Subdural Hematoma

Introduction

A subdural hematoma (SDH) is a common neurosurgical disorder that often requires surgical intervention. SDH is a type of intracranial hemorrhage that occurs beneath the dura and may be associated with other brain injuries. Essentially, it is a collection of blood over the surface of the brain. SDHs are usually caused by trauma but can be spontaneous or caused by a procedure, such as a lumbar puncture. Anticoagulation, such as with heparin or warfarin (Coumadin), may be a contributing factor.

SDHs are usually characterized based on their size, location, and age (ie, whether they are acute, subacute, or chronic). These factors, as well as the neurologic and medical condition of the patient, determine the course of treatment and may also influence the outcome.

SDHs are often classified based on the period that has elapsed from the inciting event (if known) to the diagnosis. When the inciting event is unknown, the appearance of the hematoma on CT scan or MRI can help determine when the hematoma occurred.

Generally, acute SDHs are less than 72 hours old and are hyperdense compared with the brain on CT scan. Subacute SDHs are 3-20 days old and are isodense or hypodense compared with the brain. Chronic SDHs are 21 days (3 wk) or older and are hypodense compared with the brain. However, SDHs may be mixed in nature, such as when acute bleeding has occurred into a chronic SDH.

For the most part, this review discusses acute and chronic SDHs; less information is available about the less common subacute SDHs.¹ The entity of subdural hygroma is briefly addressed with chronic SDH.

Acute SDH is commonly associated with extensive primary brain injury. In one study, 82% of comatose patients with acute SDH had parenchymal contusions.² The severity of the diffuse parenchymal injury correlates strongly (inverse correlation) with the outcome of the patient. In recognition of this fact, an SDH that is not associated with an underlying brain injury is sometimes termed a simple or pure SDH, whereas the term complicated has been applied to SDHs in which a significant injury of the underlying brain has also been identified.

Chronic SDH is a common treatable cause of dementia. Some chronic SDHs may be derived from subdural hygromas. The presence of brain atrophy or loss of brain tissue due to any cause, such as old age, alcoholism, hydrocephalus, or stroke, may provide either an increased space between the dura and the brain surface where a subdural hygroma can form (see Image 6) or traction on bridging veins that span the gap between the cortical surface and dura or venous sinuses. Hygromas probably form after a tear in the arachnoid allows cerebrospinal fluid (CSF) to collect in the subdural space. A subdural hygroma may therefore also occur after head trauma; they are frequently asymptomatic. A minority of chronic SDH cases are derived from acute SDH cases that have matured (ie, liquified) because of lack of treatment.

History of the Procedure

The practice of trephination of the head (ie, chipping or drilling a hole through the skull) has been traced back to ancient times. The author Balzac, in 1840, described a case of chronic SDH, including its traumatic origin and surgical treatment.³ In the late 19th century, with the rise of medicine, development of aseptic technique and anesthesia, and establishment of the basic principles of neurologic localization, surgery for intracranial lesions (including SDH) became more common and, later, survival rates improved. In 1883, Hulke first described successful neurosurgical treatment of chronic SDH.⁴ Although cerebral angiography could be used to localize SDH in the early–to–mid-20th century, the development of the CT scan in the late 1970s represented another leap in patient care.

Problem

Traumatic injury of the head continues to be a significant health problem in the United States and elsewhere. SDH is the most common type of intracranial mass lesion, occurring not only in patients with severe head injury, but also in patients with less severe head injuries, particularly those who are elderly or who are receiving anticoagulants. SDH can be associated with high mortality and morbidity rates, even with the best medical and neurosurgical care.

Frequency

Acute SDHs have been reported to occur in 5-25% of patients with severe head injuries, depending on the study. Chronic SDH has been reported to be 1-5.3 cases per 100,000 people per year. More recent studies have shown a higher incidence, probably because of better imaging techniques.

