Our study first presented the clinical characteristics of our patients with CSDH. Second, it introduced a direct single burr-hole aspiration-irrigation maneuver and closed drainage strategy for the treatment of CSDHs. Third, it reported that this method achieved a remarkably low recurrence rate and good outcome.
How does SBAID reduce the recurrence rate?
The reason we achieved a much lower recurrence rate may be that less air was left in the subdural space and that complete replacement of the liquid with normal saline was achieved to the greatest extent possible.
The traditional methods for treating symptomatic CSDHs have been operative evacuation through one or two burr-hole irrigations with closed subdural drainage. Although a number of modifications of these procedures have been described, none can reduce the high recurrence rate. Reoperation has been shown to affect postoperative functional outcomes4 and quality of life19. CSDH recurrence is usually defined as the reaccumulation of hematoma fluid requiring another operation19; defined in this way, the recurrence rates reported in the literature vary widely, from 0 to 76%18,19; however, the current consensus is that the reoperation rate ranges from 10–20%21. Factors that increase the risk of recurrence include drainage catheter occlusion, too much intracranial air22, bilateral CSDHs23,24, preoperative use of anticoagulant25–27 and antiplatelet25 medications, intraoperative visualization of poor brain reexpansion and thick membranes28, postoperative persistence of midline shift27, and the volume of the postoperative hematoma cavity29,30, although the data for these factors come from small studies with low events-per-variable ratios and thus must be interpreted cautiously21. In our study, the reoperation rate in the SBID group was 14%, whereas the reoperation rate after the SBAID method was only 2% (P = 0.03).
The volume of the postoperative hematoma cavity is a well-known risk factor for recurrence in patients with CSDH29,30, and our results support this. Compared to the patients in the SBID group, the patients in the SBAID group had a smaller subdural space volume 48 hours after the operation (P = 0.03). The average percentage changes after one month in the SBAID and SBID groups were 74.6% and 71.8%, respectively (p = 0.11).
Both the decreased brain plasticity caused by long-term compression from hematomas and preexisting brain atrophy can affect brain reexpansion. Thus, the postoperative hematoma cavity cannot be eliminated quickly. After surgery, patients need to remain in a supine position in bed for three to seven days. With patients lying in the supine position, the effect of gravity usually causes the parietal lobe to reexpand very quickly, and the frontal space is the last part that expands. When the tip of the catheter is located in the anterior part of the cavity, the catheter does not touch the hematoma capsule during the drainage period, even when the catheter is pulled out of the cavity.
In the SBAID group, subdural collections were replaced with normal saline as much as possible via aspiration and irrigation. To effectively replace all the contents of CSDHs with normal saline, we suggest performing the aspiration-irrigation maneuver, especially aspiration, during the operation. In every patient in our series, we always found some debris in the fluid of the CSDH, most of which could only be aspirated out. Compared to the patients in the SBID group, the patients in the SBAID group had a shorter mean duration of surgery (P = 0.02) and a shorter mean interval from procedure to discharge in days (P = 0.046). In our opinion, the aspiration process reduces the length of the operation.
The results showed that the volume of the hematoma cavity was reduced by a mean rate of 70.4%, and the recurrence rate was only 2%, which suggests that the volume of the hematoma cavity after the operation reached an optimum state through our strategy. Additionally, with our strategy, the recurrence rate in our cohort was significantly lower than that reported in the literature4,31−33. The reason one patient in our series experienced recurrence appears to be occlusion of the drainage catheter (Figs. 3–4). The patient was cured by using a second single burr-hole aspiration and irrigation technique with continuous closed subdural drainage.
Following our strategy, aspiration is safe and effective for the replacement of CSDH contents and sharply reduces the recurrence of CSDHs.
During surgery, care should be taken to aspirate the fluid of the CSDH slowly and inject normal saline into the cavity through the burr hole at the same time, ensuring that the output/input speed is equal.
In cases in which many membranes separate the hematoma into chambers in a honeycomb fashion, an open procedure cannot be avoided. However, in our series, we did not encounter any cases of multiple membranes.
The avoidance of direct contact between the catheter and the hematoma capsule may moderate the risk of postoperative seizures and limit the secondary spread of infection to intracranial compartments34. Four patients in our series (1 in the SBAID group and 3 in the SBID group) suffered from partial motor seizures, possibly due to injury to the inner capsule of the hematoma and the brain cortex. After three months of antiepileptic drug therapy, these patients stopped taking Tegretol and did not ever have another seizure. The placement of a closed drainage system may increase the infection rate of the hematoma cavity and wound, but only one patient in the two groups experienced fever symptoms and wound infection. The infection was cured after treatment with antibiotics and 7 days of wound dressing changes. Furthermore, wound infection did not affect the outcome of CSDH.
One patient in our series suffered from acute subdural hematoma on the second day after the operation (36 hours later). The patient presented with coma three hours after the catheter was removed. Head CT showed a large acute subdural hematoma on the same side as the CSDH. The patient' s family refused to allow reoperation, and the patient died four hours later (Fig. 4). The reason for this complication was not clear. The removal of the catheter may have damaged an artery of the skin, and blood may have entered the subdural space through the burr hole.
Why did we choose Wei's point༟
In addition to acute subdural hematoma, one immediate postoperative complication was tension pneumocephalus. Pneumocephalus is an independent factor for recurrence35–39. Some studies recommend that the patient's head should be fixed to ensure that the burr hole is always situated at the highest point so that the cavity can be filled with saline instead of air before closure37. To ensure that the burr hole was situated at the highest point, we chose Wei's point as the site of the burr hole. Just as the parietal eminence is usually the thickest part of the CSDH after the hairline, Wei' point is the thickest part of the anterior hematoma that is closest to the hairline. The burr holes of patients in the SBID group were made over the parietal eminence.
The patients were placed in a supine position with the head tilted slightly to the opposite side during the operation. In this way, Wei's point was the highest point of the operative field, and the air was easily evacuated. Therefore, the air volume left in the cavity in the SBAID group was much lower than that in the SBID group (p = 0.03).
Why should we choose the aspiration method༟
Certain substances (such as inflammatory mediators, plasminogen activators and fibrin degradation products) in the subdural collection of CSDHs are thought to promote the development and recurrence of CSDH29,37. These substances may be contained in the debris of the subdural collection. The most important goal of surgery should be the complete replacement of the CSDH liquid with normal saline. In the SBAID group, by using aspiration and irrigation, especially aspiration, subdural collections were almost completely replaced by normal saline, and little debris was left in the subdural space.
The data in this paper support the superiority of SBAID compared with SBID with respect to the radiographic resolution of CSDHs. In addition, we show that the SBAID method produces better results in regard to the duration of surgery, the length of hospital stay and the rate of recurrence at an average follow-up duration of 31 weeks.
Our study does have some limitations that need to be addressed. First, the sample size of this study was small. Second, the study provided only a technical description, and therefore, randomized controlled trials are required to clarify its efficacy. Third, our research was a retrospective study. Therefore, we should perform a large-scale, prospective, randomized, controlled trial to verify our strategy.