Intraoperative removal of subdural drains during surgery for chronic subdural hematoma does not increase recurrence compared with postoperative drainage

Intraoperative removal of subdural drains during surgery for chronic subdural hematoma does not increase recurrence compared with postoperative drainage | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Intraoperative removal of subdural drains during surgery for chronic subdural hematoma does not increase recurrence compared with postoperative drainage Kento Tsuburaya, Kimiyuki Kawaguchi, Takashi Matsumori, Masashi Uchida, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6516229/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background : Several reports suggest that using a subdural drain (SDD) for chronic subdural hematoma (CSDH) reduces recurrence rates. However, due to complications associated with SDD placement, we discontinued its use in initial surgeries. Methods : This study compared 150 historical cases with SDDs (SDD+ group) and 129 recent cases without SDDs (SDD- group). Results : Recurrence occurred in 18 patients (13.9%) in the SDD+ group and 12 patients (8.0%) in the SDD- group. The SDD- group had shorter operative times (40.9 vs. 54.9 min) and hospital stays (6.0 vs. 11.8 days). The overall complication rate was similar in both groups (4% vs. 1%), but the SDD+ group had serious complications related to SDD placement. Treatment costs were reduced by $811.8 per case in the SDD- group ($1978.2 vs. $1215.4). Preoperative hematoma thickness and subdural thickness on the first postoperative day were identified as independent recurrence factors, but no association was found with SDD use. Conclusions : Omitting SDD placement for CSDH did not increase the recurrence rate, shortened operative time and hospital stay, reduced costs, and minimized serious complications. By performing sufficient irrigation and reducing the residual air, it is possible that the recurrence rate will not increase even without inserting SDD, and we believe that this will serve as an opportunity to consider randomized controlled trials using a similar protocol in the future. chronic subdural hematoma subdural drain recurrence burr-hole surgery Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction The standard treatment for chronic subdural hematoma (CSDH) is burr-hole drainage, and several studies indicate that placing a subdural drain (SDD) can lower the recurrence rate [ 1 , 3 , 8 ]. At our institution, we traditionally placed an SDD after irrigating the hematoma. However, in July 2011, we encountered a case in which an acute subdural hematoma developed after SDD removal the day after surgery (POD1), necessitating a craniotomy (Fig. 1 A-D). Since then, our institution has adopted a policy of not placing SDDs, at least during initial surgery. The recurrence rate from July 2012–June 2013 was 14.6% (6/41 cases), which does not appear to have changed significantly from previous reports. Currently, we still follow a policy of not placing SDDs. This study aimed to compare cases from the period when SDDs were placed (historical controls) with cases from the current period when SDDs were not placed. The difference from previously reported randomized controlled trials (RCTs) is that we performed thorough irrigation until the drainage fluid became serous, and that we thoroughly replaced the air with saline after creating a closed subdural space. Because drains were used in all cases during the historical period, comparisons can be made without selection bias. Additionally, we examined the recurrence rate, complications, operative time, length of hospital stay, and treatment costs. Factors affecting recurrence were also retrospectively examined. Materials and Method This study was conducted in line with the principles of the Declaration of Helsinki and was approved by the Ethics Committee of St. Marianna University School of Medicine (Date: June 27, 2024; No. 6480 [B62]). All participants provided informed consent for their involvement in the study and the publication of images (Figs. 1 a-d, 2 a-c, and 3 ). We retrospectively reviewed cases of burr-hole surgery for CSDH at our institution from August 2007 onward. Between August 2007 and June 2011 (the last 4 years to stop the placement of SDDs), patients underwent SDD placement (SDD + group). Starting in July 2011, SDD placement was discontinued (SDD − group). Over the last 4 years of consecutive cases, 129 patients with SDD (August 2007–July 2011) and 150 patients without SDD (January 2020–December 2023) were evaluated. Each case was followed up for at least 3 months. Second and subsequent surgeries were excluded, and bilateral surgeries were counted as two surgeries per case. Preoperative hematomas were categorized as homogeneous or heterogeneous based on imaging features (septate or mosaic patterns, Fig. 2 A-C). Participant characteristics included age, sex, presence or absence of hypertension and dyslipidemia, use of oral antiplatelet or anticoagulant medication, hematoma side, hematoma thickness, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septum formation) (Table 1 ). Table 1 Patient charactristics Variable (preoperative) SDD+ (n = 129) SDD− (n = 150) P -value Age (years), median (range) 75.4 (13–100) 78.0 (24–100) 0.105 Sex = female (%) 43 (33) 42 (28) 0.376 Hypertension (%) 41 (31) 80 (53) < .001 Diabetes mellitus (%) 15 (12) 34 (23) 0.031 Dislipidemia (%) 15 (12) 24 (16) 0.452 Anticoagulant/Antiplatelet agent (%) 21 (16) 54 (36) < .001 Hematoma side = left (%) 75 (58) 80 (55) 0.362 Hematoma thickness pre-ope. (mm), median (range) 18.1 (9–30) 15.7 (7–37) < .001 Converted hematoma volume (ml), median (range) 90.5 (45–150) 78.5 (35–185) < .001 Hematoma side = bilateral (%) 18 (14) 32 (18) 0.179 Hematoma type = mosaic/trabecular (%) 41 (32) 54 (35) 0.566 Midline shift pre-ope. (mm), median (range) 5.3 (-6-15) 4.3 (-7-15) 0.125 SDD, subdural drain The following surgical procedures were used for burr-hole drainage in CSDH. Trepanation was performed under local anesthesia, a Nelaton catheter was inserted into the hematoma cavity, and the cavity was irrigated with 300–400 mL of warm saline until the drainage became pale blood. In the drain group, an SDD (Silascon® 785-5N; inner diameter, 2.4 mm; outer diameter, 3.8 mm) was placed to promote air evacuation. The placement position was confirmed using postoperative CT. In principle, the SDD was removed after confirming that the hematoma had not enlarged on CT the following day. In the SDD − group, the wound was closed with the Nelaton catheter in place, and the head was rotated so that the trepanation was at the highest point, saline replaced the air, and the catheter was removed. In principle, procedures other than the SDD placement were the same for the old and new surgeries. Recurrence was defined as hematoma volume expansion after surgery necessitating further surgical intervention. To investigate the postoperative residual air ratio, we defined it as the ratio of "air thickness in the slice with the maximum midline shift on CT axial imaging" to "subdural space thickness" (Fig. 3 ). We compared the recurrence rate, operation time, postoperative hospital stay, complications, treatment costs, subdural space thickness on POD1, and residual air ratio between the SDD + and SDD − groups. Treatment costs were the sum of hospitalization costs related to the duration of stay and surgery-related costs associated with the presence or absence of SDD. To identify recurrence factors, we categorized the cases into recurrent cases (30 cases) and non-recurrent cases (249 cases) and conducted univariate and multivariate analyses. The selection criteria for factors used in the multivariate analysis were those identified as independent factors for recurrence in previous reports or those that showed significant differences in the univariate analysis of this study. In the univariate analysis, the following factors were examined: age, sex, presence or absence of hypertension, diabetes, dyslipidemia, use of oral antiplatelet or anticoagulant drugs, location of hematoma, thickness of hematoma, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septal formation). Multivariate analysis (logistic regression analysis) was conducted on the use of oral antiplatelet or anticoagulant drugs, thickness of hematoma, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septum formation). For postoperative factors, subdural space thickness on POD1, midline shift, air residual ratio, and SDD were included in univariate and multivariate analyses (logistic regression). The factors identified as significant in the univariate and multivariate analyses were further examined for their association with recurrence in patients with and without SDD. Statistical analyses were performed using IBM SPSS Statistics for Windows, ver. 29.0.2 (IBM Corp., Armonk, NY, USA). Categorical variables were analyzed using the chi-square test, whereas continuous variables were assessed using the t-test or Mann–Whitney U-test based on normality. Normality was assessed comprehensively based on histograms and the Kolmogorov–Smirnov test. The confidence interval was set at 95% for normal distribution. Statistical significance was set at p < 0.05. Results Patient characteristics The mean age was 75.4 years in the SDD + group (95% confidence interval [CI], 73.3–77.7; 43 women, 86 men) and 78.0 years in the SDD − group (95% CI, 76.1–79.9; 42 women, 108 men). Preoperatively, the SDD − group had a significantly higher rate of hypertension and diabetes and use of antiplatelet and anticoagulant drugs compared to the SDD + group. Regarding preoperative hematomas, no significant differences were observed in the laterality of hematomas, bilateral hematomas, heterogeneous hematomas (mosaic or septum formation), or midline shifts between the two groups. However, the hematoma thickness was significantly greater in the SDD + group, averaging 18.1 mm (95% CI, 17.3–18.9), compared to 15.7 mm (95% CI, 14.9–16.5) in the SDD − group (p < 0.001) (Table 1 ). Analysis of postoperative factors In the SDD + group, the operation time (mean 54.9 min, 95% CI, 51.2–58.6) was significantly longer compared to that of the SDD- group (mean 40.9 min, 95% CI, 38.4–43.4; p < 0.001). The hospital stay was also significantly shorter in the SDD- group than in the SDD + group (mean 11.8 days vs. 6.0 days; p < 0.001). The drain cost was $ 49, and hospitalization costs were significantly lower in the SDD − group than in the SDD + group (mean $ 1978.2 vs. $ 1215.4; p < 0.001). The thickness of the subdural space on POD1, midline shift on POD1, and air residual ratio on POD1 were significantly higher in the SDD + group than in the SDD- group. Additionally, the recurrence rate was lower in the SDD − group than in the SDD + group; however, no significant difference was