Etiology

• Acute SDH
  • Head trauma
  • Coagulopathy or medical anticoagulation (eg, warfarin [Coumadin], heparin, hemophilia, liver disease, thrombocytopenia)
  • Nontraumatic intracranial hemorrhage due to cerebral aneurysm, arteriovenous malformation, or tumor (meningioma or dural metastases)
  • Postsurgical (craniotomy, CSF shunting)
  • Intracranial hypotension (eg, after lumbar puncture, lumbar CSF leak, lumboperitoneal shunt, spinal epidural anesthesia⁵
  • Child abuse or shaken baby syndrome (in the pediatric age group)
  • Spontaneous or unknown (rare)
• Chronic SDH
  • Head trauma (may be relatively mild, eg, in older individuals with cerebral atrophy)
  • Acute SDH, with or without surgical intervention
  • Spontaneous or idiopathic

Risk factors for chronic SDH include chronic alcoholism, epilepsy, coagulopathy, arachnoid cysts, anticoagulant therapy (including aspirin), cardiovascular disease (hypertension, arteriosclerosis), thrombocytopenia, and diabetes. In younger patients, alcoholism, thrombocytopenia, coagulation disorders, and oral anticoagulant therapy have been found to be more prevalent. Arachnoid cysts are more commonly associated with patients younger than 40 years with chronic SDH. In older patients, cardiovascular disease and arterial hypertension are found to be more prevalent. In one study, 16% of patients with chronic SDH were on aspirin therapy. Major dehydration is a less commonly associated condition and is found concurrently in only 2% of patients.

Pathophysiology

Acute subdural hematoma

The usual mechanism that produces an acute SDH is high-speed impact to the skull. This causes brain tissue to accelerate or decelerate relative to the fixed dural structures, tearing blood vessels, especially bridging veins. The primary head injury may also cause associated brain hematomas or contusions, subarachnoid hemorrhage, and diffuse axonal injury. Secondary brain injuries may include edema, infarction, secondary hemorrhage, and brain herniation.

Often, the torn blood vessel is a vein that connects the cortical surface of the brain to a dural sinus (termed a bridging vein). Alternatively, a cortical vessel, either a vein or small artery, can be damaged by direct injury or laceration. An acute SDH due to a ruptured cortical artery may be associated with only minor head injury, possibly without an associated cerebral contusion. In one study, the ruptured cortical arteries were found to be located around the sylvian fissure.⁶

In elderly persons, the bridging veins may already be stretched because of brain atrophy (shrinkage that occurs with age). 

Like other masses that expand within the skull, SDHs may become lethal by increasing pressure within the brain, leading to pathologic shifts of brain tissue (brain herniations). Two common types of brain herniation include subfalcial (cingulate gyrus) herniation and transtentorial (uncal) herniation. Subfalcial herniation may cause a cerebral infarct via compression of the anterior cerebral artery, and transtentorial herniation may cause an infarct via compression of the posterior cerebral artery. Transtentorial herniation is also associated with pressure on the third cranial nerve, causing decreased reactivity and then dilatation of the ipsilateral pupil.

With progressive transtentorial herniation, pressure on the brainstem causes its downward migration. This tears critical blood vessels that supply the brainstem, resulting in Duret hemorrhages and death. Increased intracranial pressure (ICP) may also decrease cerebral flood flow, possibly causing ischemia and edema and further increases the ICP, causing a vicious circle of pathophysiologic events.

Chronic subdural hematomas

Chronic SDHs may begin as a subdural hygroma, which begins as a separation in the dura-arachnoid interface, which is then filled by CSF. Dural border cells proliferate around this CSF collection to produce a neomembrane. Fragile new vessels then grow into the membrane. These vessels can hemorrhage and become the source of blood into the space, resulting in the growth of the chronic SDH.

Chronic SDHs may also evolve from the liquefaction of an acute SDH, particularly one that is relatively asymptomatic. Liquefaction usually occurs after 1-3 weeks, with the hematoma appearing hypodense on a CT scan.

Chronic SDHs that form from acute SDHs may have membranes between the dura and hematoma at 1 week and between the brain and hematoma at 3 weeks. As stated above, new fragile vessels may grow into these membranes. If not resorbed, the vessels in the membranes that surround the hematoma can hemorrhage repeatedly, enlarging the hematoma. Some chronic SDHs may also enlarge from an osmotic gradient, drawing more fluid into the subdural space, or through the separate mechanism of calcification (Atkinson, 2003).

In 1989, Kawakami discovered that the coagulation and fibrinolysis systems were both excessively activated in chronic SDH.⁷ This results in defective clot formation and recurrent hemorrhage. Katano et al (2006) recently reported on the status of other molecular markers within chronic SDHs.⁸

Presentation

Acute subdural hematoma

Acute SDHs are most likely to occur after head injury from a fall, motor vehicle accident, or assault. SDH is more common in men than in women, with a male-to-female ratio of approximately 3:1. Patients with SDH should be examined for related injuries (using guidelines established by the American College of Surgeons Committee on Trauma), such as cervical spine fracture, spinal cord injury, or long-bone fractures.

