Microsurgical Anatomy Of The Combined High Cervical Approach For Improvement Of Operative Approach At The Jugular Foramen

Jugular foramen(JF) is an important bony channel of the posterior fossa which is composed of the pars petrosa ossis temporalis and the pars lateralis ossis occipitalis.The best treatment for the lesions occurred on JF is surgical resection. With the development of the Imaging and microsurgical technique,it is possible to diagnosis and resect the lesions in this region.However,to operate at the JF is extremely difficult,mainly because of its deep location,safe operative approach buried by organizational structure,the complex anatomical relationship of the nerves and blood the vessels within JF,the complexity of anatomical structure of the JF itself.To correctly understand the anatomical structure of JF is of very important operative significance.There are two necessary conditions before operating on JF,to detailed understand the anatomical structure is the first one,.the other one is to select a suitable operative approach.The main purpose of this study is to improve the operative approach of the JF and investigate a new surgical approach to resect the JF lesions in one-stage, which are based on the microsurgical anatomical study of the JF.PartⅠ:Microsurgical anatomy of the combined high cervical approach for improvement of operative approach of the JFObjective To investigate surgical approach to resect the complex JF lesions in one-stage. Method Under a surgical microscope,20 cases(40 sides) adult cadaveric head specimens fixed in formalin were used to investigate the anatomic structure relatied to the JF via a combination of the transmastoid,retro- and infralabyrinthine, transjugular,extreme lateral infrajugular transcondylar transtubercular,and high cervical approaches.The procedures were described as below:1 A retroauricular curvilinear C-shaped skin incision was started approximately 2 to 3 cm posterior to the upper border of the ear.It continue posteroinferiorly into the neck over the anterior border of the sternocleidomastoid muscle(SCM) and under the mandibular angle;2 The posterolateral neck muscles could be anatomically categorized as three layers,These muscles could be separated to expose the suboccipital triangle and the structure within it;3 Following with theⅪth cranial nerve(CNⅪ) below the SCM, the entrance of the carotid sheath(CS) could be found,tracting the SCM posteriorly and the posterior belly of digastric muscle downward,the CS could be exposed at the area between the furcation of the carotid and the angle of mandible;4 The cortex over the outer mastoid triangle was removed by using a high-speed drill.The facial nerve(CNⅦ) in the fallopian canal was fully skeletonized with a diamond burr.A lateral suboccipital craniectomy was then performed with a rongeurs.The craniectomy usually extends medially toward the midline,superiorly to the inferior nuchal line,inferiorly to the posterior rim of the foramen magnum(FM),and laterally up to the occipital condyle.Removal of the posterior and medial one-third of the occipital condyle was finishied.Further drilling would expose another cortical layer of bone that covers the hypoglossal canal(HC),which was situated superior to the occipital condyle and inferior to the jugular tubercle(JT).The JT should be drilled away as much as possible to fully expose the posterior wall of JF.Total exposure of the JF could be achieved from multidirectional approaches,including supra jugular,infrajugular,postjugular and extrajugular exposures.Results 1 The posterolateral neck muscles could be anatomically categorized as three layers.The superficial layer was composed of the SCM and the splenius capitis muscles.The middle layer consisted of the longissimus capitis and the semispinalis capitis muscles.The deep layer consisted of the rectus capitis posterior major,the obliquus capitis superior,and the obliquus capitis inferior muscles(these three muscles form the suboccipital triangle).The superficial and middle layers of muscles were reflected posteriorly to expose the suboccipital triangle and the styloid diaphragm,a thick membranous structure that covered the posterior belly of the digastric muscle.The occipital artery was also covered by the styloid diaphragm and runs under the posterior belly of the digastric muscle.2 There were many significant anatomic landmarks around the JF,such as root of zygoma,spine of Henle, mastoidle,asterion,intrajugular processe(JP),transverse process of atlas(TPA), occipital condyle,Tymp-mastoid notch,stylomastoid foramen,and digastric crista. The outer mastoid triangle,which was formed by the posterior point of the root of the zygoma,the mastoid tip,and the asterion,marked the area of initial drilling for the mastoidectomy.The distance between the root of zygoma and asterion was as 38.67±2.00mm;mastoidle- asterion 46.50±2.62mm;asterion- Henle's crista 26.62±1.64mm.Tymp- mastoid notch could be regarded as surface project of the CNⅦproximately.The stylomastoid foramen was the exit of the CNⅦfrom the fallopian canal.The digastric ridge was an important landmark for defining it.The JP composed the posterior wall of the JF,it could be regarded as the bridge of the occipital condyle and the squamous part.The rectus capitis lateralis was attached to it.The asterion was defined as the junction of the lambdoid,parietomastoid,and occipitomastoid sutures,which was located over a portion of the transvers- sigmoid sinus complex in 90%(36 sides) in this research.TPA was a reliable landmark of the high cervical approach,it was detailed explain in the partⅢ.3,CNⅨ,CNⅩ,CNⅪpassed through the JF.C2 nerve