What is the best imaging study for a patient with a severe Traumatic Brain Injury (TBI) 2 months post-injury without a skull fracture and initial normal imaging findings?

MRI Head with Susceptibility-Weighted Imaging (SWI) and Diffusion-Weighted Imaging (DWI)

For a patient with severe TBI 2 months post-injury who had normal initial imaging, MRI of the brain is the best imaging study to evaluate persistent unexplained neurologic deficits and provide prognostic information. 1

Rationale for MRI at This Time Point

At 2 months post-injury, the clinical focus has shifted from acute management to understanding persistent deficits and long-term prognosis. MRI is superior to CT for this purpose because:

• MRI detects diffuse axonal injury (DAI) that CT misses in 90% of cases, as more than 80% of DAI lesions lack macroscopic hemorrhage and are only visible on MRI using T2-weighted, T2*-weighted (susceptibility-weighted), and diffusion-weighted sequences 1

• MRI identifies subtle cortical contusions and extra-axial hematomas adjacent to the calvarium or skull base that CT cannot detect, with studies showing MRI finds additional lesions in 27-33% of TBI patients with normal or stable CT findings 1

• Brainstem lesions on MRI have strong prognostic value, with a 2.49-fold increased risk of unfavorable Glasgow Outcome Scale at ≥6 months (95% CI 1.72-3.58) 2

• DAI patterns on MRI predict long-term neurologic outcome, with a 2.46-fold increased risk of unfavorable outcomes (95% CI 1.06-5.69) 2

Why Not CT at This Stage?

• CT was appropriate initially but has limited utility now - The American College of Radiology guidelines clearly state that CT is the imaging modality for acute management (0-7 days), but MRI becomes more valuable when the focus transitions to long-term prognostication 1

• Normal initial CT does not exclude significant brain injury - Approximately 27% of patients with normal acute CT show abnormalities on MRI that are clinically relevant for predicting outcomes 1

• CT cannot explain persistent neurologic deficits in this scenario - The ACR specifically recommends MRI as a follow-up study when persistent neurologic deficits remain unexplained after head CT 1

Specific MRI Sequences to Include

• T2-weighted, T2-weighted (SWI), and diffusion-weighted imaging (DWI)* are essential for detecting DAI and small hemorrhagic lesions 1

• FLAIR sequences help identify small white matter lesions and cortical contusions 3

• Standard T1-weighted sequences for anatomic detail and chronic blood products 3

Common Pitfalls to Avoid

• Ordering repeat CT instead of MRI at this subacute stage - CT will likely remain normal and provides no additional prognostic information 4, 5

• Assuming normal initial imaging means no structural brain injury - This is a critical error, as 90% of DAI is CT-negative but MRI-positive 1

• Failing to recognize that MRI findings at this stage guide prognosis, not acute management - While early MRI (within 48 hours) rarely changes acute management, MRI at 2 months helps explain persistent deficits and predict long-term outcomes 4, 5, 2