the incidence of chronic subdural hematoma ( csdh ) is about 3 per 100000 people , but it is 20 times more common among the elderly9 ) . indeed , although csdh can be treated quite easily , it can sometimes lead to disastrous results due to recurrence and complications . as the population suffering from csdhs includes many elderly patients with co - morbid medical conditions , less invasive surgical techniques have become the initial procedures of choice1,5,17 ) . current surgical treatment options also include a variety of less invasive neurosurgical modalities , such as burr - hole drainage ( bhd ) or twist - drill craniostomy ( tdc ) with closed - system drainage22 ) . it is well known that tdc carries a risk of hemorrhagic complications because it is a blind technique4,5,20 ) . however , tdc at the pre - coronal point ( pcp ) with closed - system drainage for symptomatic csdh was shown to be a safe entry point in a previous report from our institution5 ) . the aim of this study was to provide more clinical data and surgical results for patients who had appropriate indication and underwent tdc at the pcp with closed - system drainage as a continuation of the previous report ; we would like to emphasize its superiority , in terms of convenience and good outcome . this retrospective study was performed on consecutive symptomatic patients with csdh who were treated surgically at a single institution from january , 2005 to december , 2010 . among the 208 patient with csdh , 134 patients underwent tdc at the pcp with closed - system drainage ; 74 patients underwent bhd with a closed system and were excluded from the study . tdc at the pcp with closed - system drainage was selected in patients with csdh that extended beyond the coronal suture , as confirmed by preoperative ct scans . we defined the pcp for tdc in csdh to be 1 cm anterior to the coronal suture at the level of the superior temporal line ( stl ) . on brain ct scans , the level of the stl was defined as the top of the densest part of the temporalis muscle around the coronal suture . the pcp was identified in each patient in the operation room before draping ; it was measured in the usual manner with reference to the external landmarks of the coronal suture and the stl . after scalp preparation with alcohol and a povidone - iodine solution , 2% lidocaine was infiltrated . first , a hand drill equipped with a 4 cm - long steinman pin was placed perpendicular to the surface of the skull , and a mark was made on the outer skull to keep the twist drill from slipping on the surface of the skull . then , using a 6 cm - long twist drill , the skull and dura were penetrated at a 45 angle to the surface of the bone to prevent the catheter from entering the cortex . the contents of the catheter flowed freely due to the downward orientation of the catheter . the closed - system drainage was formed by attaching the catheter to a ventricular drainage bag and the catheter remained in the hematoma cavity for a few days to drain it slowly ( fig . we recorded demographic data , such as age , gender , coexisting disease , and major neurological functions . clinical performance was graded and compared using the clinical grades in markwalder 's grading scale at the preoperative period and 3 months after surgery ( table 1 ) . postoperative ct scans were routinely performed at 3 hours , 3 days and 3 months after surgery . csdh density of preoperative ct scans was classified into 4 categories : high density , isodense , low density , and mixed density . catheter failure was defined as an inappropriate position , i.e. , not in the subdural space . recurrence of csdh was defined as a confirmed post - operative hematoma expansion on postoperative ct scans and aggravation of neurological dysfunction . this retrospective study was performed on consecutive symptomatic patients with csdh who were treated surgically at a single institution from january , 2005 to december , 2010 . among the 208 patient with csdh , 134 patients underwent tdc at the pcp with closed - system drainage ; 74 patients underwent bhd with a closed system and were excluded from the study . tdc at the pcp with closed - system drainage was selected in patients with csdh that extended beyond the coronal suture , as confirmed by preoperative ct scans . we defined the pcp for tdc in csdh to be 1 cm anterior to the coronal suture at the level of the superior temporal line ( stl ) . on brain ct scans , the level of the stl was defined as the top of the densest part of the temporalis muscle around the coronal suture . the pcp was identified in each patient in the operation room before draping ; it was measured in the usual manner with reference to the external landmarks of the coronal suture and the stl . after scalp preparation with alcohol and a povidone - iodine solution , 2% lidocaine was infiltrated . first , a hand drill equipped with a 4 cm - long steinman pin was placed perpendicular to the surface of the skull , and a mark was made on the outer skull to keep the twist drill from slipping on the surface of the skull . then , using a 6 cm - long twist drill , the skull and dura were penetrated at a 45 angle to the surface of the bone to prevent the catheter from entering the cortex . the contents of the catheter flowed