Chronic subdural hematoma (CSDH) is one of the most common conditions encountered concerning neurosurgical interventions4,5). Although CSDH is a curable disease with low morbidity and mortality rates, the high rate of symptomatic recurrence is a challenge in the neurosurgical practice4). The rate of recurrence of CSDH after surgery is known to be around 9.2% to 26.5%13). The treatment of choice for symptomatic CSDH is surgical evacuation, which usually results in marked neurologic and radiographic improvement10). Although the modes of surgical treatment ranges widely from burr hole trephination to complex craniotomy with membranectomy, in the recent years, burr hole trephination has replaced the conventional craniotomy in most of the CSDH cases for many reasons such as minimal invasiveness, lower mortality and morbidity, and shorter length of hospital stay10). There have been many attempts to reduce the recurrence rate of CSDH following burr hole surgery.

In the present study, the authors have compared the post-operative recurrence rates of burr hole trephination depending on the inclusion of intraoperative saline irrigation procedure. The extent of hematoma resolution based on the follow-up CT scans has also been compared.

The charts of all adult CSDH patients above 18 years of age who underwent surgical evacuation in a single center were retrospectively reviewed. Initial diagnoses of 100 patients with symptomatic CSDH were made by computed tomography (CT) scans. All the patients had previous history of head trauma. We categorized the patients under two groups, “irrigated” and “not irrigated” depending on the inclusion of intra-operative saline irrigation of the CSDH.

All the patients underwent burr-hole trephination, dura incision and subdural catheter placement. As for the “irrigated” group, warm sterile saline was irrigated through the subdural catheter, about 20 to 50 mL at a time, and then let to drain. The irrigation process was repeated until the drained irrigant appeared almost clear in color. The drain was then connected to an external ventricular drainage bag which was kept in a dependent position for more than 48 hours (3.12±1.01 days). For the “not irrigated” group, the irrigation procedure was omitted but all other surgical procedures and post-operative managements were identical.

The first CT was taken immediately after the surgery, and following CT’s were taken prior to the removal of the catheter (3.12±1.01 days) and one month after the surgery, at the outpatient clinic. Patients were discharged home or to a local hospital after catheter removal and when they no longer needed specialized neurosurgical care (8.26±2.09 days).

The outcome between the two groups was evaluated in terms of recurrence, where second surgery was required to treat recurrent CSDH.

Radiographic outcome was evaluated with the follow-up CT results, where remnant CSDH or subdural hygroma of more than 0.5 times the skull vault thickness was termed “residual” and lesser amount was termed “resolved”.

The study population was composed of 100 subjects, and the median age was 72.5 years old (range, 3-91 years) There was male preponderance, with 74 male and 26 female patients (ratio=2.85:1). The patients’ presenting symptoms included hemiparesis, headache, and mental change, and their mean GCS at admission was 13.1 (range, 7-15). Eighty-five patients had unilateral CSDH, while 15 had bilateral CSDH. Concerning CSDH laterality, there was left side preponderance, with 52 left sided and 33 right sided hematomas (ratio=1.58:1). Five cases (10.6%) of left sided hematomas and 8 cases (32.0 %) of right sided hematomas required second surgery due to recurrence, but this was insignificant (p=0.07).

A total of six surgeons were involved in this study and the rate of irrigation applied by each surgeon was 42%, 44%, 62%, 67%, 83%, and 83%, respectively.

Intra-operative irrigation was done in 68 patients, while the procedure was omitted in 32 patients. The mean age of the patients in the “irrigated” group was 69.6 years (range, 38-86 years), while the mean age was 69.1 years (range, 39-91 years) for the “not irrigated” group. In overall, 15 patients (15%) underwent second surgery due to recurrence. Six patients (8.8 %) in the “irrigated” group and 9 patients (28.1%) in the “not irrigated” group necessitated second surgery due to recurrence (p=0.02). Association analysis showed that there were 4.04 higher chance of recurrence in the “not irrigated” group (p= 0.02, OR=4.04, 95% CI=1.23-12.6) (Table 1).

In the follow-up CT taken 1 month after the surgery, 66 patients showed total resolution whereas 34 patients had residual hygroma or CSDH. Eighteen patients in the “irrigated” group (26.5%) and 16 patients in the “not irrigated” group (50%) had residual hematoma in the follow-up CT, and the difference between the two groups was statistically significant (p=0.02). Association analysis showed that the “irrigated” group had 2.78 times higher chance of hematoma resolution at the follow-up CT (p=0.02, OR=2.78, 95% CI=1.16-6.68).

The GCS was evaluated at admission and before discharge, and the change in these values was analyzed. The mean GCS score improvement in the “irrigated” group was 1.54±0.92, whereas the value was 1.41±0.62 in the “not irrigated” group. However, there was no statistical significance (p=0.45). The data is specified in Table 2, and illustrative cases from each group are presented in (Fig. 1 and 2.)