formed a major ganglion,which set out a bigger medial branch and a smaller lateral branch.CNⅦstem departed the stylomastoid foramen lateral to the JF about 5mm,then it was divided in 5 parts.The length of the horizontal part of the CNⅦwas 12.67±2.36mm,and the perpendicular part was 15.03±1.83mm,The distance between stylomastoid foramen and the edge of parotid was as 17.00±1.83mm.The lesser occipital nerve came from the lateral branch,on the contrary,the greater occipital nerve from the medial branch.4.CS consisted of common carotid artery,internal carotid artery(ICA), external carotid artery,and internal jugular vein(IJV).Conclusion The research above described an approach was a combination of the transmastoid,retro- and infralabyrinthine,transjugular,extreme lateral infrajugular transcondylar transtubercular,and high cervical approaches.Total exposure of the JF could be achieved,and multidirectional approaches could be performed,including suprajugular(infralabyrinthine),transjugular,and infrajugular retrosigmoid/ transcondylar) exposures.Both intracranial and extracranial tumor could be removed in a one-stage procedure.Tumors at the foramen magnum and high cervical region are accessible through this approach.It offered advantages in reducing even preventing the injury of the CNⅦand other postoperative complications.PartⅡ:Microsurgical anatomy of the JFObjective To observe the anatomical base of the approaches to the JF,and to study the microsurgical anatomy of the JF and the organizations within it.Methods Same to PartⅠ.Results 1,At the intracranial end,the JF was divided into three compartments by a dural septations,including the petrosal portion anteromedially,the sigmoid portion posterolaterally and the intrajugnlar compartment located between the petrous and sigmoid portion.The dura overlying the intrajugular compartment formated two perforations.One of them was the glossopharyngeal meatus,through which CNⅨpassed.The other one was the vagal meatus,through which CNⅩand CNⅪpassed. These perforations were separated by a dural septum;2,After penetrating its dural meatus at the intracranial end of the JF,CNⅨturned sharply inferiorly and then coursed along the medial side of the intrajugular ridge just below the opening of the cochlear aqueduct.Within the JF,the nerve had two ganglia.The superior ganglion had no branches and might be difficult to see.The inferior glossopharyngeal ganglion was about 2 mm distal to the superior ganglion and located above the external end of the JF.The inferior ganglion rised to the nerve of Jacobson,which ascended vertically and then curved 160 to 170 degrees in an anteromedial direction to the tympanic canaliculus.It gave rise to the lesser petrosal nerve and then to the parasympathetic fibers to the parotid gland.The inferior ganglion also gave rise to a branch that connected to the superior ganglion of the vagus.The carotid branch of the CN IX(nerve of Hering) received fibers from the carotid sinus.After exiting the JF between the ICA and the IJV,CNⅨcoursed anteriorly,crossed the lateral surface of the ICA,and divided into its terminal branches.At its exit from the JF,CNⅨwas tethered to the ICA by dense fibrous bands.CNⅩhad multiple rootlets that, along with CNⅪ,entered the vagal meatus of the JF inferior to the glossopharyngeal meatus.Once it entered the foramen,CNⅩturned inferiorly in the same manner as CNⅨ.Within the JF,the nerve expanded at its superior ganglion where branched to and from CNⅨand CNⅪjoin.The auricular branch of Arnold also exited from the superior ganglion.This branch traveled laterally to the mastoid canaliculus and anterior to the IJV.CNⅩcontinued as the superior ganglion for the remainder of its course through the JF along the medial side of the temporal intrajugular process.CNⅩexited the JF together with CNⅪposterior to CNⅨ.At the level of the HC,CNⅩand CNⅪdiverged.Just below the JF,CNⅩexpanded into its inferior ganglion.After giving rise to the pharyngeal branch from this ganglion,the main trunk of CNⅩdescended in the neck within the CS.CNⅪwas a fusion of cranial and spinal rootlets.The cranial and spinal rootlets entered the JF through the vagal meatus either together or separately.Within the JF,CNⅪwas adherent to and indistinguishable from CNⅩ.After going out from the JF,CNⅪpassed posteriorly between the lateral surface of the IJV and the posterior belly of the digastric muscle with CNⅩ.The nerve then entered into the posterior triangle of the neck;3,The SS was the largest source of venous drainage into the JF.The sinus descended vertically in the sigmoid sulcus and then turned anteriorly toward the foramen.At the level of the occipitomastoid suture,the sinus coursed anteriorly below the petrous bone to the jugular bulb(JB).Blood then descended posterior to the tympanic bone into the IJV.The inferior petrosal sinus(IPS) linked the cavernous and basilar sinuses with the JB.It traveled along the petroclival fissure and received drainage from the inferior petroclival vein and intrapetrosal veins.The IPS did not empty directly into the JB.Instead,it formed a multichanneled confluence within the petrosal part of the JF that received drainage from the vertebral venous plexus,the hypoglossal venous plexus,and the condylar emissary vein.This confluence then emptied into the JB between CNⅨanteriorly and CNⅩposteriorly.4,As the ICA entered the carotid canal,it was separated posteriorly from the IJV by the carotid ridge or crest.Both vessels were surrounded by dense attachments of fibrous tissue formed by the CS,the periosteum of the jugular fossa,and the endosteum of the carotid canal.The inferior tympanic artery coursed with