| Objetive: To supply relevant anatomy basis for transpetrous presigmoid approach by the way of measuring the distance among the important bone structures of petrous bone of cadaveric adult heads and combining CT thin tomographic scan, and reduce the emergence of operation complications.Method: To 8 adult dry skulls, outlined bony labyrinth and facial nerve canal, but preserving partial posterior petrous wall of vestibular aqueduct, common crus, posterior semicircular canal and the petrous bone ridge as measurement marks. Making use of slide gaud and other tools to measure the distance between the relevant bone marks and function structures, such as the petrosigmoid intersection, the vertical segment of facial nerve canal, the most posterior portion of the posterior semicircular canal, the external aperture of the vestibular aqueduct, the internal auditory meatus, common crus, posterior petrous wall, the surface of mastoid process, the anterior wall of sigmoid sinus and the infralabyrintheine air cells.Ten 10% formaldehyde fixed cadaveric adult heads whose arteries had been injected with colored latex were performed CT thin tomographic scan(layers of thick 0.65mm) of petrous bone, and measured the distance between the relevant bone marks and function structures,we can define the range and depth of drilling petrous bone, comprehend the gasification of mastoid and whether or not anterior locating of sigmoid sinus.Simulating transpetrous presigmoid approach, we open the cranium with double bone valves, at first form the temperal-occipital bone valve paralleling middle cranial fossal, then form and include bone slice with superficial mastoid process with the milling cutter, expose the transverse sinus, sigmoid sinus and mastoid emissary vein, drill inwards paralleling the posterior petrous wall until the the range and depth of drilling petrous bone defined before operation, the dura incision is the " T" shape, open the dura of superior cerebellum tentorial paralleling the transverse sinus and middle cranial fossal, open the dura of posterior cranial fossal paralleling the anterior edge of sigmoid sinus until the superior jugular glomus, deligate and amputate the superior petrosal sinus at the point of 0.5cm before the intersection of the superior petrosal sinus and sigmoid sinus, so make the dura incision of superior and inferior cerebellum tentorial connect, cut off cerebellum tentorial inwards follow the edge of petrous bone at the amputation of the superior petrosal sinus, towards the edge of cerebellum tentorial behind the joint of trochlear nerve and dura, lift the temporal lobe gently, pull the transverse sinus, sigmoid sinus and cerebellum tentorial backwards, expose the petroclival region. Observe the operation exposure, measure relevant structures and take pictures. CT thin tomographic scan of petrous bone were performed after operation, observe and measure the range of posterior petrous wall drilling and adjacent structures, compare the range of real drilling petrous bone with which of the preoperative design, comprehend the reliability and possibility of the preoperative design.Result: 1. Microanatomy studying1.1 The distance from PS to PNA was 10.48±0.42mm, to the external aperture of the vestibular aqueduct was 17.26±0.86mm, to the posterior edge of the internal auditory pore was 27.64±1.20mm, to the common crus was 20.56±1.54mm, to the infralabyrintheine air cells was 23.58±3.72mm.1.2 Observation and measurement of facial nerve canal: according to its journey the facial nerve canal can be divided into: labyrinth segment(vestibule segment); tympanic segment (horizontal segment);mastoid segment(vertical segment). The length of the labyrinth segment was 3.22±0.92mm, it was the narrowest segment of the whole facial nerve canal. The length of the horizontal segment was 11.68±1.52mm. The length of the vertical segment was 13.88±1.82mm. The vertical segment has close relationships with the operation approach of the study, the distance from its lateral wall to the petrosigmoid intersection was 11.34±1.92mm, to Helen ridge was 15.02±1.28mm, the distance from its posterior wall to the posterior pyramidal wall was 7.52±1.36mm, to the anterior edge of sigmoid sinus was 7.01±1.52mm.1.3 Observation and measurement of bony labyrinth: bony labyrinth is made up of vestibule, bony semicircular canal and cochlea. The distance from the external aperture of the vestibular aqueduct to PNA was 1.78±0.92mm, to the posterior edge of the internal auditory pore was 10.46±1.48mm, to the anterior edge of sigmoid sinus was 8.26±2.42mm, to the petrous bone ridge was 8.56±1.54mm. The span of the posterior semicircular canal was 9.56±1.28mm, The height of the posterior semicircular canal was 7.40±1.16mm, the distance from PNA to the posterior pyramidal wall was 1.42±0.38mm, to the petrous bone ridge was 2.88±1.12mm, to the posterior edge of the internal auditory pore was 10.12±1.06mm, to the surface of mastoid process was 13.86±1.98mm, to the anterior edge of sigmoid sinus was 9.82±1.91mm.1.4 Resection range of the posterior and lateral part of petrous bone: the distance from PNA to the surface of mastoid process was 13.86±1.98mm, the lateral part of petrous bone could be cutting off safely at the range, since there were not important functional structures in this region. The range from the most posterior portion of the posterior semicircular canal to the anterior wall of GSS varies greatly, it could be determined the distance according to the image examination. Exposing the infralabyrintheine air cell was helpful to outline the posterior semicircular canal. If needing drilling further the bone matrix between the most posterior portion of the posterior semicircular canal and the posterior edge of the internal auditory pore, it must be quite prudent at the time, otherwise will damage the inner ear, will lead to complications.1.5 The ranges of the exposure of operation: pulled cerebellum and sigmoid sinus backward to expose the anterior part of the sigmoid sinus, many structures were exposed of trigeminal nerve, facial-cochlear nerve, anterior inferior cerebellar artery, lower cranial nerve, anterior and lateral regions of the pons; Lead to open the temporal lobe upwards, the supratentorial area of the cerebellum were exposed of oculomotor nerve , trochlear nerve , posterior cerebral artery, superior cerebellum artery; Cut off parts of cerebellum tentorial, lead to open the temporal lobe further, many structures were exposed clearly of olfactory nerve, optic nerve, optic chiasma, pituitary stalk, internal carotid artery, posterior communicating artery, posterior cerebral artery, superior cerebellum artery, basal artery.2. Image study of CT thin tomographic scan of petrous bone: the width of GSS was 11.44±1.79mm, the depth of GSS was 5.27±1.93mm, the distance from the lateral wall of GSS to the surface of mastoid process was 10.38±3.90mm, the distance from the anterior wall of GSS to the posterior wall of external auditory meatus was 13.66±2.18mm. the distance from PNA to the surface of mastoid process was 13.44±1.86mm, to the anterior edge of sigmoid sinus was 9.65± 1.76mm, to the posterior pyramidal wall was 2.92±0.98mm. In the 10 examples(20 sides), gasification type 15 sides (75% ) of mastoid process, not gasifying type 5 sides (25% ). Junglar vein bulb lies in level above OML plane accounting for 35% (7/20).Conclusion: 1. The distance from PNA to the surface of mastoid process could guide drilling the lateral wall of petrous bone safely.2. The distance from PNA to the anterior wall of GSS and the posterior wall of petrous bone could guide drilling the posterior and inferior wall of petrous bone safely, and the infralabyrintheine air cell was the important marks which could guarantee for drilling the posterior wall of petrous bone safely.3. Bone marks of petrous bone surface combined CT thin tomographic scan could guide drilling the petrous bone safely and effectively, and prevent damaging its important function structures inside.
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