Patients found to have an acute SDH are usually older than other patients with trauma. In one study, the average age of a patient with trauma but without acute SDH was 26 years, while the average age of patients with an acute SDH was 41 years. Therefore, older patients appear to be at greater risk for developing an acute SDH after head injury. This is believed to be due to older patients having more atrophy, which allows more sheer force against bridging veins immediately after impact.

The clinical presentation of a patient with an acute SDH depends on the size of the hematoma and the degree of any associated parenchymal brain injury.

Some symptoms associated with acute SDH include headache, nausea, confusion, personality change, decreased level of consciousness, speech difficulties, other change in mental status, impaired vision or double vision, and weakness. Of course, such symptoms could also be caused by other conditions.

Neurological findings associated with acute SDH may include the following:

• Altered level of consciousness
• A dilated or nonreactive pupil ipsilateral to the hematoma (or earlier: a pupil with a more limited range of reaction)
  
  
• Hemiparesis contralateral to the hematoma.

A host of findings could be associated with these, such as brisk or abnormal reflexes, aphasia (usually with a left-sided hematoma), upper-extremity drift, or impairment of cortical sensory function. Less common findings include papilledema and unilateral or bilateral cranial nerve VI palsy. Some of the above may occur later in the clinical course; for instance, coma with a dilated fixed pupil usually indicates unilateral transtentorial herniation. Lack of a finding (eg, papilledema) cannot rule out SDH.

Less commonly, the hemiparesis may be ipsilateral to the hematoma, possibly due to direct parenchymal injury or compression of the cerebral peduncle contralateral to the hematoma against the edge of the tentorium cerebelli (the Kernohan notch phenomenon). Therefore, if the findings are conflicting, the most reliable indicator (by examination) of the side of the hematoma is a dilated or nonreactive pupil, which appears on the same side as the hematoma.

Patients may have a lucid interval after the trauma that causes a SDH. In addition, initial CT scan findings may be negative (ie, delayed intracranial hemorrhage).

Although acute SDHs most often occur over the cerebral hemispheres (convexity), they may also be found between the hemispheres along the falx (interhemispheric SDH), along the tentorium, or in the posterior fossa. Interhemispheric SDHs may be asymptomatic or manifest as headache,⁹ impaired consciousness, or hemiparesis or monoparesis (more likely to affect the contralateral leg than arm). Interhemispheric subdurals are usually managed conservatively unless neurologic deterioration is found.¹⁰

Chronic subdural hematoma

Men also have a higher incidence of chronic SDH. The male-to-female ratio has been reported to be 2:1. Most adults with chronic SDH are older than 50 years, with 2 studies reporting average ages of 68 and 70.5 years.

One quarter to one half of patients with chronic SDH have no identifiable history of head trauma. If a patient does have a history of head trauma, it is usually mild. The average time between the occurrence of the head trauma and the diagnosis of chronic SDH is 4-5 weeks.

Clinical presentation for chronic SDH is often insidious, with symptoms that include decreased level of consciousness, headache, difficulty with gait or balance, cognitive dysfunction or memory loss, motor deficit (eg, hemiparesis), headache, or aphasia. Chronic SDH may have a presentation similar to that of Parkinson disease.¹¹An acute presentation is also possible, as in the case of a patient who presents with a seizure.

Neurologic examination may demonstrate mental status changes, hemiparesis, papilledema, hyperreflexia or reflex asymmetry, hemianopsia, or third or sixth cranial nerve dysfunction. Such findings may also be associated with other entities. In patients aged 60 years or older, hemiparesis and reflex asymmetry are common presenting signs. In patients younger than 60 years, headache is a common presenting symptom.

Chronic SDHs have been reported to be bilateral in 8.7-32% of cases.

Indications

The nature and timing of neurosurgical intervention depends on multiple factors, including the size, age, and location of the hematoma and the medical and neurological condition of the patient. Surgery may be urgently required, yet even emergency surgery does not guarantee a satisfactory outcome.

