Does the Diffusion-Weighted Imaging (DWI) sequence show restricted diffusion, suggesting occult ischemia or inflammation?

From the Guidelines

The DWI sequence on MRI is a highly sensitive and specific tool for detecting occult ischemia or inflammation, and its findings should be promptly correlated with clinical symptoms and managed accordingly. The ability of MRI to detect cerebral ischemia is dependent on the sequence used, and the DWI sequence is particularly useful in this regard, as it demonstrates restricted diffusion as extracellular water moves into the intracellular environment during ischemia, accompanied by swelling of cells and narrowing of the extracellular spaces 1. This restricted diffusion is a characteristic finding of ischemia, and it can be distinguished from other abnormalities, such as vasogenic edema, by correlating the DWI map with the apparent diffusion coefficient map, which demonstrates restricted diffusion as low intensity 1.

Some key points to consider in the management of patients with restricted diffusion on DWI include:

• The high sensitivity and specificity of DWI for the diagnosis of acute ischemia, as demonstrated by studies such as those by Gonzalez et al and Barber et al, which showed that DWI is significantly better than FLAIR and T2-weighted MRI, and much better than CT, for detecting an ischemic focus within 6 hours of ictus 1.
• The importance of prompt clinical correlation and potentially urgent intervention, as timely treatment with appropriate therapies (such as thrombolytics if within the treatment window) may be necessary.
• The need to review additional imaging sequences like ADC mapping to confirm true restriction versus T2 shine-through effect.
• The importance of monitoring the patient for neurological symptoms and investigating underlying risk factors for stroke or inflammatory conditions.
• The specific clinical management will depend on the location of the abnormality, timing of symptom onset, and the patient's overall clinical picture.

In terms of specific management, immediate neurology consultation is recommended if ischemia is suspected, and the patient should be evaluated for potential treatment with thrombolytics or other therapies as indicated. Additionally, the patient should be closely monitored for any changes in neurological symptoms, and underlying risk factors for stroke or inflammatory conditions should be investigated and managed accordingly.

From the Research

Restricted Diffusion on DWI Sequence

The DWI sequence demonstrates restricted diffusion, which can suggest occult ischemia or inflammation. Key points to consider include:

• Restricted diffusion is often associated with acute stroke, but can also result from other causes 2
• Distinct patterns of restricted diffusion can be seen with various disease conditions, allowing for a focused assessment to determine a specific etiology 2
• DWI is a powerful tool in neuroimaging, primarily used to identify acute ischemia in patients presenting with stroke, but also contributes useful diagnostic information in other conditions 3

Potential Causes of Restricted Diffusion

Potential causes of restricted diffusion on DWI sequence include:

• Acute ischemia, such as in the case of stroke 2, 3
• Inflammation, which can be associated with various conditions, including cardiovascular disease 4
• Other conditions characterized by cortical diffusion restriction (CDR), such as those described in 3

Diagnostic Approach

A diagnostic approach to restricted-diffusion patterns on MR imaging involves:

• Considering the clinical context and patient presentation 2
• Evaluating the pattern of restricted diffusion to determine a specific etiology 2
• Using DWI in conjunction with other imaging modalities and clinical information to inform diagnosis and treatment 3, 5