Skull drilling evacuation of hematoma with a skull drilling diameter of >5 mm is defined as minimally invasive craniotomy or TDC, that with a drilling diameter of >5 and >30 mm is defined as BHC and that with larger surgical wounds is defined as general craniotomy. In the flow chart in Fig. 1, the clinical course of patients with CSDH is illustrated according to previous studies (22).

The recurrence of CSDH is defined as the repeated accumulation of hematoma in the ipsilateral subdural hematoma cavity confirmed by imaging after the initial treatment. Repeated treatment by decompression drainage in the case of CSDH recurrence with symptoms or aggravated symptoms is known as reoperation. The first operation frequently fails due to certain technical issues or operative complications, including acute subdural hemorrhage, ineffective shunt or poor drainage. At this point, an emergency remedial surgery is required to reconstruct the drainage for intracranial decompression, which is often performed within a short time after the first operation. In the present study, remedial surgery within 48 h was used as a short-term efficacy index for assessing the success rate of surgery. As a control, the cure rate was used as a long-term index of assessing the surgical efficacy. Patients regarded as cured from CSDH were those with improvement of neurologic impairment after the first operation, including the complete clearance of hematoma without recurrence, residual hematoma in the subdural space identified during follow-up imaging, asymptomatic or no symptom aggravation. Therefore, patients who underwent a second surgery, namely a remedial operation and reoperation, and who died during follow-up, were not deemed as being cured (22).

Patients diagnosed with CSDH via head CT or magnetic resonance imaging (MRI) at Huai'an First People's Hospital (Huai'an China) between January 2016 and January 2017 were enrolled in the present study. Inclusion criteria were a clear correlation of CSDH with neurologic impairment symptoms and signs confirmed via neurological examination; the requirement of hematoma drainage and decompression; and an age >18 years for either sex. Patients with CSDH caused by systemic diseases were excluded, and surgical contraindications were excluded through appropriate biochemical examinations, electrocardiogram and chest CT. Patients who met the inclusion criteria were enrolled and randomly grouped after they and their families were informed about the details of the present study, the surgical risks and the relevant safety measures, and provided written informed consent. The present study was approved by the Ethics Committee of Huai'an First People's Hospital.

A total of 40 random numbers were generated using Statistical Product and Service Solutions (SPSS) v21.0 software (IBM Corp., Armonk, NY, USA). After the patients provided their signature to confirm the experimental scheme, one number was randomly selected from the 40 numbers and the patients were accordingly enrolled into the pre-set groups (23). Three clinicians were independently responsible for the grouping, surgery and follow-up, respectively.

According to the CT scan positioning, the center on the thickest layer was selected as a puncture point and the arteries were avoided. The electric hand drill with a 2-cm minimally invasive intracranial hematoma puncture needle was used to penetrate the skull and dura mater along the locating point to the hematoma center into the subdural hematoma cavity. The drill was then removed, the drainage hose was connected and the drill head was pulled out. The appearance of a dark red bloody fluid overflow was considered to indicate a successful puncture, and the rapid improvement in symptoms were used for verification. The highest point of drainage tube was maintained 10–15 cm higher than the head puncture point, and the symptoms were improved; the drainage tube was temporarily clipped and then opened after 2 h, and the total drainage time was 48 h. The minimally invasive puncture drainage was successful in 19 patients, and the drainage tube was removed after 48 h without the traditional irrigation according to previous studies (24–29). Through the routine post-operative review of the head CT, severe complications were excluded and the drainage tube was removed after 48 h.

A scalp incision with a length of ~4 cm was made with a skull drill of 12 mm in diameter and the drill was slightly expanded by using the rongeur. The dura mater was cut in a cross shape and washed with warm saline, and one drainage tube was placed into it.

To prevent recurrence, all patients were routinely administered statins every night. After the operation, the tube was clipped for 2 h after it was opened for drainage for 48 h and hematoma was significantly reduced on CT; the symptoms were improved and the silicone drainage tube was eventually pulled out. After the operation, in a comfortable supine position, the elderly patients were required to lie in bed and rest, but they were not strictly confined to the bed (11). The incision was disinfected and the dressing was replaced once per day. All 40 patients were followed up by independent clinicians. A new head imaging was reviewed and neurological scoring according to the mRS was performed at 3 months after the operation.

All data from the data set were input into SPSS v21.0 for windows software (IBM Corp.). Measurement data were presented as the mean ± standard deviation. The independent-samples t-test was used for intergroup comparison and the χ² test was used for enumeration data. The difference values of mRS scores prior to and after the operation and the ratio vs. the pre-operative value were compared between the two groups using the Mann-Whitney U test. P<0.05 was considered to indicate a statistically significant difference.

A total of 176 cases of CSDH were treated using different surgical methods at Huai'an First People's Hospital from January 2016 to January 2017. This population comprised 132 males and 44 females aged 19–89 years with an average age of 63.2±10.11 years. Definite diagnoses were made by brain CT or head MRI examination. On CT, the low-density, equal-density, slightly high-density or mixed-density crescent abnormal fluid areas in the subdural space frequently had a space-occupying effect. The brain parenchyma was pressed, the brain fissure disappeared, and the lateral ventricle and midline structure deviated to the opposite side to varying degrees. The symptoms/complaints of the patients included intracranial hypertension, psychiatric symptoms, hemiplegia and disturbance of consciousness. Among the 40 patients enrolled, 33 were males and 7 were females, and the age ranged from 19–86 years, with 34 cases (85%) aged >60 years and 26 cases (65%) with a history of trauma (BHC group, 14 and TDC group, 12). The duration from injury to admission ranged from 3 weeks to 4 months. A total of 14 cases (35%) denying a history of trauma were aged >60 years, and there was a significant age difference between the patients without and with history of trauma (72.36±6.37 vs. 62.73±15.36 years; F=3.81; t=2.23; P=0.03). It was indicated that a history of trauma may be associated with the formation of CSDH in patients <60 years, but not necessarily in patients >60 years. A total of 38 (95%) out of 40 patients had unilateral hematoma, while 2 cases (5%) had bilateral hematoma; no skull fracture and brain parenchymal injury were identified during the imaging examination, and the bleeding volume was 30–210 ml.

