How to Treat Chronic Subdural Hematoma? Past and Now

Treatment of chronic subdural hematoma (CSDH) is relatively straightforward, however, there is still some debate regarding the best strategy for treatment. The most practical recommendations of up to date were identified by a review of literature. The author reviewed the literature on CSDH management from the past to now to identify the best methods. Till 1970s, craniotomy was the most commonly used method. Burr hole (BH) became the most preferred method from 1980s. In 1977, twist drill (TD) craniostomy was introduced. Closed system drainage after a BH or a TD became the most frequently used surgical method. Although nonsurgical treatment is often successful, trephination has more advantages, such as rapid resolution of the symptoms and short period of hospitalization. Nonsurgical treatment is possible in asymptomatic patients with a small CSDH. For the symptomatic patients with CSDH, trephination is the treatment of choice, either by BH or TD. In gray zone between surgery and medical treatment, shared decision making can be an ideal approach. For the recurrent CSDHs, repeated trephination is still effective for patients with a low risk of recurrence. If the risk of recurrence is high, additional management would be helpful. For the refractory CSDHs, it is necessary to obliterate the subdural space.

Disappearance of Arachnoid Cyst after Burrhole Trephination: Case Series / 대한신경손상학회지

We report 3 cases of arachnoid cysts (ACs) that completely disappeared after burr hole drainage, without cyst fenestration into the subarachnoid space or cystoperitoneal shunt. The first patient was a 21-year-old female with an AC of the right cerebral convexity, found incidentally. After endoscopic AC fenestration was performed, the patient complained of persistent headache. Two-month postoperative brain imaging revealed reaccumulated AC and associated multi-stage subdural hematoma. Burr hole drainage was performed to resolve the chronic subdural hematoma (CSDH). Three months later, brain computed tomography showed that the CSDH and the AC had disappeared. The second patient was an 11-year-old male who had a history of trauma 1 month prior to presentation at the clinic. Brain magnetic resonance imaging revealed an AC in the left sylvian fissure with CSDH. We performed burr hole drainage to treat the CSDH first. Subsequently, the AC as well as the CSDH disappeared. The third case was an AC of the right parietal convexity, found incidentally. Only burr hole drainage was performed, following which, the AC disappeared. This case series shows that an AC can disappear naturally after rupture into the subdural space by trauma or the burr hole procedure.

How to Treat Chronic Subdural Hematoma? Past and Now

Treatment of chronic subdural hematoma (CSDH) is relatively straightforward, however, there is still some debate regarding the best strategy for treatment. The most practical recommendations of up to date were identified by a review of literature. The author reviewed the literature on CSDH management from the past to now to identify the best methods. Till 1970s, craniotomy was the most commonly used method. Burr hole (BH) became the most preferred method from 1980s. In 1977, twist drill (TD) craniostomy was introduced. Closed system drainage after a BH or a TD became the most frequently used surgical method. Although nonsurgical treatment is often successful, trephination has more advantages, such as rapid resolution of the symptoms and short period of hospitalization. Nonsurgical treatment is possible in asymptomatic patients with a small CSDH. For the symptomatic patients with CSDH, trephination is the treatment of choice, either by BH or TD. In gray zone between surgery and medical treatment, shared decision making can be an ideal approach. For the recurrent CSDHs, repeated trephination is still effective for patients with a low risk of recurrence. If the risk of recurrence is high, additional management would be helpful. For the refractory CSDHs, it is necessary to obliterate the subdural space.

Subarachnoid Hemorrhage with Subdural Hematoma due to Ruptured De Novo Aneurysm after Aneurysmal Clipping via Pterional Approach: An Autopsy Case / 대한법의학회지

