How to rule out subdural hematoma?

How to Rule Out Subdural Hematoma

Non-contrast CT scan of the head is the primary imaging modality to rule out subdural hematoma in the acute setting, with a sensitivity of 100% and negative predictive value of 100% when performed appropriately after head trauma. 1

Initial Evaluation and Imaging Decision

When to Obtain CT Imaging

Obtain immediate non-contrast head CT in patients with:

• Glasgow Coma Scale (GCS) score ≤14 1
• Any focal neurologic deficits 1
• Clinical signs of skull fracture 1
• Loss of consciousness or posttraumatic amnesia 1
• Age >60 years with any head trauma mechanism 1
• Patients on anticoagulation (warfarin, NOACs) or antiplatelet therapy with any head trauma 1

The evidence strongly supports CT as the definitive initial test. In a multicenter study of 2,166 patients with mild TBI (GCS >12), CT demonstrated 100% sensitivity for detecting clinically significant intracranial lesions, with none of 1,170 patients with normal CT findings requiring subsequent craniotomy. 1

CT Findings Diagnostic of Subdural Hematoma

Look for crescentic fluid collection along the brain surface, which appears:

• Hyperdense (bright white) in acute subdural hematoma 2
• Isodense or hypodense in subacute/chronic subdural hematoma 2
• Best appreciated on coronal or sagittal reformats 2

Associated findings that increase clinical significance include midline shift, mass effect, and concurrent subarachnoid hemorrhage. 3

Special Populations Requiring Enhanced Vigilance

Anticoagulated Patients

All patients on warfarin or NOACs with any head trauma require head CT regardless of normal neurologic examination. 1

• Delayed intracranial hemorrhage occurs in 0.6% (95% CI 0.2-1.5%) of anticoagulated patients with initially normal CT 1
• Consider 24-hour observation with repeat CT at 20-24 hours post-injury for anticoagulated patients, even with normal initial CT 1
• Two patients in one study returned days after negative repeat CT with subdural hematomas, highlighting the need for clear return precautions 1

Elderly Patients (>60 years)

Maintain lower threshold for imaging in elderly patients, as they have higher rates of positive CT findings (10% in those with GCS 15) and can present with subtle or atypical symptoms. 1

• Elderly patients may present with cognitive decline, gait disturbance, or dementia rather than classic trauma symptoms 4
• History of trauma may be absent or forgotten 4

Role of MRI

MRI should be obtained when:

• CT is negative but clinical suspicion remains high 1
• Evaluating for small-volume extra-axial hemorrhage not visible on CT 1
• Assessing extent of injury in patients with abnormal CT 1
• Subdural hygroma is suspected (requires MRI with contrast) 5

MRI detects additional diagnostic information in approximately 25% of patients beyond what CT reveals. 1 However, MRI is reserved for the non-emergent setting, as CT remains the gold standard for acute evaluation. 1

Critical Pitfall: Delayed Subdural Hematoma

Patients with persistent post-traumatic symptoms despite normal initial CT and neurologic examination require repeat imaging. 6

A case series documented three patients who developed large subdural hematomas requiring surgical drainage an average of 47 days after normal initial CT and examination. 6 This emphasizes:

• Provide explicit return precautions for worsening headache, focal deficits, or altered mental status 6
• Consider repeat CT for persistent symptoms even weeks after injury 6
• One patient in a large trauma series was discharged with normal examination and no CT, returning later with uncomplicated subdural hematoma 1

Patients Who Can Be Safely Managed Without CT

Patients with GCS 15, no loss of consciousness, no anticoagulation, age <60, and completely normal neurologic examination may be observed without immediate CT, though clinical judgment and mechanism of injury must be considered. 1

However, this represents a narrow subset. The evidence demonstrates that 14.8% of patients with GCS 15 had positive CT findings, and 3.2% required craniotomy. 1 When in doubt, image.

Follow-Up Imaging Indications

Obtain repeat CT if:

• Initial subdural hematoma measures >3 mm (11% enlarge, though none <3 mm required surgery) 3
• Patient has hypertension, concurrent subarachnoid hemorrhage, or initial midline shift (all predict expansion) 3
• Any clinical deterioration occurs 1
• Anticoagulated patient with initially normal CT at 20-24 hours 1

An initial subdural hematoma size of 8.5 mm best predicts need for surgical intervention (AUC 0.81). 3