Anatomical Study On The Necessity Of Complete Neuroendoscopic Resection Of Occipital Condyle Via Far Lateral Approach

Objective:Craniocervical junction lesions have been one of the most challenging operations in neurosurgery due to their proximity to the brain stem,posterior cranial nerves and other important structures,as well as their deep location,small operating space,and blocked bone structures,which lead to difficult surgical exposure and many complications.The far lateral approach is considered to be the appropriate surgical approach for the treatment of lesions in this region.For ventrolateral and ventral lesions of the brain stem,the occipital condyle or part of the occipital condyle is often abrasively or partially abrasively removed in order to expand the surgical field of vision,but complications such as vascular and nerve injury,cerebrospinal fluid leakage and atlanto-occipital joint instability are also increased.In recent years,with the rapid development of endoscopic keyhole technology,it has been increasingly used in the surgery of skull base lesions because of its wide perspective,deep illumination,less trauma,and less ineffective exposure.In this study,we compared the exposure of the anatomical structure of the craniocervical junction between neuroendoscopy and microscopic simulation through the far lateral keyhole approach,to explore the necessity of the occipital condyle removal,and to discuss the advantages and disadvantages of the endoscopic keyhole technique,so as to provide accurate anatomical data for the safe and smooth clinical operation.Methods:Five Chinese adult cadaveric head specimens(10 sides)fixed with 10%formaldehyde and infused with red and blue latex were used,including 3 males and 2 females,aged 58-70 years old,with an average age of 61 years.To simulate the far lateral approach,lateral prone position was taken,and "S" shaped skin incision was made in the posterior mastoid with a length of about 6cm.The muscles of each layer were turned over in layers,and the occipital condyle and vertebral artery were exposed.A micro-bone window with a diameter of about 3cm was milled behind the occipital condyle and 1/3 of the posterolateral occipital condyle was removed to the sublingual neural tube.SPSS 21.0 statistical software was used for data analysis.Measurement data subject to normal distribution were expressed as x±s.Comparison between groups was performed by Paired sample t-test,and P<0.05 was considered statistically significant.Results:The abducens nerve,facial auditory nerve,glossopharyngeal nerve,vagus nerve,accessory nerve,hypoglossal nerve,posterior inferior cerebellar artery(PICA),anterior inferior cerebellar artery(AICA)and the external bulbar segment of vertebral artery could be observed by the microscope through the far lateral keyhole approach.After removal of the occipital condyle,the microscopic field of the ventrolateral and ventral medulla oblongata was expanded,and the whole picture of the intracranial segment of the hypoglossal nerve and the origin of PICA discharge were visible.Through the posterior keyhole approach of the far lateral condyle,the jugular tuberosity and occipital condyle can be bypassed,and the above structures can be observed more accurately through four gaps:the facial-auditory nerve-glossopharyngeal nerve gap,the glossopharyngovagus nerve gap,the vagus-accessory nerve cranial root gap,and the ventral gap of accessory nerve spinal root.The origin of AICA,the origin of the abducens nerve from the pontine sulcus,and the intracranial opening of the sublingual neural tube were also observed.After removal of the occipital condyle,the anterior spinal artery,contralateral vertebral artery,and vertebrobasilar artery confluence could be observed.Before and after removal of the occipital condyle,the area of ventrolateral medulla under endoscopy was(331.0±6.6)mm2 and(464.7±10.6)mm2,and the difference between them was statistically significant(t=52.99,p<0.01);Before and after removal of the occipital condyle,the exposed area of the medulla oblongata under the microscope was(205.8±9.6)mm2 and(329.1±6.7)mm2,and the difference was statistically significant(t=75.07,p<0.01).Before removal of the occipital condyle,there was significant difference in the exposure area between endoscopy and microscope(t=62.18,p<0.01).After removal of the occipital condyle,there was significant difference in the exposed area between endoscopy and microscope(t=64.62,p<0.01).The exposed area of endoscopy before removing the occipital condyle and microscope grinding the occipital condyle was no statistical significance difference(t=1.63,p=0.137).Conclusion:The far lateral keyhole approach of neuroendoscopy is feasible in craniocervical junction surgery.The far lateral keyhole approach under neuroendoscopy can clearly expose part of the anatomical structure blocking the occipital condyle under the microscope without removing the occipital condyle,and extend the exposure range of the lateral and ventral view of the brainstem,which may avoid the injury caused by the removal of the occipital condyle and the related complications such as atlantooccipital joint instability.After removal of the occipital condyle through the far lateral keyhole approach,both neuroendoscopy and microscope can increase the exposure of anatomical structures and the exposure area of the ventrolateral medulla.