chronic subdural hematoma ( csdh ) is a rare complication of unruptured aneurysm clipping surgery5,12 ) . because csdh signs and symptoms may appear slowly ,
it can cause problems such as headache , dizziness , seizure , and hemiparesis , and requires surgical drainage .
mori et al.11 ) reported severe complications of surgical drainage of postoperative csdh , such as tension pneumocephalus and acute subdural hematoma , which can cause permanent neurologic deficits or death .
the general incidence of csdh after brain surgery is reported to be approximately 0.3 - 1.5%8,12 ) however , aneurysm clipping surgery is regarded as an important risk factor of postoperative csdh7,10,11 ) .
it is known that advanced age ( > 70 years ) and male gender may contribute to csdh after clipping surgery5,12 ) . additionally , postclipping csdh
considering the relatively benign course of unruptured aneurysms , it is important to prevent csdh and identify its risk factors after clipping surgery in order to minimize treatment - related morbidity .
the purpose of this study was to determine the incidence and risk factors of postoperative csdh after surgical clipping for unruptured anterior circulation aneurysms .
between january 2008 to december 2013 , 980 consecutive patients with unruptured aneurysm underwent surgical clipping in a single tertiary institute . to reduce technical variables that depend on the surgeon ,
inclusion criteria were unruptured small to large aneurysms ( size<2.5 cm ) on anterior circulation .
exclusion criteria were giant or complex aneurysms requiring complicated surgical techniques such as bypass surgery .
we also excluded distal anterior cerebral artery ( aca ) aneurysms and posterior circulation aneurysms that were approached by other than pterional approach , such as anterior frontal craniotomy , subtemporal approach , and etc .
we reviewed their medical records as well as radiological data including age , sex , size and location of aneurysm , size of craniotomy depending on the surgical approach , premature rupture , presence of arachnoid plasty , degree of preoperative brain atrophy , usage of antithrombotics and amount of immediate postoperative subdural fluid collection ( sdfc ) .
we categorized the location of aneurysm as aca , middle cerebral artery ( mca ) , and internal carotid artery ( ica ) according to the parent artery .
aneurysm sizes were divided into three groups based on diameter : tiny ( < 5 mm ) , small ( 5 - 10 mm ) , and large ( 10 - 25 mm ) .
the size of all aneurysms was its maximal diameter as measured by the three - dimensional reconstructed images of digital subtraction angiography .
the degree of preoperative brain atrophy was estimated using the bicaudate ratio ( bcr ) , which is defined as the ratio of the width of ventricles between the caudate nuclei and internal diameter of the vault at the same level2 ) .
bcrs were measured on brain computed tomography ( ct ) scans that were taken within 6 months prior to surgery . in patients without ct scans , we used magnetic resonance t2-weighted imaging scans that were obtained within same period .
postoperative sdfc was defined as the maximal distance between the inner table of the skull and the cerebral cortex .
we measured its maximal vertical depth on the ipsilateral side of the clipped aneurysm on brain ct angiography that was performed 3 or 4 days after surgical clipping .
we compared two groups who had postoperative sdfc less than or greater than 10 mm .
the indication of surgery was determined by patient 's symptom . in the case of symptomatic patients with headache or focal neurological deficit ,
a surgical intervention was performed , whereas in case of asymptomatic patients were treated with conservative management with a clinical follow - up .
we excluded the cases of csdh did not require surgical drainage because we did not perform routine radiological follow - up if they had no progressive symptoms .
after clipping surgery , brain non - contrast ct and intracranial ct angiography was performed on postoperative days 1 and 3 or 4 , respectively .
after discharge , clinical follow - ups were routinely performed 1 , 3 , and 6 months after clipping surgery at our outpatient clinic .
scheduled radiologic follow - ups using intracranial ct angiography were performed after 1 or 2 years . however , imaging studies were employed when any patient showed clinical symptoms or signs that required further evaluation .
surgical treatments were performed using a standard pterional approach or lateral supraorbital ( lso ) approach .
the surgical techniques and average craniotomy size of these two approaches have been described previously3,16 ) .
if necessary , temporary clips were placed in order to soften the aneurysm and to reduce intraoperative rupture .
arachnoid plasty has been used since april 2011 . the arachnoid plasty technique applied fibrillar [ surgical fibrillar ( ethicon llc , san lorenzo , puerto rico ) ] and fibrin glue at the dissected arachnoid surface at the end of surgery ( fig .
