Acute subdural hematomas (ASDH) are observed in one third of patients with severe traumatic brain injury.22) ASDH forms between the dura and arachnoid membranes usually due to tearing of bridging veins or arterial rupture. Management of ASDH may vary from simple observation to different surgical evacuation technique. Two most frequent surgical modalities are craniotomy (CO) and decompressive craniectomy (DC). CO procedure removes skull bone and subdural hematoma followed by replacement of original skull bone. DC also removes skull bone and hematoma, but remains the bone unclosed for possible expansion of edematous brain tissue with or without an additional expansile duroplasty.2)

Many studies have been reported showing effectiveness of DC for ASDH.156101718) However, not all patients show severe postoperative brain swelling after evacuation of hematoma where theoretical benefit of DC is questionable. DC also carries disadvantage owing to lack of bone closure.291016) The optimal surgical modality for ASDH still remains to be clarified.

The objective of this study is to analyze the surgical outcomes of CO and DC for evacuation of ASDH by comparing the preoperative clinical features, computed tomography (CT) images and postoperative complications which may possibly aid in selection of optimal surgical modality.

We retrospectively reviewed 46 cases of ASDH surgically treated with CO or DC in our hospital from January 2010 to December 2014. Demographic and preoperative medical data were reviewed including age, sex, and presence of medical illness causing coagulopathy or use of antiplatelet agents. Preoperative data that may affect the surgical outcome were also collected such as time from trauma to surgery or time from clinical deterioration to surgery, preoperative Glasgow Coma Scale (GCS), pupillary light reflex, and presence of major extracranial injury. Preoperative CT scans were analyzed for measurement of midline shift, presence of intracerebral hemorrhage (ICH) or petechial hemorrhage, obliteration of basal cistern and third ventricle, and presence of subarachnoid hemorrhage at basal cistern.

All of the patients underwent surgery for evacuation of ASDH through frontotemporoparietal CO of size 10×12 cm or larger. Decision for CO or DC was done by attending neurosurgeon (Figure 1). Cases in which evacuation ASDH were not the main goal of surgery were excluded. Thus, evacuation of large traumatic ICH, decompression for cerebral swelling, and surgery other than frontotemporoparietal CO were excluded in this study.

Postoperative midline shift was measured from immediate postoperative CT scan. Measurement of swelling above the bone flap was done for patients who underwent DC with CT scan taken within postoperative day 3 to 7 when maximal brain swelling was observed. Imaginary line on absent bone flap was drawn and brain tissue above the imaginary line was measured (Figure 2). Medical records and CT scans were reviewed for patient who underwent cranioplasty. Postoperative outcome was recorded using modified Rankin Scale (mRS) 6 months after initial surgery. Outcome was defined good for patients with mRS score 1-3, and poor for patients with scores 4-6.

Preoperative clinical features were classified for further analysis where unfavorable feature was defined as age over 70 years, anticoagulation or antiplatelet use, time to surgery >4 hours, preoperative GCS <8, one or both non-reactive pupil, and comorbid major extra-cranial injury. Preoperative CT findings with ICH or petechial hemorrhage, obliterated basal cistern or 3rd ventricle, and presence of subarachnoid hemorrhage were also classified as unfavorable preoperative feature.

Data was analyzed using Statistical Package for Social Sciences (SPSS) software for personal computers (SPSS ver. 21; IBM Corp., Armonk, NY, USA). Unpaired Student's t-test or Mann-Whitney test was used for continuous variables, and chi-squared test or Fisher's exact test was used for categorical variables. Probability value of less than 0.05 was considered as statistically significant.

ASDH are present in approximately one third of patients with severe traumatic brain injury.22) Despite advances in emergency medical services and surgical techniques, ASDH remains one of the most lethal of all intracranial injuries. Various surgical modality such as simple burr hole trephination, CO, and DC are used for evacuation of ASDH. On the Brain Trauma Foundation guidelines published in 2006, they recommended that ASDH with thickness greater than 10 mm, or midline shifting greater than 5 mm on CT scan should be treated surgically.1) Mortality rates of ASDH ranges from 55% to 79% even with surgical intervention of any modality.19)

