Indications for MRI Brain

Primary Clinical Scenarios Requiring MRI Brain

The American College of Radiology recommends MRI brain when CT is unrevealing or when higher sensitivity is required for specific pathologies, including small infarcts, encephalitis, posterior fossa lesions, subtle subarachnoid hemorrhage, and suspected intracranial masses, infections, or inflammatory conditions 1, 2
MRI serves as the second-line test when occult pathology is suspected after unrevealing head CT, with superior sensitivity for detecting small ischemic infarcts, encephalitis, and subtle cases of subarachnoid hemorrhage 1, 3
Notably, 70% of patients with missed ischemic stroke diagnoses presented with altered mental status, emphasizing MRI's critical role in this population 4, 2

MRI is complementary to CT for evaluating intracranial hemorrhage when an underlying lesion is suspected, including hemorrhagic primary or secondary brain mass, arteriovenous malformation, or cavernous venous malformation 1, 3
For suspected subtle cases of subarachnoid hemorrhage with negative CT, MRI has 95% sensitivity 2

MRI should be performed within 24-48 hours for suspected encephalitis, ideally within 24 hours of hospital admission 2
Contrast-enhanced MRI examinations should be performed if intracranial infection, tumor, inflammatory lesions, or vascular pathologies are suspected 1, 3

MRI head without IV contrast is typically the initial study for evaluating brain parenchyma and detecting hemorrhage 2
T2* gradient-echo and susceptibility-weighted imaging sequences optimally detect microhemorrhages 2
Diffusion-weighted imaging identifies acute ischemic changes and axonal injuries 2

CT remains the first-line imaging modality for suspected acute intracranial hemorrhage, mass effect, or hydrocephalus in emergent settings due to rapid acquisition and ability to maintain patient access during scanning 4, 1, 2
The diagnostic yield of MRI in new-onset delirium is low in the absence of focal neurologic deficits or history of recent falls 2

In patients with acute disorders of consciousness, MRI leads to changes in clinical management in 76% of cases, including revised diagnoses, revised levels of care, improved diagnostic confidence, and improved prognostication 2