Clinical Anatomy Of Endoscope Assisted Mastoid Approach To The Lateral Skull Base

Background:With the development of micrological technique,image technique and the endoscopic technique,the investigation in laterol skull base have been the focus of the territory of head and neck surgery.But the anatomy structure in this area was complicate,and the operative procedure was difficult.So it is very important to choseing an appropriate surgical approach in the treatment of the lesions in the latero-skull base.Our purpose in the selecting of the ssurgical approach was to relieve the distraction of the normal structure,gain well exposure,shortening the distance to the lesion,amelioration the illumination of the deep part and amplification the operation area.The operating microscope could provide satisfactory lighting and high-quality enlarged image,but which also had many shortcomings,such as the operator only can to observe the structure exactly anterior aspect the axial ray of the objective lens,and in some tomes it need to destroy the normal tissue for the exposure of the lesion.The endoscope could provide the convenient to the operative procedure in the area that it was difficult to operate under operating microscope.The image under the endoscope is different from what under the microscope and the approach can offer a direct acces to the lesion.Now the endoscope surgery has been used in the surgical treatment of the lesion of internal acoustic meatus, cerebellopontine angle,petrous apex and jugular foramen by some people.But the endoscope also has it's shortage,it could not to observe the anatomic structure behind the top of the endoscope,and it has no stereo-feel of the image under the endoscope. The anatomy under the endoscope is different from what under the microscope,thus being familiar with anatomy in lateral skull base under the endoscope is important in carrying out the endoscope surgery of lateral skull base in clinical practice.Objectives:1.To investigate the surgical approach of the jugular foramen and the clinical anatomy of the transmastoid endoscopy-assisted jugular foramen surgery.To observe the relationship between the jugular bulb and the surrounding structure,and to investigate the classification and morphology of jugular bulb.2.To investigate the anatomy of the endoscopic presigmoid-retrolabyrinthine (PSRL) approach and the endoscopic retrosigmoid(RS) approach,and to provid the data for the choice of surgical approach.To study the anatomy of external aperture of vestibular aqueduct and endolymphatic sac and to discuss the protective methods of endolymphatic sac in the PSRL approach.3.To investigate the anatomical dimension of the path to the petrous apex via the infralabyrinthine approach.4.To discourse the landmark of facial nerve in the surgery relate to the temporal bone,and to investigate the topographical relationship and the anastomosis of the nerver in humans internal auditory canal.Methods:1.The transmastoid endoscopy-assisted jugular foramen surgery was simulated in 15 adult cadaveric specimens(30 sides).The main anatomic mark in the surgical approach was studied,and the distance between the important structures to the glomus jugular has been measured. 2.In this study,we dissected 30 human temporal bones and studied 120 cases CT imaging data of temporal bone and 6 cases blood vessel cast mould specimen of the jugular bulb,to observe the morphology of jugular bulb.We made imagination plane through the medial wall of the tympanic cavity,made a level tangent line of the proximal wall of the tympanic,a vertical tangent line of the posterior wall of the tympanic,look it as coordinate axis(the X axis and Y axis),so the four quadrant (Ⅰ,Ⅱ,Ⅲ,Ⅳ) have been formed,the quadrant that with the tympanic is the quadrantⅠ.So the jugular bulb was classified according to the position of its dome.3.The endoscopic PSRL approach and the endoscopic RS approach were simulated in 15 adult cadaveric specimens.The anatomic characteristic was studied, and the distance between the importand structors to the anterior border of the bone window in each surgical approach were measured.4.Used 10case(20 sides) formalin fixed heads of people,to anatomy the external aperture of vestibular aqueduct and endolymphatic sac with surgical microscope according the presigmoid-retrolabyrithine approach.The location of external aperture of vestibular aqueduct and endolymphatic sac were measured and compared with canalis semicircularis posterior.5.Thirty dry temporal bone were discissio along the internal carotid canal.The distance from the vertical stage of the facial nerve to the lap of the internal carotid canal,the vertical stage of the facial nerve to the petrous apex,the lap of the internal carotid canal to the posterior surface of the os petrosum were all measured.10 case (20 sides) head of adult people were dissected to gain access to the petrous apex via the infrelabyrine approach.The horizontal and vertical dimensions of the access window created were measured.We also studied 60 cases spiral CT imaging data of temporal bone,and to study the main anatomy structures of the petrosal bone,the characteristic of the air cell in the petrosal,the distance from the vertical stage of the facial nerve to the lap of the internal carotid canal,the vertical stage of the facial nerve to the petrous apex,the lap of the internal carotid canal to the posterior surface of the os petrosum were all measured.6.We dissected 30 cases human temporal bones from 15 heads in order to examine the topographical relationship and the anastomosis of the nerves in the internal auditory canal.7.30 cases temporal bone have been dissected according to middle ear surgery and the facial nerve decompression surgery.28 cases of facial nerve paralysis in temporal bone fractures were performed in the facial nerve decompression surgery. The surgical marks of