The use of endoscopic-assisted burr-hole craniostomy for septated chronic subdural haematoma: A retrospective cohort comparison study

Brain Research 1678 (2018) 245–253

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The use of endoscopic-assisted burr-hole craniostomy for septated chronic subdural haematoma: A retrospective cohort comparison study Jibo Zhang a, Xuemeng Liu a, Xingyue Fan b, Kai Fu a, Chengshi Xu a, Qin Hu a, Pucha Jiang a, Jincao Chen a, Wei Wang a,⇑ a b

Department of Neurosurgery, Zhongnan Hospital of Wuhan University, Wuhan 430071, China Heilongjiang University of Chinese Medicine, Harbin 150040, China

a r t i c l e

i n f o

Article history: Received 27 August 2017 Received in revised form 6 October 2017 Accepted 17 October 2017 Available online 24 October 2017 Keywords: Endoscopic surgery Chronic subdural haematoma Minimally invasive neurosurgery Burr-hole craniostomy

a b s t r a c t Objective: To complete a retrospective comparison of endoscope-assisted burr-hole craniostomy (EBHC) and ordinary burr-hole craniostomy (OBHC) in the treatment of septated chronic subdural hematoma (SCSH). Methods: A retrospective case note review comparing EBHC and OBHC of SCSH was therefore performed. Data of patients with a SCSH for EBHC or OBHC during the period from January 2011 to December 2016 were retrospectively collected and analysed. Of 73 patients, 42 underwent EBHC and 31 patients were treated by OBHC. The primary outcome measure was recurrence rate and secondary outcome measures were clinical outcome at first postoperative day, discharge and 6 months, the length of hospital stay for neurosurgery, the operative time, and the placement time of drainage tube. Result: The rate of recurrence was significantly lower in the EBHC (0/42 0%) than in the OBHC (8/31, 25.8%) group (p = .0030). The rate of morbidity was significantly lower in the EBHC (2/42, 4.8%) than in the OBHC (11/31, 35.5%) group (p = .0121). At 30 days, mortality did not differ between groups. Significantly more patients treated with EBHC were alive at 6 months than were those with OBHC. No patient died as a consequence of the operative procedure in the both groups. A discharge GCS of 15 was recorded in more participants with EBHC than in those with OBHC. Gross neurological deficit was significantly less frequent in those with EBHC than in those with OBHC at first postoperative day and discharge, but did not differ at 6 month follow-up. The mean placement time of drainage tube was significantly less in those with EBHC (27.2 h) than in those with OBHC (52.0 h, p = .0055). The mean length of hospital stay for neurosurgery was 4 days in the EBHC group, while it was 5 days in the OBHC group (p = .0015). The mean hematoma reduction rate was significantly higher in those with EBHC than in those with OBHC at first postoperative day (85.3% vs 72.5%, p = .0037) and discharge (90.3% vs 85.1%, p = .0127). Conclusion: Comparing two minimally invasive procedure protocols for treatment of SCSH, EBHC is a safe and effective surgical technique. It significantly surpasses the results obtained in OBHC in lowering recurrence rate, morbidity rate, placement time of drainage tube, and length of hospital stay for neurosurgery. We recommend EBHC technique to be widely used in the treatment of SCSH, even common chronic subdural hematoma (CSH), subacute and acute subdural hematomas, acute epidural hematomas and empyemas to avoid large craniotomies, particularly in elderly patients, so that patients can receive the best treatment on the basis of minimal trauma. Ó 2017 Elsevier B.V. All rights reserved.

1. Introduction Chronic subdural hematoma (CSH), which was first described by Rudolf Virchow in 1857 (Virchow, 1857), is a common increasingly detected neurosurgical disease characterized by the abnormal col⇑ Corresponding author at: Department of Neurosurgery, Zhongnan Hospital of Wuhan University, Donghu Road 169, Wuhan 430071, China. E-mail address: [email protected] (W. Wang). https://doi.org/10.1016/j.brainres.2017.10.017 0006-8993/Ó 2017 Elsevier B.V. All rights reserved.

lection of blood products in the subdural space (Roh et al., 2017; Miranda et al., 2011; Maurice-Williams, 1999). It is considered the ‘‘bread and butter” of traditional neurosurgery (Shofty and Grossman, 2016). The overall incidence of CSH was reported to range from 1.72-20.6/100000 persons per year in the general population (Foelholm and Waltimo, 1975; Sarti et al., 1991; Asghar et al., 2002; Balser et al., 2015) and it raises to 58.1/100000 inhabitants in the group of patients over 65 years old (Foelholm and Waltimo, 1975; Kudo et al., 1992; Chen and Levy, 2000). A trend

