AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Background

Subdural hematomas are 1 of the 3 types of extra-axial intracranial hemorrhages (along with subarachnoid and epidural hemorrhages) and usually occur as a result of trauma. Deceleration injuries are often the cause of subdural bleeding from rupturing of veins via a shearing mechanism. Other entities, such as child abuse and ventricular decompression, also can result in subdural bleeding, and spontaneous hemorrhages may occur in patients receiving anticoagulants or patients with a coagulopathy condition. Compression of a dural sinus does not directly cause a subdural hematoma, although compression may result in a venous infarction.

Some subdural hematomas are clinically silent, whereas others cause symptoms as a result of mass effect on the adjacent brain. Some hematomas can grow large enough to result in herniation of cerebral tissue. Before computed tomography (CT) scanning and magnetic resonance imaging (MRI) technology, subdural hematomas were diagnosed only on the basis of this mass effect, which was depicted as displacement of the blood vessels on angiograms or as a calcified pituitary gland on skull radiographs. The advent of CT scan and MRI studies has made the diagnosis of even small hemorrhages routine (see Image 1).

For excellent patient education resources, visit eMedicine's Brain and Nervous System Center. Also, see eMedicine's patient education articles Head Injury, Concussion, and Aneurysm, Brain.

Pathophysiology

The meninges are composed of the dura mater, arachnoid mater, and pia mater. A space potentially exists between the arachnoid and dura (termed the subdural space), which, unlike the epidural space, is not confined by the cranial sutures. Bridging veins cross this space, extending from the cortical surface into the dural sinuses. Bleeding from these veins may occur as a result of a shearing injury (either by rotational or linear forces) along the plane of the subdural space and traumatic stretching of the veins, which can occur from rapid ventricular decompression.

Because the subdural space is not limited by the cranial sutures, blood can spread along the entire hemisphere and into the hemispheric fissure, limited only by the dural reflections (see Image 2). This ability of blood to spread relatively unchecked results in a crescent-shaped subdural hemorrhage rather than the biconvex or football shape of most epidural hematomas.

In larger, more clinically important subdural hematomas, the etiology of the bleeding is often an adjacent cortical laceration or shearing of cortical vessels. Patients with these hematomas have a worse prognosis; some studies report mortality rates in excess of 80%.

Most subdural hematomas occur along the cerebral convexities. Less common locations include the posterior fossa and along the interhemispheric fissure and tentorium (see Image 3).

In children, subdural hematomas occurring along the posterior interhemispheric fissure and the tentorium have been described as common findings following violent nonaccidental shaking (ie, shaken baby syndrome). Although these hematomas are not pathognomonic for child abuse, they should always suggest the possibility of abuse. It should be noted, however, that in children with benign external hydrocephalus, subdural hematomas and retinal hemorrhages may occur following even minor trauma. In addition, a recent study by Tung et al (2006) revealed no statistically significant difference in the incidence of interhemispheric subdural hematomas in accidental trauma relative to nonaccidental trauma in children, raising the possibility that such injuries are not a reliable method for detecting child abuse. The authors did note, however, a higher incidence of mixed-density subdural hematomas in nonaccidental trauma.

Although the vast majority of subdural hematomas result from trauma, spontaneous subdural hematomas can be seen in elderly individuals, those receiving anticoagulation, or patients with intracranial hypotension. Subdural hematomas after lumbar puncture, epidural injection, and puncture of spinal meningeal cysts have been reported. Patients with polycystic kidney disease and Prader-Willi syndrome also have an increased risk for spontaneous subdural hematomas.

Rare occurrences of subdural hematomas resulting from ruptured aneurysms (see Image 4) or dural arteriovenous malformations have been described. These diagnoses should be considered in cases of unexplained subdural hematomas, particularly recurrent subdural hematomas, which may be caused by intermittent bleeding from a dural arteriovenous malformation.

Another rare cause of chronic subdural hematomas is an arachnoid cyst. The hematoma may be preceded by cyst rupture and formation of a subdural hygroma with subsequent bleeding into the space.

Subdural hematomas are more common in the elderly and in infants because both groups have a larger subarachnoid space than young adults. The larger subarachnoid space allows for more movement between the brain and dura, predisposing these populations to the formation of subdural hematomas.

Frequency

United States

The frequency varies because many subdural hematomas are caused by trauma. One study of chronic subdural hematomas showed that this type of hematoma occurs at a rate of about 1 case per 10,000 population.

Mortality/Morbidity

• In patients with small subdural hematomas ( <1 cm in diameter), the prognosis is good. One study showed that 78% of patients undergoing burr-hole evacuation of chronic subdural hematomas had a good or complete recovery.
• Clinical outcome in patients with acute subdural hematomas is not as good because of the presence of other injuries and because of selection bias. In patients with subdural hemorrhages large enough to warrant surgery, mortality exceeds 50% and is related to the size of the hematoma and the amount of midline brain shift. However, the most important feature used to predict the outcome is the absence or presence of adjacent parenchymal contusion.
• Mortality in patients with large subdural hematomas causing mass effect on adjacent brain tissue is improved if the hemorrhage is treated surgically within 4 hours after injury. Although patients with large subdural hematomas do better when the hematoma is evacuated within the first 4 hours, a longer wait does not necessarily result in death.

