How to diagnose a subdural hematoma?

How to Diagnose Subdural Hematoma

Non-contrast head CT is the first-line diagnostic test and should be performed immediately in any patient with head trauma and concerning symptoms, as it has 98-100% sensitivity within the first 12 hours after injury. 1, 2

Immediate Imaging Indications

Obtain emergent non-contrast head CT for patients presenting with:

• Any altered mental status, loss of consciousness, or focal neurological deficits following head trauma 1
• Headache with nausea/vomiting, particularly if severe or sudden onset 1
• Age ≥65 years with any head trauma, even from ground-level falls, as this population has 34.6% mortality from low-energy mechanisms 2
• Anticoagulation use (warfarin, clopidogrel, aspirin, heparin) with any head injury, as 30% of fatal subdural hematomas occur in anticoagulated patients 2
• Clinical signs of basilar skull fracture (hemotympanum, Battle's sign, raccoon eyes, CSF rhinorrhea/otorrhea) 1

CT Timing and Sensitivity

• CT sensitivity is highest within 12 hours (98-100%), declining to 93% at 24 hours and 57-85% by day 6 1
• Acute subdural hematomas appear as hyperdense (bright) crescentic collections along the brain surface on non-contrast CT 2
• If initial CT is negative but clinical suspicion remains high, lumbar puncture should be performed to evaluate for subarachnoid blood 1

High-Risk Clinical Scenarios Requiring Lower Threshold for Imaging

Elderly patients (≥65 years):

• Brain atrophy increases bridging vein vulnerability 2
• May not exhibit typical signs of increased intracranial pressure 2
• Consider CT even for minor mechanisms (chair falls, ground-level falls) 2

Anticoagulated patients:

• Clopidogrel carries particularly high risk (OR 14.7 for mortality) 2
• Require immediate imaging and potential anticoagulation reversal 2
• Higher risk of delayed hematoma expansion 2

Specific Presenting Signs to Recognize

Classic presentations:

• Headache (74% of cases), often severe and sudden 1
• Altered consciousness (53% of cases) 1
• Focal neurological deficits: hemiparesis, cranial nerve palsies (particularly CN III), ataxia 3, 4

Atypical presentations that can delay diagnosis:

• Confusion mimicking dementia or delirium 4
• Isolated cranial nerve palsy without other focal findings 3
• Persistent headache after minor trauma with initially normal examination 5

Critical Diagnostic Pitfalls

Delayed presentation: Subdural hematomas can develop an average of 47 days after initial trauma with normal initial CT and examination 5. Repeat CT is indicated for patients with persistent or worsening symptoms despite initially normal imaging 5.

Misdiagnosis risk: Up to 12% of subdural hematomas are initially misdiagnosed, with the most common error being failure to obtain CT 1. This misdiagnosis increases mortality/disability risk 4-fold 1.

Pediatric considerations: In children, subdural hematomas are the most common finding in abusive head trauma, often appearing as multiple collections in convexity, interhemispheric, or posterior fossa locations 2.

When to Use MRI

MRI is superior for:

• Subacute or chronic subdural collections 2
• Small hematomas missed on CT 2
• Determining hematoma age (though this has limitations) 2
• Tentorial or other unusual locations 3

However, MRI should NOT delay initial diagnosis due to longer acquisition time, limited emergency availability, and difficulty scanning acutely ill patients 1.

Differential Diagnosis to Exclude

When subdural hematoma is suspected, also consider and rule out:

• Cerebral hemorrhage or edema (requires brain CT/MRI) 1
• Subarachnoid hemorrhage (perform LP if CT negative) 1
• Hyponatremia (presents similarly to subdural hematoma) 1
• Alcohol withdrawal or Wernicke's encephalopathy in chronic alcoholics 1
• Encephalitis (look for fever, stiff neck, though not always present) 1

Management Algorithm After Diagnosis

Once subdural hematoma is confirmed on CT:

• Patients with focal neurological signs require neurosurgical consultation for potential evacuation 4
• Asymptomatic patients or those with only headache can be managed with serial CT imaging 4
• Anticoagulated patients require immediate reversal and transfer to facilities capable of neurosurgical intervention 2