Stereoscopic Microsurgical Applied Anatomy Of Far-lateral Transcondylar Approach For Posterior Cranial Fossa

PrefaceFar - lateral transcondylar approach is also -called the approach of far - lateral infra - pulvinar, the approach of extreme lateral transcondylar - cervical tubercles and the approach of post - lateral infra - pulvinar. Recently, the literatures about far - lateral transcondylar approach have been reported occasionally. With regard to the lesions of the ventral and the lateral ventral of great occipital foramen; the lesions of the mid - clivus and infra - clivus as well as the ventral of brain stem; the tumors growing under dura mater at craniumcervical joint relay and the ventral of upper cervical spinal cord; the tumors growing outer dura mater at the mid - clivus and infra - clivus, occipital condyle and jugular foramen , including some rare cases; in addition, the aneurysm of vertebral artery, basilar artery and posterior inferior cerebellar artery; arteriovenous fistula and arteriovenous malformation of the ventral of craniumcervical relay joint, Because the anatomy relation is complex,the structures is important,the position is deep and the operation is difficult, the valid operational therapy is impossible performed. The field of operation of traditional oropharynx approach is narrow (there are 14cm between amphi - vertebral artery) and deep and long (9 ~ 12cm) ,the leakage of cerebrospinal fluid and infection are apt to occurrenc after operation, so it is seldom used; It is also limited in mid - position approach for posterior cranial fossa as it needs pull medulla oblongata and is apt to damage vertebral artery. But in far - lateral transcondylar approach,there have short path and broad field of operation so as to control vertebral artery better in earlier period and bite skull and vertebra off according to the operational demand, so it canincrease the exposure of the ventral of craniocervical juncture region. Especially when using endoscope, it amplifies the field of operation and rise omnicutting rate of tumors. ; It is apt to ascertain and control vertebral artery, basilar artery and its branch in earlier period in order to block the supply of blood of tumors; In far - lateral transcondylar approach, the interface between tumors and medulla oblongata and cervical spinal cord, the relationship between tumors and post group cranial nerve , vertebral artery and posterior inferior cerebellar artery that can be seen clearly from coronal side. It is easy to operate because the important structures such as medulla oblongata and cervical spinal cord can not be pulled; The post group cranial nerve can be looked steadily at and protected, the structures such as nerves and blood vessels can be pulled in minimum degree that can have tumors exposed and cut. In order to comprehend the important bony marks in anatomy such as occipital condyle, mastoid and styloid process so on and to protect vertebral artery and to understand the ralationship between post group cranial nerves and blood vessels and to solve the problem of the supply of blood and peripheral dominating nerve, the experiment of stereoscopic microsurgical applied anatomy of far - lateral transcondylar approach for posterior cranial fossa has been done to supply particular anatomic data for clinical microneurosurgery and there is important significance to promote the reliability and therapeutic efficacy in far - lateral transcondylar approach.Material and Method1 Material1. 1 Objects10 examples fixed normal adult's skull including cervical part cadaver specimen ( supplied by the department of local anatomy,China Medical University) , There are 8 Male examples and 2 Female examples that were transected at the sevevth cervical vertebra to assurance the need of operation on neck, Lacteprene mixed red and blue dye were affused to the artery and vein system to maintain the normal caliber of blood vessel that can be recognized easily.1.2 Devices and ReagentsRoutined operative devices for neurosurgery( supplied by the department of local anatomy,China Medical University) , hyperbaric injection syringe, cranip-tome, lacteprene fluid (the lacteprene factory ShenYang) , slide gaud (degree of accuracy 0.02) , gauge, protractor, lead thread, camera operation microscope that can magnify 5 ~20 times. 2. Methods2.1 Latex were affuse to the artery and vein system of cadaver's skull One side internal carotid artery (ICA) was bluntly dissected about 2 cm at section cut straight through cervical part and put in pachy - needle without apical and deligated doubly by the seventh suture. The red lacteprene fluid was af-fused to IC A; when it outflowed from opposited IC A and both vertebral arteries (VA) , the corresponding blood vessel should be tongsed; Continue to affuse lacteprene fluid until the total amount achieved 50ml, the ICA was tongsed. According to the same method, the blue lacteprene fluid was affused to internal jugular vein.2. 2 Operation and DissectionIt is two weeks after the lacteprene fluid was aflused, it began to incise skin, turn over skin flap according to the method of Babu. The muscles of neck can be divided into three layers: the anterior layer is anterior lateral sternocleido-mastoid muscle ( SCM ) and postmedialis trapezius muscle; The middle layer is splenius capitis muscle in superficial part and longissimus capitis muscle and semispinalis capitis muscle in deep part; The deep layer is infrapulvinar triangle, it is composed of medialis greater posterior rectus capitis muscle, superior late-ralis superior obliquus capitis muscle and infralateral inferior obliquus capitis muscle. Its bottom is composed of posterior lemma of atlas and posterior arch of atlas,there are many important structures such as posterior arch of atlas, the vertical part and horizontal part of the third segment of vertebral artery and so on in it. Cut off muscles and observe vertebral venous plexus, VA and Cl nerve those are arranged like " sandwich" , Meanwhile, the segment and its course of VA and other structures should be aware of.Bony structure and Ostectomy: Some anatomic landmarks such as transverse process of atlas, asterion,the tip of Mastoid, styloid process and so on used of-ten need to be distinguished in opening skull for posterior cranial fossa. Be aware of the deltoid measurement and relationship among the tip of mastoid, the tip of styloid process , transverse process of atlas and the struture of base of skull. Os-tectomy includes the