| Objective: To study the microsurgical anatomy signs of Retrosigmoid Suprameatal approach(RSSMA) by dissecting and dataing dry skull specimens and wet specimens of adult, to provide accurate anatomical data for the Retrosigmoid Suprameatal approach by quantifying related structures into the path of petroclival region. Provide theoretical guidance for increaseing surgical safety and operability, removeing the tumor greatly or even completely, reduceing the surgical trauma and postoperative complications.Materials and Methods: 10 wet craniums of adult, 10 dry skulls of adult. 10 formalin-fixed and different sex craniums (20 sides) of adult were perfuseed and simulated Retrosigmoid Suprameatal approach. Exposeing microstructures of petroclival region in layers and recording the steps detailed. The blood vessels and nerves around suprameatal tubercle were observed and measured under a microscope. The suprameatal tubercle and petrous apex were ground. The meckel cavity and tentorium cerebelli were cut. the exposed field of middle cranial fossa, upslope and trigeminal nerve were measured before and after the suprameatal tubercle and petrous apex were ground.1 The dry skullsThe skulls were cut along the level of upper edge of superciliary arch 1cm to remove roof bones, revealing the skull base bone structures. The bone structures in petroclival region were observed. transverse sulcus, sigmoid sinus, sulcus sinus petrosi superioris, impressio trigemini, aperture extreme aqueductus vestibuli, fossa subarcuata, suprameatal tubercle and petrous apex were especially recognized. The important structures related to Retrosigmoid Suprameatal approach in the area were detailed measured and shot, such as the distance asterion-superior tubercle, asterion-petrous apex, and the three dimensional parameter of superior tubercle and petrous apex. The back edge of sigmoid sinus sulcus and the lower edge of transverse sinus were marked out on the skull's surface. The bone window of Retrosigmoid Suprameatal approach was designed. The bone structures: superior tubercle and petrous apex were ground under a microscope. Measureing the three dimensional parameter of superior tubercle and petrous apex before and after they were ground.2 The wet craniumsThe craniums were simulated Retrosigmoid Suprameatal approach layer by layer. All important anatomical structures about Retrosigmoid Suprameatal approach were positioned , measured accurately, and then shot. The craniums that had been perfused with colored latex was fixed on Doro surgery head rest and designed base forward, almost to transverse sinus as the center of the inverted L-shaped incision. Do bone shape through asterion, the lower edge of transverse sinus and the posterior edge of sigmoid sinus were exposed, cerebral dura mater was radial cut and suspended. The fixed-brain tissue was hard and less flexible, the operative space was unlikely to be pulled out. So we often removaled of the lateral 1/3 of the cerebellum and Pressed it to the medial by brain spatula to expose petroclival region. The distance asterion-- suprameatal tubercle, asterion--petrous apex, suprameatal tubercle--abducens nerve, suprameatal tubercle--trigeminal nerve, suprameatal tubercle-- vestibulocochlear nerve were measured under a microscope. The nerve and blood vessel's source, distribution and mutual relations were observed, especially oculomotor nerve, trochlearis nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, superior cerebellar artery, anterior inferior cerebellar artery, posterior inferior cerebellar artery and pretrosal vein. The exposed field of middle cranial fossa, upslope and trigeminal nerve were measured by mobileing the microscope. The suprameatal tubercle and petrous apex were ground, the meckel cavity was cut. Open the tentorium of cerebellum since the edge along the ridge of petrous bone, then measure the field of middle cranial fossa, upslope and trigeminal nerve again. 3 Statistical AnalysisThe experimental results data applications SPSS16.0 statistical software for statistical analysis, the results calculated using mean±standard deviation (Mean±SD) said. trigeminal nerve and the surgical field exposure data measured were compared to independent-samples t test, P<0.05 as to determine standards is or isn't significant difference.Results: The distance of asterion--suprameatal tubercle is 53.4±4.6(49.7 --61.8)mm, asterion-petrous apex is 72.1±4.9(67.9--81.4)mm, suprameatal tubercle--outer margin of trigeminal impression is 9.7±0.9(8.7--11.2)mm, suprameatal tubercle--abducens nerve is 16.8±1.0(15.9--18.1), suprameatal tubercle--external aperture of aqueduct of vestibule is 20.1±0.8(19.2--21.3) mm, suprameatal tubercle--subarcuate fossa is 9.4±1.1(7.6--10.5)mm, suprameatal tubercle--petrous apex is 18.3±1.0(17.4--19.9)mm, the point trochlear nerve import tentorium cerebelli--petrous bone cristal is 4.8±1.1 (3.4--7.3)mm, facial nerve--trigeminal nerve is of 4.8±1.6(4.3--5.6)mm, facial nerve--glossopharyngeal nerve is 4.9±1.8 (4.4--5.5 )mm. The three dimension -al parameters of suprameatal tubercle are as follows: anteroposterior diameter is 9.8±1.7(8.3--12.8)mm, up and down diameter is 5.7±1.1(4.1--7.2)mm, trans diameter is 14.1±2.4(10.6--17.1)mm. The three dimensional parameters of petrous apex are as follows: anteroposterior diameter is 14.7±3.0(11.7--19.9) mm, up and down diameter is 17.1±1.1(15.9--18.7)mm, trans diameter is 19.3±1.1(17.5--20.9)mm. The anteroposterior diameter, trans diameter, up and down diameter of suprameatal tubercle could be ground completely, in order to not damage the trigeminal nerve and facial nerve, close to the nerve Department can stay thin bone to protect the nerves, all by the statistical test P<0.05, the difference was statistically significant. The anteroposterior diameter, trans diameter of petrous apex could be ground completely, the up and down diameter after petrous apex was ground is 9.8±1.7(7.9--12.5)mm, all by the statistical test P<0.05, the difference was statistically significant. The expand exposion of middle cranial fossa was 137.1±7.1mm2, while upslope was 83.8±7.3mm2 and the trigeminal nerve revealed a length of 9.3±0.6mm, compared with the surgery earlier by the statistical test were P<0.05, the difference was statistically significance. Superior cerebellar artery, superior cerebellar artery, posterior inferior cerebellar artery, pretrosal vein, sinus petrosus superior, oculomotor nerve, trochlearis nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve were able to identified.Conclusion: Compared with Retrosigmoid approach, the exposion of Retrosigmoid Suprameatal approach could be expanded to the middle of middle cranial fossa, the lateral of upslope, the trigeminal nerve in Meckel's cavity could also be seen. The Retrosigmoid Suprameatal approach is safe and effective approach to remove the tumor that main body is in posterior cranial fossa and the middle cranial fossa or Meckel's cavity is invaded, without the need to do supratentorial craniotomy at the same time.The vessels'course and branch in Petroclival region is variability, and the arterial's injury often cause serious complications. Therefore, the blood vessels on the surface of tumor should not be lightly electrocoagulation. We should confirm the blood vessels is the tumor's feeding arteries or bypass blood vessels under the microscope. Pretrosal vein is a group veins that drains blood from brainstem and the anterolateral of cerebellum, it can be cut off to facilitate the surgical field's exposion.Stripping superior tubercle and petrous apex is the key point of the approach. The superior tubercle could be ground completely, The up and down diameter of petrous apex was ground 7.3±1.2(6.2--8.2)mm could expose surgical field effectly.
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