Most Serious Conditions Detectable by MRI
MRI can detect numerous life-threatening conditions that may be missed by CT, particularly posterior fossa abnormalities, small infarcts, encephalitis, and subtle cases of subarachnoid hemorrhage. 1
Neurological Emergencies Detectable by MRI
Acute Ischemic Stroke: MRI with diffusion-weighted imaging can detect acute ischemic stroke with higher sensitivity than CT, particularly small infarcts that may be missed on CT. This is especially important as 70% of missed ischemic stroke diagnoses present with altered mental status. 2, 1
Intracranial Hemorrhage: MRI is superior to CT for detecting subacute and chronic hemorrhage, with susceptibility-weighted imaging (SWI) being 3-6 times more sensitive than conventional sequences in detecting hemorrhagic lesions. 1
Brain Tumors: MRI can detect and characterize intracranial mass lesions with greater sensitivity than CT, particularly in areas where CT is degraded by bone artifacts (posterior fossa, skull base, temporal regions). MRI can distinguish tumor components including tissue, cyst, necrosis, and hemorrhage. 1, 3
Encephalitis: MRI is recommended for suspected encephalitis, particularly when CT is normal or shows only subtle abnormalities. The American College of Radiology recommends MRI be performed within 24-48 hours in patients with suspected encephalitis. 1
Traumatic Brain Injury: MRI is more sensitive than CT for subtle findings adjacent to the calvarium or skull base (small cortical contusions and subdural hematomas) and for small white matter lesions in traumatic axonal injury or diffuse axonal injury (DAI). 2
Vascular Pathologies
Subtle Subarachnoid Hemorrhage: MRI can detect subtle cases of subarachnoid hemorrhage with negative CT, with a sensitivity of 95%. 1
Vascular Malformations: MRI is superior for further evaluation of intracranial hemorrhage to identify underlying vascular malformations that may cause life-threatening bleeding. 1
Posterior Reversible Encephalopathy Syndrome (PRES): This potentially life-threatening condition is best detected on MRI, which shows characteristic patterns of edema. 1
Infectious and Inflammatory Conditions
Meningitis: MRI is recommended for suspected meningitis with persistent neurological symptoms, as it can detect complications such as cerebritis, abscess formation, or venous thrombosis. 1
Central Nervous System Infections in Immunocompromised Patients: These potentially fatal infections may be subtle on CT but better characterized by MRI. 1
Multiple Sclerosis: MRI is the most sensitive method for revealing asymptomatic dissemination of white matter lesions in space and time, crucial for early diagnosis of this potentially disabling condition. 4
Clinical Scenarios Requiring Urgent MRI
Status Epilepticus with Persistent Altered Mental Status: This life-threatening condition may require MRI for proper diagnosis and management. 1
Delirium in Patients with Known Cancer: These patients should undergo urgent MRI brain to rule out metastatic disease or paraneoplastic syndromes. 2, 1
Acute Disorders of Consciousness: MRI leads to changes in clinical management in 76% of these cases, including revised diagnoses and improved prognostication. 1
Important Caveats
MRI Limitations: MRI may not be feasible in unstable patients or those requiring continuous monitoring. 1
CT Remains First-Line: CT remains the first-line imaging modality for suspected acute intracranial hemorrhage, mass effect, or hydrocephalus in emergent settings. 1
MRI Safety Concerns: MRI poses safety hazards including magnetic forces on metals, tissue heating, and contrast agent complications. Strict safety protocols must be followed to prevent potentially fatal accidents. 5
False Negatives: Despite its high sensitivity, MRI may not visualize all acute strokes, particularly very early strokes or small brainstem lesions. 6
Low Yield in Certain Scenarios: The diagnostic yield of MRI in new-onset delirium is low in the absence of focal neurologic deficits or history of recent falls. Similarly, in patients with new-onset psychosis without neurologic deficits, the yield is very low. 1