The Anatomical Basis Of Kawase Approach

Purpose: Petrosum is located at the junction between the lateral/posterior cranial fossa and middle/lateral petrocliva.Brain tumours frequently invade and destruct the structures in the surrounding region including petrous apex,cabernous sinus,petrocliva,porus acusticus internus,cerebelli hiatus and cranial nerves III-VII.Surgical treatment of tumours in this area is always challenging owing to the depth of this area,the complex anatomical nature of petrosum,the intermingled key structures(namely nerves,blood vessels etc).The Kawase Approach is one key route for the surgical procedure in the petrous region.However,this approach is not without risks.Indeed,due to lack of rapid and practical method(s)in locating pars petrosa ossis temporalis,inner Cochlea,internal carotid,geniculate ganglion and facial-acoustic nerve complex,there have been frequently occurring complications during Cochlea location and procedures to expose this area.The present study aimed to,by way of microscopic dissection,1.search for more favorable anatomical markers and methods in locating Cochlea,inner ear cannals,pars petrosa arteriae carotidis internae(PPACI);2.explore reliable way to locate and expose this area during surgery via the anterios pectrous route and 3.gather information for clinical and surgical applications.Methods.Dry adult human skulls(n=5,or 10 sides)were used.The arcuate eminence(AE),groove for greater superficial petrosal,hiatus canalis facialis,fossa of gasserian ganglion,forame inosum,porus acusticus internus were of particular interest.Abrasion drills were used to expose and subsequent measure internal Cochlea,bony semicircular canals,internal acoustic meatus(IAM)and internal carotoid artery cannals.In addition,formalin-fixed full human adult skulls(n=5,or 10 sides)were used for arterial color infrared emulsion.Again,aforementioined key structures,as well as trigeminus;trigeminal nerve,greater superficial petrosal nerve,AE,petrocliva,sinus petrosus superior were dissected.After abrasion of the surface of petrosum to expose PPACI,the surrounding structures were similarly measured.Finally,microscopic dissection was carried out on 3 formalin-fixed full skulls using X6 to X25 objectives to mimic the surgical anterior petrosum Kawase approach.The methods,observation,exposure details and measurement of the surrounding structures were recorded and analysed.Results.1.The Kawase triangle is formed between gasserian ganglion(GG),Greater Superficial Petrosal Nerve(GSPN)and petrous crest.The triangle was further divided to the anterior and posterior triangles by internal acoustic canal(IAC).The anterior triangle was formed by GG,GSPN and MAI(meatus acustici interni),the posterior by AE,postrous crest and internal acoustic canal with Bartholin,canalis semicirculares and labyrinthine segment as the neighbouring structure in the front.2.The superior wall of the bony semicircular canal(BSC)was 1.89 mm below the middle cranial fossa and,in 6 out of 10 cases immediately beneath AE.In the remaining 4,BSC was in the deep bone,anterior and latereral to AE.Cochlea located in the deep bone,lateral to the front area of Kawase triangle.Cochlea can be identified from a square defined by the cross between inferior maxillary nerve,GSPN and IAM,a definition seen in 16 full skulls.3.It was safe to abrase petrous apex between the horizontal part of internal caroid artery and the petrous crest(mean distance 9.84mm).4.The length of anterior and posterior walls of IAC were respectively 12.58 mm and 8.39 mm.It was safe and would not injure the accoustic nerve when abrasing in front of a perpandicular line drawn from the trigeminal foreman to the petrous crest.5.Resection of petrous apex can be cone in the area defined by Dorello canal at front,upper semicircular canals at rear,PPACI to the lateral and can go 14.39 mm deep to reach sulci sinus petrosi inferioris.Conclusions.1.Forame inosum,GSPN and trigenmial foreman are hallmarks to identify petrosum during the Kawase surgical approach;2.AE varies in morphology and degree of protrusion and is hard to recognise when approaching via the subdural route;3.When dissecting cerebal dura,it is safer to start from behind inferior maxillary nerve,then GSPN,cerebral dura until reaching AE.4.A new and easy method to locate chochlea,IAC and PPACI is reported;5.Knowing the macro-and micro-structure of pars petrosa ossis temporalis and its surroundings is essential in protecting the petrous Chochlea,facial accoustic nerves and carotid arteries and ultimately reducing the surgical complications.