Subtemporal Keyhole Approach: Anatomic Study And Quantitative Analysis

Part 1: Cranial cisterns opening in subtemporal keyhole approach to superior petroclival region:anatomic study and comparative analysisObjective:Quantitatively compare the exposure area and angle of approach to superior petroclival region in subtemporal keyhole approach before and after cranial cisterns opening.Methods:Study was carried out on 20 sides of cadaver heads.With use of a navigation system,the exposure area in dorsum sella and clivus,the ventrolateral area in brain stem around BA,the linear exposure of the posterior petroclinoid fold and BA trunk,and the approach angles to BA tip were evaluated.The length of oculomotor cistern and trochlear cistem,distance of oculomotor and trochlear porus,linear exposure of trigeminal nerve and the angle to the most inferior medial point in clivus were also measured.Results:The exposure area in dorsum sella and clivus(136.7±19.8mm~2),the ventrolateral area in brain stem around BA(222.8±25.8mm~2),the linear exposure of the posterior petroclinoid fold(11.5±0.6mm) and BA trunk(10.3±2.0mm),and the approach angles in the vertical axis to BA tip(13.7±1.7°) were significantly greater after cisterns opening.But the approach angles in the horizontal axis to BA tip(24.5±1.1°,24.7±0.8°) were no statistical differences.The length of oculomotor cistern and trochlear cistern,distance of oculomotor and trochlear porus,linear exposure of trigeminal nerve and the angle to the most inferior medial point in clivus were 6.7±1.3mm,10.7±2.4mm,9.6±2.3mm,15.8±1.4mm and 13.0±1.5°respectively.Conclusion:The exposure area and the angle of approach in superior petroclival region can be increased after cranial cisterns opening. Part 2: Posterior subtemporal keyhole approach combined with transchoroidal approach to the region around ambient cistern:anatomic study and quantitative analysisObjectives:To study microsurgical anatomy of the posterior subtemporal keyhole approach combined with transchoroidal approach to the region around ambient cistern and to quantitatively measure the exposure areas of inferior and superior part of the ambient cistern using these two approachs respectively.Methods:We firstly determined the proper location of craniotomy of the posterior subtemporal keyhole approach combined with transchoroidal approach on 16 sides of cadaver heads and then studied location of the confluent point of Labbe's veins within such craniotomies.We used the navigation system to quantitatively measure the exposure distance of the trigeminal nerve,the exposure distance of P2a from the posterior communicating artery to inferior border of the parahippocampal gyrus and the linear exposure on the lateral surface of brainstem in posterior subtemporal keyhole approach.We also quantitatively measure the distance between the inferior temporal sulcus to the tentorium,the distance between the inferior choroidal point to the tip of temporal horn and the linear exposure on the lateral surface of superior part of mesencefelon with or without caudal retraction of the body of hippocampus in the posterior transchoroidal keyhole approach.In addition,we provided the exposure percent of P2p in the posterior transchoroidal keyhole approach.Results:The inferior border of zygomatic arch,posterior border of auricle,the meeting point between the superomastoid crest,temporal squamous suture and parietomastoid suture could be used as the best surface or bone landmarks to find the proper location of the craniotomy.The confluent point of Labbe's veins located posterior to the posterior border of the craniotomy in 68.75%cases,on the posterior border in 18.75%, and within the craniotomy region in 12.5%.In the posterior subtemporal keyhole approach,the exposure distances of the trigeminal nerve were 10.02±0.76mm,the exposure distances of the P2a segments were 16.32±2.02mm,the linear exposure distances of mesencephalon along the lateral mesencephalic sulcus superior to the point A(the junction point of pontomensecephalic sulcus and lateral mesencephalic sulcus) were 7.5±0.19mm,the linear exposure distances of pons along the lateral mesencephalic sulcus inferior to the point A were 11.04±0.27mm,the linear exposure distances of branstem along the pontomensecephalic sulcus anterior to the point A were 15.72±0.52mm,the linear exposure distances of branstem along the pontomensecephalic sulcus posterior to the point A were 10.16±0.38mm.In the posterior transchoroidal keyhole approach,the distances between inferior temporal sulcus and tentorium were 14.6±0.43mm,the distances between the inferior choroidal point and the tip of temporal horn were 8.62±0.23mm,the vertical distances between the superior border of fimbria and the lateral geniculate body without caudal retraction of hippocampus body were 5.28±0.46mm,the vertical distances between the superior border of fimbria and the P2p segment without caudal retraction of hippocampus body were 3.8±2.1mm,the vertical distances of mesencephalon and metathalamus(from the lateral geniculate body along the lateral mesencephalic sulcus to the superior border of fimbria) with caudal retraction of hippocampus body were 11.18±0.57mm,the linear exposure distances of P2p and P3 segment with caudal retraction of hippocampus body were 12.14±1.88mm.The P2p segments could be exposed in 93.75%cases using the posterior transchoroidal keyhole approach.Conclusions:Some surface or bone landmarks are useful to dertermine the proper location of craniotomy of the posterior subtemporal keyhole approach combined with transchoroidal approach.The posterior subtemporal keyhole approach combined with incision of tentorium and retraction of quadrangular lobule is suitable to expose inferior part of ambient cistern,superior part of cerebellopontine cistern,and related structures.Whereas,the posterior transchoroidal-transsulcus keyhole approach is suitable to expose superior part of ambient cistern and related structures,especially the P2p segments.The midpoint of the rounded medial edge of the parahippocampal gyms,which can be easily recognized on coronal MRI images,provides important landmark to help choose appropriate approaches to the region around ambient cistern.