Microanatomical Study Of The Frontotemporal-zygomatic Arch-subtemporal Approach

Objective:By changing the design of the incion and simulating the frontotemporal--zygomatic arch-subtemporal approach,we took a micro- -anatomical study of the related structures and explored the indications and operatation notes of this approach .The ultimate goal was to provide anatomical data for clinical work.Method: Ten formalin-fixed,cadaveric adult heads were soaked in hydrogen peroxide and alcohol successively,anatomied the neck blood vessel, intubated and washed,perfused with color latex,then we began simulating surgery approach.We explored the ways of avoiding injury by measuring the site ralationship of temporal branch of facial nerve and superficial temporal artery. After retractored the scalp flap,cut off the zygomatic arch,separated the temporal muscle, we explored the ways of reducing temporal muscle injury.By removing the temporal bone flap,we measured the distance changes of closing to the bottom of middle cranial fossa and medial line.We observed and measured the data of neurovascular structures by analoging the subdural approach.After simulated epidural approach and observed structure,we grinded off petrous apex,measured the area and the position relationship of surrounding structure of it,explored the attention notes of grinding.We compared the area date of both sides by using small sample paired t-test and determined whether there were differences between both sides according to significance level ofα=0.05.Results: About (26.6±3.7)mm above zygomatic arch and (11.3±1.5)mm in front of tragus,Superficial temporal artery issued its frontal branch and top branch. Frontotemporal branch of the facial nerve always goes in the front of the frontal branch of superficial temporal artery.The horizontal distance between the two was (6.0～13.2)mm . The maximum removal length of zygomatic arch was (29.5±3.3)mm.By sawing zygomatic arch,retractoring temporalis muscle and grinding the lateral bone of greater wing of sphenoid bone,the distance to the middle line could be shortened (17.8±2.7)mm and about (14.5±2.3)mm close to the skull base.At the same time, the traction of temporal lobe could be reduced significantly.Posterior communicating artery always starts from lateral wall of the final segment of the internal carotid artery (C1),walks along the pool and toward the rear and inside direction.Along the way,it issues a number of perforating arteries.Among those arteries,tuberothalamic artery appears constantly and has close relationship with it. The length of PcoA was (13.8±3.5)mm and the diameter is (1.8±0.3)mm.Oculomotor nerve starts from the interpeduncular cistern in front of the midbrain,goes through the posterior cerebral artery and the superior cerebellar arteries,obliques toward the external direction and joins the lateral wall of the cavernous sinus about (10.8±1.5)mm behind the anterior clinoid process.The length of it′s pool segment was (19.5±1.7)mm.Trochlear nerve starts from the bottom of the inferior colliculus of the middle brain,goes forward around the outside of the cerebral peduncle,and through the tentorial edge and the superior cerebellar arteries ,joins the lateral wall of the cavernous sinus after the anterior clinoid process about (22.8±3.1)mm.The distance between the points whereⅢandⅣnerves goes into the tentorial edge was about (9.6±1.2)mm.In the lateral wall of cavernous sinus, the nerves arrangement from top to bottom was oculomotor nerve,trochlear nerve,ophthalmic nerve,and maxillary nerve.Then it formed four triangles:the paramedial triangle,the Parkinson′s triangle,the Mullan′s triangle and the lateralmost triangle.The traveling of trochlear nerve changes frequently.Areas of four triangles we measured were (35.8±7.1)mm~2,(60.7±11.5)mm~2,(37.5±9.4)mm~2,(29.3±8.5)mm~2.By opening the Parkinson′s triangle,we could see the posterior chamber and inside chamber of the cavernous sinus, the vertical segment and behind bend of interal carotid artery and the branches of meningohypophysial artery. Horizontal petrous ICA goes under the greater superficial petrous nerve, the length of it was (19.6±2.1)mm,and the diameter was (4.3±0.5)mm.The distance from its behind edge to petrous ridge was (10.3±0.9)mm, the vertical distance from foramen spinosum to the front edge of it was (7.1±0.6)mm and the distance between its knee segment and the GSPN foramen was (6.4±1.2)mm. Cochlea locates in the triangle which was composed by the internal auditory canal, the geniculate ganglion and the knee of ICA petrous segment.It also lies in the outside of the line from the anterior wall of the internal auditory canal to the GSPN foramen.The thickness of its surface bone was (6.2±0.8)mm,the length from its after edge to the anterior wall of the internal auditory canal was (12.7±0.9) mm.From the inner edge of it to the trigeminal impression, the length was(12.1±1.3)mm.Internal auditory canal usually locates on the bisector of the angle which was made by arcuate uplift and extension line of GSPN,and the inner wall of the internal auditory canal was cortical bone, its thickness was (1.2±0.3)mm.The grinded height of petrous apex near to internal auditory canal was (8.3±0.4)mm,the grinded height of the middle segment of petrous apex was (10.2±0.3)mm,and the grinded height of trigeminal impression was (4.1±0.2)mm.By grinding petrous apex,we formed a quadrilateral region which was formed by following four points:the anterior wall of internal auditory,the GSPN hole, the back edge of broken hole and the petroclival fissure.After opened the dura mater of posterior fossa and tentorium cerebelli,we could see the ventrolateral part of pons,ahead and upper segment of cerebellum, trigeminal nerve root, SCA,AICA and its branches,and so on.The average area of the petrous apex we grinded was 190.6㎜ 2.Area of left side and right side were calculated separatly, the left was 204.5mm~2,while the right sides was 176.7mm~2.Both sides paired t test,t=15.799,p <0.05,grinded area of the left and right sides could be believed that there were different,and left area was larger than the right.Conclusion:1 By Cutting in the temporal side of superficial temporal artery,exposuring the back end of zygomatic arch,separating between the superficial layer and deep layer of deep temporal fascia,the frontotemporal branch of the facial nerve and superficial temporal artery could be protected completely.2 We can mark the frontal branch of superficial temporal artery as the protection of the frontotemporal branch of facial nerve in the temporal related operation.3 By cutting temporal muscle in front of ears sharply, separatting the temporal muscle retrogradely from subperiosteum,fixing it by drilling holes in the superior temporal line,avoiding excessive burning,the temporal muscle atrophy after operation could be reduced effectively.4 After moved the zygomatic arch, retracted the temporal muscle,the distance to the inner and skull base can be shorted, therefore reduces the traction on the temporal lobe significantly.5 Surgery involving the posterior communicating artery should identify its perforating brainches carefully,especially the tuberothalamic artery.6 Separating from the gap of the two layer in the lateral wall of cavernous sinus and looking its triangular structure directly can help us plan the surgical approach of it.7 Mastering the structure around the petrous apex and marking the GSPN foramen as a sign of protecting petrous internal carotid artery segment and internal ear can help us reduce the grinding damage.8 This approach is applicable for the surgery of the bottom and rear part of the middle cranial fossa, adjacent to cavernous sinus, the lateral of midbrain, ambient cistern, ride middle and posterior fossa or confined to the petroclival region and P2 segment aneurysms. For the lesions which locates after or follow or outside the internal auditory canal, this approach should not be adopted.