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toward an increase in incidence has been observed, because of the overall aging population resulting from an increase in life expectancy (Farhat Neto et al., 2015; Santarius et al., 2010; Kolias et al., 2014) and the increase in the use of anticoagulation and antiaggregation therapy (Shofty and Grossman, 2016). It is expected that in 2030, its incidence will double (Iliescu, 2015). Today, the treatment for CSH is generally surgical evacuation, usually resulting in great improvement in neurological condition. Three techniques are most often used—twist-drill craniostomy, burr-hole craniostomy (BHC) and craniotomy (Weigel et al., 2003). In rare cases, CSH are compartmentalized by fibrin septa as well as an inner thicker membrane (Ducruet et al., 2012; Hellwig et al., 2000, 1996; Masopust et al., 2003), these specific cases are called septated chronic subdural hematoma (SCSH) (Fig. 2B and Fig. 3A). The nonseptated CSH can be treated easily using the BHC method (Mobbs and Khong, 2009), whereas treatment of SCSH

remains a therapeutical problem. The main problem is the division of the hematoma by neomembranes into compartments, which hinder the efflux of the hematoma fluid through one or two burr-holes. However, it’s a frequent cause of failure and recurrence in the treatment of CSH (Berhouma et al., 2014). SCSH classically requires craniotomy, which has been replaced by BHC with it carries significant morbidity and mortality rates, particularly in elderly patients (Berhouma et al., 2014). Endoscope-assisted BHC (EBHC) of CSH is an established, although not widely used technique. It is a combination of burrhole evacuation of CSH and inspection of the subdural space with an endoscope. However, the advantages and disadvantages of EBHC compared with the ordinary BHC (OBHC) in the treatment of SCSH are not clearly. The aim of this study was to complete a retrospective comparison of EBHC and OBHC in the treatment of SCSH.

Fig. 1. Trial profile.

J. Zhang et al. / Brain Research 1678 (2018) 245–253

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Fig. 2. Various intraoperative endoscopic findings: multiple septations (A, B), cortical bridging veins and after hematoma flushing is complete (C), flexible blunt drainage tube (D).

2. Material and methods The study design is a retrospective cohort comparison study. Data of patients with SCSH admitted to our institute during the period from January 2011 to December 2016 were retrospectively collected and analysed. All patients underwent either EBHC or OBHC were included in the study. Patients were excluded if (a) they underwent craniotomy or (b) conservative (medical) treatment, (c) recurrent SCSH. Of 73 patients, 42 underwent EBHC and 31 patients were treated by OBHC. The choice of surgical technique was made by the responsible consultant. After CT (computed tomography) diagnosis and clinical examination, all procedures were done under local hair-shave and infiltration with local scalp anesthesia (1% lidocaine with l:l00000 epinephrine mixed half and half with 0.5% bupivacaine), with anesthesia standby providing sedation and monitoring. In the operating theatre patients were positioned supine on a horseshoe headrest. A diameter of 1.5 cm burr holes with oblique bone edges was performed after a 2–3 cm skin incision over the area of maximal haematoma width. Following exposure and haemostasis, the dura was incised in a cruciate fashion and diathermied to the burr-hole limits. At this stage, for OBHC, the haematoma cavity was rinsed with warm isotonic with a 50 mL syringe, evacuating possibly solid haematoma clots, until the color of the sodium chloride solution

became clear. The subdural membrane loculations were not disrupted apart from those easily accessible via the burr holes. However, for EBHC, the subdural hematoma was evacuated and the subdural space rinsed with warm saline. When the coming subdural liquid was clearer, a rigid short endoscope with a 30° high definition lens (Karl Storz, Tuttlingen, Germany) was carefully introduced into the subdural space. The surgeon operated the endoscope with his own hand. Adjustable suction was used to aspirate the fibrin septa while warm saline was injected through the endoscope. The internal (visceral) membrane of the hematoma was then largely excised with microscissors and forceps and finally a bipolar suction tip allows coagulation of any bleeding visualized in the subdural space. Finally, for these two procedures, a flexible blunt drainage tube was placed in the frontal direction of subdural space to guarantee an efflux of the remaining hematoma. The burr hole is closed with absorbable gelatin compressed sponge and the skin was sutured in two layers. The drainage tube was removed after drying-up of the haematoma secretion and CT-confirmation of adequate treatment. We recorded basic patient demographics, preoperative neurological dysfunction, social history, medical history and medication history, Modified Rankin Scale (MRS), Glasgow coma scale (GCS) and the characteristics of the haematoma on CT scan. The CSH volumes were calculated with the method of XYZ/2 that has been validated with the gold standard of computer volumetric calculation

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Fig. 3. Computed tomography scan showing chronic subdural hematoma on the left side. Note compression of the left cerebral hemisphere, midline shift and heterogeneous density of the hematoma suggesting presence of septations. Small red arrows indicate SCSH with two clear compartments. (A, B). Early postoperative scan showing significant regression of hematoma, regression of midline shift and slight intracranial pneumatosis (C, D).

