Anatomical Study In Exposed Area And Operating Space Of Extended Endoscopic Endonasal Approach To The Ventral Region Of Cranio-cervical Junction

Objective The craniocervical junction is adjacent to the human's life center,therefore the neurosurgeons have considered the brain stem as the most complex,most important,and most challenging anatomical region.With the introduction and promotion of neuroendoscopic techniques,this region is constantly conquered.Due to its wide field of vision,flexible angles,and direct vision operations,neuroendoscopic surgery is favored by neurosurgeons during skull base surgery.However,there are many osseous structures in the cranial-cervical junction,and cerebrospinal fluid leakage is easily formed after bone removal.Therefore,the surgical exposure range and surgical safety have become the constraints for this approach.In this experiment,the extended endoscopic endonasal approach on the head specimens of fresh adult cadavers is to understand the key steps,the important anatomical structures and the position of this approach.Measuring the exposed area of the craniofacial junction and the operable space is to provide anatomical basis for the clinical practice.Methods From July 2017 to November 2017,10 fresh cadaveric cadaver heads were used.The 0°and 30°rigid endoscopes with a diameter of 4 mm and a length of 18 cm were used to extended endoscopic endonasal approach with double nostrils.Extended endoscopic endonasal approach to the ventral craniocervical junction,mainly through the nasal cavity,posterior pharyngeal wall,occipital large hole area to reach the cervical medulla.The cadaver specimen was fixed on the head holder,with the head tilted 45°,the right nostril into the mirror,and the left nostril into the instrument.Firstly,we should find the middle turbinate along the middle meatus under the endoscope,then remove the middle turbinate,and use the opening of the sphenoid sinus as the starting point along the upper part of the nasal septum to the inner side of the nostril to the lower nasal passage and finally return to the lower part of the sphenoid sinus opening to make a curved mucosal flap.The mucosal flap is pushed to one side.Find the posterior pharyngeal wall along the inferior meatus,identify the pharyngeal crypt,the eustachian tube round pillow and the eustachian tube pharyngeal,remove the 1/3bony structure after the nasal septum.After the incision of the mucous membrane of the pharyngeal wall,the long head muscles and the prevertebral fascia can be seen.The long head muscles attached to the slope are separated and pushed to the sides.The long muscles of the neck can be seen.The anterior membrane was removed and the anterior border of the occipital foramen,the atlas and anterior sacral foramen,and the anterior arch of the atlas were seen.The frontal nodules of the atlas and part of the anterior arch of the atlas were removed,and the odontoid,transverse ligament,apical ligament,and vertical part of the cruciate ligament were seen.Abrading the odontoid and part of the lower slope of the bone can expose the vertebral artery,the medulla oblongata and the cervical cord.In order to know the key steps of the approach,the important anatomical structures and their location relationship,we have measured the exposed area and the operable space of the craniofacial junction.Result Because of the cranial cervical junction is deep,and the distance between the nostril and the tuberculum anterius atlantis is 9.27±0.33cm,we need the special equipment for this operation.Scope of foramen magnum region,which was 4.51±0.87cm~2,can be exposed as an inverted trapezoidal,and grinding the slope area bones need to be determined according to the scope of lesions.In order to protect the sublingual neural tube and jugular vein,both sides of the border are limit to the outside of the occipital condyle and foramen lacerum cords range,so the bone window need to preoperatively plan.Conclusion The area,exposed by extended endoscopic endonasal approach in the ventral craniofacial junction,is 4.51±0.87cm~2,so this approach can be used for removing epidural tumors,such as chordoma,in the craniofacial junction,and exogenous or superficial tumors,such as meningioma,in the medulla oblongata and the midline of the ventral part of the pons.At the same time,the approach also applies to cure odontoid deformities,basilar invagination and atlantoaxial dislocation.There are four boundaries of the operation area,the lateral one is the line connecting the foramina lacerum and the lateral edge of occipital condyle,the lower one is the root of the odontoid process,and the upper one is the line connecting the foramina lacerum on both sides.