Surgical evacuation via craniotomy is often considered in patients with an acute subdural hematoma (SDH) thicker than 5 mm (as measured with axial CT scanning) who have any neurological signs, such as lethargy or other change in mental status, or a focal neurological deficit. Bullock et al recently reported that "an acute SDH with a thickness greater than 10 mm, or a midline shift greater than 5 mm on computed tomography (CT) scan should be surgically evacuated, regardless of the patient's Glasgow Coma Scale (GCS) score."¹²

Surgery for chronic SDH may be indicated if the SDH is symptomatic or is producing significant mass effect, as evaluated with diagnostic imaging.

Diagnostic imaging that shows an expanding hematoma may also indicate the need for surgery, even in some patients whose neurological status is near normal.

Relevant Anatomy

As the name implies, the subdural space is under the dura but above the pia-arachnoid that is intimately associated with the cortical surface. Subdural hematomas (SDHs) are usually hemispheric in location, but may occur along the falx, the tentorium, or in the posterior fossa.

A SDH usually forms after the rupture of a bridging vein. These run from the cortical surface to the dura. Bridging veins are most commonly found along the sagittal sinus and around the anterior tip of the temporal lobe. The source of bleeding may or may not be found at the time of surgery.

Contraindications

Contraindications to surgery are determined on a case-by-case basis, depending on factors that relate to the patient's neurological and medical condition. For example, a patient with a massive subdural hematoma (SDH) may not be a surgical candidate if he or she has concomitant brain death, anticipated severe neurologic damage, coexisting brain lesions (eg, infarction), or a medical condition that contraindicates general anesthesia or surgery (eg, coagulopathy prior to correction). What is known of the patient's and family's beliefs and instructions may play a role in this decision.

At the other end of the spectrum, small acute SDHs thinner than 5 mm on axial CT images without sufficient mass effect to cause midline shift or neurological signs may be able to be observed clinically. MRI may be more sensitive than CT scan in detecting small SDHs. A chronic SDH with minimal or no mass effect on imaging studies and no neurological symptoms or signs except mild headache is often observed with serial scans and may resolve without surgical intervention.

Workup

Laboratory Studies

• Initial blood tests
  
  
  • To determine if defective coagulation was involved in the formation of the subdural hematoma (SDH) and to guide correction of any coagulation abnormalities, a prothrombin time (PT), activated partial thromboplastin time (aPTT), and a platelet count are typically performed. A bleeding time assessment may reveal platelet dysfunction.
  • Routine trauma laboratory studies that aid in the initial patient assessment may include hemoglobin or hematocrit, electrolytes, and a drug and alcohol screening. The drug and alcohol screenings may be important for correlating the neurological examination with the imaging studies.

Imaging Studies

• CT scan of the head (without contrast)
  
  
  • An emergent head CT scan needs to be performed when an acute SDH is suspected and should be obtained immediately after the patient is stabilized using standard advanced trauma life support (ATLS) guidelines.
  • An acute SDH appears on the noncontrast head CT scan as a crescent-shaped hyperdense area between the inner table of the skull and the surface of the cerebral hemisphere (see Image 7). Acute SDHs are usually unilateral.
  • A small acute SDH may be difficult to appreciate because of the appearance of the overlying skull. Use of the bone window setting may aid in discrimination.
  • An SDH may also be located along the falx (ie, interhemispheric), along the tentorium, or in the posterior fossa. Interhemispheric SDHs are among the findings identified in some abused children. Rarely, a SDH appears –lens shaped (ie, more like an epidural hematoma).
  • All or part of an acute SDH may appear hypodense or isodense to brain if the patient’s hematocrit is low, if the clot is hyperacute (eg, <1 style="font-size: 0.85em; line-height: 0; ">13
• 
  
  
  • The characteristic evolution of an SDH appearance on CT scan is as follows: In the first week, the SDH is hyperdense to brain tissue. In the second and third weeks, the SDH appears isodense to brain tissue (see Images 3-4). After the third week, the SDH is hypodense to brain tissue.
  • Often, a chronic SDH appears as a heterogeneously dense lesion indicative of recurrent bleeding with a fluid level between the acute (hyperdense) and chronic (hypodense) components of the hematoma (see Image 2).
  • On a contrast-enhanced CT scan, the chronic SDH membrane enhances to varying degrees, depending on numerous factors. Sometimes, a contrast-enhanced scan shows evidence of an underlying cause, such as a tumor or vascular lesion (eg, in patients with acute but nontraumatic SDH).
  • Typical signs of mass effect, such as midline shift and ventricular compression, may be observed.
• Magnetic resonance imaging
  
  
  • MRI is less useful than CT in diagnosing an acute SDH because of the increased time needed to obtain the study and the inability to use metallic objects that are needed to resuscitate patients with trauma (eg, most ventilators) in the scanning environment.
  • MRI can be a useful study to evaluate associated parenchymal brain injury and predict prognosis, but only after stabilizing and treating any life-threatening lesions. MRI is more sensitive for detecting nonhemorrhagic brain lesions, contusions, and diffuse axonal injury.¹⁴
  • An MRI is helpful in imaging chronic SDH when CT scans are difficult to interpret (eg, when suspecting an isodense hematoma). MRI may be particularly helpful in diagnosing bilateral chronic SDH because a midline shift may not be apparent on CT scan.