observed between the two groups (p = 0.119). No significant differences were observed in the number of complications between the two groups, occurring in five cases (4%) in the SDD + group and two cases (1%) in the SDD − group (p = 0.182). However, among the complications in the SDD + group, three were related to SDD: two cases in which the wound had to be opened due to difficulty removing the SDD and one case of acute subdural hematoma after drain removal. The other patients had one case each of seizures and meningitis. In the SDD − group, no complications were associated with the surgical procedure itself, except for one case of intraparenchymal hemorrhage due to venous infarction and one case of subdural abscess. We also calculated recurrence rates by sex because the sex distribution differed between the two groups (Table 2 ), but there was no significant difference in the recurrence rate by sex (p = 0.369). Table 2 Postoperative factors Variable (postoperative) SDD+ (n = 129) SDD− (n = 150) P -value Operation time (min), median (range) 54.9 (17–120) 40.9 (14–90) < .001 Complication (%) 5 (4) 2 (1) 0.182 Hospital days, median (range) 12.8 (2-262) 7.0 (2–98) < .001 Cost ( $ ), median (range) 1978.2 (502-31910) 1215.4 (502-12340) < .001 Subdural thickness POD1 (mm), median (range) 10.8 (1–26) 11.9 (4–27) 0.023 Converted subdural space volume (ml), median (range) 54 (5-130) 59.5 (20–135) 0.023 Midline shift POD1 (mm), median (range) 1.8 (-5-14) 2.2 (-5-10) 0.028 Air residual ratio POD1 (%), median (range) 18.7 (0–71) 33.8 (3–73) < .001 Recurrence (%) 18 (13.9) 12 (8.0) 0.119 Variable Female (n = 85) Male (n = 194) P -value Recurrence (%) 7 (8.2) 23 (11.9) 0.369 SDD, subdural drain; POD, post operative day Identification of recurrence factors and the influence of drains In both univariate and multivariate analyses, preoperative hematoma and POD1 subdural space thickness significantly influenced recurrence (Table 3 ). Preoperative use of antiplatelet or anticoagulant drugs and heterogeneous hematomas did not affect recurrence. Therefore, we investigated the influence of preoperative hematoma thickness and POD1 subdural space thickness on recurrence, both with and without SDD (Figs. 4 , 5 , 6 , and 7 ). Table 3 Univariate and multivariate analysis of recurrence factors Variable (preoperative) Recurrence+ (n = 30) Recurrence− (n = 249) P -value (uni) P -value (multi) Age (years), median (range) 76.9 (64–92) 76.8 (13–100) 0.976 Sex = female (%) 7 (23.3) 78 (31.3) 0.369 Hypertension (%) 11 (57.9) 110 (44.2) 0.433 Diabetes mellitus (%) 8 (36.4) 41 (16.5) 0.165 Dislipidemia (%) 2 (6.7) 37 (14.9) 0.222 Anticoagulant/Antiplatelet agent (%) 8 (26.7) 66 (26.5) 0.841 0.826 Hematoma side = left (%) 20 (66.7) 135 (54.2) 0.195 Hematoma thickness pre-ope. (mm), median (range) 19.1 (8–33) 16.5 (7–37) 0.007 0.008 Hematoma side = bilateral (%) 5 (16.7) 45 (18.1) 0.85 0.816 Hematoma type = mosaic/trabecular (%) 11 (36.7) 84 (33.7) 0.749 0.83 Variable (postoperative) Recurrence+ (n = 30) Recurrence− (n = 249) P -value (uni) P -value (multi) Operation time (min), median (range) 49.2 (15–120) 47.1 (14–105) 0.581 Complication (%) 2 (6.7) 5 (2.0) 0.123 Hospital days, median (range) 10.0 (2–45) 9.7 (2-262) 0.951 Cost ( $ ), median (range) 1629.2 (501.8-5970.4) 1567.6 (501.8-32051.3) 0.924 Subdural thickness POD1 (mm), median (range) 14.9 (4–26) 10.9 (1–27) < .001 < .001 Midline shift POD1 (mm) 3.4 (-2-14) 1.9 (-5-10) 0.018 0.115 Air residual ratio POD1 (%), median (range) 26.6 (3–62) 26.8 (0–73) 0.96 0.121 Drain (%) 18 (60.0) 112 (45.0) 0.119 SDD, subdural drain; POD, post operative day In both groups, preoperative hematoma thickness tended to be greater in recurrence cases than in the non-recurrence cases, though the difference was not significant (Fig. 4 ). Regarding the relationship between preoperative hematoma thickness and SDD in recurrence and non-recurrent cases (Fig. 5 ), the average preoperative hematoma thickness in the non-recurrence group was significantly lower in the SDD- group than in the SDD + group (15.5 mm [95% CI, 14.7–16.3mm] vs. 17.8 mm [95% CI, 16.9–18.6mm]; p < 0.001). The average thickness of the hematoma in the recurrent cases was 19.9 mm (95% CI, 17.6–22.0mm) in the SDD + group and 18.0 mm (95% CI, 14.0–22.0mm) in the SDD- group, with no significant difference (p = 0.377). In summary, no strong correlation was found between preoperative hematoma thickness and the presence or absence of SDD in recurrent cases. Regarding the relationship between subdural space thickness on POD1 and recurrence, with and without SDD (Fig. 6 ), the mean subdural space thickness on POD1 in the SDD + group was significantly higher in recurrent cases (14.4 mm [95% CI, 11.8–17.0mm]) than in non-recurrent cases (10.2 mm [95% CI, 9.6–10.8mm]; p = 0.006). The mean subdural space thickness on POD1 in the SDD- group was significantly higher in recurrent cases (15.7 mm [95% CI, 12.0-19.3mm]) than in non-recurrent cases (11.6 mm [95% CI, 10.8–12.3mm]; p = 0.047). In summary, in both the SDD + and SDD − groups, subdural space thickness on POD1 was significantly higher in recurrence cases. Regarding the relationship between subdural space thickness on POD1 and SDD in recurrent and non- recurrent cases (Fig. 7 ), subdural space thickness on POD1 in non-recurrent cases was significantly smaller in the SDD + group than in the SDD- group (10.2 mm [95% CI, 9.6–10.8mm] vs. 11.6 mm [95% CI, 10.8–12.3mm]) (P < 0.003). In recurrent cases, no significant differences in subdural space thickness were observed between the two groups on POD1 (14.4 mm [95% CI, 11.8–17.0mm] for the SDD + group vs. 15.7 mm [95% CI, 12.0-19.3mm] for the SDD- group, P = 0.564). Therefore, no strong correlation was found between subdural space thickness on POD1 and the presence or absence of SDD in recurrence cases. Taken together, our findings demonstrated that preoperative hematoma thickness and subdural space thickness on POD1 tended to be greater in recurrent cases, regardless of the presence of SDD; however, no strong correlation was found between SDD placement and recurrence. In addition, we calculated an approximate formula to determine hematoma volume from thickness based on the report by Sucu et al. [ 11 ] (Eq. 1). Discussion This comparative study examined historical control cases when SDDs were implemented against current control cases where SDDs were not utilized. The main finding of our study is that not using SDDs to treat CSDH did not result in a higher recurrence rate. Furthermore, although no significant difference in recurrence rate was observed, it was lower without SDD placement, and the absence of SDD use did not contribute to recurrence. These findings differed from those of previous reports that reported using drains results in a lower recurrence rate [ 1 , 3 , 8 ]. This study is retrospective and therefore cannot be directly compared with previous RCTs. However, if the reason why the recurrence rate of CSDH did not increase without SDD placement lies in the surgical technique, conducting an RCT using the same surgical procedure as in this study may yield different results from past RCTs. In this respect, we consider this study to be meaningful, and we will discuss the potential factors that contributed to the unchanged recurrence rate. Santarius et al. reported a significantly lower CSDH recurrence rate with SDD in a single-center randomized controlled trial, showing a recurrence rate of 9.3% with drains and 24% without SDD [ 8 ]. Aljabali et al. reported a significantly lower recurrence rate with SDD in a meta-analysis of nine studies [ 1 ]. Carlsen et al. reported a recurrence rate of 14% (29/206) in the SDD group and 26% (36/138) in the non-SDD group, showing a significant with no increased incidence of complications [ 3 ]. A prospective study of 80 cases by Gurelik et al. reported recurrence rates of 19% (8/42 cases) without SDD and 10.5% (4/38 cases) with SDD. Although the recurrence rate was lower in the group with SDD than the group without SDD, the difference was not statistically significant [ 4 ]. Soleman et al. reported a randomized trial comparing SDD and subperiosteal drains. Although noninferiority criteria were not met, subperiosteal drain insertion resulted in lower recurrence rates, fewer surgical infections, and lower rates of drain misplacement [ 9 ]. Previous reports have shown recurrence rates of 19–26% without drains, but the recurrence rate in this study was lower. Major possible reason for this is the attempt to irrigate the hematoma and remove residual air. Raj et al. conducted a prospective randomized controlled trial categorizing patients into two groups based on whether they underwent subdural irrigation. Results showed an 18.3% recurrence rate in the group without irrigation (54/295) and 12.6% in the group with irrigation (37/294), indicating that irrigation led to a lower recurrence rate [ 7 ]. In this study, all patients underwent irrigation until the hematoma became serous, which may have contributed to the lower recurrence rates. Nakaguchi et al. found that residual air increases CSDH recurrence rates. They reported higher recurrence rates when air remained on the 7th day after surgery and noted that inserting a drain anteriorly reduced the recurrence rate [ 5 ]. At our institution, we rotate the head so that the burr-hole is positioned at the highest point to remove as much air as possible, replacing it with saline at the end of surgery. In this study, however, no association between residual air and recurrence was found. On the other hand, some studies suggest that residual air is a recurrence factor, and efforts to reduce it below a certain amount may have contributed to the lower recurrence rate observed. Stanisic et al. reported that the amount of residual air on postoperative CT did not affect the recurrence rate. Consistent with our findings, the residual air ratio was 18.8% in recurrent cases and 22.0% in non-recurrent cases, both of which had generally low residual air ratios. This suggests that a residual air rate below a certain threshold may not affect recurrence [ 10 ]. In a retrospective study of 90 cases, Zawy et al. found that age, sex, alcohol abuse, bilaterality, surgical method, and antithrombotic drugs did not significantly affect the recurrence rate, whereas hematoma thickness, septum, and coagulopathy did [ 14 ]. In a retrospective study of 343 patients, Torihashi et al. identified bilateral disease as an independent risk factor and found that the time to recurrence was shorter in patients taking antithrombotic agents [ 12 ]. In line with these findings, we identified hematoma thickness before surgery and subdural space thickness on POD1 as independent recurrence factors through multivariate analysis. Stanisic et al. reported that when the subdural space volume on POD1 was less than 80 ml, most