Subdural hematoma (SDH) due to spontaneous rupture of intracranial aneurysm rarely occurs. The prevalence of subarachnoid hemorrhage (SAH) with SDH is approximately 0.5%–10.3% of all aneurysmal SAH. We report a case of aneurysmal rupture with SDH and SAH due to arachnoid defect after aneurysm clipping. The decedent was a 51-year-old woman who underwent brain surgery for SAH a few years ago. Two days before she died, she had nausea and sentinel headache. She was alive in the morning and was found dead at 6 PM. Injuries in the external surface were not found. A fresh SDH, measured approximately 90 mL, was found in the right hemisphere. SAH was diffusely distributed at the base of the brain and the right sylvian fissure. Two aneurysmal clippings were found in the anterior communicating artery and right internal carotid artery. A ruptured de novo aneurysm was also found in the right proximal middle cerebral artery. An uncal herniation was also observed. The cause of death was SAH with SDH due to de novo intracranial aneurysm. The tearing caused by the adhesion between the aneurysm and arachnoid, high blood pressure, and massive bleeding has been thought to be the causative mechanism of aneurysmal SAH with SDH. However, in this case, the arachnoid defect was caused by aneurysmal clipping through pterional approach. This defect served as the passage between the subarachnoid and subdural spaces. The autopsy for recurrent intracranial aneurysm will increase according to the extending life expectancy of patients after aneurysmal clipping.

Inyección subdural: complicación en la técnica peridural lumbar: revisión bibliográfica / Subdural injection: complication in lumbar epidural block: review of the literature

Se realiza una revisión bibliográfica sobre inyección subdural en la técnica peridural lumbar. se analizan los aspectos anatómicos, se describen las diferentes formas de presentación y su imagen radiológica, se discuten los criterios diagnósticos, los posibles efectos de la inyección en dicho espacio y la conducta a tomar, una vez detectada la complicación.

A bibliographic review about lumbar epidural subdural injection is done. the anatomic aspects, the different forms of presentation, and the radiological image are described. the diagnostic criteria, the effects of injection in this space and the management of the complication are discussed.

Remote Hemorrhage after Burr Hole Drainage of Chronic Subdural Hematoma / 대한신경손상학회지

Chronic subdural hematoma (CSDH) and symptomatic subdural hygroma are common diseases that require neurosurgical management. Burr hole trephination is the most popular surgical treatment for CSDH and subdural hygroma because of a low recurrence rate and low morbidity compared with craniotomy with membranectomy, and twist-drill craniotomy. Many reports suggest that placing a catheter in the subdural space for drainage can further reduce the rate of recurrence; however, complications associated with this type of drainage include acute subdural hematoma, cortical injury, and infection. Remote hemorrhage due to overdrainage of cerebrospinal fluid (CSF) is another possible complication of burr hole trephination with catheter drainage that has rarely been reported. Here, we present 2 cases of remote hemorrhages following burr hole trephination with catheter drainage for the treatment of CSDH and symptomatic subdural hygroma. One patient developed intracerebral hemorrhage and subarachnoid hemorrhage in the contralateral hemisphere, while another patient developed remote hemorrhage 3 days after the procedure due to the sudden drainage of a large amount of subdural fluid over a 24-hour period. These findings suggest that catheter drainage should be carefully monitored to avoid overdrainage of CSF after burr hole trephination.

Inyección subdural: informe de dos casos / Subdural injection: report of two cases / Injeção subdural: reporte de dois casos

Se presentan dos casos de inyección subdural accidental durante procedimientos epidurales para control del dolor. El primero fue un hombre con dolor lumbar crónico quien sufrió dicha complicación durante la inyección epidural de esteroides por vía interlaminar; el segundo, una mujer con síndrome de hipotensión endocraneana que requirió la aplicación de un parche hemático epidural para controlar múltiples fístulas de LCR, que debió ser abortada en dos ocasiones debido al patrón subdural que se evidenció luego de la administración del medio de contraste. El bloqueo subdural accidental es una complicación rara de la inyección epidural con fines analgésicos o anestésicos. Es de suma importancia la identificación temprana del patrón de distribución subdural y epidural del medio de contraste con el fin de disminuir el riesgo y aumentar la seguridad de los procedimientos en el espacio epidural.

Two cases are reported of accidental subdural injection during epidural procedures for pain control. The first one was a man with chronic lumbar pain who suffered such complication during an epidural injection of steroids using the interlaminar approach. The second one was a woman with intracranial hypotension syndrome who required the application of an epidural blood patch in order to control multiple CSF fistulae. The procedure had to be aborted twice due to the subdural pattern observed after injection of the contrast medium. Accidental subdural block is a rare complication of epidural injection for analgesic or anesthetic procedures.