(Sucu et al., 2005). Similarly, surgical condition, the operative time, the placement time of drainage tube and the length of hospital stay for neurosurgery was compared. Patients were discharged home or to a local hospital when they no longer needed specialised neurosurgical care and when the hospital was ready to receive them. All patients were followed up according to departmental protocol with progress CT, MRS, GCS, and postoperative morbidity and mortality at on first postoperative day, at discharge, 30 days and 6 months. The primary outcome measure was recurrence rate, defined as the rate of reoperation to treat recurrent chronic subdural haematoma in patients previously treated with EBHC and OBHC. Recurrence was defined as occurrence of symptoms and signs attributable to an ipsilateral haematoma seen on a CT scan within 6 months of the original drainage procedure. Reoperation would be indicated if there were any worsening of original neurological deficit symptoms, deterioration in GCS or MRS, new focal neurological deficits or CT showing an increase in the size of CSH during the

follow-up period. Secondary outcome measures were clinical outcome at first postoperative day, discharge and 6 months, the length of hospital stay for neurosurgery, the operative time, and the placement time of drainage tube. Statistical analysis was performed with categorical frequency Chi-square test or Fisher’s Exact Test. Significance was set at 5% and all statistical analyses were done with the SPSS software version 19.0.

3. Results Over the 6-year period, 80 patients were treated surgically for SCSH, 2 patients underwent a craniotomy, 2 patients underwent medical treatment, 3 patients were recurrent SCSH and those 7 patients were excluded. Finally, 42 patients underwent EBHC and 31 patients were treated OBHC. The trial profile is shown in the Fig. 1.

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The majority of patients were male both in the EBHC group (76.2%), and in the OBHC group (70.1%, Table 1). The mean age of patients in the EBHC group was 74.3 years, compared to 75.1 years in the OBHC group (p = .5331, Table 1). Table 2 shows the preoperative neurological dysfunction of both groups. Gait disturbance, mental deterioration, acute confusion, limb weakness, headache, drowsiness or coma, and aphasic disorder were most common. About two third of patients presented with more than one symptom (30/42, 71.42% in EBHC group and 20/31, 64.5% in OBHC group). In the EBHC group, 15 (35.7%) patients had received anticoagulants or antiplatelet therapy (aspirin, plavix or warfarin), compared to 13 (41.9%) in the OBHC group (p > .05, Table 3); 14/42 (33.3%) of the EBHC group and 9/31 (29.0%) of the OBHC group had a history of alcohol abuse (p = .5432, Table 3). A history of head injury was established in 66.7% of EBHC group and 24/31, 77.4% in OBHC group (p = .1253, Table 3). Because of the patient’s age is relatively old in both groups, they have a variety of medical history, such as hypertension, diabetes, cerebrovascular accident (CVA), arrhythmia and so on. As demonstrated on CT scan (Table 4), the density of most patients were hypodense and mixed, and the average depth of the haematoma was comparable (22.5 mm EBHC vs 21.9 mm OBHC) between the two groups (p = .1049), the mean midline shift was 9.2 mm EBHC vs 8.6 mm OBHC (p = .2567), and the mean hematoma volume was 117.5 ml EBHC vs 103.2 ml OBHC (p = .2312). At examination (Table 5), most of patients had GCS of 9– 15, and about MRS score, patients were widely distributed in 1–5 points, compared with no patients had 0 point. We can find the surgical condition in Table 6, and there is no statistical difference between the two groups.

Table 1 Baseline demographics. EBHC

OBHC

p Value

Demographic Age (years old) Male gender

74.3 (67–91) 32/42 (76.2%)

75.1 (58–95) 22/31 (70.1%)

.5331 .6659

Premorbid mobility Independent Stick Frame Wheelchair Bed-bound

33/42 (78.6%) 5/42 (11.9%) 3/42 (7.1%) 1/42 (2.4%) 0/42 (0%)

23/31 (74.2%) 4/31 (12.9%) 2/31 (6.5%) 1/31 (3.2%) 1/31 (3.2%)

.3988 .1996 .3175 .3454 .5433

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy.

Burr-hole Craniostomy,

OBHC:

EBHC

OBHC

p Value

22/42 (52.3%) 12/42 (28.6%) 14/42 (33.3%) 11/42 (26.2%) 20/42 (47.6%) 10/42 (23.8%) 9/42 (21.4%) 3/42 (7.1%) 5/42 (11.9%) 1/42 (2.4%) 1/42 (2.4%) 4/42 (9.5%)

14/31 (45.2%) 11/31 (35.5%) 13/31 (41.9%) 8/31 (25.8%) 19/31 (61.3%) 9/31 (29.0%) 11/31 (35.5%) 5/31 (16.1%) 4/31 (12.9%) 1/31 (3.2%) 0/31 (0%) 3/31 (9.7%)

.4448 .1074 .3216 .2131 .4549 .6566 .7432 .2141 .2692 .6434 .6597 .4688

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy.