cases did not recur (97.4%), while most recurrent cases had volumes of 80 ml or more [ 10 ]. Using the approximation formula for subdural hematoma volume by Sucu et al. [ 11 ] (Eq. 1), a subdural space volume of 80 ml corresponded to a subdural space thickness of 16 mm. When subdural space thickness on POD1 was 16 mm or more (corresponding to a volume of 80 ml or more), the recurrence rate was 55.5% in the drain group and 26.0% in the no-drain group, both showing significantly higher recurrence rates. Yu et al. reported a significantly lower recurrence rate in the group where SDD was left in place for 3 days or more [ 13 ]. In this study, as we removed the SDD on the POD1 in the SDD + group, we could not compare results with those of long-term SDD placement. Since recurrence was more common with large postoperative subdural thickness, cases with poor brain recovery may be more prone to recurrence, making long-term SDD placement worth considering. However, prolonged SDD placement can result in complications such as device-related issues, postoperative delirium, difficulties with mobilization, increased hospital costs, and longer hospital stays. Therefore, routine long-term SDD placement remains controversial. Regarding complications associated with SDD placement, Pavlovet et al. reported a case where the SDD migrated into the brain parenchyma, causing intracerebral and intraventricular hemorrhage, resulting in severe neurological symptoms [ 6 ]. Apostolakis et al. reported serious SDD-related complications in three out of 97 cases (122 drainage procedures) for CSDH or ASDH. One patient experienced seizures, likely due to a cerebral contusion caused by the SDD, while two developed acute subdural hematomas. Both cases of acute subdural hematoma required craniotomy and hematoma removal. They noted that SDD use is a risk factor for serious complications [ 2 ]. In our study, we discontinued SDD use after an acute subdural hematoma occurred following its removal on POD1. In addition to these serious complications (life-threatening or requiring re-operation), two patients required wound opening due to difficulty in removing the SDD, resulting in a total of three SDD-related complications. No complications were noted in the SDD − group. The cause of the acute subdural hematoma is thought to be that the superficial temporal artery was wrapped around the drain fixation suture, damaging the artery during removal and causing blood to flow into the subdural space. The inability to remove the drain seems to have resulted from a procedural error in which the drain got caught during wound suturing. The independent recurrence factors identified in this study—preoperative hematoma thickness and subdural thickness on POD1—were not affected the presence or absence of SDD. Nevertheless, some reports suggest that leaving the SDD in place for an extended period (more than 3 days) significantly reduces the recurrence rate [ 13 ]. Identifying cases where the subdural space is likely to increase in thickness after surgery—specifically cases with poor brain parenchyma compliance before or during surgery—could help determine which cases require SDD placement. In this study, consecutive cases were used as historical controls, which likely reduced selection bias compared to typical retrospective studies. However, considering potential differences in the historical medical backgrounds, patient characteristics and surgical operators between groups, the results may not be sufficient to overturn existing RCTs. Our findings suggest that thorough hematoma irrigation until the drainage fluid became serous and reduction of residual air after creating a closed subdural space may have contributed to the lower recurrence rate. However, there are no RCTs that strictly standardize these surgical techniques. Therefore, conducting an RCT using a protocol that applies the same surgical techniques as in the present study may demonstrate the non-inferiority of omitting SDD placement. Based on these considerations, we believe this study serves as a meaningful step toward initiating future RCTs. Conclusion In this single-center historical control study, we compared the recurrence rates of patients with and without SDD placement after burr-hole drainage for CSDH and found that the recurrence rate did not increase in patients without SDD. Adequate irrigation and reduction of residual air may help prevent recurrence even without inserting SDD. We believe that these findings could provide a basis for considering future RCTs using a similar protocol. Since non-placement of the SDD shortens the operation time, reduces postoperative hospital stay and treatment costs, and causes no serious complications, not placing an SDD may be an option, at least for the initial surgery. Declarations Funding This work was partly supported by KAKENHI (Grant-in-Aid for Scientific Research of Japan) (grant no. 21K09156). The funders played no role in the study design, data collection and analysis, decision to publish, or manuscript preparation. Competing Interests The authors have no relevant financial or non-financial interests to disclose. CRediT Authorship Contribution Statement Kento Tsuburaya: Data curation, Writing – original draft, Software, Investigation, Visualization. Kimiyuki Kawaguchi: Data curation, Writing – original draft. Takashi Matsumori: Writing – original draft, Investigation. Masashi Uchida: Writing – original draft, Investigation. Yuichiro Kushiro: Writing – original draft, Investigation. Gaku Hidaka: Writing – original draft, Investigation. Hiroshi Takasuna: Writing – original draft, Investigation. Hidenichi Itoh: Writing – original draft, Investigation. Ichiro Takumi: Writing – original draft, Investigation. Hidetoshi Murata: Conceptualization, Methodology, Validation, Investigation, Visualization, Writing – review & editing, Supervision. Ethics approval This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of St. Marianna University School of Medicine ( June 27, 2024; No. 6480 [B62]). Consent to participate Informed consent was obtained from all participants included in the study. Consent to publish The authors affirm that human research participants provided informed consent for the publication of the images in Figures. 1a-d, 2a-c, and 3. Data availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. 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Can J Neurol Sci 34 :84–87. https://doi.org/10.1017/s0317167100005849 Nakaguchi H, Tanishima T, Yoshimasu N (2000) Relationship between drainage catheter location and postoperative recurrence of chronic subdural hematoma after burr-hole irrigation and closed-system drainage. J Neurosurg 93 :791–795. https://doi.org/10.3171/jns.2000.93.5.0791 Pavlov V, Bernard G, Chibbaro S (2012) Chronic subdural haematoma management: an iatrogenic complication. Case report and literature review. BMJ Case Rep 2012 :bcr1220115397. https://doi.org/10.1136/bcr.12.2011.5397 Raj R, Tommiska P, Koivisto T et al (2024) Burr-hole drainage with or without irrigation for chronic subdural haematoma (FINISH): a Finnish, nationwide, parallel-group, multicentre, randomised, controlled, noninferiority trial. Lancet 403 :2798–2806. https://doi.org/10.1016/S0140-6736(24)00686-X Santarius T, Kirkpatrick PJ, Ganesan D et al (2009) Use of drains versus no drains after burr-hole evacuation of chronic subdural haematoma: a randomised controlled trial. Lancet 374 :1067–1073. https://doi.org/10.1016/S0140-6736(09)61115-6 Soleman J, Lutz K, Schaedelin S et al (2019) Subperiosteal vs subdural drain after burr-hole drainage of chronic subdural hematoma: a randomized clinical trial (cSDH-drain-trial). Neurosurgery 85 :E825–E834. https://doi.org/10.1093/neuros/nyz095 Stanišić M, Hald J, Rasmussen IA et al (2013) Volume and densities of chronic subdural haematoma obtained from CT imaging as predictors of postoperative recurrence: a prospective study of 107 operated patients. Acta Neurochir (Wien) 155 :323–333; discussion 333. https://doi.org/10.1007/s00701-012-1565-0 Sucu HK, Gokmen M, Gelal F (2005) The value of XYZ/2 technique compared with computer-assisted volumetric analysis to estimate the volume of chronic subdural hematoma. Stroke 36 :998–1000. https://doi.org/10.1161/01.STR.0000162714.46038.0f Torihashi K, Sadamasa N, Yoshida K, Narumi O, Chin M, Yamagata S (2008) Independent predictors for recurrence of chronic subdural hematoma: a review of 343 consecutive surgical cases. Neurosurgery 63 :1125–1129; discussion 1129. https://doi.org/10.1227/01.NEU.0000335782.60059.17 Yu GJ, Han CZ, Zhang M, Zhuang HT, Jiang YG (2009) Prolonged drainage reduces the recurrence of chronic subdural hematoma. Br J Neurosurg 23 :606–611. https://doi.org/10.3109/02688690903386983 Zawy Alsofy S, Lewitz M, Meyer K, Fortmann T, Wilbers E, Nakamura M, Ewelt C (2024) Retrospective analysis of risk factors for recurrence of chronic subdural haematoma after surgery. J Clin Med 13 :805. https://doi.org/10.3390/jcm13030805 Equation Equation 1 Approximate equation for hematoma volume. If the hematoma volume is represented as V, the maximum thickness as x, the maximum vertical diameter as y, and the height as z, the equation V = xyz/2 applies. Rearranging for x gives x = 2V/yz. For a hematoma volume of 80 ml, with average maximum vertical diameter of 13.1 cm and height of 7.5 cm, x is calculated as 1.6 cm. V=xyz/2 x=2V/yz ↓(y=13.1, z=7.5) x=0.02V ↓(V=80) x=1.6 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6516229","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":448798668,"identity":"b9ccc6fb-485a-4324-bbf2-9d40afd5988a","order_by":0,"name":"Kento Tsuburaya","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Kento","middleName":"","lastName":"Tsuburaya","suffix":""},{"id":448798669,"identity":"ce66b724-24a3-4d6f-bcca-5839f648d81b","order_by":1,"name":"Kimiyuki Kawaguchi","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Kimiyuki","middleName":"","lastName":"Kawaguchi","suffix":""},{"id":448798670,"identity":"15218475-6f7e-4cc2-817c-7d597c57a803","order_by":2,"name":"Takashi Matsumori","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Takashi","middleName":"","lastName":"Matsumori","suffix":""},{"id":448798671,"identity":"168fc83b-5f3f-4e76-bc3b-683c9fdf3565","order_by":3,"name":"Masashi Uchida","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Masashi","middleName":"","lastName":"Uchida","suffix":""},{"id":448798672,"identity":"fa09fb3f-872f-4d4f-ab42-cce79b0386a1","order_by":4,"name":"Yuichiro Kushiro","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yuichiro","middleName":"","lastName":"Kushiro","suffix":""},{"id":448798673,"identity":"14c9836f-e5b9-4739-8116-1315ebfe6ea6","order_by":5,"name":"Gaku Hidaka","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Gaku","middleName":"","lastName":"Hidaka","suffix":""},{"id":448798674,"identity":"4565b234-f600-4baa-a136-95a64dba03fd","order_by":6,"name":"Hiroshi