Se apresentam dois casos ocorridos durante a execução de procedimentos da prática diária do especialista de dor. O primeiro, um doente com diagnóstico de dor lombar crónico quem apresenta uma injeção subdural acidental durante uma injeção epidural de esteroides por via interlaminar; o segundo uma doentecom síndrome de hipotensão endocraniana quem precisou da colocação de um curativo hemático epidural o qual teve que ser abortado em 2 ocasiões devido ao padrão subdural que se evidenciou logo da administração de meio de contraste. O bloqueio subdural acidental é uma rara complicação da injeção epidural com fins analgésicos ou anestésicos. Por tanto, resulta de suma importância a precoce identificação do padrão de distribuição do meio de contraste subdural e epidural com o fim de diminuir o risco e aumentar a segurança dos procedimentos no espaço epidural.

A Case of Subdural Hematoma due to Brandt-Daroff Habituation Excercise / 대한이비인후과학회지

Subdural hematoma is a common disease of intracranial hemorrhage that accounts for 11-21% of all head trauma patients. It is defined as a hematoma that develops between dura mater and subarachnoid space. In elder patients, mild trauma may not always be accurately recognized and symptoms may not develop slowly due to the large area of subdural space. Headache is the most common symptom of subdural hematoma and may be associated with hemiplegia, dysarthria, sensation disorder, conscious disorder, and etc. We present, with a literature review, a case of a patient who developed subacute subdural hematoma after performing Brandt-Daroff habituation exercise to treat benign paroxysmal positional vertigo.

Predicting Factors of Chronic Subdural Hematoma Following Surgical Clipping in Unruptured and Ruptured Intracranial Aneurysm

OBJECTIVE: The aim of this study is to analyze the differences in the incidence, predicting factors, and clinical course of chronic subdural hematoma (CSDH) following surgical clipping between unruptured (UIA) and ruptured intracranial aneurysm (RIA). METHODS: We conducted a retrospective analysis of 752 patients (UIA : 368 and RIA : 384) who underwent surgical clipping during 8 years. The incidence and predicting factors of CSDH development in the UIA and RIA were compared according to medical records and radiological data. RESULTS: The incidence of postoperative CSDH was higher in the UIA (10.9%) than in the RIA (3.1%) (p=0.000). In multivariate analysis, a high Hounsfield (HF) unit (blood clots) for subdural fluid collection (SFC), persistence of SFC ≥5 mm and male sex in the UIA and A high HF unit for SFC and SFC ≥5 mm without progression to hydrocephalus in the RIA were identified as the independent predicting factors for CSDH development (p<0.05). CONCLUSION: There were differences in the incidence and predicting factors for CSDH following surgical clipping between UIA and RIA. Blood clots in the subdural space and persistence of SFC ≥5 mm were predicting factors in both UIA and RIA. However, progression to hydrocephalus may have in part contributed to low CSDH development in the RIA. We suggest that cleaning of blood clots in the subdural space and efforts to minimize SFC ≥5 mm at the end of surgery is helpful to prevent CSDH following aneurysmal clipping.

Chronic Subdural Hematoma in the Aged, Trauma or Degeneration?

Chronic subdural hematomas (CSHs) are generally regarded to be a traumatic lesion. It was regarded as a stroke in 17th century, an inflammatory disease in 19th century. From 20th century, it became a traumatic lesion. CSH frequently occur after a trauma, however, it cannot occur when there is no enough subdural space even after a severe head injury. CSH may occur without trauma, when there is sufficient subdural space. The author tried to investigate trends in the causation of CSH. By a review of literature, the author suggested a different view on the causation of CSH. CSH usually originated from either a subdural hygroma or an acute subdural hematoma. Development of CSH starts from the separation of the dural border cell (DBC) layer, which induces proliferation of DBCs with production of neomembrane. Capillaries will follow along the neomembrane. Hemorrhage would occur into the subdural fluid either by tearing of bridge veins or repeated microhemorrhage from the neomembrane. That is the mechanism of hematoma enlargement. Trauma or bleeding tendency may precipitate development of CSH, however, it cannot lead CSH, if there is no sufficient subdural space. The key determinant for development of CSH is a sufficient subdural space, in other words, brain atrophy. The most common and universal cause of brain atrophy is the aging. Modifying Virchow's description, CSH is sometimes traumatic, but most often caused by degeneration of the brain. Now, it is reasonable that degeneration of brain might play pivotal role in development of CSH in the aged persons.

