Correlation of high-resolution computed tomography and gross anatomic sections of the temporal bone: Part I. The facial nerve.
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Abstract:
Detailed anatomic analysis of the human temporal bone has been made possible by correlating high-resolution computed tomography (CT) with gross anatomic sections. Serial CT scans of isolated temporal bones were obtained in the transaxial (horizontal), coronal, and sagittal planes at 1.5-mm intervals. The temporal bone was sectioned at 2.0-mm intervals in planes parallel to the CT scans. Based on a correlation of these sections, the facial nerve canal was divided into four segments and the planes in which each is best observed are described and illustrated. The first segment in the internal auditory canal is best visualized in the sagittal plane, the labyrinthine segment and geniculate ganglion in the coronal and transaxial planes, the tympanic portion in the sagittal plane, the genu, between the tympanic and mastoid portion, in the sagittal plane, and the mastoid portion and the stylomastoid foramen in the coronal and sagittal planes.Keywords:
Geniculate ganglion
Facial canal
Jugular foramen
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Objective To re-evaluate landmarks for facial nerve in middle ear surgery through temporal bone dissection and facial nerve surgery. Methods Some relative landmarks were found through 44 facial nerves dissection in cadaver and 106 cases of facial nerve decompression surgery. Results （ 1 ） Landmarks for vertical segment of the facial nerve： the vertical line in combined point between posterior and middle 1/3 horizontal semicircular canal clews file posterior edge of facial nerve; the prolong line of superior radian of incus short process clues to the anterior edge of the facial nerve, the facial nerve and horizontal semicircular canal are almost in the same plane. （2） Landmarks for horizontal segment of the facial nerve ： the facial nerve tracks forward inferior to short process of incus and anterior to horizontal semicircular canal carina in 30 angel. The facial nerve, locating posterior and superior to cochleariform process and parallel with it, forms the step of middle-superior tympanic cavity and tracks forward to geniculate ganglion. （3） location of geniculate ganglion ： The same distance prolong line of stapes head to cochleariform process clues to geniculate ganglion. （4） Location of the chorda tympani nerve ： chorda tympani nerve, leaving tympanic sulcus at 3 clock of bone canalin left ear and at 9 clock of bone canalin right ear, tracks forward along tympani sulcus and then cross between long process of incus and manubrim. It lies in the border of pars tensa and pars flaccida and is about 5-8 mm from the stylomastoid foramen to where the chorda tympani nerve leaves the facial nerve. There is no difference of facial nerve structure in temporal bone dissection and in surgery. Confusions The fixed landmarks of middle ear are the frame of reference of facial nerve, in which horizontal semicircular canal is most invariable; and the safety of surgery will be improved by the reference of the facial nerve.
Key words:
Facial nerve; Temporal bone; Microsurgery
Geniculate ganglion
Incus
Sulcus
Mastoid process
Facial canal
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Detailed anatomic analysis of the human temporal bone has been made possible by correlating high-resolution computed tomography (CT) with gross anatomic sections. Serial CT scans of isolated temporal bones were obtained in the transaxial (horizontal), coronal, and sagittal planes at 1.5-mm intervals. The temporal bone was sectioned at 2.0-mm intervals in planes parallel to the CT scans. Based on a correlation of these sections, the facial nerve canal was divided into four segments and the planes in which each is best observed are described and illustrated. The first segment in the internal auditory canal is best visualized in the sagittal plane, the labyrinthine segment and geniculate ganglion in the coronal and transaxial planes, the tympanic portion in the sagittal plane, the genu, between the tympanic and mastoid portion, in the sagittal plane, and the mastoid portion and the stylomastoid foramen in the coronal and sagittal planes.
Geniculate ganglion
Facial canal
Jugular foramen
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Objective To validate the feasibility and security of the facial nerve decompression through transmastoid extralabyrinthine subtemporal approach To get the data about this approach. Methods Under the operation microscope 20 adult temporal bones and 20 sides of cadaveric skulls were dissected through transmastoid extralabyrinthine subtemporal approach . Various distances of facial nerve and key mark were measured. Results 20 adult temporal bonesSD 1 the distance between choleariform process and the angle point of proximal end to distal end in geniculate ganglion was3.80±0.72 mm. 2 the length of horizontal segment was 11.14±0.73 mm.3 the length of labyrinthine segment was 3.35±0.68 mm. 4 the distance between basal turn of the cochlea and the labyrinthine segment was 1.04±0.14 mm. 5 the tegmen thickness in most distal point of labyrinthine segment was 2.82±0.64 mm. 6the shortest distance between facial canal in horizontal segment and the lateral semicircular canal was 1.27±0.21 mm.7the distance between facial canal in horizontal segment and middle point of anterior semicircular canal ampulla was 2.47±0.21 mm. 20 sides of cadaveric skullsSD 1the distance between long process of incus and horizontal segment was 2.33±0.26 mm. 2 the distance between short process of incus and facial nerve was 3.06±1.01 mm. 3 the distance between capitulum of malleus and the horizontal segment was 2.17±0.87 mm. 4 the distance between capitulum of malleus and tegmen tympani was 2.31±0.87 mm. 5 the length of vertical segment was 16.27±0.58mm. 6the angle of proximal end to distal end in geniculate ganglion was 74.3±2.47°. 7 7the angle of pyramidal segment was 110.2±8.30°. Conclusion This study provided the safe scope manipulation room and the angle of the transmastoid extralabyrinthine subtemporal approach and these data can be reference for the surgeon.