Histologic Findings

Acute SDHs usually contain both liquid and clotted blood. Intact erythrocytes are usually found within the clot. Associated skull fractures and underlying focal traumatic parenchymal damage are often present.

Fibroblastic membranes form on the dural side and arachnoid side of the chronic SDH, with the dural neomembrane being more vascular. The neomembrane consists of many capillaries, intact and lysed erythrocytes, hemosiderin-laden macrophages, and granulation tissue.

Treatment

Medical Therapy

Acute subdural hematoma

Emergency medical treatment of a patient with an acute subdural hematoma (SDH) that causes impending transtentorial herniation may include bolus administration of mannitol (in patients whose fluid levels have been adequately resuscitated and who have adequate blood pressure). Surgical evacuation of the lesion is the definitive treatment. Hyperventilation might be required but may decrease cerebral blood flow, thereby causing cerebral ischemia.

A patient with coagulopathy or a patient with an acute SDH who is receiving anticoagulant medication should be transfused with fresh frozen plasma (FFP), platelets, or both to maintain the prothrombin time (PT) within the reference range and the platelet count above 100,000. Heparin may need to be reversed with protamine; patients receiving warfarin are given vitamin K. Platelet infusion may also need to be considered if the platelet count is adequate but platelet function is impaired. The use of other factors, such as recombinant factor VII is under investigation. In patients who are receiving therapeutic anticoagulation, the potential effects of reversing the anticoagulation need to be considered.

The use of sequential CT scanning is important. Although each patient must be treated individually, patients who have small acute SDHs thinner than 5 mm on axial CT images without sufficient mass effect to cause midline shift or neurological signs have been observed clinically, with acceptable results (see Image 1). Hematoma resolution should be documented with serial imaging because an acute SDH that is treated conservatively can evolve into a chronic hematoma. For serial imaging, MRI may be more sensitive, but CT may be more convenient and less expensive.

Chronic subdural hematoma

In patients who have no significant mass effect on imaging studies and no neurological symptoms or signs except mild headache, chronic SDHs have been observed with serial scans and have been seen to remain stable or to resolve.

Although hematoma resolution has been reported, it cannot be reliably predicted, and no medical therapy has been shown to be effective in expediting the resolution of acute or chronic SDHs.

Surgical Therapy

Acute subdural hematoma

Surgery to manage an acute SDH usually consists of a large craniotomy (centered over the thickest portion of the clot) to decompress the brain, to stop any active subdural bleeding, and if indicated, to evacuate intraparenchymal hematoma in the immediate vicinity of the acute SDH. An acute SDH usually has a consistency that is too firm to allow removal through burr holes alone.

Including the sylvian fissure in the craniotomy exposure should be considered, since this is a likely location of a ruptured cortical vessel. If brain injury and edema are associated with the SDH, an ICP monitor may need to be placed. Bullock and colleagues (2006) stated that "all patients with acute SDH in coma (Glasgow coma scale [GCS] score less than 9) should undergo intracranial pressure monitoring."¹² Craniectomy (ie, the removal of the bone plate or flap) is also sometimes required, such as when increased ICP is present or anticipated. Different methods for storing the bone flap for possible later replacement exist.

Chronic subdural hematoma

Various surgical techniques for the treatment of chronic SDH have been described. Liquefied chronic SDHs are commonly treated with drainage through 1 or 2 burr holes. The burr holes are placed so that conversion to a craniotomy is possible, if needed. A closed drainage system is sometimes left in the subdural space for 24-72 hours postoperatively. Drainage via twist-drill craniotomy at the bedside has also been described.^{15, 16} Recently, a new system, the Subdural Evacuating Port System, has been introduced, with encouraging results.¹⁷

Under certain circumstances, craniotomy is recommended for chronic SDH, depending on factors such as recurrence, the consistency of the hematoma, and the presence of membranes.