Burr-hole Craniostomy,

OBHC:

EBHC

OBHC

p Value

Social history Smoker Drinker

10/42 (23.8%) 14/42 (33.3%)

12/31 (38.7%) 9/31 (29.0%)

.3652 .5432

Medical history Diabetes Hypertension Dementia CVA IHD Arrhythmia DVT/PE COPD Head injury

8/42 (19.0%) 15/42 (35.7%) 3/42 (7.1%) 7/42 (16.7%) 3/42 (7.1%) 5/42 (11.9%) 1/42 (2.4%) 1/42 (2.4%) 28/42 (66.7%)

6/31 (19.4%) 12/31 (38.7%) 2/31 (6.5%) 8/31 (25.8%) 5/31 (16.1%) 7/31 (22.6%) 1/31 (3.2%) 0/31 (0%) 24/31 (77.4%)

.6841 .2568 .8635 .3685 .3564 .7531 .2348 .5677 .1253

Medication history Aspirin Plavix Warfarin

14/42 (33.3%) 0/42 (0%) 1/42 (2.4%)

12/31 (38.7%) 1/31 (3.2%) 0/31 (0%)

.1431 .1342 .2372

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy, OBHC: Ordinary Burr-hole Craniostomy, CVA: Cerebrovascular Accident, IHD: Ischemic Heart Disease, DVT: Deep Vein Thrombosis, PE: Pulmonary Embolism, COPD: Chronic Obstructive Pulmonary Disease.

Table 4 CT features on admission. EBHC

OBHC

p Value

Localization Left Right Bilateral

21/42 (50.0%) 20/42 (47.6%) 1/42 (2.4%)

17/31 (54.8%) 12/31 (38.7%) 2/31 (6.5%)

.1287 .2018 .1847

Density Hypodense Isodense Mixed

17/42 (31.5%) 3/42 (7.1%) 22/42 (52.4%)

14/31 (45.2%) 5/31 (16.1%) 12/31 (38.7%)

.1784 .6533 .1060

Mean distribution Frontal Temporal Parietal Occipital

8/42 (19.0%) 27/42 (64.3%) 18/42 (42.9%) 0/42 (0%)

6/31 (19.4%) 20/31 (64.5%) 14/31 (45.2%) 0/31 (0%)

.2877 .3675 .1094 .1593

Mean hematoma 117.5 (30.3–200.2) 103.2 (37.6–171.5) .2312 volume (ml) Mean maximal width (mm) 22.5 (10.1–32.2) 21.9 (11.8–38.9) .1049 Mean midline shift (mm) 9.2 (0–19
5) 8.6 (0–23.3) .2567 Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy, Burr-hole Craniostomy, CT: Computed Tomography.

OBHC: Ordinary

Ordinary

Table 2 Preoperative neurological dysfunction.

Gait disturbance Mental deterioration Acute confusion Limb weakness Headache Drowsiness or coma Aphasic disorder Seizure Incontinence Visual disturbance Vomiting Non-specific deterioration

Table 3 Social history, past medical history and medication history.

Ordinary

The rate of recurrence was significantly lower in the EBHC than in the OBHC group (p = .0030, Table 7). To be exact, no patient relapsed in the EBHC group, and the rate of recurrence was 8/31 (25.8%) in the OBHC group. Of the 31 patients who underwent OBHC, 5 patients (16.1%) developed a symptomatic recurrence, 7 patients (22.6%) developed an ipsilateral haematoma seen on a CT scan. 5 (16.1%) requiring reoperation. No any basic factor had a statistical significant association with recurrence (p > .05). The rate of morbidity was significantly lower in the EBHC (2/42, 4.8%) than in the OBHC (1/31, 35.5%) group (p = .0121, Table 7). Postoperatively, two patients who were treated with EBHC developed intracranial pneumatosis compared to six in the OBHC group. One patient suffered seizures following EBHC compared to four patients in the OBHC group. And one patient (2.5%) suffered intracerebral haematoma in the OBHC group. In the group of EBHC, one patient had both postoperative intracranial pneumatosis and seizures. After conservative treatment, all patient symptoms were significantly relieved or disappeared. There were no wound complications, delayed intracranial haemorrhage, intracranial infection

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Table 5 Admission GCS and MRS score. EBHC

OBHC

p Value

GCS 13–15 9–12 3–8

31/42 (73.8%) 8/42 (19.0%) 3/42 (7.1%)

22/31 (71.0%) 8/31 (25.8%) 1/31 (3.2%)

.2351 .4672 .5773

MRS 0 1 2 3 4 5

0/42 (0%) 6/42 (14.3%) 7/42 (16.7%) 7/42 (16.7%) 10/42 (23.8%) 12/42 (28.6%)

0/31 (0%) 3/31 (9.7%) 4/31 (12.9%) 5/31 (16.1%) 11/31 (35.5%) 8/31 (25.8%)

.4575 .1235 .7645 .2126 .2331 .3876

MRS (median)

4

4

.2561

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy, OBHC: Ordinary Burrhole Craniostomy, GCS: Glasgow coma scale, MRS: Modified Rankin Scale.