Takasuna","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Hiroshi","middleName":"","lastName":"Takasuna","suffix":""},{"id":448798675,"identity":"2b58ceae-f6ed-4a2f-b69c-5817db99196c","order_by":7,"name":"Hidenichi Itoh","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Hidenichi","middleName":"","lastName":"Itoh","suffix":""},{"id":448798676,"identity":"729ad026-d1b7-4ae5-bec2-be48dff9b63a","order_by":8,"name":"Ichiro Takumi","email":"","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Ichiro","middleName":"","lastName":"Takumi","suffix":""},{"id":448798677,"identity":"1fdcbcee-aac3-4e87-a00e-1f2bc85f925a","order_by":9,"name":"Hidetoshi Murata","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYBACAygtByIOIEmwEdCSwGBMupbEBqIdZi52xuzDzx926Wvbzz488HPHHXkGiQTGDz8Y+PJwabGcnWM8sychOXfbmXSDg71nnhk2SCQwS/YwsBXjdNjtHGMGngTm3G0H0hgO8LYdZtx/I4FBGugXnE4FaWH8k1Cfbnb+GcPBv22H7UG2/CakhZkn4XCC2Y00hsNAWxKBWtgI2JJWzCyTdtxw241nDIdl2w4nN/A8bLPsMcDnl+TNjG9squXNzqcxf3zbdti2gT358I0fFcdwhhg2wAh0ksGxBFK0gEEN6VpGwSgYBaNguAIA/G1YJdkn27MAAAAASUVORK5CYII=","orcid":"","institution":"St. Marianna University School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Hidetoshi","middleName":"","lastName":"Murata","suffix":""}],"badges":[],"createdAt":"2025-04-24 02:08:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6516229/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6516229/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82137944,"identity":"91744e59-d218-439c-960e-4017a7175383","added_by":"auto","created_at":"2025-05-07 06:21:44","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":327960,"visible":true,"origin":"","legend":"\u003cp\u003eCase of an 80-year-old man who underwent bilateral burr-hole drainage for chronic subdural hematoma (CSDH) with subdural drains (SDDs) placed on both sides. Postoperative CT scans showed no hematoma growth, and bilateral SDDs were removed. One hour later, the patient developed impaired consciousness and right hemiplegia. A CT scan revealed a left acute subdural hematoma with a midline shift, requiring emergency craniotomy and hematoma removal.\u003cbr\u003e\n\u003cstrong\u003ea\u003c/strong\u003e Preoperative CT showing bilateral CSDH.\u003cbr\u003e\n\u003cstrong\u003eb\u003c/strong\u003e Postoperative CT, one day after bilateral burr-hole drainage with SDDs placed on both sides.\u003cbr\u003e\n\u003cstrong\u003ec\u003c/strong\u003e Postoperative CT after SDD removal, showing a left acute subdural hematoma and midline shift, following the patient's loss of consciousness and right-sided paralysis.\u003cbr\u003e\n\u003cstrong\u003ed\u003c/strong\u003e Postoperative CT after left craniotomy and hematoma removal.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/3e51061563fd1bce91f20d65.png"},{"id":82140218,"identity":"cb2e009b-3d9c-4a6f-8795-ab2d72fc1843","added_by":"auto","created_at":"2025-05-07 06:29:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":239879,"visible":true,"origin":"","legend":"\u003cp\u003eHematoma classification.\u003cbr\u003e\n\u003cstrong\u003ea\u003c/strong\u003e Homogeneous hematoma.\u003cbr\u003e\n\u003cstrong\u003eb\u003c/strong\u003e Hematoma with septum.\u003cbr\u003e\n\u003cstrong\u003ec\u003c/strong\u003e Mosaic-like hematoma.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/b1560ec067ec2c6e0075d516.png"},{"id":82142292,"identity":"9526212f-60ba-40b2-b15e-4e3b43c8a9a4","added_by":"auto","created_at":"2025-05-07 06:37:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":152643,"visible":true,"origin":"","legend":"\u003cp\u003eResidual air rate calculation, defined as the ratio of air thickness in the slice with the maximum midline shift on axial CT (a) to subdural space thickness (b).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/ec4dab970b5ece993a720677.png"},{"id":82137946,"identity":"fdf0265b-54e3-4a73-8fbb-21d0b2df0b99","added_by":"auto","created_at":"2025-05-07 06:21:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":74556,"visible":true,"origin":"","legend":"\u003cp\u003ePreoperative hematoma thickness and recurrence. In both the SDD+ (a) and SDD- (b) groups, hematomas were generally thicker in recurrence cases. Error bars represent the 95% confidence interval (CI).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/399e5f5f4dd27cbae100b091.png"},{"id":82137949,"identity":"3514ae3e-c406-40f0-b17c-d8764f866094","added_by":"auto","created_at":"2025-05-07 06:21:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":68875,"visible":true,"origin":"","legend":"\u003cp\u003ePreoperative hematoma thickness. In the non-recurrence group, the SDD+ group had significantly thicker preoperative hematomas than the SDD- group (P\u0026lt;0.001) (a). No significant difference in preoperative hematoma thickness was found in the recurrence group between SDD+ and SDD- cases (b). Error bars represent the 95% CI.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/5faa69e6b0ab1f7a57564041.png"},{"id":82137951,"identity":"f5f0bee6-9eea-48c2-a8b1-382cd94cfc54","added_by":"auto","created_at":"2025-05-07 06:21:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":72084,"visible":true,"origin":"","legend":"\u003cp\u003eSubdural thickness on POD1. The subdural thickness was significantly greater in recurrence cases for both the SDD+ (a) and SDD- (b) groups. Error bars represent the 95% CI.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/2824ddaa51756bb5de93d18d.png"},{"id":82144466,"identity":"5e471cb7-cc7d-4886-a25f-ac9e5b2958b4","added_by":"auto","created_at":"2025-05-07 06:45:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":65054,"visible":true,"origin":"","legend":"\u003cp\u003eSubdural thickness at POD1. In the non-recurrence group, subdural thickness at POD1 was significantly greater in the SDD- group than in the SDD+ group (a). In the recurrence group, no significant difference in subdural thickness was observed between SDD+ and SDD- cases (b). Error bars represent the 95% CI.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/333d069a9e6b1d42930463e3.png"},{"id":83025252,"identity":"ba00f44e-3233-43b1-aaa9-e6764cd04ecf","added_by":"auto","created_at":"2025-05-19 08:17:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1925421,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6516229/v1/29f46990-c4fb-4f45-b200-490e459b9d1f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Intraoperative removal of subdural drains during surgery for chronic subdural hematoma does not increase recurrence compared with postoperative drainage","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe standard treatment for chronic subdural hematoma (CSDH) is burr-hole drainage, and several studies indicate that placing a subdural drain (SDD) can lower the recurrence rate [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. At our institution, we traditionally placed an SDD after irrigating the hematoma. However, in July 2011, we encountered a case in which an acute subdural hematoma developed after SDD removal the day after surgery (POD1), necessitating a craniotomy (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-D). Since then, our institution has adopted a policy of not placing SDDs, at least during initial surgery. The recurrence rate from July 2012\u0026ndash;June 2013 was 14.6% (6/41 cases), which does not appear to have changed significantly from previous reports. Currently, we still follow a policy of not placing SDDs. This study aimed to compare cases from the period when SDDs were placed (historical controls) with cases from the current period when SDDs were not placed. The difference from previously reported randomized controlled trials (RCTs) is that we performed thorough irrigation until the drainage fluid became serous, and that we thoroughly replaced the air with saline after creating a closed subdural space. Because drains were used in all cases during the historical period, comparisons can be made without selection bias. Additionally, we examined the recurrence rate, complications, operative time, length of hospital stay, and treatment costs. Factors affecting recurrence were also retrospectively examined.\u003c/p\u003e"},{"header":"Materials and Method","content":"\u003cp\u003e This study was conducted in line with the principles of the Declaration of Helsinki and was approved by the Ethics Committee of St. Marianna University School of Medicine (Date: June 27, 2024; No. 6480 [B62]). All participants provided informed consent for their involvement in the study and the publication of images (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-d, \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-c, and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3\u003c/span\u003e). We retrospectively reviewed cases of burr-hole surgery for CSDH at our institution from August 2007 onward. Between August 2007 and June 2011 (the last 4 years to stop the placement of SDDs), patients underwent SDD placement (SDD\u0026thinsp;+\u0026thinsp;group). Starting in July 2011, SDD placement was discontinued (SDD\u0026thinsp;\u0026minus;\u0026thinsp;group). Over the last 4 years of consecutive cases, 129 patients with SDD (August 2007\u0026ndash;July 2011) and 150 patients without SDD (January 2020\u0026ndash;December 2023) were evaluated. Each case was followed up for at least 3 months. Second and subsequent surgeries were excluded, and bilateral surgeries were counted as two surgeries per case. Preoperative hematomas were categorized as homogeneous or heterogeneous based on imaging features (septate or mosaic patterns, Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e2\u003c/span\u003eA-C).