A total of 17 cases (42.5%) had chronic progressive medical characteristics of intracranial hypertension, including headache, nausea and optic disc edema. A total of 29 cases (72.5%) presented with focal neurologic impairment due to the hematoma compression, including hemiparesis, epilepsy, alalia and eating difficulty, including 6 cases (15%), in which the impairment was severe with manifestations including disturbance of consciousness, psychiatric symptoms, behavioral abnormalities and mental retardation, and 5 cases (12.5%) with urinary incontinence prior to admission, but whose consciousness as well as respiratory pulse and other vital signs were stable. The medical history of the cases was as follows: 20 cases (50%) were complicated with varying degrees of hypertension and diabetes mellitus, and 2 cases (5%) had a history of underlying cerebrovascular disease with unilateral hemiplegia. Furthermore, 2 cases (5%) had a history of tumor, 1 case (2.5%) had a history of renal insufficiency and 1 case (2.5%) used to take antiplatelet drugs, e.g., aspirin, prior to admission. In all patients enrolled in the present study, statin drugs were used to prevent hematoma recurrence. No significant differences in the general clinical characteristics were identified between the two groups (Table I).

One case in the TDC group received the remedial operation due to no obvious improvement of symptoms and poor hematoma drainage on head CT review at 48 h after the operation (TDC vs. BHC; P=0.31; Table I). However, it cannot be reasoned that the failure rate of TDC was significantly higher than that of BHC. In the BHC group, 3 patients had a pre-operative mRS score of 5 points, among which the hematoma of 2 cases was significantly improved on head CT review at 48 h after the operation, but the mRS score was still 5 points. Furthermore, 2 patients died at 32 days after discharge (36 days post-operation) and 45 days after discharge (49 days post-operation). In the TDC group, 4 cases had a pre-operative mRS score of 5 points, among which 1 case was discharged 5 days after admission, but his mRS score was 4 points, and he died of epilepsy and pulmonary infection after 1 month. The hemiplegia symptoms of one 80-year-old case were not alleviated, the patient could not take care of themselves, and the head CT at the 3-month follow-up indicated no increase in the hematoma. No difference in the mortality rate was identified between the two groups (P=0.55). In addition, the head CT at the 3-month follow-up indicated that the intracranial hematoma of a total of 4 patients in the two groups was completely removed, including 3 cases in the TDC group and 1 male case aged 19 years in the BHC group (TDC vs. BHC; P=0.29; Table I). In the remaining patients, residual hematoma was present after 3 months (Fig. 2). The BHC group contained 3 cases of intracranial hypertension, 2 of which were diagnosed with a recurrence of CSDH, and received the secondary operation at 30 and 47 days after the first operation. One other case was diagnosed with a secondary intracranial infection and received the incision and drainage again due to fever, scalp incision swelling and other central nervous system infection symptoms, as well as a mixed-density shadow in the subdural space on head CT. In the TDC group, those patients with improved symptoms within 48 h of surgery had stable symptoms until the 3-month follow-up, and none of the patients was required to undergo a secondary operation (TDC vs. BHC; P=0.07). It was also identified that patients with a high pre-operative score retained these increased scores at 48 h after the operation (P<0.001), indicating that the symptoms may be obviously improved by the two types of surgery within 48 h. The average LOS after TDC was 9.00±2.91 days, which was significantly shorter than that after BHC (14.75±5.95 days; P<0.01). To further compare the curative effects of the two types of operation, the differences in mRS scores prior to the operation vs. 48 h post-operation (V_{pre-48 h}), prior to the operation vs. 3 months post-operation (V_{pre-3 m}) and 48 h vs. 3 months after the operation (V_{48 h-3 m}) were determined, and the ratio of these three variables vs. the pre-operative mRS score was also calculated [V_{(pre-48 h)/pre}, V_{(pre-3 m)/pre} and V_{(48 h-3 m)/pre}, respectively]. The Mann-Whitney U test was performed and the results indicated that the variation values V_{pre-3 m} and V_{48 h-3 m}of the mRS sore at 3 months after the operation and the ratios V_{(pre-3 m)/pre} and V_{(48 h-3 m)/pre} in the TDC group were obviously different compared with those in the BHC group (P<0.05; Table II), suggesting that the improvement of neurological function in the TDC group after the operation was more obvious than that in the BHC group. According to the traditional definition, the remedial operation (1 case in the TDC group) and secondary operation (3 cases in the BHC group) were considered to indicate a recurrence of CSDH in the present study, and the recurrence rate was not significantly different between the two groups (P=0.29; Table I). Although 18 patients (90%) in the TDC group were cured (the operation was successful and the survival time was >3 months without recurrence), there was no significant difference in the cure rate compared with that in the BHC group (P=0.21).