The Study On The Meningeal Structural Anatomy And Histology Of Lower Cranial Nerves Through Jugular Foramen

Background and ObjectiveThe meningeal structure of intracranial nerves includes its myelin sheath、 neurilemma、pia mater、arachnoid mater and dura mater,there is the enlargement of subarachnoid space between arachnoid mater and pia mater,which forms the brain cistern where the cerebrospinal fluid lies,the arachnoid mater and brain cistern were focused by experts of the department of neurosurgery before twentieth century.Subsequently,arachnoid mater and brain cistern were described in detail during the stages of study on anatomy、imaging、microscopic neurosurgery.Nowadays,the procedure of dissecting arachnoid mater in turn、opening the brain cistern and taking advantage of the natural space has become the basic principle of modern microneurosurgery,as said by Yarsargil,brain cistern was route map to neurosurgeon who should dissect the cistern from one to another during operation,so it is of great clinical significance to master the anatomical structure of arachnoid mater and brain cistern.With the study on arachnoid mater and brain cistern,we can:1、judge the relationship between tumor and arachnoid mater before operation,understand the condition and choose the best approach;2、make the brain smaller and avoid the injury by opening the cistern and releasing the cerebrospinal fluid;3、expose the tumor when neurovascular structure contracting where arachnoid mater being dissecting;4、find the anatomical interface between tumor and other surrounding structure.then avoid the injury of normal neurovascular structure;5、protect the neurovascular structure of adjacent cistern when we dissect arachnoid mater in one cistern;6、diagnose and operate on aneurysm by knowing and dissecting arachnoid mater.The shape and distribution of arachnoid mater has been observed microscopically by Lv jian;Vinas classified the arachnoid mater into convex、 concave、trabecular by microscopic observation;Rhoton classified the tumors into five kinds by the relationship between tumor and cistern.The comprehension of the arachnoid mater favors the development of neurosurgery.So far there has been a history of more than300years to know arachnoid mater and over100years to research brain cistern,but there has not completely elucidated on the study of the distribution characteristics about arachnoid mater.Nowadays,there is intensive study on diseases and microscopic anatomy of meningeal structure about abducens nerve、facial nerve、vestibulocochlear nerve,but rare study about lower cranial nerves through jugular foramen.Lower cranial nerves through jugular foramen start form medullar oblongata,move in the cistern,and leave the cranium at jugular foramen.there is not systematic detailed histological reports about the distribution of pertinent meningeal structure as for myelin sheath、pia mater、arachnoid mater、dura mater in the region,further study is needed,for the distribution of pertinent meningeal structure supplies the anatomical data to the organic and functional diseases in jugular foramen region.The organic and functional diseases in the region mainly include jugular foramen schwannomas and vago-glossopharyngeal neuralgia respectively.Jugular foramen schwannomas accounts for2.9-4.0%of introcranial schwannomas,in the1990’s,Samii classified the schwannomas into four kinds in the region,which has been accepted by all,for the purpose of development of micro neurosurgery.Sutiono classified the jugular foramen schwannomas by the interface of meningeal structure according to Samii typing respectively:subarachnoid type(type A);foramen type(type B);epidura type(type C);epi-subdura type(dumbbell type D),regrettedly,there is not reviews supplying the basal anatomy systematically and clearly,the pertinent experiments is required to make clear characteristic of the start-stop and distribution of dura mater、arachnoid mater and pia mater and understand the jugular foramen schwannomas typing and operate in the region according to the interface and layers of meningeal structures.In addition,cerebrospinal fluid leakage is a dangerous kind of complication in jugular foramen region.it is of great significance to protect and repair dura mater as the ultimate shelter.obviously we should master the start-stop and distribution of dura mater.There is the relationship between glossopharyngeal neuralgia and its surrounding pia mater and arachnoid mater,so the study on its start-stop and distribution supplies anatomical data. Beyond all doubt,it is of high innovative significance and practical value to grasp pertinent meningeal structure for the judgement of the position relationship between tumors and nerves、intraoperative surgical technique、the preservation of lower cranial nerves and the improvement of the prognosis for the patient.Glossopharyngeal neuralgia is an kind of paroxysmal severe pain in the glossopharyngeal distributed region,because vagus nerve close to glossopharyngeal nerve starting from medulla oblongata,then easy to be affected together,there are reviews reports vaso-glossopharyngeal neuralgia.Neuralgia is thought as central myelin sheath at root entry zone is compressed by vessels currently.The anatomical study on root entry zone of central myelin sheath and