Chronic subdural hematoma (CSDH) is one of the most common conditions encountered in neurosurgical interventions4,5). The number of CSDH is increasing in developed countries6), and it is common among elderly patients, and its incidence is 58/100,000 for elderly population aged above 70 years, about 12 times higher than the general population13). About 60-80% of the patients with CSDH had history of head injuries. However, variation is possible because most head injuries leading to CSDH are trivial: these events are easily forgotten or not actually considered important by patients13). Treatment of choice for symptomatic CSDH is surgical evacuation, which usually results in marked neurologic and radiographic improvement10). The modes of surgical treatment ranges from burr hole trephination to complex craniotomy with membranectomy. The most common surgical treatments include twist drill craniostomy, burr hole trephination, and craniotomy, result in differing degrees of reoperation rates from 5% to 27.8%9). The rate of recurrence varied in many literature reviews. In the literature, the re-operation rate for CSDH treated with burr hole trephination was 6.6%, which proved significant from the 24.1% among craniotomy patients9). Secer et al. presented that symptomatic recurrence of CSDH has been noted in 8%-37%11). Generally, burr hole trephination reduced recurrence and re-operation6, and it has been the most preferred technique in treating patients with CSDH5). In the recent years, burr hole trephination has replaced the conventional craniotomy in most of the CSDH cases for many reasons such as less invasiveness, lower mortality and morbidity, shorter length of hospital stay, and overall patient satisfaction10).

The recurrence rate of CSDH may differ according to individual characteristics of each patient, pathogenesis of CSDH, and surgical procedure. Patients’ characteristics include factors such as age, alcoholism, and coagulation disorders11).

There have been many attempts to reduce the recurrence rate of CSDH, and various surgical and post-operative management styles and techniques are practiced by many neurosurgeons according to their preference. These include one or two burr hole trephination, using or not using intra-operative saline irrigation, open or closed drainage system, etc4,11). In the present study, the primary goal was geared towards comparison of burr-hole trephination with and without intraoperative irrigation in treating CSDH. Several papers analyzed the outcomes of CSDH treatment depending on whether or not irrigation was done. Kumar et al. reported that burr hole trephination with saline irrigation is a simple, fast, and safe procedure for treating CSDH with a favorable outcome5). In the other literature, Gurelik et al. reported that there was no significant difference between the recurrence rates in the irrigation group and in the no-irrigation group3). Erol et al. stated that there was no difference in recurrent rates between the two groups, but burr hole with irrigation was more effective when recovery rates and postoperative complication are concerned1).

Although there were differences in the results of previous studies, the authors found statistically significant differences in the retreatment rates between both groups of patients undergoing burr hole trephination to treat CSDH.

There are several factors associated with increased recurrence rate. Firstly, the thick remnant hemorrhagic fluid may act as a dead space, and this can cause an impaired adhesion between the inner and outer neo-membranes and promote the recurrence of CSDH8). After this subdural space had been created, cells in the dural border begin to proliferate, representing the first step in the pathogenesis of CSDH. Mori et al. presented that persistence of an enlarged subdural space, or poor re-expansion of the brain, in patients undergoing evacuation of CSDH creates the potential for reaccumulation of the hematoma7). By irrigation, the authors speculated that quicker drainage of the diluted hemorrhagic fluid and elimination of dead space would be possible, in turn would result in quicker brain re-expansion and thus lower the chance of recurrence.

Secondly, the contents of the hematoma itself may act as inducing factors for recurrent hematoma formation2,12). Shono et al. explained that the high concentration of VEGF within the hematoma could induce neovascularization with abnormally dilated sinusoids and incomplete basement membrane which allows excessive permeability and hence increase the rebleeding risk12). The CSDH fluid is also rich in inflammatory mediators such as kallikrein, bradykinin, and platelet-activating factor. After initial trauma, the sequence of events in the natural course of the CSDH consists of local inflammation2). Further inflammation caused by the release of these proinflammatory factors create a self-enhancing vicious cycle that is responsible for frequent rebleeding and enlargement of the CSDH2). High levels of fibrin degradation products (FDP) within the CSDH fluid is also known to promote recurrent hematoma formation by increasing tissue plasminogen activator and affecting the coagulation cascade; activated plasmin depletes coagulation factors to produce more FDPs and the vicious cycle is continued, resulting in increased bleeding risk of the defective neovasculature. By intra-operative hematoma irrigation with saline, much of these angiogenic, proinflammatory and anticoagulatory factors are physically washed away, and their effect in promoting rebleeding are expected to be minimized11).

There are a number of limitations in our study. First, the study was conducted retrospectively and is therefore subject to potential sources of bias and variation. Subsequently, the choice of the procedure was decided by each surgeon’s preference rather than by randomization. Second, some of the widely accepted predisposing factors such as the patient age and underlying conditions such as alcoholism and diabetes mellitus, and other coagulopathies have not been taken into consideration in the present study. Thus, further well-designed randomized prospective studies with larger study samples may be needed to further support our arguments and reach other important findings concerning the recurrence of CSDH.

Based on the results of this study, the authors believe that burr hole trephination for CSDH present different clinical and radiographic results depending on the use of saline irrigation. Intra-operative saline irrigation reduced recurrence and retreatment rate, as well as the resolution rate in the CT scan. However, there was no significance concerning the GCS change between the two groups. Consequently, it can be implied that burr hole trephination with irrigation may be a simple and effective method in reducing recurrence and retreatment in CSDH.