freely due to the downward orientation of the catheter . the closed - system drainage was formed by attaching the catheter to a ventricular drainage bag and the catheter remained in the hematoma cavity for a few days to drain it slowly ( fig . we recorded demographic data , such as age , gender , coexisting disease , and major neurological functions . clinical performance was graded and compared using the clinical grades in markwalder 's grading scale at the preoperative period and 3 months after surgery ( table 1 ) . postoperative ct scans were routinely performed at 3 hours , 3 days and 3 months after surgery . csdh density of preoperative ct scans was classified into 4 categories : high density , isodense , low density , and mixed density . catheter failure was defined as an inappropriate position , i.e. , not in the subdural space . recurrence of csdh was defined as a confirmed post - operative hematoma expansion on postoperative ct scans and aggravation of neurological dysfunction . of the csdh patients , 60 ( 44.8% ) had hypertension , 27 ( 20.1% ) had diabetes mellitus , and 21 ( 15.7% ) had taken anticoagulant medications . csdh developed in the right hemisphere in 64 ( 47.8% ) , in the left in 53 ( 39.6% ) , and bilaterally in 17 ( 12.7% ) . the mean thickness of the csdh at the pcp was 21.1 ( range , 7.1 - 39.9 ) mm on brain ct scans . the mean mid - line shift of brain parenchyma was 10.45 ( range , 0 - 27.34 ) mm on brain ct scans at the pcp . low - density csdh was seen in 38 cases ( 28.4% ) , high - density csdh in 16 cases ( 11.9% ) , and mixed density csdh in 22 cases ( 16.4% ) . the mean operation time was 21 min for both unilateral and bilateral cases ( range , 7 - 63 min ) . the mean duration of subdural catheter indwelling was 4 ( range , 1 - 8 ) days . all postoperative tdc except two had congruent points with the measured area in the preoperative brain ct scans . we found air accumulation in 11 patients ( 7.7% ) on postoperative brain ct scans . clinical performance data as analyzed by the markwalder grading scale ( mgs ) are shown in table 5 ; a lower grade on this scale indicates better cognitive functioning . on admission , the mgs results showed that 109 ( 81.3% ) patients were in grade 1 , 21 ( 15.7% ) in grade 2 , four ( 2.8% ) in grade 3 , and none in grade 4 . postoperative performance scores were lower ; 114 ( 85.1% ) were grade 0 , or normal ; 15 ( 11.2% ) were grade 1 , one ( 1.4% ) was grade 2 , and three ( 2.3% ) were grade 3 . , we removed the catheter immediately and performed a craniotomy and hematoma evacuation due to the occurrence of an acute epidural hematoma . in the other patient recurrence was seen in eight ( 5.9% ) patients at a mean of 24.8 ( range , 7 - 42 ) days after tdc at the pcp with closed - system drainage ( table 6 ) . of these , seven patients underwent revised bhd at the hematoma maximal point . the mean hematoma thickness was 19.2 ( range , 11.1 - 31.5 ) mm . in seven of the eight ( 87.5% ) patients with recurrence , the hematoma location was on the right . in seven patients , the hematoma density of the postoperative ct scan was higher than that of the preoperative ct scans . of the csdh patients , 60 ( 44.8% ) had hypertension , 27 ( 20.1% ) had diabetes mellitus , and 21 ( 15.7% ) had taken anticoagulant medications . csdh developed in the right hemisphere in 64 ( 47.8% ) , in the left in 53 ( 39.6% ) , and bilaterally in 17 ( 12.7% ) . the mean thickness of the csdh at the pcp was 21.1 ( range , 7.1 - 39.9 ) mm on brain ct scans . the mean mid - line shift of brain parenchyma was 10.45 ( range , 0 - 27.34 ) mm on brain ct scans at the pcp . low - density csdh was seen in 38 cases ( 28.4% ) , high - density csdh in 16 cases ( 11.9% ) , and mixed density csdh in 22 cases ( 16.4% ) . the mean operation time was 21 min for both unilateral and bilateral cases ( range , 7 - 63 min ) . the mean duration of subdural catheter indwelling was 4 ( range , 1 - 8 ) days . all postoperative tdc except two had congruent points with the measured area in the preoperative brain ct scans . we found air accumulation in 11 patients ( 7.7% ) on postoperative brain ct scans . clinical performance data as analyzed by the markwalder grading scale ( mgs ) are shown in table 5 ; a lower grade on this scale indicates better cognitive functioning . on admission , the mgs results showed that 109 ( 81.3% ) patients were in grade 1 , 21 ( 15.7% ) in grade 2 , four ( 2.8% ) in grade 3 , and none in grade 4 . postoperative performance scores were lower ; 114 ( 85.1% ) were grade 0 , or normal ; 15 ( 11.2% ) were grade 1 , one ( 1.4% ) was grade 2 , and three ( 2.3% ) were grade 3 . catheter failure was seen in two cases on postoperative brain ct scans . in both , catheters were inserted in the epidural space . in the first case , we removed the catheter immediately and performed a craniotomy and hematoma evacuation due to the occurrence of an acute epidural hematoma . in the other patient , we performed bhd at the same entry point ( fig . recurrence was seen in eight ( 5.9% ) patients at a mean of 24.8 ( range , 7 - 42 ) days after tdc at the pcp with closed - system drainage ( table 6 ) . of these , seven patients underwent revised bhd at the hematoma maximal point . the mean hematoma thickness