central-peripheral myelin sheath transitional zone trace back100years ago,which was thought they existed in brain and spinal cord,peripheral myelin sheath was consisted of schwannomas cells and supportive tissue as as fibroblast cell、collagenous fibre and nerve root sheath cell,central myelin sheath was consisted of oligodendroglia and nerve fibre.The principal position of vascular compression lies in root entry zone,where central myelin sheath and peripheral myelin sheath intersected,and transitional zone also being called Obersteiner-Redlich zone was sensitive to pulsating and striding vascular compression,trigeminal neuralgia、facial spasm、tinnitus and vertigo vaso-glossopharyngeal neuralgia was caused by vascular compression of trigeminal nerve、facial nerve、vestibulocochlear nerve、glossopharyngeal and vagus nerve repectively, but not caused at peripheral nerve axon outside the zone with the wrap of schwannomas cell.The traditional views hold cranial nerve vascular compression syndromes have their conflicting vessels situated at the root entry zone considered as harbouring anatomical-physiological sensitiveness and excitability.The morbidity of vaso-glossopharyngeal neuralgia is less than trigeminal neuralgia,so is anatomical experiment.Four problems are required to solve:1、There is somewhat relationship between vaso-glossopharyngeal neuralgia and adhesion of arachnoid mater,how about the meningeal structural distribution surrounding glossopharyngeal and vagus nerves;2、Neuralgia arises from demyelination of glossopharyngeal and vagus nerves.how about the distribution of central myelin sheath and peripheral myelin sheath.is there transitional zone;3、The terms related to microvascular decompression includes transitional zone、root entry zone、central myelin sheath、peripheral myelin sheath.By definition,the term root entry zone refers to the anatomic junction between the nerve and the brainstem specifically,some authors have considered the root entry zone and central-peripheral myelin transitional zone to be one and the same,however,others have claimed that the terms root entry zone and transitional zone describe distinct structures and should be used separately.Are the root entry zone and transitional zone the same position?how about the relationship between the root entry zone and transitional zone of lower cranial nerves through jugular foramen;4、The morbidity of vaso-glossopharyngeal neuralgia is less than trigeminal neuralgia,there is possible relationship between the length of central myelin sheath and neuralgia,then how about the length of central myelin sheath of glossopharyngeal nerve and vagus nerve,whether is it shorter than trigeminal nerve as reported or not.Is there transitional zone between central myelin sheath and peripheral myelin sheath according to accessory nerve,is there difference of central myelin sheath between glossopharyngeal nerve and vagus nerve,is there difference between both above-mentioned and accessory nerve.It is worth while to note not all the cases neurovascular compression lies on the central myelin sheath.There is not neurovascular compression on the central myelin sheath during microvascular decompression,but neurological symptoms has been improved after operation,the causes still are explored.According to the above-mentioned questions,the experiment is designed to explore the microanatomy of surrounding meningeal structure and the histology of myelin sheath of lower cranial nerves through jugular foramen、the histology of surrounding meningeal structure of lower cranial nerves through jugular foramen in order to observe the start-stop and distribution of pia mater、arachnoid mater and dura mater related to glossopharyngeal nerve、vagus nerve and accessory nerve,observe and measure their length of central myelin sheath,which supplies pathological anatomical data and operative foundation during the organic diseases such as jugular foramen schwannomas and the functional diseases such as vaso-glossopharyngeal neuralgia,which supplies the anatomical basis according to the layers and interface of meningeal structure during operation.Objectives(1)The study on microanatomy and histology of surrounding meningeal structure of lower cranial nerves through jugular foramen is intended to understand the start-stop and distribution of surrounding dura mater、arachnoid mater、pia mater, which supplies anatomical data for growth pattern、differential diagnosis and operative attentions of the diseases related to the meningeal structure of lower cranial nerves such as schwannomas;(2)The study on the histology of central myelin sheath、peripheral myelin sheath、transitional zone and root entry zone of lower cranial nerves through jugular foramen is intended to supplies anatomical data for comprehension of pathogenesis and micrvascular decompression of vaso-glossopharyngeal neuralgia.Materials and Methods1.The study on microanatomy and histology of myelin sheath of surrounding meningeal structure of lower cranial nerves through jugular foramen1.1Materials11(22sides)adult cadaveric heads including6males and5females fixed in10%formalin.the common microscopical surgical operating instruments、microscope and camera,device for histology, reagent for hematoxylin-eosin staining and luxol fast blue staining(supplied by the