Raquianestesia: prós e contras / Spinal anesthesia: pros and cons

O desenvolvimento da raquianestesia vem acontecendo há pouco mais de 100 anos. Da técnica inicial, muito se mudou, com instrumentais diferenciados, fármacos com melhor perfil, refinamento da técnica, assim como indicações e contraindicações mais precisas. Hoje, grande parte das cirurgias infraumbilicais é passível de serem realizadas sob raquianestesia, provendo estabilidade clínica e excelente analgesia pós-operatória. Para alguns segmentos populacionais, como idosos e gestantes, essa técnica ganhou ainda mais importância. Contudo, apesar de ser amplamente difundida, o bloqueio subaracnóideo tem limitações de uso, trazendo consigo, como qualquer outra técnica, vantagens e desvantagens. Este trabalho de revisão visa a relatar as principais vantagens e desvantagens do bloqueio subaracnóideo, elencando seu papel em grupos especiais e abordando as mais recentes descobertas sobre essa técnica.

The development of spinal anesthesia has been underway for just over 100 years. Much has changed from the initial technique, with different instruments, drugs with better profile, technical refinement and more precise indications and contraindications. Today, much of the infra-umbilical surgeries are likely to be performed under spinal anesthesia, providing clinical stability and excellent postoperative analgesia. For some population groups such as the elderly and pregnant women, this technique gained even more importance. However, despite being widespread, the spinal block has limitations of use, bringing with it like any other technique, advantages and disadvantages. This review paper aims at reporting the main advantages and disadvantages of spinal block, listing its role in special groups and addressing the latest discoveries about this technique.

History of Chronic Subdural Hematoma / 대한신경손상학회지

Trephination or trepanation is an intentional surgical procedure performed from the Stone Age. It looks like escaping a black evil from the head. This technique is still used for treatment of chronic subdural hematoma (SDH). Now, we know the origin, pathogenesis and natural history of this lesion. The author try to explore the history of trephination and modern discovery of chronic SDH. The author performed a detailed electronic search of PubMed. By the key word of chronic SDH, 2,593 articles were found without language restriction in May 2015. The author reviewed the fact and way, discovering the present knowledge on the chronic SDH. The first authentic report of chronic SDH was that of Wepfer in 1657. Chronic SDH was regarded as a stroke in 17th century. It was changed as an inflammatory disease in 19th century by Virchow, and became a traumatic lesion in 20th century. However, trauma is not necessary in many cases of chronic SDHs. The more important prerequisite is sufficient potential subdural space, degeneration of the brain. Modifying Virchow's description, chronic SDH is sometimes traumatic, but most often caused by severe degeneration of the brain. From Wepfer's first description, nearly 350 years passed to explore the origin, pathogenesis, and fate of chronic SDH. The nature of the black evil in the head of the Stone Age is uncovering by many authors riding the giant's shoulder. Chronic SDH should be categorized as a degenerative lesion instead of a traumatic lesion.

Comparision between Brain Atrophy and Subdural Volume to Predict Chronic Subdural Hematoma: Volumetric CT Imaging Analysis / 대한신경손상학회지

OBJECTIVE: Brain atrophy and subdural hygroma were well known factors that enlarge the subdural space, which induced formation of chronic subdural hematoma (CSDH). Thus, we identified the subdural volume that could be used to predict the rate of future CSDH after head trauma using a computed tomography (CT) volumetric analysis. METHODS: A single institution case-control study was conducted involving 1,186 patients who visited our hospital after head trauma from January 1, 2010 to December 31, 2014. Fifty-one patients with delayed CSDH were identified, and 50 patients with age and sex matched for control. Intracranial volume (ICV), the brain parenchyme, and the subdural space were segmented using CT image-based software. To adjust for variations in head size, volume ratios were assessed as a percentage of ICV [brain volume index (BVI), subdural volume index (SVI)]. The maximum depth of the subdural space on both sides was used to estimate the SVI. RESULTS: Before adjusting for cranium size, brain volume tended to be smaller, and subdural space volume was significantly larger in the CSDH group (p=0.138, p=0.021, respectively). The BVI and SVI were significantly different (p=0.003, p=0.001, respectively). SVI [area under the curve (AUC), 77.3%; p=0.008] was a more reliable technique for predicting CSDH than BVI (AUC, 68.1%; p=0.001). Bilateral subdural depth (sum of subdural depth on both sides) increased linearly with SVI (p<0.0001). CONCLUSION: Subdural space volume was significantly larger in CSDH groups. SVI was a more reliable technique for predicting CSDH. Bilateral subdural depth was useful to measure SVI.

