Differentiating Chronic from Subacute Subdural Hematoma
Chronic subdural hematoma (CSDH) is favored over subacute subdural hematoma (SSDH) based on imaging characteristics, time course, and clinical presentation, with CSDH typically appearing as a hypodense crescent-shaped collection on CT with characteristic outer neomembranes. 1
Imaging Characteristics
CT Findings
- CSDH typically appears as:
- Hypodense (dark) crescent-shaped collection on non-contrast CT
- Best appreciated on sagittal or coronal reformats
- Often with layering of fluid in the subdural space
- May show membrane formation at the periphery
MRI Findings
- More sensitive than CT for detecting subdural collections
- Chronic subdural hematomas show:
- T1-weighted: Variable signal intensity depending on age (typically hyperintense)
- T2-weighted FLAIR: Irregular shape with gyrus patterns in chronic cases
- Diffusion-weighted imaging: May show two-layered hematoma structure 2
Time Course Differentiation
| Phase | Time Frame | Characteristics |
|---|---|---|
| Acute | <7 days | Fresh blood, hyperdense on CT |
| Subacute | 1-6 weeks | Transitioning density, isodense to brain |
| Chronic | >6 weeks | Hypodense, encapsulated collections with neomembranes [3] |
Clinical Considerations
Patient Demographics
- CSDH is more common in:
- Elderly patients (typically >70 years)
- Males
- Patients on anticoagulant/antiplatelet therapy 1
Clinical Presentation
- CSDH often presents with:
- Gradual onset of symptoms
- Fluctuating consciousness
- Headache
- Focal neurological deficits
- History of minor trauma or no recalled trauma
Pathophysiological Differences
CSDH is characterized by:
- Encapsulated blood collections within dural border cells
- Characteristic outer "neomembranes"
- Repeated microhemorrhages from fragile neovascularization
- Hyperfibrinolytic activity within the hematoma 1
Management Implications
The distinction matters because:
- CSDH is typically managed with burr hole craniostomy with closed-system drainage 4
- Acute on chronic SDH may require craniotomy or craniectomy rather than simple burr holes 5
- Subacute SDH sometimes requires small craniotomy if solid components are present 2
Common Pitfalls
- Misdiagnosing CSDH as SSDH can lead to inappropriate surgical approach
- Failing to recognize mixed density collections that represent acute bleeding into a chronic hematoma
- Overlooking bilateral hematomas (present in approximately 20-25% of cases)
- Not identifying underlying coagulopathy or vascular abnormalities
Special Considerations
- In young patients (<60 years), always consider underlying pathology such as:
The ACR Appropriateness Criteria recommends MRI as the most useful initial imaging for evaluation of subacute or chronic head trauma when rapid detection of acute intracranial hemorrhage is no longer the primary clinical focus 3. This helps distinguish between different types of subdural collections and identify underlying causes.
In summary, the diagnosis of chronic versus subacute subdural hematoma is based on a combination of imaging characteristics, time course, and clinical presentation, with important implications for surgical management and patient outcomes.