department of anatomy.Southern Medical University)1.2MethodsAll the cadaveric heads(11cases,22sides)were exposed to jugular foramen region.the distribution of surrounding pia mater、arachnoid mater and dura mater of glossopharyngeal nerve、vagus nerve and accessory nerve were observed by surgical microscope and then photographed.The tissue from the spot where glossopharyngeal nerve、vagus nerve and accessory nerve leave medulla oblongata(including a portion of medulla oblongata) to the internal orifice of jugular foramen was taken from every side of specimens,except for one head(2sides) was used to coronal slices,all the sides of the specimens is used to make horizontal slices by different nerve classification,then labeled them.Every tissue block from different nerve of every side was fixed、dehydrated、waxdip、embeded、sliced,and then hematoxylin-eosin staining was taken as routine screening procedure,luxol fast blue staining was taken to differentiate central myelin sheath(oligodendroglia) and peripheral myelin sheath(schwannomas),the central myelin sheath、peripheral myelin sheath%transitional zone and root entry zone of glossopharyngeal nerve、vagus nerve、accessory nerve respectively was obeserved by microscope,the length of medial and lateral aspects of central myelin sheath of different nerve from the spot leaving the medulla oblongata to the spot where central myelin sheath meets with peripheral myelin sheath were measured respectively(represent a、b respectively),the perpendicular distance from ultimate spot of transitional zone to the link of terminals of medial and lateral aspects was measured(c),the length of central myelin sheath is equal to the sum of half a and half b and c。1.3Statistical AnalysisOne-factor analysis of variance of SPSS13.0was taken to compare the length of central myelin sheath of glossopharyngeal nerve、vagus nerve and accessory nerve.Paired t-test of SPSS13.0was taken to compare the medial and lateral aspects of central myelin sheath of glossopharyngeal nerve、vagus nerve and accessory nerve respectively.The shape of transitional zone is determined by the ratio of c to the length of hemline(the link of terminals of medial and lateral aspects).2. The study on the histology of surrounding meningeal structure of lower cranial nerves through jugular foramen2.1Materials 9(18sides)fetal cadaveric heads fixed in10%formalin.the common microscopical surgical operating instruments、microscope and camera,device for histology, reagent for masson staining and siriusred picric acid staining(supplied by the department of anatomy,Southern Medical University)2.2Methods9fetal cadaveric heads(18sides)were randomly divided into three groups.the sagittal plane、horizontal plane、coronal plane slices were manufactured including lower cranial nerves through jugular foramen.The above-mentioned18sides tissue blocks were fixed、dehydrated、waxdip、embeded、sliced,and then masson staining、 siriusred picric acid staining were taken,the start-stop and the distribution of surrounding pia mater、arachnoid mater and dura mater of glossopharyngeal nerve、 vagus nerve and accessory nerve were observed by surgical microscope and then photographed.Results(1) The glossopharyngeal nerve、 vagus nerve、accessory nerve penetrate from behind the postolivary sulcus in the medulla oblongata,pass obliquely forward、 downward、outward into jugular foramen,there are surrounding dura mater、arachnoid mater、pia mater and the transitional zone between central myelin sheath and peripheral myelin sheath;(2)Dura mater surrounding lower cranial nerves through jugular foramen is thick and tough,including the internal layer.namely,meningeal layer and the external layer,namely,periosteal layer,there are some sinuses such as inferior petrosal sinus、 sigmoid sinus between two layers;the dura mater forms dura pocket at jugular foramen,lower cranial nerves enter jugular foramen through dura pocket,there is dura fold up the inner orifice of jugular foramen;glossopharyngeal nerve lies up vagus nerve、accessory nerve.which forms glossopharyngeal meatus and vagus meatus respectively,there is dura septum which separates them;in jugular foramen,lower cranial nerves keep bunchy,vagus nerve shows many tracts.the other two shows one or two tracts.all the tracts are surrounded by connective tissue sheath;all the nerve tracts lie medial to jugular bulb,and there is inferior petrosal sinus between glossopharyngeal nerve and vagus nerve;(3)There is natural space between arachnoid mater and dura mater surrounding lower cranial nerves through jugular foramen,there is some cistern between arachnoid mater and pia mater,where connective tissue trabecula links them;arachnoid mater goes to superior ganglion of glossopharyngeal nerve and vagus nerve like sleeves at jugular foramen.and arachnoid mater disappears after the ganglion;(4)The pia mater surrounding lower cranial nerves through jugular foramen clings to medulla oblongata where nerve root enters rather than enters jugular foramen like arachnoid mater and dura mater,pia mater disappears after lower cranial nerves leave medulla oblongata without the wrap and protection of nerves;(5)There are central myelin sheath and peripheral myelin sheath of lower cranial nerves through jugular foramen.the former is consisted of oligodendroglia and the