Microanatomy Of The Membranes In The Cerebellopontine Cistern

Objective: To illuminate the shape and range of every cistern in CPA and the anatomy about nerves and vessels in cerebellopontine cistern by studying microanatomy of cerebellopontine cistern,mainly focused on distribution of arachnoid in internal auditory cannal and membranous structures about acoustic neuroma.To provide anatomic basis for protection of facial nerve and cochlear nerve in the acoustic neuroma surgery.Methods:(1)Observing the anatomical structure of CPA cistern by watching surgery video s of microvacular decompression(MVD).(2)Observe the shape and membrane structure of e very cistern,and relationships between nerve and vessels under microscope by retrosigmoid a pproach on 3 cadaver heads(6 sides)after cutting the arachnoid.Observation and measureme nt work was repeated after cutting cerebral hemisphere above the level midbrain.(3)The petr ous bones were cutting down with internal auditory canal and decalcified.The arachnoid stru cture was distinguished under microscope after slicing and dyeing of HE.Results:(1)There are three cisterns in cerebellopontine angle which are the prepontine cistern,the cerebellopontine cistern and the cerebellomedullar cisterna lateralis.The closet one about acoustic neuroma surgery is cerebellopontine cistern.It is located in the space of brainstem,cerebellum and petrous bone.The front part is adjacent to the prepontine cistern,the top part is next to cisterna ambiens,the bottom part is next to cerebellomedullar cisterna lateralis,the inner side is adjacent to pons,the posterior part is covered by quadrate lobe of cerebellum and upper crescentic lobe,the posteromedial part adjoins pontomedullary sulcus,the outboard part extended into internal auditory canal and Meckel cave along petrous bone.There are trigeminal nerve,facial nerve,vestibulocochlear nerve,anterior inferior cerebellar artery,internal auditory artery,anterolateral pontinevein,lateral pontine vein and superior petrosal vein.(2)The cranial nerves were found packaged by the arachnoid sheath after leaving brainstem in the videos of MVD surgery of 20 patients.Facial nerve and vestibulocochlear nerve were accompanied by the arachnoid sheath until arriving at the bottom of the internal auditory canal.No arachnoid division was observed in the arachnoid sheath which separate vestibular nerve from cochlear nerve and facial nerve in internal auditory canal.Conclusions:(1)The anatomy in cerebellopontine angle is complex,but most structure is normal without variation.Cranial nerves were packed by arachnoid sheath in the cisterns which formed barriers among cranial nerves adjacent.(2)Most acoutic neuroma is derived from subarachnoid.The capsule found intraoperation acturally is the perineurium of vestibular nerve which was confirmed connective tissue but not arachnoid.(3)Doctors should seek,confirm,persist this perineurium and follow the principle of seperating sub-perineurium strictly in the acoustic neruoma surgery.It is vital important to protect facial nerve and cochlear nerve.