What is the best imaging modality to diagnose Posterior Reversible Encephalopathy Syndrome (PRES)?

From the Guidelines

Magnetic Resonance Imaging (MRI) is the best imaging modality to diagnose Posterior Reversible Encephalopathy Syndrome (PRES). This recommendation is based on the highest quality and most recent evidence available, which emphasizes the superiority of MRI in detecting and characterizing the brain changes associated with PRES [ 1 ]. The use of MRI, particularly T2-weighted and fluid-attenuated inversion recovery (FLAIR) sequences, allows for the clear visualization of vasogenic edema in the parieto-occipital regions, which is a hallmark of PRES. Additionally, diffusion-weighted imaging (DWI) can help distinguish PRES from acute ischemic stroke by showing increased apparent diffusion coefficient (ADC) values, indicative of vasogenic rather than cytotoxic edema.

Key Points for Diagnosis

• MRI is significantly more sensitive than computed tomography (CT) for diagnosing PRES.
• T2-weighted and FLAIR MRI sequences are particularly valuable for demonstrating vasogenic edema.
• DWI is helpful in distinguishing PRES from acute ischemic stroke.
• MRI can detect subtle abnormalities that CT might miss, especially in mild cases or atypical presentations.
• The superior soft tissue contrast of MRI allows for better assessment of the extent of involvement and monitoring of resolution over time.

Clinical Considerations

When diagnosing PRES, it is crucial to consider the clinical context, including symptoms such as headache, visual disturbances, and seizures, which can be associated with hypertensive emergencies [ 1 ]. The absence of a specific blood pressure threshold to define hypertensive emergencies underscores the importance of individualized assessment and the role of MRI in confirming the diagnosis of PRES. Furthermore, guidelines suggest that noncontrast MRI examinations of the brain are usually sufficient for assessing intracranial complications related to hypertensive emergency, including PRES [ 1 ].

From the Research

Imaging Modalities for Diagnosing Posterior Reversible Encephalopathy Syndrome (PRES)

• Magnetic Resonance Imaging (MRI) is the most commonly used imaging modality for diagnosing PRES, as it can detect the characteristic vasogenic edema in the posterior circulation territories 2, 3, 4.
• Diffusion-Weighted Imaging (DWI) is a useful complement to MRI in the diagnosis of PRES, as it can help differentiate between vasogenic and cytotoxic edema 2, 5, 3.
• Apparent Diffusion Coefficient (ADC) maps can also be used to assess the extent of edema and predict the progression to infarction 3.

Characteristics of PRES on Imaging

• Hyperintensity on T2-weighted and fluid-attenuated inversion recovery (FLAIR) images is a common finding in PRES 2, 4.
• Restricted diffusion and hemorrhage are rare, but can occur in some cases 4.
• The parieto-occipital lobes are the most commonly affected region, but other areas such as the frontal lobes, temporal lobes, basal ganglia, cerebellum, brainstem, and thalamus can also be involved 4.

Importance of Imaging in Diagnosing PRES

• Imaging plays a crucial role in diagnosing PRES, as the clinical presentation can be variable and non-specific 2, 4.
• A combination of MRI, DWI, and ADC maps can help establish the diagnosis of PRES and assess the extent of edema and potential for reversibility 2, 3.
• Recognition of the typical and atypical imaging manifestations of PRES is essential for making an accurate diagnosis and guiding management 4.