latter is consisted of schwannomas.Central myelin sheath leaves from root entry zone,then arrive at peripheral myelin sheath,transitional zone lies where they encounter,which shows blunt/short arch;(6)There are different length between medial and lateral aspects of central myelin sheath from root entry zone to peripheral myelin sheath of lower cranial nerves through jugular foramen.medial side is shorter than lateral side,the length of medial side(0.41±0.19mm) of glossopharyngeal nerve is shorter than lateral side(0.69±0.34mm),and medial side(0.37±0.18mm) short than lateral side(0.54±0.24mm) for vagus nerve, medial side(0.35±0.13mm) is longer than later side(0.25±0.10mm) as for accessory nerve,in which there are preeminently statistical significance(P<0.001);(7)Central myelin sheath accounts for first1/4length of its cistern segment,the length of central myelin sheath of glossopharyngeal nerve、vagus nerve、accessory nerve is0.78±0.31mm、0.66±0.23mm、0.46±0.14mm.The statistical analysis by SPSS13.0shows there is not statistical significance between glossopharyngeal nerve and vagus nerve(P>0.05), while there is statistical significance between above-mentioned both and accessory nerve(P<0.05).ConclusionsThis experiment is used to explore the meningeal structure related to lower cranial nerves through jugular foramen by microanatomy and histological staining.there are new cognition compare with the past bibliographical information:(1)Lower cranial nerves through jugular foramen penetrates from behind postolivary sulcus of medulla oblongata rather not in the middle of the sulcus.glossopharyngeal nerve、vagus nerve and accessory nerve shows one or many tracts,surrounded by connective tissue sheath;(2)There are central myelin sheath and peripheral myelin sheath of lower cranial nerves through jugular foramen including glossopharyngeal nerve、vagus nerve and accessory nerve,transitional zone appears where they encounter,which is not the same as root entry zone,central myelin sheath consisted of oligodendroglia which lacks of the protection of schwannomas is susceptible to compression of vascular pulsation,then neuralgia arises;(3)There is not statistical significance of comparison of length of central myelin sheath between glossopharyngeal nerve and vagus nerve,which are shorter than trigeminal nerve reported;maybe that is why morbidity of vaso-glossopharyngeal neuralgia less than trigeminal neuralgia;there is central myelin sheath of accessory nerve,there is statistical significance of length compare with above-mentioned both,which suggests the length of central myelin sheath of motor nerve is shorter than sensory nerve.However,it is well known that the pain from vaso-glossopharyngeal neuralgia can resolve after vascular decompression at more distal sites,which suggests the effects of surgical decompression are caused by another mechanism;(4)There are different length in different direction as for the same central myelin sheath of one nerve,it is possible lateral vascular oppression leads to neuralgia but medial vascular oppression correspondingly in the same section.If vaso-glossopharyngeal neuralgia is caused exclusively by vascular compression of the central myelin sheath,which can be cured after microvascular decompression;(5)The surrounding meningeal structure of lower cranial nerves through jugular foramen shows distinct feature of start-stop and distribution.For the purpose of development of microneurosurgery,jugular foramen schwannomas types by Samii become subarachnoid type、foramen type、epidura type、epi-subdura type respectively.but so far there is not the systematic and detailed reports supplies anatomical data to this region.the start-stop and distribution of meningeal structure in this experiment supplies the gap.The meningeal structure determines the meningeal protection of nerve and vessel,which supplies anatomical foundation to operation according to the layers and interface of meningeal structure;(6)Dura mater surrounding lower cranial nerves through jugular foramen is divided into two layers,periosteal layer and meningeal layer,the former is the ultimate layer of nerve protection,as the last barrier,it favors protection of nerve and decreasing of cerebrospinal fluid leakage when keep it intact;the latter forms dura septum、dura fold.Lower cranial nerves through jugular foramen were separated by dura septum.which is used under arachnoid mater adhesion circumstances;jugular foramen dura fold may be identification marks of lower cranial nerves;(7) Arachnoid mater surrounding lower cranial nerves through jugular foramen goes to superior ganglion of glossopharyngeal nerve and vagus nerve like sleeves at jugular foramen,and arachnoid mater disappears after the ganglion,so arachnoid mater may become the operative interface to subarachnoid tumors during microneurosurgery,the surgical field may enlarge by opening the cistern;(8)Pia mater surrounding lower cranial nerves through jugular foramen clings to medulla oblongata where nerve root enters rather than not enters jugular foramen like arachnoid mater and dura mater,pia mater disappears after lower cranial nerves leave medulla oblongata.it may be pathological mechanism of vaso-glossopharyngeal neuralgia without the wrap and protection of nerves when problem vessel compressing.