.11: Length of common crus (n = 32) Length Min Max Mean (mm) 2,13 ± 0,60 + Distance from subarcuate artery to common crus Table 3.14: Distance from subarcuate artery to common crus (n = 32) Distance Min Max Mean (mm) 3,9 2,61 ± 0,61 3.1.3 Descriptive anatomy of bony SCCs 3.1.3.1 Width of bony SCCs: Table 3.15: Width of bony SCCs (n = 30) Width (mm) Min Max Mean Anterior SCC 2,7 5,7 4,26 ± 0,68 Lateral SCC 1,9 5,6 3,19 ± 0,63 Posterior SCC 2,0 4,0 3,24 ± 0,49 13 3.1.3.3 Thickness of bony SCCs: Table 3.18: Thickness of bony SCCs (n =32) SCC (mm) Thickness Min Max Mean Near ampulla 0,4 2,7 1,08 ± 0,46 Middle 0,3 2,1 1,12 ± 0,46 End common crus 0,4 2,6 1,53 ± 0,54 Near ampulla 0,5 2,8 0,88 ± 0,42 Middle 0,6 5,5 1,40 ± 1,07 End common crus 0,5 4,9 1,26 ± 0,86 Near ampulla 0,6 5,0 1,75 ± 0,77 Middle 0,6 5,1 1,93 ± 0,93 End common crus 0,6 2,9 1,68 ± 0,64 Anteror Lateral Posterior 3.1.3.3 Diameter of ampulla of bony SCCs Table 3.21: Diameter of ampulla of bony SCCs (n =32) Diameter (mm) Min Max Mean Anterior 0,9 2,1 1,52 ± 0,35 Lateral 1,2 2,1 1,56 ± 0,24 Posterior 1,0 1,9 1,47 ± 0,23 3.1.3.4 Diameter of bony SCCs Table 3.24: Diameter of bony SCCs (n =32) SCC (mm) Anterior Lateral Diameter Min Max Mean Near ampulla 0,5 1,8 1,01 ± 0.31 Middle 0,3 1,2 0,73 ± 0,25 End crus 0,2 2,0 0,75 ± 0,37 Near ampulla 0,8 1,5 1,12 ± 0,19 Middle 0,5 1,1 0,82 ± 0,18 End crus 0,5 1,5 0,84 ± 0,25 14 SCC (mm) Diameter Min Max Mean Near ampulla 0,1 3,0 0,93 ± 0,51 Middle 0,4 2,0 0,94 ± 0,40 End crus 0,4 1,2 0,80 ± 0,22 Posterior 3.1.3.5 Length of SCC: Table 3.27: Length of SCC (n = 32) SCC (mm) Min Max Mean Anterior 5,3 7,9 6,73 ± 0,66 Lateral 4,7 6,9 5,74 ± 0,40 Posterior 4,4 7,0 5,61 ± 0,73 3.1.3.6 Distance from subarcuate artery to SCC: Table 3.30: Distance from subarcuate artery to SCC (n =32) SCC (mm) Anterior Lateral Posterior Distance Min Max Mean Near ampulla 3,6 5,8 4,65 ± 0,53 Middle 2,6 4,6 3,54 ± 0,45 End crus 1,4 3,9 2,73 ± 0,61 Near ampulla 4,2 11,1 6,75 ± 1,54 Middle 3,2 7,5 5,48 ± 0,89 End crus 1,5 5,9 3,98 ± 1,02 Near ampulla 6,2 9,0 7,52 ± 0,68 Middle 4,2 7,0 5,46 ± 0,63 End crus 1,6 4,4 3,09 ± 0,63 3.1.4 Variation in morphology of SCC: In our research, there is double posterior SCC; lateral horseshoe SCC and hammock posterior SCC 15 3.2 Relation of SCCs and nearby structures 3.2.2 The lateral sinus Table 3.34: Relation to lateral sinus (n=32) Cases Percentage  Grade 18,75 Grade 23 71,88 Grade 9,37 Lateral sinus 3.2.3 Middle cranial fossa Table 3.35: Relation to middle cranial fossa (n=32) Cases Percentage  Grade 14 43,75 Grade 15 46,88 Grade 9,37 Midde cranial fossa 3.2.4 Distance between the buttress and the bony cover of the SCCs Bảng 3.36: Distance between the buttress and the bony cover of the SCCs (n=32) Distance Min Max Mean Anterior SCC 7,3 11,2 9,15 ± 0,96 Lateral SCC 1,1 4,8 3,21 ± 0,83 Posterior SCC 8,0 10,9 9,09 ± 0,76 3.2.5 Distance between the third segment of the facial nerve and the bony cover of the SCCs Table 3.39: Distance between the third segment of the facial nerve and the bony cover of the SCCs (n =32) Distance Min Max Mean Lateral SCC 2,4 6,0 3,66 ± 0,81 Posterior SCC 4,3 9,5 6,49 ± 1,21 16 3.2.6 Perilabyrinthine air cells 3.2.6.1 Superior prelabyrinthine air cells Table 3.42: Superior prelabyrinthine air cells (n=32) Cases Percentage  Grade 23 71,87 Grade 28,13 Grade 00 Superior prelabyrinthine air cells 3.2.6.2 Intralabyrinthine air cells Table 3.43: Intralabyrinthine air cells (n=32) Cases Percentage  Grade 24 75,0 Grade 25,0 Grade 00 Intralabyrinthine air cells 3.2.6.3 Supralabyrinthine air cells Table 3.44: Supralabyrinthine air cells (n=32) Cases Percentage  Grade 26 81,25 Grade 18,75 Grade 00 Supralabyrinthine air cells 3.2.6.4 Retrolabyrinthine air cells Table 3.45: Retrolabyrinthine air cells (n=32) Cases Percentage  Grade 24 75,0 Grade 18,75 Grade 2 