The Microanatomical Study Related To The Anterior Aneurysms Of Willis Circle And The Clinical Application Of The Microsurgical Techniques And The Analysis Of Treatment Outcome

The spontaneous SAH is mainly caused by the rupture of intracranialaneurysms. The incidence of aSAH is 85% in spontaneous SAH. Thesurvivors of the first bleeding will be threatened by death owing to thefollowed rebleeding. Nowadays, microsurgery and intravascular occlusion arethe chief methods to the intracranial aneurysms. The microsurgery is still themost important and ideal method. The microanatomical knowledge andmicrosurgical techniques and experience of the neurosurgeons still play theimportant role in the prognosis .The 90% of the intracranial aneurysms arelocated at the anterior willis circle. The majority of them can be clipped viathe pterional approach. Therefore, mastering the microanatomical knowledgerelated to the pterional approach is very important to performing theoperation .On addition, the trend of early operation at present needs the fastand correct diagnosis to the intracranial aneurysms . The exploring of thefactors directly related to the prognsis will add to improve the effect of thetreatment.Objective: On the basis of the microsurgical experience managing theaneurysms of anterior Willis circle, the vessels, nervous structures and cisternsrelated to anterior Willis circle were studied systemically, so as to improve themicrosurgical techniques associated with the pterional approach to managethe ipsilateral and contralateral aneurysms arising from the anterior Williscircle . Simultaneously, the fast and correct diagnostic methods were explored.The factors influencing prognosis were analyzed to put up the level ofmicrosurgical treatment .Methods: It was studied that the microanatomy of the vessels,nervousstructures and cisterns associated with the anterior Willis circle by thepterional approach . The solid anatomical relationships of these structureswere recorded and the related parameters were measured. Based on thesestudied outcomes, the clinical materials of 310 patients with aneurysms ofanterior Willis circle (All patients were operated on by the author himself)were retrospectively analyzed .The best diagnostic methods and themicrosurgical techniques were explored. The influencing factors directlyrelated to the prognosis were analyzed.Results:In order to extend the exposed extent of the vessels and nervousstructures around the anterior Willis circle , the outer space of transpterionalapproach must be widened. For this aim,the sphenoidal ridge should beremoved thoroughly . At the same time ,the inferior side of the bony windowmust be kept at the same level to the resected sphenoidal ridge. After this stepwas fulfilled , the microscopic visual angle of the outer approach will beenlarged 15oand the distance from the bony window to Willis circle beshortened 1.0～1.5cm . Because the numerous arachnoid trabeculae existbetween the cisterns,them must be cut to expose the vessels and nervousstructures within the cisterns . These cisterns include Sylvian cistern ,ICAcistern ,chiasm cistern and lamina terminalis cistern . In Sylvian cistern,the considerable anatomical variation of the MCA and its branchesexists ,but branches arising from the M1 trunk never supply the frontallobe .Because of this consistent anatomy, it is easier to retract the frontal lobeaway from the MCA than to retract the temporal lobe . The presence of thisfrontal corridor influences head position ,extent of bony removal ,andmicrosurgical exposure .After opening the above cisterns , some cavities willbe displayed , including : ①the cavity before chiasm. In this cavity , theinside wall of ICAC2 segment and a group of perforating arteries arising fromit can be seen under contralateral optic nerve . Owing to the difference ofdistance from chiasm to sphenoidal platform, the chiasms are classified intothe three types, them is the normal ,anterior and posterior types .In theanterior type , the inside wall of ICAC2 segment can not be displayed via thecontralateral pterional approach . In the later two types, 2.o～7.0mm insidewall of ICAC2 segment can be exposed .The above types are the anatomicalbasis whether the ANs on the inside wall of ICAC2 segment can be managedby using contralateral pterional approach;②The cavity between optic nerveand ICAC2 Segment . There are perforating arteries arising from the insideand inferior wall of ICAC2 segment and PComA(3/10);③Lamina terminaliscavity. The AComA complex exists in this cavity;④The outside cavity ofICAC2 Segment .The PcomA ,AchA and the branches arising from them canbe displayed . After removing the anterior clinoidal process , the optic nervewithin the optic canal and OA can be showed .Getting across the optic nerveand chiasm, the contralateral ICA cistern and Sylvian cistern can beopened , after that the distal ICAC2 segment and its bifurcation ,ACAA1segment ,MCAM1 segment ,AchA and PcomA can be displayed . The aboveexposed extent is the anatomical basis to clip the contralateral and bilateralANs of anterior Willis circle via a pterional approach .Based On the anatomical study , the 310 patients with ANs of anteriorWillis circle were treated by the author using the microsurgical technique .The 118 men and 192 women were included in this series. The age range ofpatients is from 26 to 84 years and 22cases older than 65 years. The 87 caseswere companied by hypertension (28.06%).The clinical manifestation of 295cases in 310 patients