Recommended Imaging for Suspected Subdural Hematoma
Non-contrast CT of the head is the gold standard and first-line imaging modality for suspected subdural hematoma, with a rating of 9 (usually appropriate) by the American College of Radiology. 1
Initial Imaging Approach
Non-contrast head CT should be performed immediately in any patient with suspected subdural hematoma, as it provides rapid acquisition, widespread availability, excellent sensitivity for acute blood, and allows assessment of mass effect and midline shift 1, 2
CT without contrast is specifically designated as the "gold standard test" for clinically suspected parenchymal hemorrhage and hematoma by ACR guidelines 1
The non-invasive nature and speed of CT make it ideal for acute settings where rapid diagnosis is critical for surgical decision-making 2
When MRI Should Be Considered
MRI head without IV contrast (rating 8) is an appropriate alternative when CT is contraindicated or when subacute/chronic subdural collections need better characterization 1
MRI with susceptibility-weighted imaging (SWI) may be as sensitive as CT in detecting hemorrhage and provides superior detection of small hematomas, subacute blood products, and associated injuries 1, 3
MRI head without and with IV contrast (rating 7-9) is preferred for proven parenchymal hemorrhage to evaluate for underlying enhancing masses or vascular malformations that may have caused the subdural hematoma 1
MRI offers superior soft tissue resolution for determining potential secondary causes such as dural-based neoplasms 2
Critical Pitfalls to Avoid
Isodense subdural hematomas can be missed on non-contrast CT alone - if clinical suspicion remains high despite negative initial CT, contrast-enhanced CT or MRI should be obtained, as contrast enhancement of cortical vessels and subdural membranes improves detection 4
Delayed subdural hematomas can develop after initially normal CT scans - patients with persistent post-traumatic symptoms despite normal initial imaging should undergo repeat CT scanning, as subdural hematomas may not be visible immediately after trauma 5
In patients on anticoagulation with minor head trauma and normal initial CT, observation with repeat imaging at 20-24 hours is recommended, as delayed intracranial hemorrhage occurs in approximately 0.6-2% of cases 1
Special Population Considerations
In pediatric patients (3-month-old infants), non-contrast CT remains first-line for acute diagnosis, though subdural hemorrhage at this age is highly concerning for non-accidental trauma and requires immediate evaluation for bleeding disorders 3
In elderly patients on anticoagulation, even ground-level falls warrant CT imaging given significantly elevated mortality risk, particularly in those on clopidogrel (OR = 14.7 for mortality) 6
Vascular Imaging Considerations
CTA head with IV contrast (rating 8) should be obtained after initial non-contrast CT if there is concern for underlying vascular malformation, aneurysm, or traumatic vascular injury 1
CTA can be performed immediately following non-contrast CT while the patient remains on the scanner table 1
Catheter angiography may be required for definitive pretreatment evaluation if vascular abnormality is suspected 1
Follow-up Imaging Protocol
Non-contrast head CT (rating 8-9) is appropriate for short-term follow-up of patients with known subdural hematoma to assess hemorrhage evolution and evaluate for complications 1
Surgical evacuation is indicated when subdural hematoma thickness exceeds 10 mm or midline shift exceeds 5 mm on CT, regardless of Glasgow Coma Scale score 7
Patients with chronic subdural hematoma showing maximum fluid collection thickness >1 cm on imaging require operative intervention 8