6,25 Retrolabyrinthine air cells 17 Chapter 4: DISCUSSION 4.1 Anatomy of the semicircular canals Our study show that after removing mastoid cells, bony sheaths of three semicircular canals are differentiated clearly in 13 ears (40.6%) and not clearly in 19 ears (59.4%) As a result, bony sheaths of lateral semicircular canals are clearly differentiated in all cases; this is true because it is easy to damage lateral semicircular canals while surgical approaching to mastoid, especially in cases with cholesteatoma After drilling into bony sheaths at medial wall of semicircular canals (cutting along the orange zone), osseous canals are approached If we keep cutting osseous canals, membranous canals are exposed Our study noted that most of membranous canals are located on the superior wall of the osseous canals (27 ears, 84.4%) and the others are located on the lateral wall of the osseous canals (5 ears, 15.6%) This information is helpful for surgeons to open the semicircular canals because the position of canal’s opening is usually on superior wall Therefore surgeons should be careful to approach the membranous semicircular canal; if not, membranous canals can be cut and lead to the mix of perilymph and endolymph, which causes vestibular dysfunction and failure of the surgery The posterior crura of the anterior and posterior semicircular canals join together to form a common crus before opening into utricle The median length of common crus in our study is 2.13 ± 0.60 mm Anterior crura of anterior and lateral membranous SCC become dilated to form ampullae before opening into utricle; As a result of our dissection study, ampullae of these membranous SCC occupy a great portion of ampullae of osseous SCC (28 ears, 87.5%), only in ears (12.5%), membranous SCC occupy all of ampullae of osseous SCC Ampullae of anterior and lateral membranous SCC are 18 separated by a bony wall of osseous SCC After removing this bony wall, there was no membranous wall separated ampullae as we thought In addition, when we separated these ampullae, we recognised that they have a direct contact with each other (32 ears, 100%) In the middle of SCC, there is a subarcuate artery (SAA) By dissecting 32 ears, we noted that all SAA locate on the wall of anterior SCC, including at the middle point of the wall (only in ears, 6.25%), posterior deviation (most of the others, 25 ears, 78.13%), lateral deviation (2 ears, 6.25%) and superior deviation (3 ears, 9.37%) Because there are many variations of SAA’s position, the distance between SAA and common crus of SCCs variable widely and the average value of it is 2.61 ± 0.61 mm Therefore, this structure is not a landmark for identifying the location of SCC Every SSC is surrounded by a solid bone, called a bony sheath; the width of each bony sheath is varied The average width of anterior SCC’s bony sheath is 4.27 ± 0.68 mm We could not measure the bony sheath width of anterior SCC in ears because there were many air cells between bony sheath and middle skull base, so we dissected through mastoid to enter anterior SCC and expose the bony sheath of it without dissecting skull base For that reason, we can not measure the sheath width of anterior SCC Osseous SCC locates inside the bony sheath of it The thickness of the bony sheath is variable depending on the position of it and is investigated at different position in our study: at the ampullae, middle, posterior end of SCC Our result on anterior SCC is that: the average thickness of bony sheath at the ampulla position is 1.08 ± 0.46 mm, at the middle position of SCC is 1.12 ± 0.46 mm, at the posterior end is 1.53 ± 0.54 mm On lateral SCC, the average thickness of bony sheath at positions is 0.88±0.42 mm, 1.40±1.07 mm and 1.26± 0.86 mm respectively On posterior SCC, the average thickness of bony sheath 19 at positions is 