Geniculate ganglion
Incus
Cadaveric spasm
Facial canal
Malleus
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Facial nerve is the main motor supply to the part of facial skeleton system responsible for expressions. The reported rate of iatrogenic injury to the facial nerve in primary mastoid surgeries was 0.6% to 3.7%. Temporal bone is one of the most complex anatomical parts of human body. A variety of facial nerve courses has been described in literature. Normally, horizontal segment of the facial nerve traverses from geniculate ganglion to second genu which is usually situated medial and inferior to lateral semicircular canal. From here it passes posteriorly and laterally along the medial wall of the middle ear. Mastoid or vertical segment extends from the second genu to stylomastoid foramen deep to tympano-mastoid suture line from where the nerve exits out of the temporal bone. During our endoscopic dissection we encountered a grossly anomalous course of facial nerve in which after turning at second genu, the nerve curves posteriorly and lies in the floor of mastoid cavity and traverse’s its whole length of mastoid and instead of moving out of foramen it travels towards sinus plate and then takes another (3rd) turn to travel anteriorly towards the tip of mastoid from where it finally exits.
Geniculate ganglion
Sigmoid sinus
Facial canal
Sinus (botany)
Jugular foramen
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Objective To study the anatomy features and the location of the facial nerve during the temporal approaches.Methods The mastoidotympanectomy,the facial recess approaches,the facial nerve decompression,the middle cranial fossa approach and the infrelabyrine approach were simulated on 15 adult cadaveric specimens(30 sides).The topographical features and the relationship of facial nerve with the surrounding structures were explored.30 dry temporal bones were cut along the facial canal,for exploring the relationship of the facial canal and the surrounding structures.Results(1) The distance from the vertical part of the facial nerve to the glomus was about(3.58±1.33)mm,and to the sigmoid sinus(6.42±2.65)mm.(2) The air cells of lateral facial recess was found in 26 cases(86.67%),which is helpful for locating the facial recess and the facial nerve.(3) The lateral lap of the facial nerve was under the point between the posterior and middle 1/3 of the lateral semicircular canal about(1.70±0.33)mm.The vertical line connected this point to the anterior extremity of the conker's crista represented the vertical part of the facial nerve.(4) Geniculate ganglion located anteriorly to the cochleariform process about(2.48±0.23)mm.(5) The fundus of internal acoustic meatus was in the anterior aspect of the lateral point of the eminence of superior semicircular.The ramus lacrimales nervi petrosi superficialis majoris was the convenient signal for locating the labyrinthine segment of the facial nerve.Conclusions It is valuable for locating the facial nerve through its relationship with the surrounding structures,the topography and the features of substantia ossea surrounding the facial nerve,during the temporal approach.
Facial canal
Sigmoid sinus
Geniculate ganglion
Middle cranial fossa
Cadaveric spasm
Mastoid process
Meatus
Posterior Semicircular Canal
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Aberrant pathways of the facial nerve through the temporal bone are related to the severity and type of congenital ear deformity. A facial nerve crossing the middle ear cavity with no bone covering cannot be shown by radiologic techniques but may be inferred from: (1) abnormalities of the first part of the facial nerve canal in the region of the geniculate ganglion, (2) absence of the Fallopian canal, (3) absence of the oval window, (4) absence of the pyramidal eminence, and (5) an exit foramen through the floor of the middle ear. Demonstration of these features is discussed with tomographic and histologic correlation in 2 cases, tomographic and surgical correlation in 31.
