The Microanatomic Study Of The Petroclival Region Via Different Endoscope-assisted Keyhole Approaches

Background and objective:Peroclival diseases remain one of the most challenging to treat surgically due to their location deep within the skull base and their association with multiple neural and vascular structures.Over the years,many skull base approaches have been described that are meant to improve resection and decrease patient morbidity.Central to all approaches to the petroclival region is the ability to visualize the tumor and the important neural and vascular structures that these tumors are adjacent to, compressing and encasing.Recently,different keyhole approaches have been developed to access this region.Increased evidences have been demonstrated that most of neural and vascular structures in peroclival region can be exposed sufficiently via various keyhole approaches,including temporal keyhole approach, suboccipito-retrosigmoidal keyhole approach and retro-condylar keyhole approach. Some of diseases in peroclival region can be removed in success via these keyhole approaches.Moreover,the usage of keyhole approach can avoid effectively the pulling of cerebular tissue with minimal injury.However,limited to direct visual angle of operating microscope,it is still difficult to exposure the entire of the nerves and blood vessels within the peroclival region,as well as the ventral aspect of the brain stem.With multiple visual angles,the endoscopy can provides a clear view on the entire site of the operation,especial to the deep structures.So,the usage of endoscopy should be providing a potential to solve questions abovementioned. Although numerous studies have been performed on endoscopic anatomy of different keyhole approaches,excluding the retro-condylalr keyhole approach, ambiguities in operation of keyhole approaches were still existed.Moreover,the previous studies were excessively focused on measurement of related structures. Undoubtedly,it is difficult to measure the distances among the structures,although the accurate data is helpful to surgical treatment.In our opinion,it will be practical to explore the endoscopic anatomical features of structures in peroclival region, including the location of the structure,position change under different visual angles of endoscope and etc.So,the endoscopic anatomical features of the peroclival region via temporal keyhole approach,suboccipito-retrosigmoidal approach and retro-condylar keyhole approach were observed in present study based on the previous studies.Exposure scopes of peroclival region with endoscope or operating microscope were emphasized.Additionally,the main points about the skin incision, bony window formation and insert of endoscope were focused on in order to provide accurate anatomical basis for clinical applications.Methods:1.20 adult cadavers head fixed with formalin and injected with colored emulsion were used in present study.2.Mimicry of subtemporal keyhole approach:The vertical skin incision was performed 1.0 cm anterior to the external auditory canal and 5cm in length.The lower board of skin incision was above inferior margin of zygomatic arch.After the exposure of temporal squama sufficiently,2.5cm bony window were prepared. The petrous apex was stripped based on identification of related bony structures. The superior margin of zygomatic arch was removed to adapt the observation using operation microscope.3.Mimicry of suboccipito-retrosigmoidal keyhole approach:A postauricular skin incision was carried out,which was C shape and below to the superior margin of auricle and above to the level of intertragic incisures.After the skin flap dissection and outlines of mastoid process and osseous labyrinth in turn,a 3cm×4cm bony window was prepared.4.Mimicry of the retro-condylar keyhole approach:A skin incision was performed posterior to mastoid process,which was S in shape and 7cm in length.The muscles in the occipital region and nuchal region were dissected carefully to exposure the V3 segment of vertebral artery.A bony window was designated to 3cm in diameter for microscopic observation,lateral margin of great occipital foramen medially,medial board of sigmoid sinus laterally,and posterior margin of occipital condyle inferiorly.As to endoscopic observation,the bony windows were diminished to 2cm in diameter and moved backward.5.Observation with microscope:The structures in the perclival region were observed with operating microscope and recorded.6.Observation with endoscope:The structures in the perclival region were observed with endoscope.7.Related data were obtained and analyzed with SPSS.Results:1.Most of structures in upper petroclival region were observed under microscope via subtemporal keyhole approach.,including part of midbrain and pons,trochlear nerve and oculomotor nerve,basilar artery and the supraclinoidal portion of internal carotid artery and their branches,including posterior cerebral artery,superior cerebellar artery,posterior communicating artery,middle cerebral artery,anterior cerebral artery.Adjusting optical angle of microscope,the mamillary body,pituitary stalk and optic chiasma were also found.2.Beside of structures abovementioned,the unilateral or bilateral trigeminal nerve, abducent nerve,facial nerve,vestibulocochlear nerve,intermediate nerve,internal auditory artery interpeduncular fossa,ventral aspect of pons were observed with endoscope inserted into intracephalic spaces via subtemporal keyhole approach. The distance from internal carotid artery to oculomotor nerve was 8.26±0.97mm; The distance from posterior communicating artery to tentorium of cerebellum was 8.81±1.56mm;The distance from anterior choroidal artery to posterior communicating artery was 5.57±0.90mm.3.Under microscope,the trigeminal nerve,facial nerve,vestibulocochlear