1 ) . mean and frequency comparisons were performed using student 's t - tests , chi - square (  ) tests , mann - whitney u tests , or fisher 's exact tests as appropriate .
univariate statistical analyses (  tests or fisher 's exact tests ) were performed to assess associations between variables and csdh , the categorical variable .
the variables with p - values < 0.10 in univariate analyses were selected for multivariate models using multiple logistic regression analyses .
statistical analyses were performed using spss 19.0 software ( spss inc . , chicago , il , usa ) .
surgical treatments were performed using a standard pterional approach or lateral supraorbital ( lso ) approach . the surgical techniques and average craniotomy size of these two approaches
have been described previously3,16 ) . if necessary , temporary clips were placed in order to soften the aneurysm and to reduce intraoperative rupture .
arachnoid plasty has been used since april 2011 . the arachnoid plasty technique applied fibrillar [ surgical fibrillar ( ethicon llc , san lorenzo , puerto rico ) ] and fibrin glue at the dissected arachnoid surface at the end of surgery ( fig .
mean and frequency comparisons were performed using student 's t - tests , chi - square (  ) tests , mann - whitney u tests , or fisher 's exact tests as appropriate .
univariate statistical analyses (  tests or fisher 's exact tests ) were performed to assess associations between variables and csdh , the categorical variable .
the variables with p - values < 0.10 in univariate analyses were selected for multivariate models using multiple logistic regression analyses .
the patients enrolled in this study ( n=518 ) consisted of 173 males and 345 females aged 56.579.03 years ( meanstandard deviation ) .
table 1 summarizes the baseline characteristics of patients . of these , 16 ( 3.1% )
patients suffered from postoperative csdh , which required burr hole drainage surgery . in univariate analyses ,
multivariate analyses also showed similar results [ p=0.017 , odds ratio ( or ) 4.037 , range 1.287 - 12.688 ] . in this study , we observed no statistically significant correlation with advanced age ( 65 years vs. < 65 years , 4.4% vs. 2.7% , p=0.257 based on fisher 's exact test ) .
the group with higher bcr indices tended to show larger postoperative sdfc in this study ( 4.0 vs. 4.2 , p=0.083 based on mann - whitney u test ) .
in addition , the bcr index was associated with postoperative csdh whereas sdfc was not ( table 2 ) .
the location and diameter of aneurysms were positively associated with risk of symptomatic csdh in univariate analyses .
compared to other locations , aca aneurysms had higher incidences of csdh in fisher 's exact test ( 6 cases , 5.4% , p=0.051 ) . additionally , larger aneurysms resulted in a higher incidence of csdh in fisher 's exact test ( 3 cases , 12% , p=0.030 ) .
however , these differences were not significantly different in multivariate analyses using logistic regression test ( p=0.231 and p=0.243 , respectively ) .
these findings were statistically significant in uni- and multivariate analyses ( p=0.004 , or 4.854 , range 1.658 - 14.085 ) .
all patients who received surgical treatment recovered completely and experienced no complications or permanent neurologic deficits .
no patient had recurrence of csdh , and complete csdh resorption was confirmed by follow - up brain ct scans .
in this study , we found that male gender was associated with csdh , which agrees with the findings of previous studies5,12 ) .
but , the reason of male preponderance ca n't be explained by the results of this study .
kanat et al.6 ) suggested that the male preponderance of csdh in adults may be due to more brain atrophy and increased in cerebrospinal fluid ( csf ) in male gender and estrogens may have a protective effect on the capillaries .
brain atrophy was also associated with postoperative csdh in this study , but other factors such as increment of csf or hormonal effect should be considered again in future study . in addition , previous studies have demonstrated that postoperative sdfc and advanced age were associated with postoperative csdh5,12,15 ) .
we hypothesized that the degree of preoperative brain atrophy estimated by bcr and the degree of postoperative sdfc affect the development of postoperative csdh17 ) .
postoperative sdfc can result from a newly developed artificial csf tract from the torn arachnoid membrane to the subdural space created by surgical dissection9 ) .
if a patient has a higher degree of brain atrophy , the maximal depth of postoperative sdfc could also be higher .
csdh tends to occur in elderly people because brain atrophy causes enlargement of the subarachnoid space and stretching of the bridging veins .
these pre - existing conditions facilitate tearing of the arachnoid membrane and leakage of bloody csf into the subdural space after a neurosurgical procedure , thus producing overdrainage of csf from the subarachnoid space or the ventricular system13 ) .
a previous study demonstrated that sdfc after aneurysm clipping might contribute to csdh12 ) . in theory , these explanations appear to be acceptable .
our data indicate that higher bcr indices tended to show larger sdfc . however , sdfc itself was not associated with csdh .
these differences can be explained by the following : first , the maximal vertical depth of the sdfc did not represent its total volume .
if the exact volume of sdfc could be measured , the results might be different .
second , the timing of brain ct scans differed and we did not checked serial follow - up ct scans , which can determine whether sdfc increased .
changes in sdfc might be more predictive of the incidence of csdh rather a single measurement of sdfc . in this study
, the degree of brain atrophy using bcr is a better predictor than age or sdfc to predict postoperative csdh . in order to prevent csf leakage from the subarachnoid space to the subdural space , arachnoid plasty
the arachnoid plasty is not a generally accepted procedure in unruptured aneurysm surgery , but sealing of dissected arachnoid plane as an effort to prevent csf leakage seems to be convincing . if sdfc after craniotomy was related to csdh occurrence , effective arachnoid plasty would reduce postoperative csdh .