Table 6 Surgical condition. EBHC

OBHC

p Value

0/42 (0%) 0/42 (0%) 5/42 (11.9%) 20/42 (47.6%) 8/42 (19.0%) 9/42 (21.4%)

0/31 (0%) 1/31 (3.2%) 3/31 (9.7%) 17/31 (54.8%) 5/31 (16.1%) 5/31 (16.1%)

.3431 .1332 .6745 .4574 .8653 .2110

Subdural fluid pressure Low 2/42 (4.8%) Medium 14/42 (33.3%) High 22/42 (52.4%) Very high 4/42 (9.5%)

2/31 (6.5%) 13/31 (41.9%) 14/31 (45.2%) 2/31 (6.5%)

.1458 .6747 .6727 .2455

Membrane Thin Thick Very thick

13/31 (41.9%) 16/31 (51.6%) 2/31 (6.5%)

.5434 .2353 .1232

Subdural fluid Absent Clear Straw Engine oil Fresh blood Mixture

19/42 (45.2%) 20/42 (47.6%) 3/42 (7.1%)

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy, OBHC: Ordinary Burrhole Craniostomy.

and low intracranial pressure within either group. At 30 days, mortality did not differ between groups (Table 7). Significantly more patients treated with EBHC were alive at 6 months than were those

with OBHC. In the EBHC group, one patient died of myocardial infarction, while one died of severe pneumonia, 2 died of heart failure in the OBHC group. No patient died as a consequence of the operative procedure in the both groups. No any basic factor had a statistical significant association with recurrence (p > .05). A discharge GCS of 15 was recorded in more participants with EBHC than in those with OBHC. Gross neurological deficit was significantly less frequent in those with EBHC than in those with OBHC at first postoperative day, at discharge, and at 6 month follow-up. Favourable MRS scores (0–3) at first postoperative day, discharge and 6 months were recorded in significantly more patients with EBHC than with OBHC. Comparison of requirements for care at 6 months between the both groups shows a nonsignificant difference with p = .5624. The mean placement time of drainage tube was significantly less in those with EBHC (27.2 h) than in those with OBHC (52.0 h, p = .0055). The mean operative time was slightly longer in the EBHC group (56.5 min) than OBHC group (39.7 min, p = .0147). The mean length of hospital stay for neurosurgery was 4 days in the EBHC group, while it was 5 days in the OBHC group (p = .0015). The mean hematoma reduction rate was significantly higher in those with EBHC than in those with OBHC at first postoperative day (85.3% vs 72.5%, p = .0037) and discharge (90.3% vs 85.1%, p = .0127). The mean hematoma reduction rate was obtained from (preoperative hematoma volume minus postoperative hematoma volume)/preoperative hematoma volume. No any basic factor had a statistical significant association with the above outcome (p > .05). All of the above data can be found in Table 7. 4. Discussion We all know the risk factors of recurrence are the following: tendency of bleeding, intracranial hypotension, recurrent neomembrane hemorrhages and the persistence of the subdural area due to the insufficient expansion (Iliescu, 2015). The division of the hematoma by fibrin membranes into compartments within the subdural space can hinder the efflux of the hematoma fluid through burr-hole. However, it’s a frequent cause of failure and recurrence in the treatment of SCSH. In this study, the rate of recurrence was significantly lower in the EBHC than in the OBHC group (8/31, 25.8%), which represents a disappointing high percentage. To be exact, no patient relapsed in the EBHC group. For OBHC,

Table 7 Primary and secondary outcome.

Recurrence Morbidity Mortality At 30 days At 6 months Rankin (MRS 0–3) At first postoperative day At discharge At 6 months GCS of 15 (at discharge) Gross focal neurological deficit At first postoperative day At discharge At 6 months High level of care at 6 months Mean placement time of drainage tube (hours) Mean operative time (minutes) Mean length of hospital stay for neurosurgery (days) Mean hematoma reduction rate At first postoperative day At discharge

EBHC

OBHC

p Value

0/42 (0%) 2/42 (4.8%)

8/31 (25.8%) 11/31 (35.5%)

.0030 .0121

0/42 (0%) 1/42 (2.4%)

0/31 (0%) 3/31 (9.7%)

