J Neurosurg 126:1905–1911, 2017CLINICAL ARTICLE

ChroniC subdural hematoma (CSDH) is a frequent condition with incidence rates varying from 5.3 to 13.5 cases per 100,000 persons/year in the general

population, with a higher incidence among older adults.5,9 With aging populations and the increasing use of anticoag-ulants, higher incidence rates are to be expected. Despite the fact that CSDH is a frequent condition with high rates of retreatment, there is no standardized treatment strategy.

A CSDH is a slowly growing collection of fluid con-taining blood and its breakdown products. It can be speci-fied as unilateral (uCSDH) or bilateral (bCSDH). While uCSDHs are seen more frequently, bCSDHs are by no means rare, comprising 16%–24% of observed CSDHs.2,3,8 The majority of clinicians consider bCSDH to be equiva-

lent to uCSDH and employ the same treatment strategies for the two. However, studies have demonstrated that cases of bCSDH are associated with higher rates of retreat-ment.12,14,15 The clinical presentations of bCSDH have been described as more diverse than unilateral cases, delaying both diagnosis and treatment.6 In some cases of bCSDH, asymmetrical hematoma volumes or lateralized clinical symptoms are followed by surgical treatment of only the largest or the symptomatic hematoma, leaving the other hematoma untreated. All in all, this suggests that bCSDH should be distinguished from unilateral cases to establish an appropriate surgical treatment strategy.

To date, research on bCSDH has been limited compared with that on uCSDH and has been based on small patient

ABBREVIATIONS bCSDH = bilateral CSDH; CSDH = chronic subdural hematoma; ICD-10 = International Classification of Diseases, 10th Revision; RR = retreatment rate; uCSDH = unilateral CSDH.SUBMITTED November 15, 2015. ACCEPTED April 29, 2016.INCLUDE WHEN CITING Published online July 8, 2016; DOI: 10.3171/2016.4.JNS152642.

Bilateral chronic subdural hematoma: unilateral or bilateral drainage?Nina Christine Andersen-Ranberg, MD,1 Frantz Rom Poulsen, MD, PhD,2 Bo Bergholt, MD,3 Torben Hundsholt, MD,4 and Kåre Fugleholm, MD, PhD1

1Department of Neurosurgery, Rigshospitalet University Hospital, Copenhagen; 2Department of Neurosurgery, Odense University Hospital, Odense; 3Department of Neurosurgery, Aarhus University Hospital, Aarhus; and 4Department of Neurosurgery, Aalborg University Hospital, Aalborg, Denmark

OBJECTIVE Bilateral chronic subdural hematoma (bCSDH) is a common neurosurgical condition frequently associated with the need for retreatment. The reason for the high rate of retreatment has not been thoroughly investigated. Thus, the authors focused on determining which independent predictors are associated with the retreatment of bCSDH with a focus on surgical laterality.METHODS In a national database of CSDHs (Danish Chronic Subdural Hematoma Study) the authors retrospectively identified all bCSDHs treated in the 4 Danish neurosurgical departments over the 3-year period from 2010 to 2012. Univariate and multivariate analyses were performed to determine the relationship between retreatment of bCSDH and clinical, radiological, and surgical variables.RESULTS Two hundred ninety-one patients with bCSDH were identified, and 264 of them underwent unilateral (136 pa-tients) or bilateral (128 patients) surgery. The overall retreatment rate was 21.6% (57 of 264 patients). Cases treated with unilateral surgery had twice the risk of retreatment compared with cases undergoing bilateral surgery (28.7% vs 14.1%, respectively, p = 0.002). In accordance with previous studies, the data also showed that a separated hematoma density and the absence of postoperative drainage were independent predictors of retreatment.CONCLUSIONS In bCSDHs bilateral surgical intervention significantly lowers the risk of retreatment compared with unilateral intervention and should be considered when choosing a surgical procedure.https://thejns.org/doi/abs/10.3171/2016.4.JNS152642KEY WORDS bilateral chronic subdural hematoma; surgical management; elderly; recurrence; vascular disorders

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cohorts containing 14–41 patients.6,14 Existing studies13,16 have identified advanced age (> 75 years), coagulopathy, and use of anticoagulant and/or antiplatelet treatment as risk factors for bCSDH.

In this retrospective analysis of 291 cases of bCSDH in Denmark, we aimed to identify risk factors for retreat-ment, with a special focus on surgical laterality.