Age

Subdural hematomas may occur at any age as a result of various types of trauma. In children, shaken baby syndrome usually occurs before the age of 1 year. In older persons, a subdural hematoma is more likely related to a fall. Both the elderly and infants are predisposed toward subdural hematomas because of their relatively large subarachnoid spaces.

Anatomy

See Pathophysiology.

Clinical Details

Subdural hematomas may be clinically silent when small and discovered only when imaging of the brain is performed as part of the workup for trauma. Some patients may complain of headache or dizziness when an isolated subdural hematoma is present. When the hematoma is larger, symptoms usually result from mass effect on the brain tissue or from adjacent parenchymal injuries. Decreased mental status, unsteady gait, headache, deviated gaze, and respiratory depression may be presenting symptoms.

Preferred Examination

CT scanning is usually the first evaluation in patients with suspected acute subdural hematoma because CT scans depict acute hemorrhage and skull fractures well, they are relatively fast to obtain, and CT scanning is more readily available than MRI. Smaller hemorrhages may be missed on CT scans, and in the nonacute setting, MRI is the study of choice because of its high sensitivity and specificity.

Limitations of Techniques

CT scanning may fail to depict small hemorrhages because of the similarity in attenuation between blood and adjacent bone and because of streak artifacts in the posterior fossa and inferior middle cranial fossa. MRI aids in the detection of small hematomas because of its multiplanar capabilities.

DIFFERENTIALS

Section 3 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Other Problems to be Considered

Brain atrophy

RADIOGRAPH

Section 4 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Findings

In the past, the finding of pineal gland displacement on skull radiographs was used as an indication of the presence of intracranial hemorrhage, but this is no longer clinically relevant.

CT SCAN

Section 5 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Findings

CT scan findings in subdural hematomas depend on the age of the hemorrhage.

In the acute phase, subdural hematomas appear as a crescent-shaped extra-axial collection with increased attenuation that, when large enough, causes effacement of the adjacent sulci and midline shift. The attenuation changes as the hematoma ages (see Images 5-6).

Subacute subdural hematomas may be difficult to detect because they may have isoattenuation compared with adjacent gray matter (see Image 7). Displacement of the gray matter–white matter junction is an important sign that indicates the presence of a space-occupying lesion. Although often administered in the past to help detect displacement of cortical vessels, contrast medium is not necessary with the capabilities of current scanners.

Chronic subdural hematomas have isoattenuation relative to the cerebrospinal fluid (CSF). In rare cases, such hematomas may calcify, resulting in an unusual appearance that can be mistaken for a calcified mass.

Unlike epidural hematomas, subdural hematomas are not restricted by dural tethering at the cranial sutures; they can cross suture lines and continue along the falx and tentorium. However, they do not cross the midline because of the meningeal reflections.

When a subdural hematoma is discovered on a CT scan, it is important to check for the presence of other related injuries, such as skull fracture (see Image 1), intraparenchymal contusions, and subarachnoid blood. The presence of adjacent parenchymal injury in patients with a subdural hematoma is the most important factor in predicting their clinical outcome.

Rebleeding into subdural hematomas also may occur and is depicted as a layer of high-attenuation hemorrhage within a lower attenuation hematoma (see Image 7).

Degree of Confidence

Differentiating subdural from epidural hematomas may be difficult when the hemorrhage is small, because the image of the blood may not demonstrate a typical shape in either condition. Follow-up imaging to ensure that the hematoma is not expanding and to check for an adjacent skull fracture is typical.

False Positives/Negatives

Small subdural hematomas may not be depicted because the attenuation may be similar to the adjacent inner table of the skull. Viewing the images with a wider window and level (eg, 240 and 80 HU) assists in detection in these cases (see Image 1); however, CT scanning fails to depict a certain number of small hemorrhages. In 1988, Gentry et al found that only 53% of acute and subacute subdural hematomas were revealed on CT scan studies compared with MRI; however, this study was performed using older CT technology.

In older patients with cerebral atrophy, an appearance of bilateral frontal subdural hygromas may be seen when the patient is in the supine position. However, the lack of mass effect and the presence of general atrophy suggest that this appearance is merely the result of settling of the atrophic brain rather than a pathologic subdural collection. A similar finding can be seen in young children (benign enlargement of the subarachnoid space), which should resolve in the first few years of life (see Image 8).

Posttraumatic subdural hygromas can also be confused with chronic subdural hematomas. These develop days or weeks following trauma and result from tears in the arachnoid and resulting leakage of CSF into the subdural space. They are self-limited and usually resolve after several months.