.3741 .0072

31/42 38/42 39/41 38/42

16/31 19/31 24/28 17/31

(51.6%) (61.3%) (85.7%) (54.8%)

.0144 .0056 .0412 .0052

11/42 (26.2%) 8/42 (19.0%) 1/41 (2.4%) 2/41 (4.9%) 27.2(23–46) 56.5(48–69) 4(3 7)

16/31 (51.6%) 11/31 (35.5%) 5/28 (17.9%) 2/28 (6.5%) 52.0(36–73) 39.7(35–58) 5(4 9)

.0032 .0071 .0115 .5624 .0055 .0147 .0015

85.3% 90.3%

72.5% 85.1%

.0037 .0127

(73.8%) (90.5%) (95.1%) (90.5%)

Notes: EBHC: Endoscope-assisted Burr-hole Craniostomy, OBHC: Ordinary Burr-hole Craniostomy, GCS: Glasgow coma scale, MRS: Modified Rankin Scale.

J. Zhang et al. / Brain Research 1678 (2018) 245–253

the subdural membrane loculations were not disrupted apart from those easily accessible via the burr holes. However, for EBHC, with the help of a rigid short endoscope with a 30° high definition lens, the internal membrane of the hematoma could be largely excised, as many hematomas as possible could be washed out and any bleeding point could be coagulated visualized in the subdural space. So we found in the study that the mean hematoma reduction rate was significantly higher in those with EBHC than in those with OBHC at first postoperative day (85.3% vs 72.5%) and discharge (90.3% vs 85.1%). We thereby realized the effectiveness of EBHC. As far as we know, this is the first time for the description of mean hematoma reduction rate, which has not been found in previous studies. We found that the rate of morbidity was significantly lower in the EBHC (2/42, 4.8%) than in the OBHC (11/31, 35.5%) group. Intracranial pneumatosis, seizures and intracerebral haematoma were the main morbidity in the both group. The most feared complication is acute bleeding with the damage to bridging veins and cortical surface after CSDH removal. However, there was no acute bleeding in the EBHC group. At 6 months follow up, no patient died as a consequence of the operative procedure in the both groups. Berhouma et al. (2014) believed that the following methods could avoid complications as much as possible: a) Preoperative completed imaging examinations were performed to assess the number and location of the fibrin septa. b) The diameter of burr hole should be slightly enlarged so as to ensure the operability of the operation. c) The endoscope tip must precede the instruments’ tips to control the surgeon’s movements and the surgeon should manipulate lightly and softly in order to avoid any injury to the cerebral cortex. d) Special care was needed when removing the septa in order to not generate any cortical bleeding. e) The inner membrane should be opened as wide as possible to not miss any non-communicating compartment. f) Before closing the burr hole, the subdural space should be emptied with warm saline to prevent pneumocephalus. In addition to these aspects, we believe that postoperative routine use of antiepileptic and hemostatic drugs, as well as regular routine review of head CT are also necessary. In our study, gross neurological deficit was significantly less frequent in those with EBHC than in those with OBHC at first postoperative day. The result is similar to the result of mean hematoma reduction rate for both groups. At discharge, we found gross neurological deficit was also less frequent in EBHC than OBHC, the GCS of 15 was recorded in more participants with EBHC than in those with OBHC, and the same result can be found on favourable MRS scores (0–3). Therefore, we can see that the effect of EBHC is obviously better than OBHC in a short period of time. However, at 6 month follow-up, gross neurological deficit and favourable MRS scores (0–3) were also less frequent in EBHC than OBHC. We think this is related to the recurrence of some patients. The mean placement time of drainage tube was significantly less in those with EBHC (27.2 h) than in those with OBHC (52.0 h). We all know that the longer the time of placement of the drainage tube, the greater chance of wound and intracranial infection. Although in the present study, both groups had no intracranial infection and wound infection cases, the effective removal of the drainage tube as soon as possible is a sufficient affirmation of the effectiveness of the operation and to some extent alleviate the patients’ pain because of stay in bed for a long time. Additionally, the mean length of hospital stay for neurosurgery, an almost 20% cut in the EBHC group than the OBHC group. The length of hospital stay for neurosurgery has a direct impact on lowering of treatment costs in this disease and the bed turnover of neurosurgery. Similarly, this also shows the effectiveness of EBHC, we all know that if the patient needs to receive further treatment, we will not let them discharged. The mean operative time was slightly longer in

