For Posterior Reversible Encephalopathy Syndrome (PRES), should I order an MRI with or without contrast?

MRI Without Contrast is the Recommended Imaging Modality for PRES

For Posterior Reversible Encephalopathy Syndrome (PRES), MRI brain without IV contrast is the most appropriate initial imaging choice.

Rationale for MRI Without Contrast in PRES

MRI without contrast provides superior visualization of the characteristic vasogenic edema pattern in PRES, particularly in the parieto-occipital regions, without exposing patients to the risks of contrast agents. The American College of Radiology guidelines consistently recommend non-contrast MRI as the initial imaging modality for conditions with suspected vasogenic edema and acute neurological changes 1.

Key advantages of non-contrast MRI for PRES include:

• Better detection of subtle white matter changes characteristic of PRES
• Superior soft tissue characterization compared to CT
• Ability to identify the distinctive parieto-occipital pattern of vasogenic edema
• No risk of contrast-induced nephropathy (important as PRES often occurs in patients with renal dysfunction) 2

Optimal MRI Protocol for PRES

The recommended MRI sequences for PRES evaluation include:

• T1-weighted imaging
• T2-weighted imaging
• FLAIR (Fluid-Attenuated Inversion Recovery)
• DWI (Diffusion-Weighted Imaging)
• SWI (Susceptibility-Weighted Imaging) or T2* gradient echo

These sequences collectively allow for comprehensive assessment of the characteristic vasogenic edema pattern while ruling out other potential causes of neurological symptoms 1.

When Contrast May Be Considered

While non-contrast MRI is sufficient for most PRES cases, there are specific scenarios where contrast-enhanced MRI might be considered:

1. When initial non-contrast imaging is inconclusive
2. To rule out other conditions in the differential diagnosis that might enhance with contrast
3. When there is suspicion of an underlying inflammatory or infectious process

However, since PRES is often associated with renal dysfunction 2, 3, and many patients may have compromised kidney function, avoiding contrast is generally preferred to prevent potential contrast-induced nephropathy.

Clinical Context

PRES typically presents with:

• Headache
• Altered mental status
• Visual disturbances
• Seizures
• Hypertension (in most cases)

The condition is commonly associated with:

• Hypertensive emergencies
• Renal disease
• Cytotoxic medications
• Autoimmune disorders
• (Pre)eclampsia
• Sepsis 4, 5

Conclusion

MRI without contrast should be the first-line imaging modality for suspected PRES, as it provides optimal visualization of the characteristic vasogenic edema pattern while avoiding potential complications from contrast administration in a patient population often with compromised renal function.