Ransohoff et al.18) reported recovery rate of 40% for ASDH treated with hemicraniectomy followed by hematoma removal. After the report, DC for ASDH has been recommended as a surgical modality of choice, and performing DC in ASDH patients seemed to be attractive.1478131420) Girotto et al.7) reported DC technique of adequate size, early surgery, and GCS of 6 to 8 group would contribute significantly to better outcome by reducing morbidity and mortality. Meier and Gräwe17) reported that DC benefits on overall outcome of patients with traumatic brain injury. The rationale behind performing DC lies in control of postoperative brain swelling and overwhelming intracranial hypertension, but little is known on the degree of postoperative swelling after evacuation of hematoma. Empirical decision for DC or CO is made by the neurosurgeon based on patients' clinical status and CT findings which may be confounding unless brain swelling is noted intraoperatively after evacuation of hematoma.

The analysis of postoperative brain swelling is difficult since the postoperative CT findings or intracranial pressure measurements will vary depending on closure or opening bone flap. Different trauma setting among patients makes randomized trial for CO and DC impossible and unethical. Nevertheless, there were several retrospective series that compared the outcome of CO and DC.35121521) Woertgen et al.21) compared the surgical outcomes in ASDH which were not significantly different between CO and DC. They concluded that signs of herniation at presentation, and increasing age had most influence to patient outcome. So, preoperative clinical feature influenced most on outcome and DC does not seem to have a therapeutic advantage over CO in ASDH. More recent study by Chen et al.3) also reported similar results in 102 patients where DC group had higher mortality rate which may be due to poorer preoperative clinical status. The study by Li et al.15) is notable where they tried to diminish the effect of preoperative clinical status by using CRASH-CT prognostic model. Predicted outcome was calculated in 85 patients in a retrospective fashion. Favorable outcomes were observed in 45% of CO versus 42% of DC (p=0.83), but standardized morbidity ratio (observed/expected unfavorable outcome) was 0.90 for CO group and 0.75 for DC group.

Our study showed poorer outcome in DC group compared with CO group (poor mRS 77%, 20 of 26 patients in DC group vs. 40%, 8 of 20 patients in CO group; p=0.004). This results are may be due to more patients with low GCS score (GCS<8), unresponsive pupil, and comorbid CT lesion in DC group. Our results carry similar selection bias that neurosurgeons tend to perform DC when patients' preoperative clinical status is poor. To clarify this point, we counted on number of unfavorable features for each patient that may influence on poor outcome. On average, DC group had more adverse features than CO group, and thus poor outcome for DC group can be explained.

One notable finding is that in patients with few unfavorable features (<6), good outcome (mRS less than 3) was achieved in majority of patients in CO group. However, similar results were not obtained in DC group with few unfavorable features. This implies that further stratification of unfavorable clinical features is needed which has larger impact on outcome. Nonetheless, it seems that some patients with few preoperative unfavorable features can benefit with CO without the need for bone removal.

Furthermore, various possible complications of DC need awareness of neurosurgeons. Subgaleal hemorrhage, herniation through the cranial defect, subdural effusion, syndrome of the trephined (sinking skin flap syndrome), and hydrocephalus were reported complications of DC.1123) In our series, 1 patient underwent reoperation due to subgaleal hematoma and 2 patients had severe sinking of skin flap where difficulty was in cranioplasty resulted in complication. DC also have disadvantage of requiring subsequent cranioplasty which harbor additional risk of complication.21116) Gooch et al.9) reported that immediate post-operative complication rate of cranioplasty after DC was as high as 34% which were infection, wound breakdown, intracranial hemorrhage, and bone resorption. We also experienced complications of cranioplasty in our patients (4 of 12; epidural hematoma 2, infection 1, cerebrospinal fluid leakage 1) which interrupted patients' recovery. In this context, there may be some advantage of CO in evacuation of ASDH.

However, this study is a retrospective single center study with small patient population. Limitations of selection bias hinder any conclusion on role of CO or DC for ASDH. We think further investigation with larger patient population and carefully selected criteria is needed to clarify the optimal surgical modality for patient with ASDH.

In selective cases of few unfavorable clinical findings, CO may also be an effective surgical option for ASDH. Although DC remains to be standard of surgical modality for patients with poor clinical status, CO can be an alternative considering the possible complications of DC. Controlled prospective study with larger patient population is needed clarify this point.