milling of occipital condyle, jugular tubercle (JT) and the part or whole milling of atlantooccipital joint ( AOJ) and Lateral mass of atlas ( LM). Be aware of avoiding damaging sigmoid sinus ( SS) too. The range of bone matrix resection includes the more part of occipital squama one side, opening the post exterior rim of great occipital foramen, cutting off the posterior arch of Cl ( or adding C2) , opening transverse foramen of Cl, freeing VA and pulling it to post inside to protect VA properly and diplay AOJ better. Meanwhile, be aware of recognizing the interrelationship between the structure of paracondyle and hypo-glossal canal ( HC ) .Infra - dura mater exposure and intracranial microdissection: This procedur includes shearing dura mater on the basis of " Y" shape, reserving " cuff type" dura mater structure, pulling cerebellum and exposing cerebellomedullary cistern, opening subarachnoid space to view numerous and important nerves and blood vessels such as vertebral artery, basilar artery and its branch, V , VII ~ XII cranial nerve , brain stem and so on. ; observing the course of nerves and the relationship among nerves, blood vessels and peripheral structures, especially being aware of the component and adjacent of HC and jugular foramen. To proceed anatomic investigation about the spacing, length, width, depth of post-group cranial nerve is necessary.To measure the data of important structure and all the data were expressed according to average ± standard error(x ± s).ResultMastoid process, styloid process, stylomastoid foramen,lateral tip of atlas' transverse process, jugular fossa, occipital condyle and extra - pulvinar process et al were important anatomical signs, Inferior occipital triangle was formed by muscle rectus capitis posterior major ,muscle obliquus capitis superior,and muscle obliquus capitis inferior, Its base was formed by posterior atlantooccipitalmembrane and Posterior arch of atlas, the important mark for distinguishing vertebral artery. There were major structures around it such as VA, AOJ, SS, jugular foramen; Posterior lacerate foramen, postgroup cranial nerve, the venous plexus surrounding VA, cervical nerves I , II and so on. Measure and investigate the distance and three - dimensional structure among the main bony marks and correlative important structures, Collect numerous data and analysis it by statistics. The charts from one to ten are revealed about the structures clearly.DiscussionFar - lateral transcondylar approach involves in important and numerous nerves and blood vessels, it is easy to damage VA and cranial nerve et al. It request neurosurgery doctor to have more accurate relationship of topography and the feel of stratification to every muscle. Though the approach has deep and special position, narrow space and involving in numerous important structures such as nerves, blood vessels and brain stem those can not be damaged, under the doctrine of microneurosurgery that is utilize physio - interspace, under the condition that is to pull soft tissues sufficiently and cut off the bone matrix more e-nough that blocks the sight, it forms the conical operation space from back lateral to infraventral and it reaches lateral ventral of great occipital foramen directly without pulling brain stem,nerves and blood vessels. Regardless of the lesion at posterior cranial fossa or craniocervical juncture region ( CCJR) , VA and occipital condyle are the main factor that restrains to reach the target. Understanding the course of VA and the interface between VA and peripheral structures may a-void damaging VA. When milling occipital condyle, it is necessary to comprehend the relationship between hypoglossal and occipital condyle, biodynamics' investigation has made it clear that milling 1/2 occipital condyle can produce transparent, transient craniumcervical, so from the point of exposure in great occipital foramen, the exposure may be sufficient when milling 1/3 occipital condyle and it is not necessary to mill more. There are deep position and complicated relationship where jugular foramen is and the structures are very important through jugular foramen. The measurement of spacing of close cranial nerve hassome instructional significance to some operations those are carried out through the interspace from VII cranial nerve to XII cranial nerve. At present, there are some debates about the status of disposing lesion around foramen magnum in far - lateral transcondylar approach, Samii et al thought that it might adopt to traditional infrapulvinar middle part or lateral approach with regard to the ventral and lateral tumor around foramen magnum. In traditional approach, the tumor could not be cut off completely, not because of the insufficient exposure, but the factor that the tumor wrap up VA and its branches, cranial nerve. Though the rate of omnicutting of tumor has not notable difference among the three approaches, some investigations support the application of far - lateral transcondylar approach not only because the depth of operative field shallows, almost levelly to watch the front of medulla oblongata, and the observation dead angle of iso - side internal os of hypoglossal canal has been precluded, but also it is more important because the approach is helpful to decrease complications as medulla oblongata and cervical spinal cord are almost pulled, it can expose and control V A and its branches in earlier period, expose the postgroup cranial nerve sufficiently, make it more safe and convenient to separate tumour and these structures to solve the main problem that can not be cut off completely that Samii pointed out.ConclusionThe experiment can supply particular anatomic data for clinical microneuro-surgery through the observation, data measurement and statistics analysis of correlative anatomic structure about far - lateral transcondylar approach.The approach can expose sufficiently the inferior segment of slope, and the wide space of the brain stem and the ventral cervical spinal cord from foramen magnum to C5, and brain stem and cervical spinal cord are not pulled because the structures suh as occipital condyle,SS,VA,JT,AOJ,LM that hampered operative field have been disposed specially from lateral direction, the area from inferior segment of slope to superior segment of cervical spinal cord can be exposed well through the single approach; the operative approach has short path and broad operative field that can control VA in operative arlier period, ascertain...