What are the recommended diagnostic tests for a subdural hematoma?

Diagnostic Testing for Subdural Hematoma

Primary Recommendation

Non-contrast CT of the head is the gold standard and first-line diagnostic test for suspected subdural hematoma, with a rating of "usually appropriate" (rating 9/9) by the American College of Radiology. 1, 2, 3

Initial Diagnostic Approach

Non-Contrast Head CT

• Perform immediately when subdural hematoma is clinically suspected based on head trauma history, altered mental status, focal neurological deficits, or unexplained headache 1
• CT demonstrates the characteristic crescent-shaped collection that crosses cranial sutures, distinguishing it from epidural hematoma (which is lens-shaped and limited by suture lines) 3
• Advantages include widespread availability, rapid acquisition time (critical in emergency settings), and non-invasive nature 4
• Best appreciated on sagittal or coronal reformats for optimal visualization 3

Clinical Decision Rules for CT Imaging

• For mild head trauma (GCS 13-15): CT is usually appropriate when imaging is indicated by clinical decision rules (e.g., 2008 ACEP Clinical Policy) 1
• For moderate (GCS 9-12) or severe (GCS 3-8) head trauma: Non-contrast CT is always indicated 1
• CT is the primary examination to exclude treatable lesions like subdural hematoma in patients presenting with dementia-like symptoms 1

Important Diagnostic Pitfalls

Isodense Subdural Hematomas

• Critical limitation: Approximately 25% of subdural hematomas may appear isodense (same density as brain tissue) on non-contrast CT, making them difficult to detect 5
• In 70-80% of isodense cases, diagnosis can still be made based on characteristic ventricular deformity patterns 5
• Contrast-enhanced CT is essential when isodense subdural hematoma is suspected but not clearly visible on non-contrast imaging 6
• Contrast enhancement of cerebral cortex, cortical vessels, and subdural membranes improves diagnostic accuracy to nearly 100% in isodense cases 6

Delayed Presentation

• Repeat CT may be necessary in patients with persistent post-traumatic symptoms despite initially normal CT, as subdural hematomas can develop over days to weeks (average 47 days in some cases) 7
• False-negative rates on initial CT can reach 10% in some series 8

MRI as Alternative or Adjunct Imaging

When to Use MRI

• MRI without contrast (rating 8/9) is an appropriate alternative to CT, particularly for detecting hemorrhage with susceptibility-weighted imaging (SWI) sequences 1
• MRI with and without contrast (rating 9/9) is preferred for proven parenchymal hemorrhage to evaluate for underlying enhancing masses or vascular malformations 1
• MRI provides superior characterization of subacute and chronic subdural collections and can detect smaller hematomas missed on CT 2
• Consider MRI for subacute or chronic head trauma with unexplained cognitive or neurological deficits 1

MRI Advantages

• Greater soft tissue contrast and superior anatomic detail compared to CT 1
• Better for determining potential secondary causes (e.g., dural-based neoplasms) 4
• No ionizing radiation exposure 1

MRI Limitations

• Longer acquisition time than CT (less practical in acute emergency settings) 4
• Less widely available than CT 4
• Caution: Care should be taken when attempting to determine the age of subdural hematomas by imaging alone 2

Follow-Up Imaging Protocol

Short-Term Follow-Up

• Non-contrast head CT is usually appropriate for short-term follow-up in patients with:
  • Unchanged neurological examination and positive initial findings (e.g., subdural hematoma) 1
  • New or progressive neurological deficits 1
• Exception: Patients with normal neurological examination and intracranial hemorrhage <10 mL may not require routine repeat imaging 1

High-Risk Patients Requiring Serial Imaging

• Anticoagulated patients: Repeat CT at 24 hours is critical, as anticoagulation dramatically increases risk of hematoma expansion 2, 3
• Patients on clopidogrel have particularly high mortality rates (OR = 14.7) after traumatic intracranial hemorrhage 2
• 30% of patients who died following ground-level falls were anticoagulated with aspirin, warfarin, clopidogrel, heparin, or multiple agents 2

Special Population Considerations

Elderly Patients (≥65 Years)

• Lower threshold for imaging: Ground-level falls account for 34.6% of all deaths in this age group 2
• Brain atrophy creates more space for brain movement during impact, increasing strain on bridging veins 2
• Even minor head trauma warrants close monitoring and imaging, as typical signs of serious injury may be absent 2

Pediatric Patients

• Subdural hematomas are the most common intracranial abnormality in abusive head trauma 2
• Often present as multiple, convexity, interhemispheric, or posterior fossa collections 2

Vascular Imaging (When Indicated)

Not Routinely Required for Initial Diagnosis

• CTA, MRA, or catheter angiography are rated 4/9 ("may be appropriate") for clinically suspected parenchymal hemorrhage 1
• Vascular imaging should be considered after diagnosis is confirmed to evaluate for underlying vascular malformations or masses 1