Bilateral chronic hematomas may require drainage from both sides, usually during the same operation by means of burr holes placed on each side of the head.

Preoperative Details

Phenytoin (Dilantin) is administered to decrease the risk of developing early posttraumatic seizures (within the first 7 d after the injury). Patients have an estimated risk of greater than 20% for developing posttraumatic epilepsy after an acute SDH. Whether this risk is modifiable with prophylactic anticonvulsants remains debatable.

Intraoperative Details

The surgical technique for removing an acute SDH is well described in most standard texts of neurosurgery. When an acute SDH is evacuated, intraoperative ultrasonography may be helpful for locating intraparenchymal clots, which also may require evacuation, depending on the risks and benefits involved. Perioperative antibiotics may be administered to decrease the risk of postoperative infection.

Postoperative Details

Acute subdural hematoma

After the evacuation of an acute SDH, medical treatment is aimed at controlling the ICP below 20 mm Hg and maintaining the cerebral perfusion pressure above 60-70 mm Hg.

A follow-up CT scan is usually obtained within 24 hours of acute SDH removal and as needed to monitor for residual hematoma and recurrence.

If elevated ICP is an issue postoperatively, an urgent CT scan should be obtained to look for a new intracranial mass lesion or reaccumulation of the SDH.

Postoperative coagulation studies (PT, aPTT) and platelet counts should be observed closely and adjustments made, when possible, to lessen the risk of additional bleeding.

Chronic subdural hematoma

After the evacuation of a chronic SDH, adequate patient hydration is needed to help reexpand the brain. In addition, the patient may be maintained on bedrest with the head of the bed flat to aid brain reexpansion by increasing the intracranial venous pressure.

Follow-up

Acute subdural hematoma

Serial neurological examinations are used to determine the patient's subsequent clinical course (whether the patient is stable, improving, or deteriorating). Coagulation tests (PT, aPTT) and platelet counts may need to be observed and adjustments made in certain patients in order to decrease the risk of rebleeding.

Depending on the severity of the neurologic injury, patients may require physical therapy, occupational therapy, long-term rehabilitation, or even nursing-home placement.

Although CT imaging alone is usually sufficient for short-term management, a brain MRI is sometimes used (after a patient is stabilized) to look for associated brain injuries.

Serial imaging studies may be necessary to confirm that the acute SDH has fully resolved; a residual hematoma could become a symptomatic chronic SDH. This transformation can occur regardless of whether the hematoma has been managed surgically or conservatively.

Chronic subdural hematoma

As with acute SDH, serial neurological examinations are used and coagulation parameters may need to be followed. Serial CT scans are used to document the resolution of the chronic SDH.

Depending on the patient, physical therapy, occupational therapy, long-term rehabilitation, or even nursing home placement may be needed.

If the patient was on anticoagulation therapy preoperatively, when to restart anticoagulation therapy is complicated. No solution is perfect. The risks and benefits of anticoagulation must be weighed against the risks of rebleeding to determine when to restart therapy.

Complications

Acute subdural hematoma

As mentioned above, parenchymal brain injury is commonly associated with acute subdural hematoma (SDH) and can lead to increased ICP. Residual neurologic problems, as well as secondary events, can result from these associated injuries.

As with every medical condition and treatment, inherent risks exist. Postoperatively, recurrent or residual hematoma might be present, which, if symptomatic, may require repeat operative intervention. As many as one third of patients experience posttraumatic seizures after a severe head injury. Wound infection and CSF leak are possible after craniotomy. Meningitis or cerebral abscess can occur after any intracranial procedure, and constitutional signs of infection, delayed neurological deterioration, or signs of meningeal irritation may require further evaluation.

A long list of potential complications may also be related to anesthesia and hospitalization.

Chronic subdural hematoma

Among patients with chronic SDH who underwent surgical drainage, 5.4-19% experienced medical or surgical complications. Medical complications, including seizures, pneumonia, empyema, and other infections, occurred in 16.9% of cases. Surgical complications, including acute SDH formation, intraparenchymal hematoma, or tension pneumocephalus, occurred in 2.3% of cases.

After surgery for SDH, even with normalization of ICP, a persistent space may exist between the brain and dura, since the brain may not expand to fill this space. Residual hematoma has been found on 92% of postoperative CT scans within 4 days of operation; however, clinical improvement may proceed regardless of the size of this collection.

