Radiography
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.
Computed Tomography
Findings
CT scan findings in subdural hematomas depend on the age of the hemorrhage.4,9,10
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).
Late subacute subdural hematoma has decreased attenuation compared with adjacent brain tissue. Attenuation of the hematoma remains higher than that of cerebrospinal fluid.
Computed 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.
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.
Late subacute-to-chronic subdural hematoma with a blood-fluid level indicating acute hemorrhage into the chronic collection.
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. 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.11,12
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).
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.
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.
Magnetic Resonance Imaging
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).
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.
T2-weighted magnetic resonance imaging in a patient with subdural hematoma shows blood products of differing ages (same patient as in Image 8).
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.
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.
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.
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
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.
More on Subdural Hematoma |
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 Imaging: Subdural Hematoma |
| Follow-up: Subdural Hematoma |
| Multimedia: Subdural Hematoma |
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References
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Further Reading
Related eMedicine topics
Subdural Hematoma (from Emergency Medicine)
Subdural Hematoma (from Neurology)
Subdural Hematoma (from Neurosurgery)
Subarachnoid Hemorrhage
Epidural Hemorrhage
Clinical guidelines
Surgical Management of Acute Subdural Hematomas
Clinical and other studies
Teen Online Problem Solving (TOPS) - An Online Intervention Following TBI
Keywords
subdural hematoma, SDH, subdural hemorrhage, subdural bleed, brain hemorrhage, intracranial hemorrhage, extraaxial hemorrhage, extra-axial hemorrhage, intracranial hemorrhage, cranial bleeding, head trauma, brain injury, brain trauma, acute subdural hematoma, subacute subdural hematoma, chronic subdural hematoma, shaken baby syndrome, shaken-baby syndrome, child abuse