is SAH .The diagnosis methods of ANs and the numberof patients are as follows :CTA 224 cases,DSA 56 cases ,DSA+CTA 15case ,MRA 10 cases . The five patients were directly operated on withoutcerebral vascular angiography. After the ruptured ANs were clipped in 22cases with MIA , the unrupture ANs in 17 cases of 22 patients also weremanaged at the same time (11 cases) and separately clipped (6 cases). The 21patients with UIAs received microsurgical treatment. The admission andpreoperative HHS in 310 patients were as follow :GradeⅠ113,GradeⅡ 116,GradeⅢ 64, GradeⅣ13 and Grade V 4 cases .The number of patients invarious surgical periods were as follows :the early (within 72h after SAH) 137,the median (4-14d after SAH) 70 and the late period (14d later after SAH )103cases.All the operations were performed by using pterional approachexcept 1 case with ACAA4 AN. The two clinoidal segment carotid artery ANswere clipped via contralateral pterional approach .The bilateral aneurysms ofanterior Willis circle were managed via one approach in two patients .Thedecompressive craniectomy was used in 19 cases. The 202 cases in 310patients were followed up from one month to nine years and three months,more than 1 year in 145 cases. The outcome at discharge was categorized asthe fair, the slight morbidity, severe morbidity and death . The GOS was usedin follow-up .The GOS 5 and 4 was regarded as good-prognsis,GOS 3, 2 and1 as poor –prognosis . The statistical analysis used SPSS software, rank sumtest. The p<0.05 was determined as a significant difference.There were no false positive and negative diagnostic outcomes of ANs in224 cases with CTA and 56 cases with DSA. The showed smallest AN usingthe both methods was 3.0 mm. The controlling outcome between the CTA andDSA in 15 patients was all the same. The false aneurysm localization wasfound in one of 10 patients with MRA. The intraoperative aneurysm rupture(IAR) took place in 60 cases (18.98%). The intraoperative temporaryocclusion of parent arteries was performed in 92 patients (29.68%). There wasno significant difference in GOS outcome between the both rupture versusunrupure groups and temporary occlusion versus no temporary occlusiongroups (P>0.05). The decompressive craniectomy was given 19 patientspresenting with severe brain edema and swelling and the rate ofgood-prognosis was 69.23%. The favorable outcome was obtained in 93.33%of cases with UIAs. The 100% of 13 followed patients with MIA showed goodprognosis. There was no significant different outcomes to HHS Grade Ⅰ-Ⅲ patients in different surgical periods(p>0.05).The 12 HHS Grade Ⅲpatients not received surgical treatment within 72h after SAH all showedpoor-prognosis . The 9 cases given early operation in 13 HHS Grade Ⅳpatients was far better than the cases operated on in other periods anduntreated ones .The rate of good-prognosis in HHS Grade Ⅰ-Ⅴ patients was94.44%,85.14%,71.11%,3/8 and 1/4 respectively .The outcome in the elderly(>65 years) and the patients with hypertension showed no significantdifferences in comparison with other groups (p>0.05).The good prognosis inall 310 patients was gained in 82.18% (182/202).Conclusions: The majority of aneurysms arising from the anterior Williscircle can be clipped via a pterional approach .By way of the sphenoidal ridgebeing removed thoroughly and keeping it at the same level with the inferiorside of bony window ,the outer space of approach will be widened .It is a veryimportant step .Under the circumstances,it extend the exposed extent ofvessels and nervous structures around the anterior Willis circle with slightbrain retraction .Because of the presence of frontal corridor ,Sylvian fissureshould be opened by means of retracting the frontal lobe . After the relatedcisterns are anatomized respectively , a lot of vessels and nerves can bedisplayed ,as well as the blood in subarachnoid space be cleared away .Theipsilateral and contralateral exposed extent of anterior Willis circle revealedby anatomical study offers microanatomical basis for managing the bilateralMIA or contralateral aneurysms via a pterional approach .In evaluating the features of ANs and early diagnosis ,CTA is superior toDSA and MRA .By a pterional approach , not only the ipsilateral aneurysmsof anterior Willis circle can be clipped ,but also contralateral aneurysms bemanaged , including the ANs arising from ICAC2 segment,ICA-AchA,ICA-PcomA,ICA bifurcation ,ACAA1 and M1 segment .The decompressivecraniectomy used in the patients presenting with severe brain edema andswelling can decrease the mortality and morbidity .With perfect microsurgicaltechniques ,the intraoperative aneurysm rupture and temporaryocclusion(<20min)of the parent arteries did not increase the rate ofpoor-prognosis .For unruptured aneurysms ,the "risk –benefit" should beassessed before determining microsurgical treatment .In MIA, after theruptured aneurysms are clipped ,the unruptured aneurysms should be managedif only a approach can do it ,otherwise ,the separate clipping be selected .Theearly surgery is suitable for all the patient with HHS GradeⅠ-Ⅴ.If thepatients with HHS Grade Ⅰ-Ⅱ get worse (Grade Ⅲ-Ⅴ) in 72h later afterSAH ,the operation should be postponed. For the elderly and the patients withhypertension, the favor able outcome can be obtained after the acquiring goodintraoperative and complex management. The microanatomical knowledgeand microsurgical techniques and experience of the neurosurgeons is anotherimportant influencing factor to the prognosis.