MethodsThis work is part of the Danish Chronic Subdural He-

matoma Study (DACSUHS), a retrospective multicenter study in which all Danish neurosurgical departments par-ticipate: Rigshospitalet University Hospital, Odense Uni-versity Hospital, Aarhus University Hospital, and Aalborg University Hospital. Patients were identified in the Danish National Patient Register, which contains information on all hospital admittances, with diagnoses and operations recorded according to the International Classification of Diseases, 10th Revision (ICD-10; http://www.who.int/classifications/icd/en/). The first author (N.C.A.R.) trav-eled over 10 months (November 1, 2013, to October 31, 2014) to all the neurosurgical departments where she re-viewed every single set of medical records and CT scans. Patients with an ICD-10 diagnosis code S065C (CSDH) and a preoperative CT scan showing bCSDH were includ-ed in this study.

Clinical and demographic information included age, sex, use of anticoagulant and/or antiplatelet medication, and history of head trauma. A history of head trauma was defined as recognized head trauma within the last 12 months before diagnosis. All patients had their anticoagu-lation status optimized before surgery, ensuring a preop-erative international normalized ratio (INR) between 1 and 2. It was managed in various ways depending on the type of anticoagulant treatment and local guidelines. In some departments surgeons could guide the anticoagu-lant reversal based on thromboelastography (TEG) and multiplate analysis (platelet function test). Agents used to reverse anticoagulant medications were phytonadione (vi-tamin K1), thrombocytes, blood plasma, tranexamic acid, prothrombin complex concentrate (Octaplex), and desmo-pressin analogs.

To qualify the hematoma as chronic, at least 14 days had to have elapsed between head trauma and time of sur-gery to be included in the study. Patients with ventriculo-peritoneal shunts were excluded because of a possible dif-ference in pathogenesis and pathophysiology (15 patients).

Radiological data were obtained from all preoperative CT scans. The size of each hematoma was calculated using the XYZ/2 method.17 Total (bilateral) hematoma volume was obtained by adding the volumes assigned to each he-matoma. Brain atrophy was estimated as a ratio of the total brain parenchyma to the intracranial diameter between the coronal suture on each side. This ratio was measured on comparable image slices in the axial plane (showing the 2 frontal horns of the lateral ventricles and the septum pel-lucidum). Hematoma density was classified into 4 groups: homogeneous, mixed, membranous, and separated (as de-scribed in Nakaguchi et al.11).

Surgical information included unilateral or bilateral

intervention, surgical procedure, drainage, and surgical complications. No medical adjuncts were used to man-age bCSDH. Retreatment (recurrence) was defined as a reaccumulation of the CSDH requiring ipsilateral, contra-lateral, or bilateral reoperation after discharge from the primary treatment.

Statistical AnalysisEach variable was subjected to univariate analysis to

determine its relationship with retreatment. For categori-cal variables, a chi-square test was employed; for contin-uous data, a Student t-test or ANOVA test was applied. Those variables showing a relationship stronger than p < 0.25 were subsequently used in a multivariate analysis. A multiple logistic regression model was used to identify in-dependent risk factors among these selected variables. All analysis was performed in the statistical software package R (http://www.r-project.org), and a p value < 0.05 was con-sidered significant.

EthicsThe study was approved by the Danish Data Protection

Agency.

ResultsA total of 291 patients met the requirements for inclu-

sion in the study. Clinical and radiological data are sum-marized in Table 1. Of the 291 patients, 207 (71.1%) were male and 84 (28.9%) were female. Ages ranged from 40 to 98 years, with a mean age of 73.0 years for males and 76.7 years for females. Age distribution had a negative skew of -0.56. Approximately half of the study population (47.8%) received anticoagulant or antiplatelet therapy upon ad-mission. One patient using a novel oral anticoagulant was not treated differently regarding optimization of coagula-tion status. A history of head trauma was obtained in 155 patients (53.3%). Radiological data of bCSDH showed a mean total hematoma volume of 180.9 cm3 with an SD ± 69.5 cm3, indicating high variation in total hematoma volume.

Surgical data are summarized in Table 1. A total of 264 patients (90.7%) underwent surgical treatment. Sur-gical drainage was performed bilaterally in 128 patients (48.5%), whereas 136 patients (51.5%) underwent unilat-eral drainage. The majority of patients underwent a 1–bur hole craniostomy (92.0%) as opposed to a 2–bur hole cra-niostomy (2.6%) and craniotomy (5.3%). A closed drainage system with either subgaleal or subdural placement was used in 250 (94.7%) of 264 patients. Postsurgical drainage time varied from 24 to 48 hours.