Migration of an Intracranial Subdural Hematoma to the Spinal Subdural Space: A Case Report

A 57-year-old man complained of severe lower back pain and radicular pain in both legs for 1 week after falling from a ladder. Magnetic resonance imaging (MRI) of the spine showed a subdural hematoma (SDH), which was surgically removed. The patient had no back pain or the radicular leg pain at 2 weeks post-surgery. However, he complained of diffuse headaches upon follow-up. Brain computed tomography (CT) and MRI revealed an intracranial SDH, which was immediately removed by surgery. During his 1-year follow-up, he reported that the pain had resolved without recurrence. Simultaneous spinal and intracranial SDH are rare and no standard treatment exists for this condition. This case suggests that it is possible that an intracranial SDH can migrate into the cerebrospinal fluid (CSF) space through an arachnoid tear. CSF circulation allows the intracranial SDH to enter subarachnoid spaces encasing the spinal cord. In order to prevent irreversible damage, surgical intervention should be considered for case of spinal SDH with progressive neurological deficits.

Encapsulated Unresolved Subdural Hematoma Mimicking Acute Epidural Hematoma: A Case Report / 대한신경손상학회지

Encapsulated acute subdural hematoma (ASDH) has been uncommonly reported. To our knowledge, a few cases of lentiform ASDH have been reported. The mechanism of encapsulated ASDH has been studied but not completely clarified. Encapsulated lentiform ASDH on a computed tomography (CT) scan mimics acute epidural hematoma (AEDH). Misinterpretation of biconvex-shaped ASDH on CT scan as AEDH often occurs and is usually identified by neurosurgical intervention. We report a case of an 85-year-old man presenting with a 2-day history of mental deterioration and right-sided weakness. CT scan revealed a biconvex-shaped hyperdense mass mixed with various densities of blood along the left temporoparietal cerebral convexity, which was misinterpreted as AEDH preoperatively. Emergency craniectomy was performed, but no AEDH was found beneath the skull. In the subdural space, encapsulated ASDH was located. En block resection of encapsulated ASDH was done. Emergency craniectomy confirmed that the preoperatively diagnosed AEDH was an encapsulated ASDH postoperatively. Radiologic studies of AEDH-like SDH allow us to establish an easy differential diagnosis between AEDH and ASDH by distinct features. More histological studies will provide us information on the mechanism underlying encapsulated ASDH.

Zero drift of intraventricular and subdural intracranial pressure monitoring systems / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>To assess zero drift of intraventricular and subdural intracranial pressure (ICP) monitoring systems.</p><p><b>METHODS</b>A prospective study was conducted in patients who received Codman ICP monitoring in the neurosurgical department from January 2010 to December 2011. According to the location of sensors, the patients were categorized into two groups: intraventricular group and subdural group. Zero drift between the two groups and its association with the duration of ICP monitor were analyzed.</p><p><b>RESULTS</b>Totally, 22 patients undergoing intraventricular ICP monitoring and 27 receiving subdural ICP monitoring were enrolled. There was no significant difference in duration of ICP monitoring, zero drift value and its absolute value between intraventricular and subdural groups (5.38 d+/-2.58 d vs 4.58 d+/-2.24 d, 0.77 mm Hg+/-2.18 mm Hg vs 1.03 mm Hg+/-2.06 mm Hg, 1.68 mm Hg+/-1.55 mm Hg vs 1.70 mm Hg+/-1.53 mm Hg, respectively; all P larger than 0.05). Absolute value of zero drift in both groups significantly rose with the increased duration of ICP monitoring (P less than 0.05) while zero drift value did not. Moreover, daily absolute value in the intraventricular group was significantly smaller than that in the subdural group (0.27 mm Hg+/-0.32 mm Hg vs 0.29 mm Hg+/-0.18 mm Hg, P less than 0.05).</p><p><b>CONCLUSION</b>This study demonstrates that absolute value of zero drift significantly correlates with duration of both intraventricular and subdural ICP monitoring. Due to the smaller daily absolute value, ICP values recorded from intraventricular system may be more reliable than those from subdural system.</p>

