From the Guidelines
An MRI of the brain is warranted in a patient with subacute altered mentation and a negative CT head scan. This recommendation is based on the higher sensitivity of MRI in detecting ischemia, encephalitis, or subtle cases of subarachnoid hemorrhage, as noted in the 2024 update of the ACR Appropriateness Criteria for altered mental status, coma, delirium, and psychosis 1. The use of MRI as a second-line test after a negative CT head scan can provide valuable information for diagnosing and managing patients with altered mental status.
Key points to consider include:
- MRI's higher sensitivity for detecting subtle abnormalities such as small ischemic infarcts, which are often missed by CT scans 1.
- The utility of MRI in evaluating suspected intracranial mass lesions, intracranial infection, nonspecific regions of edema, ischemia, and cases of intracranial hemorrhage when an underlying lesion is suspected 1.
- The potential for MRI to change clinical management, as seen in a study where review of head MRI examinations led to changes in clinical management of 76% of patients with acute disorder of consciousness 1.
When considering an MRI, it is essential to weigh the potential benefits against any contraindications, such as implanted metallic devices or severe claustrophobia. However, in the context of subacute altered mentation and a negative CT head scan, the potential benefits of MRI in terms of morbidity, mortality, and quality of life outcomes make it a warranted diagnostic step.
From the Research
Diagnostic Approach for Subacute Altered Mentation
When a patient presents with subacute altered mentation and a negative CT head scan, the decision to proceed with an MRI warrants consideration of several factors, including the patient's clinical presentation, risk factors, and the potential diagnostic yield of MRI.
Indications for MRI
- Patients with symptoms concerning for stroke or sudden onset of impaired consciousness may benefit from an MRI, as it can provide additional diagnostic information not visible on CT scans 2.
- Elderly patients with a history of prior stroke or transient ischemic attack may also benefit from an MRI, as they are at higher risk for CT-occult or minor ischemic strokes 3.
- Patients with vague neurologic symptoms, such as dizziness and altered mental status, may require an MRI to rule out minor strokes or other conditions not visible on CT scans 3.
Diagnostic Yield of MRI
- MRI can detect brain signal changes that reinforce the clinical suspicion of encephalitis, especially when the causative agent is not identified by lumbar puncture 4.
- MRI can also suggest a particular pathogen based on the pattern of brain abnormalities and rule out important differential diagnoses (vascular, tumoral, or inflammatory causes) 4.
- In ICU patients with altered mental status, MRI can provide additional diagnostic information, including the detection of acute communicable findings such as hemorrhage, mass effect, infarction, and hydrocephalus 5.
Considerations for Ordering an MRI
- The decision to order an MRI should be based on the patient's individual clinical presentation and risk factors, rather than a blanket approach for all patients with subacute altered mentation and negative CT head scans 6, 2.
- The potential benefits of MRI should be weighed against the costs and availability of the test, as well as the patient's overall clinical condition 6.