mino et al.9 ) reported that arachnoid plasty using fibrin glue prevented sdfc after ruptured aneurysm surgery .
differences between the mino et al.9 ) study and our study included aneurysm status ( ruptured vs. unruptured ) and number of patients .
additionally , fibrin glue could spontaneously deteriorate over time , thus resulting in continuous csf leakage .
however , the number of patients included in the previous study was relatively small ; therefore , it is difficult to conclude that arachnoid plasty has significant general efficacy .
further studies are required to determine the detailed technical procedure as well as the role of arachnoid plasty in aneurysm surgery .
the reported incidence of postoperative csdh after brain tumor removal is 0.4% , and the incidence after aneurysm clipping surgery is 2.4%12 ) .
the main difference between these types of surgery is the extent of arachnoid dissection . in this study ,
aca location tended to be associated with csdh in univariate analyses and may have correlated with the range of cisternal dissection to soften the brain and expose the aneurysm .
aca aneurysm surgery usually requires dissection of the sylvian fissure , chiasmatic cistern , and interhemispheric cistern ; however , other procedures require less .
these procedures create a new csf tract from the subarachnoid space to the subdural space4 ) .
although immediate sdfc was not associated with the incidence of postoperative csdh , considering the higher incidence of csdh in clipping surgery , perhaps the continuous leakage of csf through the surgically - dissected cisternal space may contribute to delayed csdh that requires surgical intervention .
the maximal depth and amount of immediate postoperative sdfc can be larger in mass debulking surgeries , such as brain tumor removal , compared to aneurysm clipping .
indeed , most subdural fluid collections are asymptomatic and disappear spontaneously and have thus not received much attention15,17 ) .
authors thought that the association of aca aneurysms with csdh could suggest that more extensive cisternal dissection would have a clinical role in the development of postoperative csdh . in our data set , we observed a strong association between csdh and the use of antithrombotic medication . in our perioperative antithrombotic management strategy ,
we stopped medications such as aspirin or clopidogrel 7 days before surgery . in patients using antithrombotics , we corrected the bleeding tendency just before surgery .
antithrombotic therapy was started again after we confirmed there was no evidence of hemorrhage on brain non - contrast ct scans 1 day post - surgery .
the use of antithrombotic medication is known as an independent risk factor for csdh in general1,14 ) .
therefore , patients using antithrombotic medication require special attention due to the potential risk of csdh
. also optimal timing of resuming antithrombotics to reduce postoperative csdh should be identified in further study .
we did not set routine radiological follow - up protocol for observing natural changes of asymptomatic postoperative csdh .
second , the history of coexisting medical diseases was not fully considered , and could increase the risk of bleeding .
prospective studies are necessary to further elucidate the incidence and risk factors of postoperative csdh after surgical clipping .
this study shows that male gender , degree of brain atrophy , and the use of antithrombotic medication were associated with postoperative csdh .
 objectivechronic subdural hematoma ( csdh ) is a rare complication of unruptured aneurysm clipping surgery . 
 the purpose of this study was to identify the incidence and risk factors of postoperative csdh after surgical clipping for unruptured anterior circulation aneurysms.methodsthis retrospective study included 518 patients from a single tertiary institute from january 2008 to december 2013 . 
 csdh was defined as subdural hemorrhage which needed surgical treatment . 
 the degree of brain atrophy was estimated using the bicaudate ratio ( bcr ) index . 
 we used uni- and multivariate analyses to identify risk factors correlated with csdh.resultssixteen ( 3.1% ) patients experienced postoperative csdh that required burr hole drainage surgery . in univariate analyses , male gender ( p<0.001 ) , size of aneurysm ( p=0.030 ) , higher bcr index ( p=0.004 ) , and the use of antithrombotic medication ( p=0.006 ) were associated with postoperative csdh . in multivariate analyses using logistic regression test , 
 male gender [ odds ratio ( or ) 4.037 , range 1.287 - 12.688 ] , high bcr index ( or 5.376 , range 1.170 - 25.000 ) , and the use of antithrombotic medication ( or 4.854 , range 1.658 - 14.085 ) were associated with postoperative csdh ( p<0.05 ) . 
 postoperative subdural fluid collection and arachnoid plasty were not showed statistically significant difference in this study.conclusionthe incidence of csdh was 3.1% in unruptured anterior circulation aneurysm surgery . 
 this study shows that male gender , degree of brain atrophy , and the use of antithrombotic medication were associated with postoperative csdh . 
INTRODUCTION
MATERIALS AND METHODS
Operative technique
Statistical analyses
RESULTS
DISCUSSION
CONCLUSION