nerve, glossopharyngeal nerve,vagus nerve accessory nerve were observed via suboccipito-retrosigmoidal keyhole approach,as well as the lateral ventral aspect of pons,anterior inferior cerebellar artery,superior petrous vein,excluding the abducent nerve,trochlear nerve and ventral aspect of brain stem.4.Beside of structures abovementioned,the abducent nerve,trochlear nerve and ventral aspect of brain stem were observed under endoscope via suboccipito-retrosigmoidal keyhole approach with absence of the superficial bone substance of sigmoid sinus,as well as the vertebral artery,basilar artery, intermediate nerve and internal auditory artery.5.The distances of anterior margin of bony window to posterior lip of orifice of internal acoustic meatus were 14.24±2.70 mm(8.50～17.56 mm).6.Originating from the external carotid artery,the vertebral artery entered suboccipital triangle in nuchal region and wrapped with venous plexus.The C₁ nerve ran through the space between vertebral artery and posterior arch of atlas.7.Under the operating microscope,the rootlets of glossopharyngeal nerve,vagus nerve were observed via the retro-condylar keyhole approach,as well as the cranial roots and spinal roots of accessory nerve,hypoglossal nerve and vertebral artery.The jugular foramen was not exposed due to the jugular tubercle. Adjusting head position and visual angle of microscope,the facial nerve, vestibulocochelear nerve,anterior inferior cerebellar artery posterior inferior cerebellar artery and the initiated segment of basilar artery were observed.8.Beside of structures,the outlets of posterior group cranial nerves,including jugular foramen and hypoglossal canal,were exposed under endoscope via the retro-condylar keyhole approach,as well as the ventral aspect of brain stem and the extremity of vertebral artery.Complex relationship among the cranial nerves and blood vessels was also found.9.The distance of lateral margin of bony window to internal orifice of jugular foramen was 17.29±2.80mm.Conclusions:1.The frontal branch of facial nerve and superficial temporal vessels can be protect sufficiently while the skin incision were performed between the superficial fascia and deep fascia.2.The stripping of petrous apex neednot be performed as routine technique in temporal keyhole approach.3.The surgical exposure of upper perclival region under endoscope,which is more extensive compared with those exposed under operating microscope.4.The structures in upper petroclival region may be localized by combination of different markers.The bony structure,such as orifice of internal auditory canal, can be applied as marker.5.The natural intracephalic spaces,including posterior communicating artery, trigeminal nerve,posterior communicating artery -anterior thalamal perforating artery,posterior communicating artery-perforating artery ones.Sufficient utilization of these spaces ensures operation in success.6.Protection of sigmoid sinus is pivotal issue in mastoid outline.Exposure of posterior margin of sigmoid is helpful to the operating field.7.Posterior bony semicircular canal can be localized based on the density change of os petrosum.8.Both of the facial nerve,vestiblocochlear nerve and the orifice of internal auditory canal can be used as marker to localize the structures in peroclival region.The later one is preferable due to its unchangeable position.9.Utilization of endoscope can improve significantly the surgical exposure compared with those under operating microscope.10.Usage of endoscope can diminish the bony window in retro-condylar keyhole approach;11.Without removal of occipital condyle and jugular tubercle,the anatomical structures within the lower peroclival region can be exposed entirely including the ventral of the brain stem under endoscope compared to those under microscope.12.Both of the spinal root of accessory nerve and internal orifice of jugular foramen can be used as marker in endoscopy assisted retro-condylar keyhole approach to lower peroclival region.The later one is preferable due to its bony structure and unchangeable position.13.Usage of endoscope in three different keyhole approaches abovementioned can improve the surgical field sufficiently.Endoscopic anatomical features of structures in the peroclival region due to the change of position,adjacent of structures under endoscope. 14.Individuation may be carried out in surgical therapy according to various diseases. So,combination the microscope and endoscope is acceptable to remove the pathological tissues in success.New ideas:1.To define that the structures in upper petroclival region need be localized by combination of various markers instead of single marker in endoscopic operation via subtemporal keyhole approach.2.Beside of the protection of sigmoid sinus as pivotal issue in mastoid outline,the further view what exposure of posterior margin of sigmoid is helpful to the operating field in endoscope-assisted suboccipito-retrosigmoidal keyhole approach to peroclival region.To validate that both of the facial nerve,vestiblocochlear nerve and the orifice of internal auditory canal can be used as marker to localized the structures in peroclival region.3.A novel outlook was raised in this study that usage of endoscope can diminish the bony window in retro-condylar keyhole approach.Not only the occipital condyle but also jugular tubercle can be remained due to the utilization of endoscope with the entire exposure of structures in lower peroclival region.The viewpoint was indicated in first time that both of the spinal root of accessory nerve and internal orifice of jugular foramen can be used as marker in endoscope assisted retro-condylar keyhole approach to the lower peroclival region.4.The selection of marker need according to various diseases,The bony structure was prefer to soft tissue.