\u003c/p\u003e \u003cp\u003eParticipant characteristics included age, sex, presence or absence of hypertension and dyslipidemia, use of oral antiplatelet or anticoagulant medication, hematoma side, hematoma thickness, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septum formation) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePatient charactristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable (preoperative)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSDD+ (n\u0026thinsp;=\u0026thinsp;129)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSDD\u0026minus; (n\u0026thinsp;=\u0026thinsp;150)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75.4 (13\u0026ndash;100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e78.0 (24\u0026ndash;100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.105\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex\u0026thinsp;=\u0026thinsp;female (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43 (33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42 (28)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.376\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypertension (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41 (31)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80 (53)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15 (12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34 (23)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.031\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDislipidemia (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15 (12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24 (16)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.452\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnticoagulant/Antiplatelet agent (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21 (16)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54 (36)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma side\u0026thinsp;=\u0026thinsp;left (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75 (58)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80 (55)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.362\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma thickness pre-ope. (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.1 (9\u0026ndash;30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.7 (7\u0026ndash;37)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConverted hematoma volume (ml), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90.5 (45\u0026ndash;150)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e78.5 (35\u0026ndash;185)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma side\u0026thinsp;=\u0026thinsp;bilateral (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18 (14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32 (18)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.179\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma type\u0026thinsp;=\u0026thinsp;mosaic/trabecular (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41 (32)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54 (35)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.566\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMidline shift pre-ope. (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.3 (-6-15)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.3 (-7-15)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.125\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eSDD, subdural drain\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe following surgical procedures were used for burr-hole drainage in CSDH. Trepanation was performed under local anesthesia, a Nelaton catheter was inserted into the hematoma cavity, and the cavity was irrigated with 300\u0026ndash;400 mL of warm saline until the drainage became pale blood. In the drain group, an SDD (Silascon\u0026reg; 785-5N; inner diameter, 2.4 mm; outer diameter, 3.8 mm) was placed to promote air evacuation. The placement position was confirmed using postoperative CT. In principle, the SDD was removed after confirming that the hematoma had not enlarged on CT the following day. In the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group, the wound was closed with the Nelaton catheter in place, and the head was rotated so that the trepanation was at the highest point, saline replaced the air, and the catheter was removed. In principle, procedures other than the SDD placement were the same for the old and new surgeries. Recurrence was defined as hematoma volume expansion after surgery necessitating further surgical intervention. To investigate the postoperative residual air ratio, we defined it as the ratio of \"air thickness in the slice with the maximum midline shift on CT axial imaging\" to \"subdural space thickness\" (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe compared the recurrence rate, operation time, postoperative hospital stay, complications, treatment costs, subdural space thickness on POD1, and residual air ratio between the SDD\u0026thinsp;+\u0026thinsp;and SDD\u0026thinsp;\u0026minus;\u0026thinsp;groups. Treatment costs were the sum of hospitalization costs related to the duration of stay and surgery-related costs associated with the presence or absence of SDD.\u003c/p\u003e \u003cp\u003eTo identify recurrence factors, we categorized the cases into recurrent cases (30 cases) and non-recurrent cases (249 cases) and conducted univariate and multivariate analyses. The selection criteria for factors used in the multivariate analysis were those identified as independent factors for recurrence in previous reports or those that showed significant differences in the univariate analysis of this study. In the univariate analysis, the following factors were examined: age, sex, presence or absence of hypertension, diabetes, dyslipidemia, use of oral antiplatelet or anticoagulant drugs, location of hematoma, thickness of hematoma, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septal formation). Multivariate analysis (logistic regression analysis) was conducted on the use of oral antiplatelet or anticoagulant drugs, thickness of hematoma, bilateral hematoma, and heterogeneous hematoma (mosaic hematoma or septum formation). For postoperative factors, subdural space thickness on POD1, midline shift, air residual ratio, and SDD were included in univariate and multivariate analyses (logistic regression). The factors identified as significant in the univariate and multivariate analyses were further examined for their association with recurrence in patients with and without SDD.\u003c/p\u003e \u003cp\u003eStatistical analyses were performed using IBM SPSS Statistics for Windows, ver. 29.0.2 (IBM Corp., Armonk, NY, USA). Categorical variables were analyzed using the chi-square test, whereas continuous variables were assessed using the t-test or Mann\u0026ndash;Whitney U-test based on normality. Normality was assessed comprehensively based on histograms and the Kolmogorov\u0026ndash;Smirnov test. The confidence interval was set at 95% for normal distribution. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePatient characteristics\u003c/h2\u003e \u003cp\u003eThe mean age was 75.4 years in the SDD\u0026thinsp;+\u0026thinsp;group (95% confidence interval [CI], 73.3\u0026ndash;77.7; 43 women, 86 men) and 78.0 years in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group (95% CI, 76.1\u0026ndash;79.9; 42 women, 108 men). Preoperatively, the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group had a significantly higher rate of hypertension and diabetes and use of antiplatelet and anticoagulant drugs compared to the SDD\u0026thinsp;+\u0026thinsp;group. Regarding preoperative hematomas, no significant differences were observed in the laterality of hematomas, bilateral hematomas, heterogeneous hematomas (mosaic or septum formation), or midline shifts between the two groups. However, the hematoma thickness was significantly greater in the SDD\u0026thinsp;+\u0026thinsp;group, averaging 18.1 mm (95% CI, 17.3\u0026ndash;18.9), compared to 15.7 mm (95% CI, 14.9\u0026ndash;16.5) in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eAnalysis of postoperative factors\u003c/h3\u003e\n\u003cp\u003eIn the SDD\u0026thinsp;+\u0026thinsp;group, the operation time (mean 54.9 min, 95% CI, 51.2\u0026ndash;58.6) was significantly longer compared to that of the SDD- group (mean 40.9 min, 95% CI, 38.4\u0026ndash;43.4; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The hospital stay was also significantly shorter in the SDD- group than in the SDD\u0026thinsp;+\u0026thinsp;group (mean 11.8 days vs. 6.0 days; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The drain cost was \u003cspan\u003e$\u003c/span\u003e49, and hospitalization costs were significantly lower in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group than in the SDD\u0026thinsp;+\u0026thinsp;group (mean \u003cspan\u003e$\u003c/span\u003e1978.2 vs. \u003cspan\u003e$\u003c/span\u003e1215.4; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The thickness of the subdural space on POD1, midline shift on POD1, and air residual ratio on POD1 were significantly higher in the SDD\u0026thinsp;+\u0026thinsp;group than in the SDD- group. Additionally, the recurrence rate was lower in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group than in the SDD\u0026thinsp;+\u0026thinsp;group; however, no significant difference was observed between the two groups (p\u0026thinsp;=\u0026thinsp;0.119). No significant differences were observed in the number of complications between the two groups, occurring in five cases (4%) in the SDD\u0026thinsp;+\u0026thinsp;group and two cases (1%) in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group (p\u0026thinsp;=\u0026thinsp;0.182).\u003c/p\u003e \u003cp\u003eHowever, among the complications in the SDD\u0026thinsp;+\u0026thinsp;group, three were related to SDD: two cases in which the wound had to be opened due to difficulty removing the SDD and one case of acute subdural hematoma after drain removal. The other patients had one case each of seizures and meningitis. In the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group, no complications were associated with the surgical procedure itself, except for one case of intraparenchymal hemorrhage due to venous infarction and one case of subdural abscess. We also calculated recurrence rates by sex because the sex distribution differed between the two groups (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), but there was no significant difference in the recurrence rate by sex (p\u0026thinsp;=\u0026thinsp;0.369).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePostoperative factors\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable (postoperative)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSDD+ (n\u0026thinsp;=\u0026thinsp;129)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSDD\u0026minus; (n\u0026thinsp;=\u0026thinsp;150)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOperation time (min), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54.9 (17\u0026ndash;120)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.9 (14\u0026ndash;90)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComplication (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2 (1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.182\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHospital days, median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12.8 (2-262)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.0 (2\u0026ndash;98)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCost (\u003cspan\u003e$\u003c/span\u003e), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1978.2 (502-31910)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1215.4 (502-12340)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubdural thickness POD1 (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.8 (1\u0026ndash;26)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.9 (4\u0026ndash;27)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.023\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConverted subdural space volume (ml), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54 (5-130)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59.5 (20\u0026ndash;135)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.023\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMidline shift POD1 (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.8 (-5-14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.2 (-5-10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.028\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAir residual ratio POD1 (%), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.7 (0\u0026ndash;71)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.8 (3\u0026ndash;73)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRecurrence (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18 (13.