Figure 1 illustrates preoperative hematoma volumes of the right and left side and their relation to surgical inter-vention. Unilateral surgery was performed in patients hav-ing asymmetrical hematoma volumes on each side. The hematoma that underwent surgical drainage was signifi-cantly larger than the nonoperated hematoma (p < 0.0001). In those cases that underwent bilateral drainage, there was no significant difference between the hematoma volumes (p = 0.50).

The overall retreatment rate (RR) was 21.6% (57 of 264

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Surgical management of bilateral chronic subdural hematoma

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surgical patients). The RR for patients receiving bilater-al surgery was 14.1% (18 cases), which was significantly lower than the RR in patients receiving unilateral surgery (28.7%; p < 0.004). Retreatment in the unilateral surgery group occurred in 39 cases, on the ipsilateral side (pri-mary operation site) in 16 cases and on the contralateral side (opposite the primary operation site) in 23 cases (Fig. 2 and Table 2). The mean and median times from primary treatment until retreatment were 72.8 and 34 days, respec-tively.

Table 2 shows results from the univariate analysis of the association between retreatment and individual risk factors. We could not demonstrate any significant asso-ciation between retreatment and sex, age, antiplatelet and/or anticoagulation therapy, history of head trauma, hema-toma size, brain atrophy, surgical procedure type, or surgi-

cal complications. Multivariate logistic regression analysis (Table 3) demonstrated that a separated hematoma density (OR 2.56, p = 0.035), no postoperative drainage (OR 4.31, p = 0.020), and unilateral surgery (OR 3.05, p = 0.002) were independent risk factors in the prediction of retreat-ment, which is in accordance with results on univariate analysis.

In the unilateral surgery group further analysis was performed to investigate the size of the operated hema-toma in relation to ipsilateral versus contralateral retreat-ment. There was no significant difference in hematoma size among the 3 groups: no retreatment, ipsilateral re-treatment, and contralateral retreatment. The same anal-ysis was performed on the nonoperated hematoma and, similarly, no significant difference was found (data not shown). Neither was the size of the operated or nonoper-ated hematoma correlated with the site of retreatment.

The complication rates for unilateral and bilateral sur-geries were 8.8% and 13.3%. There was no significant difference in complication rates between the 2 treatment groups (p = 0.25). Infection and acute SDH were the most frequent complications. There were 5 cases of infection in the unilateral group, 2 of which required reoperation, and 3 infections with 1 reoperation in the bilateral group. Reoperations due to complications were performed during primary admission and were not categorized as retreat-ment. Postoperative seizures were observed in 2 cases in the unilateral group and 4 cases in the bilateral group. Sei-zures were limited to the postoperative phase; no patients were treated with anticonvulsive medicine after discharge.

DiscussionIn this study, the overall retreatment rate of bCSDH was

21.6%, as opposed to 11.5% reported in a recent meta-anal-ysis of 250 studies about primarily uCSDH.1 Our findings are in accordance with previous data identifying bCSDH as a risk factor for retreatment.12,14,15,19 We identified uni-lateral surgery for bCSDH as an independent risk factor for retreatment. Unilateral intervention is often based on hematoma size, which also seemed to be the case in our study (Fig. 1). Lateralization of symptoms may also affect this decision. Surgeons tend to operate on the larger hema-toma or on the more symptomatic side.

Intuitively, one would expect the RR to be twice as high with bilateral drainage since each surgical procedure has an independent risk of retreatment, which then would be additive. This assumption rests on the idea that each he-matoma is an isolated disease process, which is probably not the case. Given our data, it seems that hematomas are indeed influenced by the fate of the contralateral hemato-ma (Fig. 3). While ipsilateral retreatment in the unilateral surgery group (11.8%) is close to the known overall risk of retreatment for CSDH, contralateral retreatment com-poses a substantial part of the retreatments in the unilat-eral surgery group. Although the operated hematoma in the unilateral surgery group was managed successfully, the patient’s condition was not since unilateral drainage led to another surgery.