Intrauterine fetal bradycardia after accidental administration of the anesthetic agent in the subdural space during epidural labor analgesia: A case report / 대한마취과학회지

Subdural injection of epidural anesthesia is rare and is usually undiagnosed during epidural anesthesia causing severely delayed maternal hypotension, hypoxia, and fetal distress. A 38-year-old primiparous woman was administered epidural labor analgesia at 40(+6) weeks' gestation, and developed progressive maternal respiratory depression, bradycardia, and hypotension after accidental subdural administration of the anesthetic agent. Furthermore, fetal distress occurred soon after administration. The patient was managed with oxygen, position changes, fluid resuscitation, and ephedrine. Intrauterine fetal resuscitation was successfully performed with atropine before cesarean section, and a healthy baby was delivered. Although subdural injection is uncommon, this case emphasizes the importance of anesthesiologists monitoring patients for a sufficient period after epidural labor analgesia, and being prepared to perform maternal or fetal resuscitation.

Spinal Subdural Hematoma Following Cranial Subdural Hematoma : A Case Report with a Literature Review

Coexistence of cranial and spinal subdural hematomas is rare and only a few cases have been reported in the literature. Herein, we report a case of cranial and spinal subdural hematomas after previous head trauma. As the pathogenesis of simultaneous intracranial and spinal subdural hematoma yet remains unclear, we developed an alternative theory to those proposed in the literature for their coexistence, the migration of blood through the subdural space.

Effects of Newly Designed Drainage Catheter in Treating Chronic Subdural Hematoma / 대한신경손상학회지

OBJECTIVE: Chronic subdural hematoma (cSDH) is a common disorder that is readily surgically treated but has high recurrence rate. This is a preliminary report to evaluate the effectiveness of a newly designed catheter compared with the conventional one in treating cSDH. METHODS: We conducted a retrospective study of 111 patients with unilateral chronic subdural hematoma treated by burr hole craniostomy with closed-system drainage from November 2009 to September 2012. Group A was defined as patients treated with an external ventricular drainage (EVD) catheter and B as patients treated with the new catheter. We measured changes of thickness of hematoma and midline shifting in brain computed tomography (CT), amount of drainage and recurrence rate in both groups. RESULTS: Group A consisted of 54 and B of 57 cases. The mean duration for total removal of hematoma was 42.6+/-13.9 hours in group A and 30.3+/-11.9 hours in group B (p<0.05). The mean amount of drainage counted per six hours cumulatively differed significantly between groups. The result (p<0.05) showed that the newly designed catheter effectively removed the hematoma. The total recurrence rate in group A was 11% and 3.5% in group B. CONCLUSION: The study showed that the newly designed catheter effectively removed the hematoma in less time than the conventional one. This helps re-expand the brain block CSF from flowing into the subdural space and decrease the recurrence rate.

The Influence of Postoperative Lesion-Down Head Position on the Recurrence Rate in Chronic Subdural Hematoma after Burr-Hole Surgery / 대한신경손상학회지

OBJECTIVE: Chronic subdural hematoma is a common disorder observed in neurosurgical care and the recurrence rate is relatively high. In this report, we evaluated the relationship between the recurrence rate of chronic subdural hematoma and the postoperative head position of the patient. METHODS: We conducted a retrospective study of 72 patients with unilateral chronic subdural hematoma treated by burr hole surgery with closed system drainage from October 2009 to May 2011. In group A, there was no restriction in head position for days keeping the catheter. In group B, the patients were placed with the lesion side of the head downward after the operation. We analyzed the recurrence rate, amount of postoperative drainage and changes in computed tomography finding of group A and B. RESULTS: Group A and group B consisted of 36 cases, respectively. The mean amount of total postoperative drainage was 248.8+/-127.2 mL in group A and 176.3+/-98.9 mL in group B (p=0.01). The improvement rates of midline shifting before and after surgery showed 60.5+/-25.6% in group A and 73.4+/-26.3% in group B (p=0.039). The total recurrence rate in group A was 11.1% and 5.6% in group B. CONCLUSION: By facing the lesion downward after surgical treatment, chronic subdural hematoma is thought to help reexpand the brain and to prohibit cerebrospinal fluid from flowing into subdural space and to decrease the recurrence rate better than having a free position.