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the EBHC group than OBHC group, but we didn’t find any bad results that associated with it. Since CSH was first described by Rudolf Virchow in 1857 (Virchow, 1857), many different therapeutic regimens in the therapy of CSH had been proposed. Over the years, with the development of diagnostic methods and surgical techniques, the treatment of CSH has evolved. Currently, there are also studies (Xu et al., 2016; Liu et al., 2016; Kutty and Peethambaran, 2017; Henaux et al., 2017; Chan et al., 2017) of conservative treatment beside the various surgical techniques, which however have not been applied very often. But now the most popular treatment for CSH is generally surgical evacuation and three techniques are most often used—twist-drill craniostomy, BHC and craniotomy. However, the treatment of SCSH remains a therapeutical problem and it is also full of controversy. SCSH, as a special form of CSH, has a high degree of difficulty in treatment and relatively poor prognosis. The main problem is the division of the hematoma by neomembranes into compartments, which hinder the efflux of the hematoma fluid. Conventional operative therapy of SCSH requires craniotomy, which has the advantage of exposing an important part of the brain, whereas it is usually practiced under general anesthesia and it is the most invasive of the treatment options because it takes a lot of time and it presupposes a lot of intraoperatory blood loss which leads to significant morbidity and mortality rates, particularly in elderly patients. This technology is now solely indicated in treatment of: Repeated recurrence of the hematoma; Solid consistency of the hematoma; Lack of reexpansion of the shifted brain tissue; and Space occupying brain edema of the involved hemisphere. Hellwig et al. (1996) demonstrated that endoscopic operative method combined with a closed drainage system should be used rather than craniostomymembranectomy. They used endoscopy and resection of neomembranes in the treatment of 13 out of 14 patients successfully who had had burr-hole drainage and no recurrence occurred. We agree with their points that a less invasive approach that provides similar results is helpful and the results of this study are similar with theirs. In 2011, we introduced EBHC techniques into treatment of SCSH based on previous studies. Although it is not widely used, it has clear advantages compared to OBHC. EBHC technology has many advantages in the treatment of SCSH: a) Complete evacuation of hematoma and excision of fibrous membrane under direct vision. b) Insertion of a catheter under direct visual control preventing brain/vessel injury. c) Detection of event, source of acute bleeding and hemostasis. d) Improvement of surgical depth and enlargement of the visual field. e) Single bore and can be completed under local anesthesia, which belongs to minimally invasive surgery. It also has some disadvantages: a) The greatest risk may be the potential damage to bridging veins and cortical surface. Because some surgeons may not feel comfortable working in a 2D environment while using endoscope and some are not so skilled (Mobbs and Khong, 2009; Lind et al., 2003). However, such a complication has been neither encountered in our series nor reported in the literature. The corridor to introduce endoscopy should be suitable and surgeons must use both hands on the endoscope to avoid plunging into the cortex. b) Extra equipment/training needed. Endoscopy really need some additional expenses, but it can be used not only in SCDH, even common CSH, subacute and acute subdural hematomas, acute epidural hematomas and empyemas to avoid large craniotomies, particularly in elderly patients. c) Slightly prolonged operative time. It can be considered as a waste of time to arrange endoscopy devices and the visualization tools. But with a wholistic vision, it gives the chance to save time to reduce the recurrence rate and avoid reoperation. And in this study, we didn’t find any bad results that associated with the slightly prolonged operative time.

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The first use of endoscopy for CSDH surgery was published by Karakhan et al. in 1988 (Karakhan, 1988). Since then, several other authors have reported slight modifications of the technique. Most authors report using flexible instruments (Hellwig et al., 2000, 1996; Májovsky´ et al., 2016; Shiomi et al., 2002; Gruber and Crone, 1997; Drapkin, 1997) arguing that the flexible endoscope permitted penetrating much farther than a rigid instrument. The use of the rigid endoscope was limited by the size of the haematoma. Too small haematomas would not make for a safe introduction of the endoscope without traumatizing the brain by any inadvertent perforation of the inside of the neomembrane. Yet, Masopust et al. (2003) thought that similar limitations applied also to the flexible endoscope. Its working portion was, as a rule, too short, and if it was to reach the remotest part of an averagesized CSH, it would have to pass through the transcranial region already with its non-flexible end. The technique of transcranial introduction at an angle for CSH revision would have to be combined with a skilful use of the flexible instrument. Vice versa, the rigid endoscope and its straight trajectories could be easily manipulated. This is, to our knowledge, the first and the largest series reported to study the surgical treatment (EBHC and OBHC) of SCDH. Although there was an abundance of literatures discussing the best technique for CSH, few studies have been conducted on SCSH. We assessed and compared the baseline characteristics, surgical condition, the operative time, the placement time of drainage tube and the length of hospital stay for neurosurgery. All patients were followed up according to departmental protocol with progress CT, MRS, GCS, and postoperative morbidity and mortality at on first postoperative day, at discharge, 30 days and 6 months. All of this makes our results more reliable. We would like to acknowledge several limitations in our study. It is a single institution experience from the department rather than a multicentre study. Certain basic endoscopic skills and special equipment are needed. The neurosurgeons typically chose their operative technique because of individual preference rather than on the basis of some other structured criteria. The study design is a retrospective cohort comparison study in nature, further randomised controlled trial would be needed to help rationalise treatment.