1.75±0.77 mm, 1.93±0.93 mm and 1.68±0.64 mm This result shows that the bony sheath of posterior SCC is thicker than other SCC When osseous SCC is completely opened, there are two ampullae adjacent to each other: ampulla of anterior and lateral SCC On cadaver dissection, these two ampullae have nearly the same size After measuring, our result is as follows The average diameter of anterior SCC’s ampulla is 1.52 ± 0.35 mm, the average diameter of lateral SCC’s ampulla is 1.56 ± 0.24 mm; the ampulla of posterior SCC is smaller than ones of the anterior and lateral SCC and the average of its diameter is 1.47 ± 0.23 mm We measured the diameter of osseous SCC at locations: near ampulla, at the middle of the SCC and at the end of SCC Our result is as follows: the average diameter of anterior SCC at location are 1.01 ± 0.31 mm, 0.73 ± 0.25 mm and 0.75 ± 0.37 mm respectively The average diameter of lateral SCC at location are 1.12±0.19 mm, 0.82±0.18 mm and 0.84±0.25 mm respectively The average diameter of posterior SCC at location are 0.93±0.51 mm, 0.94±0.41 mm and 0.80±0.22 mm Comparing the average diameter of three osseous SCC at the middle point of each SCC between our study and the studies of author Ricardo Canalis: R Canalis is mm, Trinh Van Minh is 0.8 mm, our study is 0.83 mm In our findings, the average length (or curvature radius, or distance between two crura of osseous SCC) of anterior osseous SCC is 6.73 ± 0.66 mm; the average length of lateral osseous SCC is 5.74±0.40 mm; the average length of posterior osseous SCC is 5.61±0.73 mm R Canalis notes the median length of SCC is 6.5 mm, our study is 6.02 mm There are many variations of location of the subarcuate artery (SAA) on the wall of superior SCC In our study, distances from 20 SAA to three points of the superior SCC, including the ampulla point, middle point and end point of the SCC, are measured Our results are as follows: the average distance from SAA to ampulla of anterior SCC is 4.65 ± 0.53 mm, to middle point of SCC is 3.54 ± 0.45 mm and to end point of SCC is 2.73 ± 0.61 mm; the average distance from SAA to three points of lateral SCC is 6.75 ± 1.54 mm; 5.48 ± 0.81 mm and 3.98 ± 1.02 mm respectively; the average distance from SAA to three points of posterior SCC is 7.52±0.68 mm, 5.46±0.63 mm and 3.09±0.63 mm respectively Morphological changes of semicircular canals In our results, the biggest morphological change which is even unrecognisable is the double deformation of posterior SCC’s bony sheath We noticed a case that has a normal appearance of the bony sheath outside but a morphological change of the osseous SCC inside The osseous SCC has a normal size but the shape of a horseshoe, so the diameter of it is shortest in three SCCs Membranous SCC has clearly changes in morphology We noticed one ear has a morphological change of membranous SCC although its bony sheath has normal appearance This membranous SCC has the shape of hammock with the concave downward instead of upward like osseous SCC although its ampulla and posterior crus are normal 4.2 Relations between SCCs and adjacent structures The lateral sinus: has three different forms: flat, protruding (mild or severe)[113] Our study recorded flat form (18.75%), 23 mild protruding (71.88%) and severe protruding (9.37%) For ears with severe protruding lateral sinus, SCCs are obscured, we must drill the protruding bone of the lateral sinus to be able to open the SCCs The middle cranial fossa: has forms: flat, mild (protruding ≤ mm) and severe protruding (protruding > mm) There are 14 ears 21 with flat forms (43.75%); 15 ears with mild protruding forms (46.88%) and ears with severe protruding forms (9.37%) Flat skull base is very convenient when performing mastoid dissection; The mild protruding skull base causes difficulty for the surgeon, but with careful