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12 (8.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVariable\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eFemale (n\u0026thinsp;=\u0026thinsp;85)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMale (n\u0026thinsp;=\u0026thinsp;194)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eP\u003c/b\u003e\u003cb\u003e-value\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRecurrence (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7 (8.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23 (11.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.369\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eSDD, subdural drain; POD, post operative day\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eIdentification of recurrence factors and the influence of drains\u003c/h3\u003e\n\u003cp\u003eIn both univariate and multivariate analyses, preoperative hematoma and POD1 subdural space thickness significantly influenced recurrence (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Preoperative use of antiplatelet or anticoagulant drugs and heterogeneous hematomas did not affect recurrence. Therefore, we investigated the influence of preoperative hematoma thickness and POD1 subdural space thickness on recurrence, both with and without SDD (Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e5\u003c/span\u003e, \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e6\u003c/span\u003e, and \u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eUnivariate and multivariate analysis of recurrence factors\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable (preoperative)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRecurrence+ (n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRecurrence\u0026minus; (n\u0026thinsp;=\u0026thinsp;249)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value (uni)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value (multi)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e76.9 (64\u0026ndash;92)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e76.8 (13\u0026ndash;100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.976\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex\u0026thinsp;=\u0026thinsp;female (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7 (23.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e78 (31.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.369\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypertension (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11 (57.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e110 (44.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.433\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8 (36.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41 (16.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.165\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDislipidemia (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (6.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37 (14.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.222\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnticoagulant/Antiplatelet agent (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8 (26.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66 (26.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.841\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.826\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma side\u0026thinsp;=\u0026thinsp;left (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20 (66.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e135 (54.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma thickness pre-ope. (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19.1 (8\u0026ndash;33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.5 (7\u0026ndash;37)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.008\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma side\u0026thinsp;=\u0026thinsp;bilateral (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (16.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45 (18.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.816\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematoma type\u0026thinsp;=\u0026thinsp;mosaic/trabecular (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11 (36.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e84 (33.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.749\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVariable (postoperative)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eRecurrence+ (n\u0026thinsp;=\u0026thinsp;30)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eRecurrence\u0026minus; (n\u0026thinsp;=\u0026thinsp;249)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eP\u003c/b\u003e\u003cb\u003e-value (uni)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eP\u003c/b\u003e\u003cb\u003e-value (multi)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOperation time (min), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e49.2 (15\u0026ndash;120)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47.1 (14\u0026ndash;105)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.581\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComplication (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (6.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 (2.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.123\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHospital days, median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.0 (2\u0026ndash;45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.7 (2-262)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.951\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCost (\u003cspan\u003e$\u003c/span\u003e), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1629.2 (501.8-5970.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1567.6 (501.8-32051.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.924\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubdural thickness POD1 (mm), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.9 (4\u0026ndash;26)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.9 (1\u0026ndash;27)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMidline shift POD1 (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.4 (-2-14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.9 (-5-10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.115\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAir residual ratio POD1 (%), median (range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.6 (3\u0026ndash;62)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.8 (0\u0026ndash;73)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.121\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDrain (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18 (60.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e112 (45.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eSDD, subdural drain; POD, post operative day\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn both groups, preoperative hematoma thickness tended to be greater in recurrence cases than in the non-recurrence cases, though the difference was not significant (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Regarding the relationship between preoperative hematoma thickness and SDD in recurrence and non-recurrent cases (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e5\u003c/span\u003e), the average preoperative hematoma thickness in the non-recurrence group was significantly lower in the SDD- group than in the SDD\u0026thinsp;+\u0026thinsp;group (15.5 mm [95% CI, 14.7\u0026ndash;16.3mm] vs. 17.8 mm [95% CI, 16.9\u0026ndash;18.6mm]; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The average thickness of the hematoma in the recurrent cases was 19.9 mm (95% CI, 17.6\u0026ndash;22.0mm) in the SDD\u0026thinsp;+\u0026thinsp;group and 18.0 mm (95% CI, 14.0\u0026ndash;22.0mm) in the SDD- group, with no significant difference (p\u0026thinsp;=\u0026thinsp;0.377). In summary, no strong correlation was found between preoperative hematoma thickness and the presence or absence of SDD in recurrent cases.\u003c/p\u003e \u003cp\u003eRegarding the relationship between subdural space thickness on POD1 and recurrence, with and without SDD (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e6\u003c/span\u003e), the mean subdural space thickness on POD1 in the SDD\u0026thinsp;+\u0026thinsp;group was significantly higher in recurrent cases (14.4 mm [95% CI, 11.8\u0026ndash;17.0mm]) than in non-recurrent cases (10.2 mm [95% CI, 9.6\u0026ndash;10.8mm]; p\u0026thinsp;=\u0026thinsp;0.006). The mean subdural space thickness on POD1 in the SDD- group was significantly higher in recurrent cases (15.7 mm [95% CI, 12.0-19.3mm]) than in non-recurrent cases (11.6 mm [95% CI, 10.8\u0026ndash;12.3mm]; p\u0026thinsp;=\u0026thinsp;0.047). In summary, in both the SDD\u0026thinsp;+\u0026thinsp;and SDD\u0026thinsp;\u0026minus;\u0026thinsp;groups, subdural space thickness on POD1 was significantly higher in recurrence cases.\u003c/p\u003e \u003cp\u003eRegarding the relationship between subdural space thickness on POD1 and SDD in recurrent and non- recurrent cases (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e7\u003c/span\u003e), subdural space thickness on POD1 in non-recurrent cases was significantly smaller in the SDD\u0026thinsp;+\u0026thinsp;group than in the SDD- group (10.2 mm [95% CI, 9.6\u0026ndash;10.8mm] vs. 11.6 mm [95% CI, 10.8\u0026ndash;12.3mm]) (P\u0026thinsp;\u0026lt;\u0026thinsp;0.003). In recurrent cases, no significant differences in subdural space thickness were observed between the two groups on POD1 (14.4 mm [95% CI, 11.8\u0026ndash;17.0mm] for the SDD\u0026thinsp;+\u0026thinsp;group vs. 15.7 mm [95% CI, 12.0-19.3mm] for the SDD- group, P\u0026thinsp;=\u0026thinsp;0.564). Therefore, no strong correlation was found between subdural space thickness on POD1 and the presence or absence of SDD in recurrence cases.