Contralateral reoperation is rarely discussed in the lit-erature. Mori et al.10 retrospectively analyzed 500 cases of

TABLE 1. Baseline clinical, radiological, and surgical data from 291 patients

Factor No. (%)

Sex Male 207 (71.1) Female 84 (28.9)Mean age in yrs* Male 73.0 ± 11.1 Female 76.7 ± 10.6Anticoagulation treatment Yes 139 (47.8) No 152 (52.2)History of head trauma Yes 155 (53.3) No 136 (46.7)CT hematoma density Homogeneous 123 (42.3) Mixed 42 (14.4) Membranous 79 (27.1) Separated 47 (16.2)Mean total hematoma vol in cm3* 180.9 ± 69.5Mean brain atrophy ratio* 0.72 ± 0.1Treatment Conservative 27 (9.3) Surgical 264 (90.7)Surgical location Unilat surgery 136 (51.5) Bilat surgery 128 (48.5)Surgical procedure 1–bur hole craniostomy 243 (92.0) 2–bur hole craniostomy 7 (2.6) Craniotomy 14 (5.3)Drain Yes 250 (94.7) No 14 (5.3)Complications 29 (11.0)

* Mean values expressed with standard deviation.

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CSDH (unilateral and bilateral) and found 49 recurrences, 18 cases of which were on the contralateral side. These cases were initially classified as uCSDH, but reexamina-tion of the preoperative CTs revealed that 14 cases demon-strated a thin SDH or effusion on the contralateral side at the primary operation. The authors deemed this phenom-enon to be a causative factor for hematoma recurrence. Small hematomas or effusions, normally treated conser-vatively, may give rise to a growing CSDH after drainage of the contralateral hemisphere. In our study the size of the operated and nonoperated hematoma was not corre-

lated with the site of retreatment. Hence, contralateral or ipsilateral retreatment was not predicted by the size of the operated or nonoperated hematoma. The unilateral surgi-cal intervention seems to be the causative factor for the higher RR and is not influenced by hematoma size.

This phenomenon may be explained by unilateral sur-gery causing a decrease in intracranial pressure, which permits expansion of the nonoperated contralateral hema-toma. Unilateral drainage may also cause displacement of the brain toward the operated side, increasing the contra-lateral subdural space. Persistence of an enlarged subdural

FIG. 1. Box plot illustrating the relationship between preoperative hematoma size of the right and left side and surgical interven-tion. Figure is available in color online only.

FIG. 2. Flowchart illustrating surgery groups and RRs. The unilateral operation group is subcategorized into ipsilateral and contra-lateral retreatment, illustrating their individual contributions to RR. Figure is available in color online only.

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space creates potential for hematoma accumulation in the absence of the tamponading effect of the displaced brain.

To find twice as high an RR in the unilateral surgery group is, however, surprising, leading to the suggestion that more patients with bCSDH should be treated with bi-lateral drainage. However, in some cases of bCSDH, small hematomas on one side make bilateral intervention dif-ficult and inadvisable because of the small distance to the cortex, thereby increasing the risk of damaging the brain during surgery.

The interventional effect of bilateral drainage was cal-culated with a number needed to treat (NNT) of 6.8 pa-tients. Given the limited amount of additional resources required for bilateral drainage (as opposed to unilateral drainage) and the insignificant increase in related compli-cations documented in our study, it may be beneficial to perform bilateral drainage on more patients with bCSDH. The possible advantages should be weighed against com-

plication rates and rehospitalization. Complication rates favored the unilateral approach, although the factor did not reach statistical significance in our study. It is impor-tant, however, to recognize that complication rates for retreatment procedures are generally considered to be higher than in primary surgery. Patients with CSDH are mainly older, which makes it especially important to pre-vent rehospitalization. Older patients are at particular risk for loss of function in activities of daily living,4 develop-ing delirium,20 and acquiring hospital-related infections18 during hospital admittance. Rehospitalization of older pa-tients is thereby associated with a higher risk of morbidity and mortality.

The primary limitation of this study is its retrospec-tive design; thus, there is a risk of selection bias in the 2 surgery groups (unilateral and bilateral). Given our data and personal communications with neurosurgeons in each of the participating departments, we believe that the sur-geon’s choice of surgical procedure was based on symp-toms and hematoma size. Comorbidity does not seem to influence the choice of treatment. Randomized studies of unilateral and bilateral surgical interventions in bCSDH would overcome such a selection bias.

All patients were identified by an ICD-10 diagnosis of CSDH and validated by reviewing the medical records and CT scans for each individual. However, we may have missed some cases that were misclassified with a wrong diagnosis, although the Danish National Patient Register is considered to have good validity.7 Nonetheless, the major strengths of our study are its inclusion of all neurosurgical departments in Denmark and the number of complete data sets, including at least 1 year of follow-up for all patients. Our findings regarding previously identified risk factors are consistent with previous studies on CSDH. This study is, to our knowledge, the first of its kind to comprise a national, consecutively sampled cohort of CSDH patients.