Reoperation rates for reaccumulation of hematoma have been reported to be from 12-22%. When the reoperation for burr-hole drainage was compared with craniotomy drainage, similar rates of 18.5% and 12.5% were found. However, the total number of craniotomies performed in this series was small. Of the patients who require a second operation to drain a reaccumulated hematoma, 26.6% (a total of 4 patients) required a third procedure to drain reaccumulated hematoma. Two of these 4 patients who underwent 3 operations developed subdural empyema. In another series, contralateral hematomas formed in 4% of patients who underwent drainage of unilateral chronic SDHs. These occurred from 3 days to 6 weeks postoperatively.¹⁸

Postoperative seizures have been reported in 3-10% of patients. Whether prophylactic anticonvulsants therapy can decrease this risk is debatable. Subdural empyema, brain abscess, and meningitis have been reported to occur in less than 1% of patients after operative drainage of a chronic SDH. In these patients, numerous potential complications are also related to anesthesia, hospitalization, patient age, and concurrent medical conditions.

Outcome and Prognosis

Acute subdural hematoma

The mortality rate of acute subdural hematoma (SDH) has been reported to range from 36-79%. Many survivors do not regain previous levels of functioning, especially after an acute SDH severe enough to require surgical drainage. Favorable outcome rates after acute SDH range from 14-40%.

Several series have shown an increase in favorable outcome in younger patients.¹⁹ Ages younger than 40 years were associated with a mortality rate of 20%, whereas ages of 40-80 years were associated with a mortality rate of 65%. Ages older than 80 years carried a mortality rate of 88%.

Findings demonstrated by CT scan (or MRI) may help indicate prognosis. Such findings may include the thickness or volume of the hematoma, the degree of midline shift, the presence of associated traumatic intradural lesions, and the compression of the brainstem or basal cisterns.²⁰ The first CT scan may underestimate the size of parenchymal contusions.

Elevated ICP postoperatively indicates a poor prognosis and may indicate the severity of the underlying brain injury (eg, trauma, secondary infarction).

In general, a poor preoperative neurologic status may be a harbinger of a poor outcome. In addition to factors discussed above, poor prognostic indicators for acute SDH have been reported to include the initial and postresuscitation Glasgow coma scale (GCS), the GCS motor score on admission, pupillary abnormalities, alcohol use, injury by motorcycle, ischemic damage,²¹ hypoxia or hypotension, and overall ability to control ICP.^{22, 23, 20}

Regarding surgical timing, the adage "the sooner the surgery is done, the better" may not always be accurate. This is for various reasons and depends on the individual case.²³ Even 15 years ago, Wilberger and colleagues concluded that "the time from injury to operative evacuation of the acute SDH in regard to outcome morbidity and mortality was not statistically significant when examined at hourly intervals".²² However, in patients with acute SDH and indications for surgery, surgical evacuation should be performed as soon as possible.¹²

Chronic subdural hematoma

Outcome after drainage of a chronic SDH has also been found to correlate with preoperative neurologic status (seeImage 5). Early diagnosis before a significant neurologic deterioration may correlate with a more favorable prognosis. No correlation has been found between preoperative CT scan findings and postoperative outcome.

The mortality rate within 30 days of surgery is 3.2-6.5%. Eighty percent of patients resume their prehematoma level of function. Sixty-one percent of patients aged 60 years or younger and in 76% of patients older than 60 years have favorable outcomes. In a relatively recent series, 89.4% of patients with chronic SDH who were treated with a closed drainage system had a good recovery and 2.2% worsened.²⁴ Mori et al found that old age, pre-existing cerebral infarction, and subdural air after surgery correlated with poor brain expansion.²⁵ Stanisic et al (2005) reported a 14.9% postoperative recurrence rate; various factors were associated with this.²⁵

Future and Controversies

Although surgical intervention may be able to successfully remove the hematoma itself, patients with acute subdural hematomas (SDHs) are often difficult to treat and may have a poor outcome due to underlying brain injury. The medical issues, especially in older patients with SDH, may be complex.

The mechanism, exact pathophysiology, and optimal treatment for chronic SDH has still not been definitively determined. Further work in delineating why membranes form and how to prevent or reverse their formation may lead to improvements in treatment strategies.

Future studies of patients with brain injuries, including those who have SDH, will hopefully lead to improved strategies for prevention of secondary injury and improved recovery from the primary brain injury.