Subdural Hematoma (SDH)
- Hemorrhagic collection within the relatively weak dural border cell layer between the meningeal dura mater and the arachnoid mater
- Location/Morphology
- Supratentorial convexity (See Figure 1 and 2; for additional images reference Skull Fractures chapter) is the common location followed by peritentorial (See Figure 3)
- Crescent-shaped and spreads diffusely over affected hemisphere
- Does not cross dural attachments
- Freely crosses sutures
- May extend along falx cerebri, tentorium cerebelli, floor of anterior and middle cranial fossa
- Location/Morphology
Neuroimaging
- Modalities
- CT without contrast and bone CT is the primary screening study for trauma
- Coronal and sagittal reformats are best for small SDH
- MRI is sometimes useful for determining the age of SDH
- CT Findings
- CT without contrast
- Hyperacute SDH (≤ 6 hours) – heterogenous density
- Acute SDH (6 hours to 3 days) –
- 60% cases are homogenously hyperdense
- 40% cases are heterogeneous density and may show swirl sign if there is active bleeding
- Rarely they are isodense as in cases of coagulopathy, anemia with Hgb < 8-10 g/dL
- If no new hemorrhage occurs, the density slowly decreases
- Chronic hematoma appears hypodense (See Figure 4)
- CT with contrast
- Hematoma displaces cortical veins
- Dural membranes enhance when the hematoma is subacute
- CT without contrast
- MRI Findings
- MRI signal of SDH is quite variable
- Often displays similar evolution to intraparenchymal hemorrhage
- Recurrent hemorrhage is common because of which acute and chronic blood products are noted even on the initial exam
- Recurrent hemorrhage also often makes SDH signal very variable, making age estimation unreliable (See Figure 5)
- Pia-arachnoid membrane tears can lead to CSF leakage into SDH collections that may further alter signal intensity by CSF dilution
- For aging of blood on MRI, see Epidural Hematoma chapter
- T1WI with contrast may show enhancement of the displaced cortical veins
- Subacute or chronic hematoma may show enhancement of the overlying dura or internal enhancement on delayed scan (See Figure 6)
- Diffusion weighted imaging is nonspecific showing heterogeneous signal
- Angiographic Findings
- CT Angiogram (CTA) shows mass effect from extraaxial collection with displacement of cortical veins away from inner table
- Digital subtraction angiography is performed if an underlying vascular lesion, such as an aneurysm or AV malformation is suspected on CTA
- Differential Diagnosis for subdural hematoma
- Subdural hygroma
- Subdural effusion and empyema
- Epidural Hematoma
- Pachymeningopathies (Thickened Dura)
- Tumor
- Chemical Shift Artifact (on MRI)
For more information, please see the corresponding chapter in Radiopaedia.
Contributor: Priya Rajagopalan, MD
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