Geniculate ganglion
Facial canal
Oval window
Jugular foramen
Foramen
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The morphology of macrosections of the normal adult temporal bone were correlated with high resolution computed tomographic findings of 6 axial, coronal and sagittal sections.1) The micro-structure of the temporal bone was almost perfectly demonstrated by axial, coronal and sagittal sections. Axial sections provided more information on the structure of the temporal bone than did coronal sections. Sagittal sections gave little information.2) Axial sections effectively demonstrated the facial nerve canal (labyrinthine segment-geniculate ganglion-tympanic segment), majorr petrous nerve canal, short process of the incus, stapes (especially foot plate), and relationship of the malleus head to the incus body.3) Coronal sections were useful in demonstrating the cochlear aqueduct, facial nerve canal (mastoid segment), crista transverse, tensor tympani and ossicle (incus body, incus long process, stapes head, stapes crus).4) Sagittal sections were useful in demonstrating, the facial nerve canal (tympanic segment, mastoid segment), vestibular aqueduct, and the relationship of the malleus head to the incus long process.5) To understand the complicated structure of the temporal bone it was necessary to perform CT in many dimensions. The most useful section was the axial. Coronal and sagittal sections were sometimes useful.
Incus
Malleus
Geniculate ganglion
Facial canal
Vestibular aqueduct
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To describe the anatomic variations of the subarachnoid space (SAS) in the facial nerve canal from human temporal bone specimens.The SAS in the facial canal usually is assumed to terminate in the petrosal segment of the canal. This temporal bone study indicates that in 12% of temporal bones the SAS extends laterally into or beyond the tympanic segment of the facial canal.Histologic sections through the petrosal and tympanic segments of the facial canal were examined by light microscopy in 1 fetal (30 weeks) and 163 adult human temporal bones. The arachnoidal membrane of the SAS was judged to fall into three types according to its lateral extension in the fallopian canal.One hundred forty-four (88%) of the adult temporal bones contained an SAS limited to the petrosal fallopian canal (type I). Thirteen temporal bones (8%) demonstrated an SAS that extended into the tympanic or geniculate portions of the facial nerve (type II). There were six temporal bones (4%) in which the SAS extended lateral to the tympanic facial nerve or into a separate bony compartment (type III).Most (88%) temporal bones contain an SAS that is limited to the petrosal fallopian canal. In 12% of temporal bones, however, the SAS may extend laterally in the fallopian canal and present clinically as an asymptomatic enlargement of the canal by computed tomography or as cerebrospinal fluid otorrhea.
Facial canal
Geniculate ganglion
Subarachnoid space
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The middle cranial fossa approach to lesions of the geniculate ganglion and internal auditory canal preserves cochlear function and affords access to the lateral internal auditory canal. The labyrinthine portion of the facial nerve tends to course near the basal turn of the cochlea, just beneath the middle cranial fossa floor, and is usually dissected in this approach. To determine the distance from the labyrinthine portion of the facial nerve to the basal turn of the cochlea, measurements were obtained in the temporal bones of 24 subjects (48 ears) 9 to 76 years of age. These subjects had no history of facial nerve or ear disease, and had normal audiograms. The distances ranged from 0.06 to 0.80 mm, with 21 of 24 right ears (87.5%) showing distances less than the standard size of the smallest diamond drills (0.6 mm), and 18 of 24 (75%) less than 0.5 mm. Incidental note is made of the distance from the geniculate ganglion to the ampulla of the superior semicircular canal, which ranged from 2.06 to 4.88 mm in the 48 specimens. These measurements can serve as guidelines for the surgeon working in the middle cranial fossa.
Geniculate ganglion
Middle cranial fossa
Facial canal
Spiral ganglion
Internal auditory meatus
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Citations (19)
Objective:To study the sectional anatomy and the high-resolut ion computed temography of facial nerve in the temporal bone and provide anatomi cal data for image diagnosis and operation treatment of this area. Methods:15 no rmal adult cadaver heads were scanned taking canthomeatal line(CML) as basic lin e to obtain images of CT (1.0 ㎜ in depth ,1.0㎜ in thickness ). And then ,those samples were used to made continuative thin sections (1.0 ㎜ in thickness ) tak ing temporal bone as the center. Thin sections were compared with CT scans, and found out all the intratemporal regions of facial nerve, auditory ossicle, osseo us semicircular canals, vestibule, cochlea et al. Results:(1)The geniculate ga nglion (GG) was in the layer of lateral semicircular canal .(2)Cochleariform pro cess was in the same layer with malleoincudal articulation . (3)Pyramidal eminen ce laid in the same layer with promontory . Conclusions:The labyrinthine facial nerve, GG and the first part of horizontal facial nerve present a reverse V-shap e in the layer of lateral semicircular canal. Vertical part of facial nerve loca tes deeply in the facial recess. Facial recess, pyramidal eminence, and sinus ty mpani look like a
Geniculate ganglion
Facial canal
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