was 19.2 ( range , 11.1 - 31.5 ) mm . in seven of the eight ( 87.5% ) patients with recurrence , the hematoma location was on the right . in seven patients , the hematoma density of the postoperative ct scan was higher than that of the preoperative ct scans . many studies have demonstrated that tdc using closed - system drainage is an effective operation technique for csdh5,13,18 ) . , many studies have demonstrated that tdc using closed - system drainage is an effective procedure for csdh as a definitive treatment modality16,22 ) . however , the reports to date make reference to the craniostomy performed in many different locations , such as the rostral or anterior part2,4,21 ) or the maximal thickness site15,20,22 ) . we hypothesized that tdc is more comfortable , easy and fast procedure if definite entry point was set up5 ) . therefore , our institute set up pcp for tdc based on the brain image and the surface landmark of the scalp . we defined pcp for tdc against csdh to be 1 cm anterior to coronal suture at the level of the stl . to prevent the twist drill and catheter from entering the cortex first , a hand drill equipped with a steinman pin with 4 cm length is placed perpendicularly to the surface of the skull and a mark was made on the outer skull to keep the twist drill from slipping down the skull . second , using the twist drill with 6 cm length , the skull and dura are penetrated at 45 angle to the surface of the bone . our study was analyzed concerning patients ' good outcome to compare with other reports . as the result of our study , one - hundred - and - fourteen ( 85.1% ) of total 134 patients showed improved clinical symptom and neurological function . muzii et al.11 ) reported a prospective series of 22 patients treated with tdc and closed suction drainage . although operation method was different from other reports , outcome was better than other reports . in our series , operation time including measuring pcp was average 21 minutes . muzii et al.11 ) reported a prospective series of 22 patients treated with tdc and closed suction drainage . the mean operation time was 25.2 minutes and their operation time was faster than bhd . acute epidural hematomas may result from detachment of dura from the inner surface of the skull as a result of a relatively blunt drill , without penetrating into the sdh cavity20 ) , or rapid decompression of csdh . we have experienced catheter failure on epidural space in 2 cases . based on our experience , we recommend two important things during tdc ; first is to confirm crank - oil color hematoma draining , and second is to twist fast to penetrate dura mater . it is easy to twist slowly because the inexperienced operator may fear from penetration brain injury . unintentional brain damage can be avoided by drilling through the skull and passing the catheter into the subdural cavity tangentially1,3,5 ) . in our series , so , many other reports did not recommend first line choice to treat tdc in csdh patients because of high recurrence rate9,19,22 ) . other reports are to propose post - operative hematoma density6,8,12 ) and air accumulation in recurrence factor7,8,19 ) . our series showed relatively low recurrence rate ( 5.9% ) possibly because of low incidence of air accumulation than other reportsr7,19 ) . we had only 7.7% in postoperative air accumulation rate . however , our recurrent cases had higher density than preoperative hematoma density and showed air accumulation in 7 cases . patients with recurrent accumulation underwent second operation with bhd with closed - system in maximal thickness point and the patients improved after surgery . the pcp for tdc was defined as 1 cm anterior to the coronal suture at the level of the stl . tdc at the pcp with closed - system drainage is proved to be safe and effective for patients with symptomatic csdh whose hematomas extended beyond the coronal suture .
objectivetwist - drill craniostomy ( tdc ) with closed - system drainage and burr - hole drainage ( bhd ) with a closed system are effective treatment options for chronic subdural hematoma ( csdh ) . 
 the aim of this study was to analyze clinical data and surgical results from symptomatic csdh patients who underwent tdc with closed - system drainage at the pre - coronal point ( pcp).methodswe analyzed data for 134 symptomatic csdh patients who underwent tdc at the pcp with closed - system drainage . 
 we defined the pcp for tdc to be 1 cm anterior to the coronal suture at the level of superior temporal line . 
 tdc at the pcp with closed - system drainage was selected in patients with csdh that extended beyond the coronal suture , confirmed by preoperative ct scans . 
 medical records , radiological findings , and clinical performance were reviewed retrospectively.resultsof the 134 csdh patients , 114 ( 85.1% ) showed improved clinical performance and imaging findings after surgery . 
 catheter failures were seen in two cases ( 1.4% ) ; the catheters were inserted in the epidural space . 
 recurrent cases were seen in eight patients ( 5.6% ) , and they were improved with a second bhd with a closed - system operation.conclusiontdc at the pcp with closed - system drainage is safe and effective for patients with symptomatic csdh whose hematomas extend beyond the coronal suture .