ConclusionsThis study establishes unilateral surgery of bCSDH as

an independent risk factor for retreatment. Unilateral or bilateral drainage of bCSDH is a decision made by the

TABLE 2. Univariate analysis of factors associated with the retreatment of bCSDH

FactorNo Retreatment

(%)Retreatment

(%)Univariate Analysis

No. of patients 207 (78.4) 57 (21.6)Sex Male 141 (68.1) 45 (78.9) 0.113 Female 66 (31.9) 12 (21.1)Mean age in yrs 73.9 ± 11.1 73.8 ±11.4 0.973Anticoagulation treat-

ment Yes 115 (55.5) 25 (43.9) 0.117 No 92 (44.4) 32 (56.1)CT hematoma density Homogeneous 83 (40.1) 23 (40.3) Mixed 33 (15.9) 5 (8.8) Separated 27 (13.0) 17 (29.8) 0.013* Membranous 64 (30.9) 12 (21.1)Mean preop hema-

toma vol in cm3185 ± 67.3 197.6 ± 66.8 0.210

Mean brain atrophy ratio

0.72 ± 0.1 0.71 ± 0.1 0.206

Surgery localization Unilat surgery 97 (46.9) 39 (68.4) 0.004* Bilat surgery 110 (53.1) 18 (31.6)Surgical procedure 1–bur hole cranios-

tomy188 (90.8) 53 (93)

2–bur hole cranios- tomy

5 (2.4) 2 (3.5) 0.609

Craniotomy 14 (6.8) 2 (3.5)Drain Yes 8 (3.9) 6 (10.5) No 199 (96.1) 51 (89.5) 0.046*Complications 22 (10.6) 7 (12.3) 0.724

* Statistically significant.

TABLE 3. Multivariate logistic regression analysis of factors associated with retreatment of bCSDH

Factor OR 95% CI p Value

Sex (male) 1.98 0.93–4.47 0.086Anticoagulant and/or

platelet therapy (yes) 1.55 0.82–2.95 0.182

Total hematoma vol 1.003 0.998–1.008 0.264Hematoma density Separated 2.56 1.07–6.18 0.035* Mixed 0.57 0.17–1.60 0.309 Membranous 0.64 0.27–1.42 0.280Atrophy 0.06 0.002–2.18 0.124Drainage (no drain) 4.31 1.22–14.83 0.020*Surgery location (unilat) 3.05 1.55–6.23 0.002*

* Statistically significant.

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clinician primarily on the basis of hematoma volume and clinical symptoms. In light of our current findings, we sug-gest that the increased risk of retreatment from unilateral drainage should be considered in the risk assessment and decision making for surgical drainage of bCSDH.

AcknowledgmentsNina Christine Andersen-Ranberg received grants from the

Re search Foundation of Rigshospitalet and the Hetland Olsen Foundation.

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FIG. 3. Examples of 2 bCSDHs requiring retreatment. A and D: CT scans obtained before the primary surgery. B and E: CT scans obtained before the second surgery (retreatment). C and F: Four weeks postoperative control scans. A–C: Scans il-lustrating how a small hematoma gives rise to a growing hematoma after drainage of the contralateral hemisphere. It would not be advisable to drain the right hematoma at the primary treatment because of its small size, but drainage of the contralateral hema-toma has consequences for the nonoperated hematoma. D–F: Scans of bCSDHs for which bilateral intervention was possible; however, unilateral treatment led to growth of the contralateral hematoma, requiring retreatment.

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DisclosuresThe authors report no conflict of interest concerning the materials or methods in this study or the findings specified in this paper.

Author ContributionsConception and design: Andersen-Ranberg, Fugleholm. Acqui-sition of data: all authors. Analysis and interpretation of data: Andersen-Ranberg, Fugleholm. Drafting the article: Andersen-Ranberg. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Andersen-Ranberg. Statistical analysis: Andersen-Ranberg. Administrative/technical/material support: Andersen-Ranberg, Fugleholm.

CorrespondenceNina Christine Andersen-Ranberg, Store Kongensgade 61A, 3 sal, Copenhagen 1264, Denmark. email: nina_andersenranberg@hotmail.com.

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