Anatomic Study Of Endoscopic Transcerebellomedullary Fissure Keyhole Approach And Endoscopic Aqueduct Stent Placement

Part I: Anatomic Study of Midline Suboccipital Endoscopic Transcerebellomedullary Fissure Keyhole ApproachObjective: To study the endoscopic anatomy of the fourth ventricle and lateral brainstem regions via the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach assisted by a neuronavigation system and discuss the feasibility and indications of this approach.Methods: Craniotomy procedures performed via the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach were simulated on 8 adult cadaveric heads fixed by formalin,and the related anatomic structures in the fourth ventricles or around the brainstem were observed through the 0° endoscope or alternatively 30° one.A neuronavigation system was used to measure the exposed area of the floor of fourth ventricle,the maximum exposure range,the length of the floor of fourth ventricle,the shortest distance from the midpoint of posterior arch of atlas to the opening of the aqueduct in the fourth ventricle and to the jugular foramen on both sides,respectively.Results: All the anatomic structures within the fourth ventricle and partial anatomic landmarks around brainstem were identified by means of the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach.The exposed area of the floor of 4th ventricle is 459.68±73.71mm2.However,the total exposed area is 1601.70±200.76mm2.The length of the floor of fourth ventricle is 36.08±2.63 mm.The shortest distance from the midpoint of posterior arch of atlas to the opening of the aqueduct in the fourth ventricle is 63.87±2.97 mm,to the jugular foramen on both sides,respectively,is 40.11±2.47mm/40.30±2.31 mm.Conclusion: Midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach can basically meet the medial and lateral route of the transcerebellomedullary fissure approach.A tumor within the fourth ventricle or near the jugular tubercle extending into the fourth ventricle through the cerebellomedullary fissure can be removed by this approach.Part II: Comparative Study of Two Surgical Approaches of Endoscopic Aqueduct Stent Placement Based on the Technique of the Magnetic Resonance ImagingObjective: Endoscopic aqueduct stent placement have two surgical approaches,ie trans-lateral ventricle one and trans-fourth ventricle one,each has its advantage and disadvantage.There is no consensus on the standard approach so far.The first part of this article was to perform route planning of two approaches and compare their respective advantages and disadvantages,based on the magnetic resonance imaging technology.Methods: Eight adult cadaveric heads fixed by formalin received cranial magnetic resonance scanning.Two simulated approaches of endoscopic aqueduct stent placement were performed.The operating distance,the length of aqueduct stent and endoscopic operating angle were measured respectively.And the statistical comparative analysis of the two approaches was performed.At the same time,the relevant data of the aqueduct,passed by the two approaches,were measured.Results: The average operating distance of the trans-lateral ventricle approach was 87.1±5.2mm,the average length of aqueduct stent was 119.9±4.4mm,and the average endoscopic operating angle was 19.1°±1.9° for the approach.The average operating distance of the trans-fourth ventricle approach was 50.0±3.6mm,the average length of aqueduct stent was 78.0±3.6mm,and the average endoscopic operating angle was 18.2°±2.2°.Statistical analysis: the average endoscopic operating angle of the trans-lateral ventricle approach and the trans-fourth ventricle one were similar,no significant difference existed between the two approaches;while the average operating distance and the average length of aqueduct stent of the trans-lateral ventricle approach were longer than the trans-fourth ventricle approach with significant difference.The cortical injury distances of the trans-lateral ventricle approach was 37.9±5.1mm,while the cortical injury distances of the trans-fourth ventricle one was not produced.The mean length of the aqueduct was 14.1±0.9mm.The mean width of five parts of the aqueduct were as follows: 3.7±0.5mm?1.9±0.5mm?2.6±0.6mm?1.7±0.3mm?3.3±0.6mm.The average angle between the rostral segment of the aqueduct and the third ventricle was 30.6°±5.0°.The caudad segment angulation of the aqueduct relative to the long axis of the rostral segment was 35.0°±4.3°.Conclusions: In endoscopic aqueduct stent placement,the operating distance and the length of aqueduct stent of the trans-fourth ventricle operation was shorter than the the trans-lateral ventricle operation.The trans-fourth ventricle approach could be a more minimally invasive approach theoretically,which avoided the the cortical injury.And awareness of these normal morphometrics was very useful when stent placement is an option during aqueductoplasty.The reported data were valuable in guiding neuroendoscopic treatment of hydrocephalus and aqueductal stenosis.Part III: Anatomic Study of Endoscopic Trans-fourth Ventricle Aqueduct Stent PlacementObjective: In this part of the study,the endoscopic trans-fourth ventricle aqueduct stent placement was performed in cadaveric head specimens.The details of the operation process were observed,summarized and discussed,to provide anatomic basis for the clinical application.Methods: Eight formalin-fixed adult cadaveric heads were scanned by magnetic resonance imaging,and the related image data were introduced in the neuronavigation system.With assistance of the navigation system,the 0° endoscope was introduced into the fourth ventricle via the trans-fourth ventricle approach in the cadaveric heads.During the procedures,the related structures were observed,then aqueductoplasty and aqueduct stent placement were performed successively.Results: The cadaveric heads were placed prone and fixed in a 3-point headholder,and the navigation registration was completed.A 4 cm midline skin incision was made at the craniocervic junction and a 2 cm occipital craniotomy was performed.The dura mater was incised longitudinally,then cisterna magna was revealed.The arachnoid membrane of cisterna magna was dissected sharply in order to expose the foramen of Magendie.The introduction of the 0° rigid endoscope into the foramen of Magendie allowed endoscopic visualization of choroid plexus,median sulcus,the second half of the floor of fourth ventricle,striae medullares,colliculus facialis,superior medullary velum and middle cerebellar peduncle.The opening of the aqueduct in the fourth ventricle was verified by navigation system.With gentle inflation of the balloon catheter,which was softly inserted into the aqueduct,the aqueduct was dilated.A stent catheter,which was cut according to the measured distance and had several small side holes on both ends,was advanced into third ventricle via aqueduct.The distal end of the stent was fixed on the dura mater to prevent migration.Conclusions: Endoscopic trans-fourth ventricle aqueduct stent placement could be performed with bone flap of 2 cm in diameter and longitudinal incision of the dura mater.The opening of the aqueduct in the fourth ventricle could be verified by navigation system.The length of the stent was the distance between the interthalamic adhesion and the site of the bone flap.The distal end of the stent,which fixed on the dura mater,could prevent migration.