the facial nerve have been studied.Results:1.The distance between the glomus jugular and the vertical segmental of the facial nerve,the anterior wall of the glomus jugular to the facial nerve and the glomus jugular to the posterior semicircular canal were(3.58±1.33)mm,(5.07±2.93)mm and (4.68±3.47)mm.In 30 cases,the top of the glomus jugular inferior the tympanic cavity in 33%(10 cases),17%(5cases)were behind the facial nerve and the tympanic, 40%(12cases) the facial nerve was in the middle of the glomus jugular,7%(2 cases) were near the inferior wall of internal auditory meatus and 3%(1cases)was protruded into the tympanic cavity.The cranial nerve and blood vessel in the jugular foramen was clearly to be show.2.Some jugular bulb was flat type and others were prominent types.The classification in the group of the CT image:typesⅠ,11 case;typesⅡ,63cases;typesⅢ,25cases;typesⅣ,21cases.Classification in the group of the specimen:typesⅠ,1 case;typesⅡ,11 cases;typesⅢ,8cases;typesⅣ,10cases.Each type of the jugular bulb has different effect on the operative approach.3.The distance between the craniotomy to the internal auditory canal,the trigeminal nerve and the pneumogastric nerve in the endoscopic PSRL approach were (14.04±3.56) mm,(28.62±1.62) mm and(12.53±4.11) mm;and that in the endoscopic RS approach were(28.66±3.78) mm,(42.06±2.42) mm and (33.16±4.71) mm.The endoscope near parallel to the posterior surface of the pars petrosa in PSRL approach,and have some angles in the RS approach.And the relationships between anatomy structures were different.4.The projection circumscription of the external aperture of vestibular aqueduct on the well of mastoid cavity was only 3 mm post eroinferior the posterior semicircularis canalis,and only in 4 cases the external aperture of vestibular aqueduct was lower than the posterior semicircularis canalis.In the 20 cases of endolymphatic sac,typeⅠ12 cases,typeⅡ7 cases and typeⅢ1 cases.The caudal end of the endolymphatic sac can exceed the sigmoid sinus.5.The vertical stage of the facial nerve to the lap of the internal carotid canal in dry temporal bone and in CT image were(13.26±1.66) mm and(14.45±1.73)mm;the facial nerve to the petrous apex were(34.48±1.07)mm and(34.42±2.03) mm,the lap of the internal carotid canal to the posterior surface of the petrous were(9.68±1.53) mm and(11.70±1.38)mm;the mean dimensions of the window in dissected bone was (5.76±3.38) mm vertically and(6.42±2.65)mm horizontally.13 sides have been doing well with the infralabyrinthine approach.6.(1) In 11 cases,the facial nerve was anterosuperior to the vestibulocochlear nerve in the whole portion of the internal auditory canal,and in 19 cases,the facial nerve was revolved 30°-90°to the anteroinferior direction from the base of the internal auditory canal to the pores acusticus,which is at the similar direction to that of the cochlear.(2)Vestibulo-facial anastomosis occurs in 25 cases of which 67%(16 cases) appears near the porus acusticus,33%(8 cases) between the base and intermedial portion of internal auditory canal.(3).Vestibulocochlear anastomosis occurs in 24 cases,among which,some brush-like nerve fiber bundles of the cochlear nerve were seen to enter the acculus proprius directly in 13 cases.Transverse vestibulocochlear anastomosis in the fundus of internal acoustic meatus occurred in 15 cases,including 2 cases with more anastomoses.No vestibulocochlear nerve anastomosis found in 6 cases in this study.7.The lateral lap of the facial nerve was(1.70±0.33) mm under the point between posterior and middle 1/3 of lateral semicircular canal.The vertical line combined this point and the anterior extremity of the conker's crista clews the vertical part of the facial nerve.The line combined the super range of the fenestra vestibuli and the super range of the foot of the cochleariform process clews the inferior edge of the horizontal segment of the facial nerve.And on the prolong line(2.84±0.23)mm anteriad the cochleariform process is the geniculate ganglion,the air cells lateral facial recess is hopeful to locating the facial recess and the facial nerve,and the air cells was in the lateral of the facial nerve 0-2mm.Conclusions:1.It is a sample and little damaged way to use the transmastoid endoscopy-assisted jugular foramen surgery and it is hopeful to protect the function of the facial nerve,acoustic nerve and the post- cranial nerve.It is a sample and three-dimensional way that the classification method with the four quadrants,it is hopeful to the imaging diagnosis and the preoperative design.2.The distance from the cortical skull table to the cerebellopontine angle in the endoscopic PSRL approach is shorter than it in the RS approach.The endoscopic PSRL approach have better visual field of the gastrocerebellum,and the the RS approach have better visual field of the posterior surface of the pars petrosa.In order to protect the endolymphatic sac,it should be remaining 3mm distance to the canalis semicircularis posterior when we stripping the bone beside the canalis semicircularis posterior.The incision of endocranium shouldn't exceed the marg of the endolymphatic sac.It is hopeful to protect the acouesthesia.3.The possibility of this anatomical variation should be considered when the surgical approach to the petrous apex lesion the infralabyrinthine approach being planned.And the infralabyrinthine approach is useful to the patients with good hearing.4.The vestibulo-facial anastomoses and the vestibulocochlear anastomosis do existting,and the topographical relationship and the anastomosis of the nerve in human internal auditory canal are variably.The landmark in the facial nerve in the temporal bone:the fenestra vestibuli,the cochleariform process,lateral semicircular canal,superior semicircular canals,and the air cells lateral facial recess caould be dependable and reliable landmark for the facial nerve.