5. Conclusion Comparing two minimally invasive procedure protocols for treatment of SCSH, EBHC is a safe and effective surgical technique. It significantly surpasses the results obtained in OBHC in lowering recurrence rate, morbidity rate, placement time of drainage tube, and length of hospital stay for neurosurgery. We recommend EBHC technique to be widely used in the treatment of SCSH, even common CSH, subacute and acute subdural hematomas, acute epidural hematomas and empyemas to avoid large craniotomies, particularly in elderly patients, so that patients can receive the best treatment on the basis of minimal trauma.

Statement of non-duplication We certify that this manuscript is a unique submission and is not being considered for publication by any other source in any medium. Further, the manuscript has not been published, in part or in full, in any form.

Conflict of interest statement We certify that we have no affiliations with any organization or entity with any financial interest or non-financial interest.

Ethical approval Since this is a retrospective study, formal consent is not required. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Authors’ contributions Jibo Zhang was the lead investigator and contributed with Wei Wang to writing the report. Wei Wang was the chief investigator and the senior author of the report. Pucha Jiang and Jincao Chen assisted with setting up the project and its promotion and helped with editing of the report. Chengshi Xu, Qin Hu, Xuemeng Liu and Kai Fu contributed to acquisition and analysis of the data. Xingyue Fan contributed to editing the grammar and syntax. All authors read and approved the final manuscript. Availability of data and materials The data that support the findings of this study are available on request from the corresponding author [Wei Wang]. Acknowledgements Thanks are due to Jie Zhang for assistance with the study and to Xinyu Zhao for valuable discussion. In addition, I would like to thank the editor and anonymous reviewers, who have helped to improve the paper. References Virchow, R., 1857. Das Hamatom der Dura Mater. Verh. Phys. Med. Ges. Wiirzburg 7, 134–142. Roh, D., Reznik, M., Claassen, J., 2017. Chronic subdural medical management. Neurosurg. Clin. N. Am. 28 (2), 211–217. Miranda, L.B., Braxton, E., Hobbs, J., Quigley, M.R., 2011. Chronic subdural hematoma in the elderly: not a benign disease. J. Neurosurg. 114 (1), 72–76. Maurice-Williams, R.S., 1999. Chronic subdural haematoma: an everyday problem for the neurosurgeon. Br. J. Neurosurg. 13 (6), 547–549. Shofty, B., Grossman, R., 2016. Treatment options for chronic subdural hematoma. World Neurosurg. 87, 529–530. Foelholm, R., Waltimo, O., 1975. Epidemiology of chronic subdural haematoma. Acta Neurochir. (Wien) 32 (3–4), 247–250. Sarti, C., Tuomilehto, J., Salomaa, V., Sivenius, J., Kaarsalo, E., Narva, E.V., et al., 1991. Epidemiology of subarachnoid hemorrhage in Finland from 1983 to 1985. Stroke 22 (7), 848–853. Asghar, M., Adhiyaman, V., Greenway, M.W., Bhowmick, B.K., Bates, A., 2002. Chronic subdural haematoma in the elderly–a North Wales experience. J. R. Soc. Med. 95 (6), 290–292. Balser, D., Farooq, S., Mehmood, T., Reyes, M., Samadani, U., 2015. Actual and projected incidence rates for chronic subdural hematomas in United States Veterans Administration and civilian populations. J. Neurosurg. 123 (5), 1209– 1215. Kudo, H., Kuwamura, K., Izawa, I., Sawa, H., Tamaki, N., 1992. Chronic subdural hematoma in elderly people: present status on Awaji Island and epidemiological prospect. Neurol. Med. Chir. (Tokyo) 32 (4), 207–209. Chen, J.C., Levy, M.L., 2000. Causes, epidemiology, and risk factors of chronic subdural hematoma. Neurosurg. Clin. N. Am. 11 (3), 399–406. Farhat Neto, J., Araujo, J.L., Ferraz, V.R., Haddad, L., Veiga, J.C., 2015. Chronic subdural hematoma: epidemiological and prognostic analysis of 176 cases. Rev. Col. Bras. Cir. 42 (5), 283–287. Santarius, T., Kirkpatrick, P.J., Kolias, A.G., Hutchinson, P.J., 2010. Working toward rational and evidence-based treatment of chronic subdural hematoma. Clin. Neurosurg. 57, 112–122. Kolias, A.G., Chari, A., Santarius, T., Hutchinson, P.J., 2014. Chronic subdural haematoma: modern management and emerging therapies. Nat. Rev. Neurol. 10 (10), 570–578. Iliescu, I.A., 2015. Current diagnosis and treatment of chronic subdural haematomas. J. Med. Life 8 (3), 278–284.

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