\u003c/p\u003e \u003cp\u003eTaken together, our findings demonstrated that preoperative hematoma thickness and subdural space thickness on POD1 tended to be greater in recurrent cases, regardless of the presence of SDD; however, no strong correlation was found between SDD placement and recurrence.\u003c/p\u003e \u003cp\u003eIn addition, we calculated an approximate formula to determine hematoma volume from thickness based on the report by Sucu et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] (Eq.\u0026nbsp;1).\u003c/p\u003e\n"},{"header":"Discussion","content":"\u003cp\u003eThis comparative study examined historical control cases when SDDs were implemented against current control cases where SDDs were not utilized. The main finding of our study is that not using SDDs to treat CSDH did not result in a higher recurrence rate. Furthermore, although no significant difference in recurrence rate was observed, it was lower without SDD placement, and the absence of SDD use did not contribute to recurrence. These findings differed from those of previous reports that reported using drains results in a lower recurrence rate [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This study is retrospective and therefore cannot be directly compared with previous RCTs. However, if the reason why the recurrence rate of CSDH did not increase without SDD placement lies in the surgical technique, conducting an RCT using the same surgical procedure as in this study may yield different results from past RCTs. In this respect, we consider this study to be meaningful, and we will discuss the potential factors that contributed to the unchanged recurrence rate.\u003c/p\u003e \u003cp\u003eSantarius et al. reported a significantly lower CSDH recurrence rate with SDD in a single-center randomized controlled trial, showing a recurrence rate of 9.3% with drains and 24% without SDD [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Aljabali et al. reported a significantly lower recurrence rate with SDD in a meta-analysis of nine studies [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Carlsen et al. reported a recurrence rate of 14% (29/206) in the SDD group and 26% (36/138) in the non-SDD group, showing a significant with no increased incidence of complications [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. A prospective study of 80 cases by Gurelik et al. reported recurrence rates of 19% (8/42 cases) without SDD and 10.5% (4/38 cases) with SDD. Although the recurrence rate was lower in the group with SDD than the group without SDD, the difference was not statistically significant [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Soleman et al. reported a randomized trial comparing SDD and subperiosteal drains. Although noninferiority criteria were not met, subperiosteal drain insertion resulted in lower recurrence rates, fewer surgical infections, and lower rates of drain misplacement [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrevious reports have shown recurrence rates of 19\u0026ndash;26% without drains, but the recurrence rate in this study was lower. Major possible reason for this is the attempt to irrigate the hematoma and remove residual air. Raj et al. conducted a prospective randomized controlled trial categorizing patients into two groups based on whether they underwent subdural irrigation. Results showed an 18.3% recurrence rate in the group without irrigation (54/295) and 12.6% in the group with irrigation (37/294), indicating that irrigation led to a lower recurrence rate [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In this study, all patients underwent irrigation until the hematoma became serous, which may have contributed to the lower recurrence rates.\u003c/p\u003e \u003cp\u003eNakaguchi et al. found that residual air increases CSDH recurrence rates. They reported higher recurrence rates when air remained on the 7th day after surgery and noted that inserting a drain anteriorly reduced the recurrence rate [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. At our institution, we rotate the head so that the burr-hole is positioned at the highest point to remove as much air as possible, replacing it with saline at the end of surgery. In this study, however, no association between residual air and recurrence was found. On the other hand, some studies suggest that residual air is a recurrence factor, and efforts to reduce it below a certain amount may have contributed to the lower recurrence rate observed.\u003c/p\u003e \u003cp\u003eStanisic et al. reported that the amount of residual air on postoperative CT did not affect the recurrence rate. Consistent with our findings, the residual air ratio was 18.8% in recurrent cases and 22.0% in non-recurrent cases, both of which had generally low residual air ratios. This suggests that a residual air rate below a certain threshold may not affect recurrence [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn a retrospective study of 90 cases, Zawy et al. found that age, sex, alcohol abuse, bilaterality, surgical method, and antithrombotic drugs did not significantly affect the recurrence rate, whereas hematoma thickness, septum, and coagulopathy did [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In a retrospective study of 343 patients, Torihashi et al. identified bilateral disease as an independent risk factor and found that the time to recurrence was shorter in patients taking antithrombotic agents [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In line with these findings, we identified hematoma thickness before surgery and subdural space thickness on POD1 as independent recurrence factors through multivariate analysis.\u003c/p\u003e \u003cp\u003eStanisic et al. reported that when the subdural space volume on POD1 was less than 80 ml, most cases did not recur (97.4%), while most recurrent cases had volumes of 80 ml or more [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Using the approximation formula for subdural hematoma volume by Sucu et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] (Eq.\u0026nbsp;1), a subdural space volume of 80 ml corresponded to a subdural space thickness of 16 mm. When subdural space thickness on POD1 was 16 mm or more (corresponding to a volume of 80 ml or more), the recurrence rate was 55.5% in the drain group and 26.0% in the no-drain group, both showing significantly higher recurrence rates.\u003c/p\u003e \u003cp\u003eYu et al. reported a significantly lower recurrence rate in the group where SDD was left in place for 3 days or more [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In this study, as we removed the SDD on the POD1 in the SDD\u0026thinsp;+\u0026thinsp;group, we could not compare results with those of long-term SDD placement. Since recurrence was more common with large postoperative subdural thickness, cases with poor brain recovery may be more prone to recurrence, making long-term SDD placement worth considering. However, prolonged SDD placement can result in complications such as device-related issues, postoperative delirium, difficulties with mobilization, increased hospital costs, and longer hospital stays. Therefore, routine long-term SDD placement remains controversial.\u003c/p\u003e \u003cp\u003eRegarding complications associated with SDD placement, Pavlovet et al. reported a case where the SDD migrated into the brain parenchyma, causing intracerebral and intraventricular hemorrhage, resulting in severe neurological symptoms [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Apostolakis et al. reported serious SDD-related complications in three out of 97 cases (122 drainage procedures) for CSDH or ASDH. One patient experienced seizures, likely due to a cerebral contusion caused by the SDD, while two developed acute subdural hematomas. Both cases of acute subdural hematoma required craniotomy and hematoma removal. They noted that SDD use is a risk factor for serious complications [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In our study, we discontinued SDD use after an acute subdural hematoma occurred following its removal on POD1. In addition to these serious complications (life-threatening or requiring re-operation), two patients required wound opening due to difficulty in removing the SDD, resulting in a total of three SDD-related complications. No complications were noted in the SDD\u0026thinsp;\u0026minus;\u0026thinsp;group. The cause of the acute subdural hematoma is thought to be that the superficial temporal artery was wrapped around the drain fixation suture, damaging the artery during removal and causing blood to flow into the subdural space. The inability to remove the drain seems to have resulted from a procedural error in which the drain got caught during wound suturing.\u003c/p\u003e \u003cp\u003eThe independent recurrence factors identified in this study\u0026mdash;preoperative hematoma thickness and subdural thickness on POD1\u0026mdash;were not affected the presence or absence of SDD. Nevertheless, some reports suggest that leaving the SDD in place for an extended period (more than 3 days) significantly reduces the recurrence rate [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Identifying cases where the subdural space is likely to increase in thickness after surgery\u0026mdash;specifically cases with poor brain parenchyma compliance before or during surgery\u0026mdash;could help determine which cases require SDD placement.\u003c/p\u003e \u003cp\u003eIn this study, consecutive cases were used as historical controls, which likely reduced selection bias compared to typical retrospective studies. However, considering potential differences in the historical medical backgrounds, patient characteristics and surgical operators between groups, the results may not be sufficient to overturn existing RCTs. Our findings suggest that thorough hematoma irrigation until the drainage fluid became serous and reduction of residual air after creating a closed subdural space may have contributed to the lower recurrence rate. However, there are no RCTs that strictly standardize these surgical techniques. Therefore, conducting an RCT using a protocol that applies the same surgical techniques as in the present study may demonstrate the non-inferiority of omitting SDD placement. Based on these considerations, we believe this study serves as a meaningful step toward initiating future RCTs.