MRI

Section 6 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Findings

MRI is more sensitive than CT scanning in the detection of subdural hematomas because the multiplanar and superior tissue differentiation of MRI makes detection easier. In particular, a sensitivity of more than 95% has been described with T2-weighted images of subdural hematomas because of the marked difference in signal intensity between blood products and adjacent structures (see Images 9-10).

The shape of the subdural hematoma on axial images is the same crescent-shaped pattern seen on CT scan images. Coronal images are useful in evaluating the extent of subdural hematomas and in detecting temporal and tentorial hemorrhages, 2 aspects that are poorly depicted on CT scans.

In subdural hematomas, the signal depends on the age of the hemorrhage and follows the signal pattern of intraparenchymal hematomas in acute and subacute cases (see Brain, MRI Appearance of Hemorrhage). Chronic subdural hematomas, which appear as isoattenuation relative to CSF on CT scans, often demonstrate increased signal intensity on T1-weighted images because of the presence of free methemoglobin, though the intensity decreases over time. Hemosiderin is usually not present and is believed to result from the lack of a dural blood–brain barrier.

When hemorrhages of differing ages exist within a subdural collection, septae may separate the different blood products (see Image 11). In addition, a blood–fluid level may be seen. When blood products of various ages are depicted on MRIs in a child, particularly when the blood is at multiple sites, child abuse must be suspected (see Image 12). Posterior interhemispheric and tentorial subdural hematomas are also suggestive of child abuse because they are associated with shaken baby syndrome.

Degree of Confidence

MRI is the most sensitive imaging test available for the detection of subdural hematomas. Small subdural hematomas are occasionally difficult to distinguish from epidural hemorrhages.

ANGIOGRAPHY

Section 7 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Findings

Before the advent of CT scanning and MRI technology, subdural hematomas were often diagnosed by angiography. However, angiography is no longer an appropriate imaging tool in this setting.

INTERVENTION

Section 8 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Medical/Legal Pitfalls

• In children, posterior interhemispheric and tentorial subdural hematomas have been associated with child abuse.
• The radiologist should be concerned about possible child abuse when a posterior subdural hematoma is seen, particularly in association with other suggestive imaging results, such as the depiction of blood products of differing ages.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

Media file 1:  Axial head computed tomography scan demonstrates a skull fracture with an adjacent, small subdural hematoma. Window and level values are widened over standard values, which aids in the detection of small hemorrhages.
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Media type:  CT

Media file 2:  Subacute subdural hematoma with extension into the anterior interhemispheric cistern. Note that the sutures do not contain the spread of these hemorrhages.
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Media type:  MRI

Media file 3:  Tentorial subdural hematoma in an adult with trauma. In children with this pattern of injury, abuse should be considered.
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Media type:  CT

Media file 4:  Subdural hematoma with adjacent subarachnoid hemorrhage was the result of a ruptured middle cerebral artery aneurysm. Aneurysms are unusual causes of subdural hematomas.
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Media type:  CT

Media file 5:  Late subacute subdural hematoma has decreased attenuation compared with adjacent brain tissue. Attenuation of the hematoma remains higher than that of cerebrospinal fluid.
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Media type:  CT

Media file 6:  Ccomputed tomography scan in a patient with a subacute right frontal subdural hematoma. The blood has the same attenuation as that of the adjacent gray matter and is difficult to distinguish. Note that the gray matter–white matter junction is displaced medially, and midline shift is seen, indicating the presence of a space-occupying extra-axial lesion.
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Media type:  CT

Media file 7:  Late subacute-to-chronic subdural hematoma with a blood-fluid level indicating acute hemorrhage into the chronic collection.
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Media type:  CT

Media file 8:  Axial computed tomography scan demonstrates the benign enlargement of the subarachnoid space that occurs in children. The extra-axial fluid does not cause mass effect and normally resolves within the first 2 years of life.
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Media type:  CT

Media file 9:  Axial T1-weighted magnetic resonance imaging demonstrates bilateral subacute subdural hematomas with increased signal intensity. Areas of intermediate intensity represent more acute hemorrhage into the subacute collections.
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Media type:  MRI

Media file 10:  T2-weighted magnetic resonance imaging in a patient with subdural hematoma shows blood products of differing ages (same patient as in Image 8).
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Media type:  MRI

Media file 11:  T2-weighted magnetic resonance imaging in a patient with a subdural hematoma and rebleeding clearly shows hemorrhages of 3 different ages; these are hyperintense, isointense, and hypointense relative to brain tissue.
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Media type:  MRI

Media file 12:  Computed tomography (CT) scan demonstrating a patient with subdural hematomas of varying ages. This patient had a CT 1 week prior that demonstrated a chronic subdural hematoma (represented by the low density fluid on this study). Over the next week, his clinical condition progressively declined, then he collapsed shortly before this image was obtained. The gray blood represents subacute hemorrhage, whereas the white blood represents acute.
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Media type:  CT

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Angiography
• Intervention
• Multimedia
• References

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Article Last Updated: Nov 17, 2006