operation, complications usually not occur; but the severe protruding skull base will make it very difficult for the surgeon because it obscure part or all of the structure that needs to be approached, making all manipulations become more difficult; especially in deep structures The distance between the buttress and the bony cover of the SCCs Measure from the buttress to the midpoint of bony bone of each SCC, the results we obtained are: to the middle of bony cover of anterior SCC is average of 9.15 ± 0.96 mm, to the middle of bony cover of lateral SCC is average of 3.21 ± 0.83 mm, to the middle of bony cover of posterior SCC is average of 9.09 ± 0.76 mm This result shows that the distance from the buttress to bony cover of the lateral SCC is closest, the remaining distance to the superior and posterior SCCs is similar to each other In terms of anatomy, the buttress is near the short crus of the incus, and is very close to the lateral SCC; moreover, since the lateral SCC is protruding in the epitympanum, the distance from the buttress to the midpoint of the lateral SCC is the shortest This also warns the surgeon due to the close distance between the lateral SCC and the buttress (or the short crus of the incus) so when it is necessary to open the lateral SCC, the surgery have to be careful because just sliding the drill, it will be easy to injure the incus and possible consequences are profound hearing loss The distance between the third segment of the facial nerve and the bony cover of the SCC: our study determined the distance 22 from the third segment of facial nerve to the midpoint of the bony cover of SCCs with the aim to identify SCCs as well as to avoid facial nerve injury Our study recorded that the average distance from the third segment of facial nerve to the midpoint of the bony cover of lateral SCC is 3.66 ± 0.81 mm, the average distance to the midpoint of the bony cover of posterior SCC is 6.49 ± 1.21 mm Because the midpoint of the bony cover of lateral SCC curve and is closer to the second genu than the midpoint of the bony cover of posterior SCC; moreover, the bony cover of posterior SCC goes further than the lateral SCC; so the distance from the third segment of facial nerve to the midpoint of the bony cover of lateral SCC is shorter than the midpoint of the bony cover of posterior SCC Because the anatomical feature of the ampulla of the posterior SCC is deep, inferior to the third segment of facial nerve When intervening in the second genu or second segment of facial nerve, surgeons must pay attention to the lateral SCC because it is close to the lateral SCC; so when intervening in this area, we are very careful to avoid unnecessary injuries Perilabyrinthine air cells: Superior prelabyrinthine air cells: In dissection, we recorded 23 ears (71.87%) with many superior prelabyrinthine air cells (grade 0); the remaining ears (9 ears, 28.13%) have few superior prelabyrinthine air cells (grade 1), only have a few air cells in the superior and medial surfaces of the bony cover of superior SCC; there are not any ear without superior prelabyrinthine air cells (grade 2) Intralabyrinthine air cells: Our study recorded that there are 24 ears (75.0%) with many intralabyrinthine air cells (grade 0), while group of few intralabyrinthine air cells (grade 1) include ears (25.0%) and no ears without intralabyrinthine air cells (grade 2) 23 Supralabyrinthine air cells: In dissection, we noted that group of many these air cells (grade 0) was found in 26 ears (81.25%); group of few these air cells (grade 1) included ears (18.75%) and no ears without these air cells (grade 2) Retrolabyrinthine air cells: Our study recorded that group of many these air cells (grade 0) was found in 24 ears (75.0%), group of few these air cells (grade 1) included ears (18.75%) and there were ears (6.25%) without these air cells (grade 2) CONCLUSION Through analysis 32 ears from 16 cadavers of Vietnamese, we have conclusions: Anatomy of the semicircular canals: The morphology of the SCCs is almost the same between the clear and not clear group All the subarcuate arteries origines from the wall of anterior SCC and deflect to the posterior of the wall The membranous SCC is near to the osseous SCC and involve partial of the osseous SCC All ampulla of lateral SCC and anterior SCC contact to each other The median length of common crus in our study is 2.13 ± 0.60 mm The median distance between SAA and common crus of SCCs is 2.61 ± 0.61 mm The average width of anterior SCC’s bony sheath is wider than that of lateral and posterior SCC The average thickness of bony sheath at the ampulla position of posterior SCC is thicker than that of anterior and lateral SCC The mean diameter of ampulla of anterior and lateral SCC is larger than posterior SCC The mean diameter of middle point of posterior SCC is larger than that of anterior and lateral SCC The median length of anterior SCC is larger than that of the two others On the other hand, the mean distance from subarcuate artery to middle point of lateral 24 SCC and middle point of posterior SCC is almost equal The morphology of the SCC:t he study found that one SCC changed in double form; horseshoe SCC and one hammock SCC Relations between SCCs and adjacent structures: With buttress: The distance between the buttress and the bony cover of the anterior and posterior SCC is almost equal and larger than that of lateral SCC The distance between the buttress and the bony cover of the posterior SCC is larger than that of the lateral SCC Most of the middle cranial fossa is grade or grade and lateral sinus is grade ; while most of the perilabyrinthine air cells is grade and grade All of these structure affect to the pathway to approach the SCCs LIMITATION OF THESIS The number of ear dissected is only 32 ears, not representative for Vietnamese adult Not measure diameter’s mean of membrane semicircular canals RECOMMENDATION Research details about bony and membrane vestibular system: utricle, saccule, cochlear duct, vestibular duct, endolymphatic sac, cochlear, nerve, vessels of semicircular… by microdissection or pathology and application in examination and treatment for patient Application in ear surgery for treatment vertigo caused by vestibular system lesions such as: benign parosxymal positional vertigo, cholesteatoma affected semicircular canals, trauma to vestibular system, tumor of eight nerve … LIST OF RELATIVE THESIS AND RESEARCH Nguyen Thanh Vinh, Tran Ngoc Anh, Nguyen Hoang Vu, Le Gia Vinh, Pham Ngoc Chat (2018), “The distance between incus and SCC as seen in microdissection”, Vietnam Medical Journal, Vol 470, No 1, page 26-29 Nguyen Thanh Vinh, Tran Ngoc Anh, Nguyen Hoang Vu, Le Gia Vinh, Pham Ngoc Chat (2018), “The relation between semicircular canal and facial nerve as seen in microdissection”, Vietnam Medical Journal, Vol 470, No 2, page 39-42 Nguyen Thanh Vinh, Tran Ngoc Anh, Nguyen Hoang Vu, Pham Ngoc Chat (2018), “Semicircular canal Anatomy: Human cadaveric temporal bone study”, Journal of Military Pharmacomedecine, Vol 43, No 8, page 118-123 ... SCC Identify the length of the third segment of VII CN, reserve the buttress Open the aditus and attic, exopose the preattic The microsurgery through the cranial fossa: Open the skull by 4x5... structures: With buttress: The distance between the buttress and the bony cover of the anterior and posterior SCC is almost equal and larger than that of lateral SCC The distance between the buttress and... into bony sheaths at medial wall of semicircular canals (cutting along the orange zone), osseous canals are approached If we keep cutting osseous canals, membranous canals are exposed Our study