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this single-center historical control study, we compared the recurrence rates of patients with and without SDD placement after burr-hole drainage for CSDH and found that the recurrence rate did not increase in patients without SDD. Adequate irrigation and reduction of residual air may help prevent recurrence even without inserting SDD. We believe that these findings could provide a basis for considering future RCTs using a similar protocol. Since non-placement of the SDD shortens the operation time, reduces postoperative hospital stay and treatment costs, and causes no serious complications, not placing an SDD may be an option, at least for the initial surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis work was partly supported by KAKENHI (Grant-in-Aid for Scientific Research of Japan) (grant no. 21K09156). The funders played no role in the study design, data collection and analysis, decision to publish, or manuscript preparation.\u003c/p\u003e\n\u003cp\u003eCompeting Interests\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003eCRediT Authorship Contribution Statement\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eKento Tsuburaya:\u0026nbsp;\u003c/strong\u003eData curation, Writing \u0026ndash; original draft, Software, Investigation, Visualization. \u003cstrong\u003eKimiyuki Kawaguchi:\u0026nbsp;\u003c/strong\u003eData curation, Writing \u0026ndash; original draft. \u003cstrong\u003eTakashi Matsumori:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Masashi Uchida:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Yuichiro Kushiro:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Gaku Hidaka:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Hiroshi Takasuna:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Hidenichi Itoh:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Ichiro Takumi:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Investigation.\u003cstrong\u003e\u0026nbsp;Hidetoshi Murata:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Validation, Investigation, Visualization, Writing \u0026ndash; review \u0026amp; editing, Supervision.\u003c/p\u003e\n\u003cp\u003eEthics approval\u003c/p\u003e\n\u003cp\u003eThis study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of St. Marianna University School of Medicine ( June 27, 2024; No. 6480 [B62]).\u003c/p\u003e\n\u003cp\u003eConsent to participate\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from all participants included in the study.\u003c/p\u003e\n\u003cp\u003eConsent to publish\u003c/p\u003e\n\u003cp\u003eThe authors affirm that human research participants provided informed consent for the publication of the images in Figures. 1a-d, 2a-c, and 3.\u003c/p\u003e\n\u003cp\u003eData availability\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAljabali A, Sharkawy AM, Jaradat B, Serag I, Al-Dardery NM, Abdelhady M, Abouzid M (2023) Drainage versus no drainage after burr-hole evacuation of chronic subdural hematoma: a systematic review and meta-analysis of 1961 patients. \u003cem\u003eNeurosurg Rev\u003c/em\u003e \u003cstrong\u003e46\u003c/strong\u003e:251. https://doi.org/10.1007/s10143-023-02153-7\u003c/li\u003e\n\u003cli\u003eApostolakis S, Vlachos K (2023) Complications from subdural drains in burr hole drainage of chronic and subacute subdural haematomas: a single-centre experience. \u003cem\u003eCureus\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e:e39068. https://doi.org/10.7759/cureus.39068\u003c/li\u003e\n\u003cli\u003eCarlsen JG, Cortnum S, S\u0026oslash;rensen JC (2011) Recurrence of chronic subdural haematomata with and without post-operative drainage. \u003cem\u003eBr J Neurosurg\u003c/em\u003e \u003cstrong\u003e25\u003c/strong\u003e:388\u0026ndash;390. https://doi.org/10.3109/02688697.2011.558945\u003c/li\u003e\n\u003cli\u003eGurelik M, Aslan A, Gurelik B, Ozum U, Karadag O, Kars HZ (2007) A safe and effective method for treatment of chronic subdural haematoma. \u003cem\u003eCan J Neurol Sci\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e:84\u0026ndash;87. https://doi.org/10.1017/s0317167100005849\u003c/li\u003e\n\u003cli\u003eNakaguchi H, Tanishima T, Yoshimasu N (2000) Relationship between drainage catheter location and postoperative recurrence of chronic subdural hematoma after burr-hole irrigation and closed-system drainage. \u003cem\u003eJ Neurosurg\u003c/em\u003e \u003cstrong\u003e93\u003c/strong\u003e:791\u0026ndash;795. https://doi.org/10.3171/jns.2000.93.5.0791\u003c/li\u003e\n\u003cli\u003ePavlov V, Bernard G, Chibbaro S (2012) Chronic subdural haematoma management: an iatrogenic complication. Case report and literature review. \u003cem\u003eBMJ Case Rep\u003c/em\u003e \u003cstrong\u003e2012\u003c/strong\u003e:bcr1220115397. https://doi.org/10.1136/bcr.12.2011.5397\u003c/li\u003e\n\u003cli\u003eRaj R, Tommiska P, Koivisto T et al (2024) Burr-hole drainage with or without irrigation for chronic subdural haematoma (FINISH): a Finnish, nationwide, parallel-group, multicentre, randomised, controlled, noninferiority trial. \u003cem\u003eLancet\u003c/em\u003e \u003cstrong\u003e403\u003c/strong\u003e:2798\u0026ndash;2806. https://doi.org/10.1016/S0140-6736(24)00686-X\u003c/li\u003e\n\u003cli\u003eSantarius T, Kirkpatrick PJ, Ganesan D et al (2009) Use of drains versus no drains after burr-hole evacuation of chronic subdural haematoma: a randomised controlled trial. \u003cem\u003eLancet\u003c/em\u003e \u003cstrong\u003e374\u003c/strong\u003e:1067\u0026ndash;1073. https://doi.org/10.1016/S0140-6736(09)61115-6\u003c/li\u003e\n\u003cli\u003eSoleman J, Lutz K, Schaedelin S et al (2019) Subperiosteal vs subdural drain after burr-hole drainage of chronic subdural hematoma: a randomized clinical trial (cSDH-drain-trial). \u003cem\u003eNeurosurgery\u003c/em\u003e \u003cstrong\u003e85\u003c/strong\u003e:E825\u0026ndash;E834. https://doi.org/10.1093/neuros/nyz095\u003c/li\u003e\n\u003cli\u003eStani\u0026scaron;ić M, Hald J, Rasmussen IA et al (2013) Volume and densities of chronic subdural haematoma obtained from CT imaging as predictors of postoperative recurrence: a prospective study of 107 operated patients. \u003cem\u003eActa Neurochir (Wien)\u003c/em\u003e \u003cstrong\u003e155\u003c/strong\u003e:323\u0026ndash;333; discussion 333. https://doi.org/10.1007/s00701-012-1565-0\u003c/li\u003e\n\u003cli\u003eSucu HK, Gokmen M, Gelal F (2005) The value of XYZ/2 technique compared with computer-assisted volumetric analysis to estimate the volume of chronic subdural hematoma. \u003cem\u003eStroke\u003c/em\u003e \u003cstrong\u003e36\u003c/strong\u003e:998\u0026ndash;1000. https://doi.org/10.1161/01.STR.0000162714.46038.0f\u003c/li\u003e\n\u003cli\u003eTorihashi K, Sadamasa N, Yoshida K, Narumi O, Chin M, Yamagata S (2008) Independent predictors for recurrence of chronic subdural hematoma: a review of 343 consecutive surgical cases. \u003cem\u003eNeurosurgery\u003c/em\u003e \u003cstrong\u003e63\u003c/strong\u003e:1125\u0026ndash;1129; discussion 1129. https://doi.org/10.1227/01.NEU.0000335782.60059.17\u003c/li\u003e\n\u003cli\u003eYu GJ, Han CZ, Zhang M, Zhuang HT, Jiang YG (2009) Prolonged drainage reduces the recurrence of chronic subdural hematoma. \u003cem\u003eBr J Neurosurg\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e:606\u0026ndash;611. https://doi.org/10.3109/02688690903386983\u003c/li\u003e\n\u003cli\u003eZawy Alsofy S, Lewitz M, Meyer K, Fortmann T, Wilbers E, Nakamura M, Ewelt C (2024) Retrospective analysis of risk factors for recurrence of chronic subdural haematoma after surgery. \u003cem\u003eJ Clin Med\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e:805. https://doi.org/10.3390/jcm13030805\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Equation","content":"\u003cp\u003e\u003cstrong\u003eEquation 1\u003c/strong\u003e Approximate equation for hematoma volume. If the hematoma volume is represented as V, the maximum thickness as x, the maximum vertical diameter as y, and the height as z, the equation V = xyz/2 applies. Rearranging for x gives x = 2V/yz. For a hematoma volume of 80 ml, with average maximum vertical diameter of 13.1 cm and height of 7.5 cm, x is calculated as 1.6 cm.\u003c/p\u003e\n\u003cp\u003eV=xyz/2\u003c/p\u003e\n\u003cp\u003ex=2V/yz\u003c/p\u003e\n\u003cp\u003e\u0026darr;(y=13.1, z=7.5)\u003c/p\u003e\n\u003cp\u003ex=0.02V\u003c/p\u003e\n\u003cp\u003e\u0026darr;(V=80)\u003c/p\u003e\n\u003cp\u003ex=1.6\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"chronic subdural hematoma, subdural drain, recurrence, burr-hole surgery","lastPublishedDoi":"10.21203/rs.3.rs-6516229/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6516229/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e: Several reports suggest that using a subdural drain (SDD) for chronic subdural hematoma (CSDH) reduces recurrence rates. However, due to complications associated with SDD placement, we discontinued its use in initial surgeries.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e: This study compared 150 historical cases with SDDs (SDD+ group) and 129 recent cases without SDDs (SDD- group).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e: Recurrence occurred in 18 patients (13.9%) in the SDD+ group and 12 patients (8.0%) in the SDD- group. The SDD- group had shorter operative times (40.9 vs. 54.9 min) and hospital stays (6.0 vs. 11.8 days). The overall complication rate was similar in both groups (4% vs. 1%), but the SDD+ group had serious complications related to SDD placement. Treatment costs were reduced by $811.8 per case in the SDD- group ($1978.2 vs. $1215.4). Preoperative hematoma thickness and subdural thickness on the first postoperative day were identified as independent recurrence factors, but no association was found with SDD use.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e: Omitting SDD placement for CSDH did not increase the recurrence rate, shortened operative time and hospital stay, reduced costs, and minimized serious complications. By performing sufficient irrigation and reducing the residual air, it is possible that the recurrence rate will not increase even without inserting SDD, and we believe that this will serve as an opportunity to consider randomized controlled trials using a similar protocol in the future.\u003c/p\u003e","manuscriptTitle":"Intraoperative removal of subdural drains during surgery for chronic subdural hematoma does not increase recurrence compared with postoperative drainage","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-07 06:21:39","doi":"10.21203/rs.3.rs-6516229/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"155abb04-5d4e-401a-802b-c1d157a2fcea","owner":[],"postedDate":"May 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-19T08:09:02+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-07 06:21:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6516229","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6516229","identity":"rs-6516229","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}