Jacobson's nerve into the carotid crest.The lower cranial nerves coursed between the ICA and the IJV at the skull base,with CNⅨlaterally and CNsⅩand CNⅪmedially.Conclusion:It was more significancent to divide the JF into petrosal portion,sigmoid portion and intrajugular compartment.To detailed understand the anatomical structure of the venous sinuses could help pretecting these sinus,Asterion wais a reliable landmark to locate the transvers-SS complex.The detailed micro-anatomic study might improve the success of surgery,protect cranial nerves and prevent from unnecessary injury.PartⅢ:Microsurgical anatomy of the Transverse process of atlasObjective To assess the clinical anatomical significance of the transverse process of the atlas(TPA) as a reference guideMethods 20 cases(40 sides)cadavers were dissected with a lateral cervical approach to explore the upper lateral neck.Cervical skin and platysma muscle were elevated to expose the underlying SCM.The digastric muscle was detached from the digastric groove to expose the TPA,which was marked as a reference center,to explored systematically the spaces in anterior,superior,and posterior respectively. With the aid of microscopy,the lymphoareolar tissues were removed carefully,in order to preserve the neurovascular structures.Parotidectomy,mastoidectomy and CNⅦrerouting were performed to enable better exploration.The fascia around TPA was removed to expose the underlying musculature.Result With the TPA used as a reference landmark in the dissection of the upper lateral neck,all of the important strutures in this space were easily identifiable.The posterior belly of digastric muscle and stylohyoid muscle could be identified lateral to the TPA.The occipital artery located at the medial to the posterior belly of the digastric muscle but superolateral to the TPA.The occipital artery was transected, and the posterior belly of the digastric muscle was detached from the digastric groove of the temporal bone and retracted inferiorly for further dissection and exposure.The styloid process could be identified anterior to the TPA.The IJV,CNⅩ,spinal accessory nerve CNⅪ,and CNⅫlocated between the styloid process and the TPA.The ICA could be identified at the anterior and medial to the IJV.The origin of 3 styloid muscles could be identified from the styloid process.The origin of the styloglossus muscle located on the anterior aspect.The styloglossus muscle directed anteroinferiorly to the posterolateral border of the tongue,where its muscle fiber intermixed with the hyoglossus muscle.Along the lateral border of the styloglossus,the stylohyoid ligament connected the styloid process with the lesser horn of the hyoid bone.Posteromedial to the styloglossus muscle showed the stylopharyngeus muscle.The stylopharyngeus muscle originated from the osteromedial aspect of the styloid process.On the posterior surface of the stylopharyngeus muscle,the CNⅨand its only motor branch could be identified. The CNⅨand the stylohyoid ligament pierced the space between superior and middle pharyngeal constrictor muscles to the tonsillar fossa and the lesser horn of the hyoid bone,respectively.Amputation of the styloid process exposed the distal ICA and CNⅨ,CNⅩ,CNⅪ,andCNⅫ.The longus capitis muscle could be observed deep in the ICA,on the anterior surface of the vertebral column.The JF and carotid canal could be reached by tracing the CS upward.However,the exposure was limited by the mastoid process,parotid gland,CNⅦ,and styloid process.To overcome this limitation,we performed a superficial parotidectomy and a cortical mastoidectomy.Small muscular branches of the CNⅦto the posterior belly of the digastric muscle and the stylohyoid muscle could be found around the stylomastoid foramen.Medial to these muscles,the posterior auricular artery and its stylomastoid branch sit nearby.The CNⅨemerged from the cranial cavity through the medial part(pars nervosa) of this foramen.The IJV,CNⅩand spinal accessory nerve leave the cranial cavity through the lateral part(pars venosa).The CNⅫemerged from the cranial cavity through the HC.Drilling of the temporal bone around the jugularforamen could expose the JB and posterior cranial fossa.The opening of the carotid canal was at the anteromedial to the JF.Amputation of the styloid process significantly exposed the distal ICA.Exposing the petrous part of the ICA required a dissection of the infratemporal fossa.For posterolateral exploration, the SCM muscle was detached from the mastoid process.The levator scapulae and splenius capitis muscles appeared after the SCM muscle was everted.After the splenius capitis was detached from the occipital bone,the longissimus capitis appeared.The longissimus capitis was carefully detached from the occipital bone to preserve the distal occipital artery,which located at just underneath this muscle. After the longissimus capitis was detached,the adipose tissue and deep cervical fascia were dissected around the TPA to display the underlying musculature and to expose the suboccipital triangle.This muscular triangle is bounded by the superior and inferior obliquus capitis muscles and by the posterior rectus capitis major muscle.Within this muscular triangle,on the superior surface of the C1 posterior arch,the terminal extradural segment of the vertebral artery can be found.Finally, through the posterior part of the atlanto-occipital membrane,the vertebral artery enters the FM. Conclusion The deep part of the upper lateral neck is a space of great anatomic complexity.Surgeons can use the TPA as a very useful surgical landmark in this space to help identify important structures and to prevent unnecessary morbidity.