PRES syndrome, sometimes written as PRESS, stands for posterior reversible encephalopathy syndrome. It is a neurological condition where fluid leaks from blood vessels into surrounding brain tissue, causing swelling primarily in the back of the brain. The name reflects the key features: it affects the posterior (back) brain regions, and in most cases, the damage is reversible with prompt treatment. Despite the reassuring name, severe cases can lead to lasting problems or even death if not recognized quickly.
How PRES Develops
The brain has a built-in system that keeps blood flow steady regardless of what your blood pressure is doing at any given moment. When blood pressure spikes above roughly 160 mmHg systolic, that system gets overwhelmed. The tiny blood vessels in the brain can no longer compensate, and the increased pressure forces fluid through the walls of those vessels into the surrounding tissue. This fluid buildup is called vasogenic edema.
The back of the brain is especially vulnerable because the blood vessels there have fewer built-in safeguards against pressure changes compared to those at the front. That’s why swelling tends to concentrate in the parietal and occipital lobes, the regions responsible for processing vision and spatial awareness.
High blood pressure isn’t the only pathway. Certain medications, particularly immunosuppressants used after organ transplants and some chemotherapy drugs, can directly damage the lining of blood vessels, making them leaky even without extreme blood pressure. Conditions like sepsis (a body-wide response to infection) and autoimmune diseases can also trigger inflammation that weakens the barrier between blood vessels and brain tissue.
Common Triggers
The most frequent triggers are severe high blood pressure, kidney failure, eclampsia (a dangerous blood pressure complication of pregnancy), sepsis, and autoimmune disorders. Medications are another major category. Immunosuppressants like cyclosporine and tacrolimus, commonly prescribed after transplants, are well-known culprits. Chemotherapy drugs, including certain platinum-based agents, can also set it off.
In children, the trigger list is broader and includes sickle cell anemia, bone marrow transplants, kidney diseases, and even blood transfusions. The estimated incidence in children overall is about 0.04%, rising to 0.7% among children with cancer.
Symptoms to Recognize
PRES typically comes on quickly, over hours to days. The hallmark symptoms are seizures, visual disturbances, headaches, and confusion or altered mental status. In one study of children with cancer who developed PRES, every patient had high blood pressure at the time of diagnosis. Seizures were the second most common symptom, occurring in nearly 80% of cases, followed by nausea and vomiting, altered mental status, headaches, and visual changes.
The visual problems can range from blurry vision to complete temporary blindness, which makes sense given that the swelling concentrates in the part of the brain that handles sight. Some people also experience fatigue, dizziness, or weakness on one side of the body. The combination of sudden seizures with vision problems and high blood pressure is a strong signal that PRES may be happening.
How It’s Diagnosed
An MRI is the primary tool for confirming PRES. The classic finding is symmetrical swelling in both parietal and occipital lobes, visible as bright areas on certain MRI sequences. This pattern appeared in 100% of cases in one imaging study. However, PRES doesn’t always stay in the textbook zones. About 30% of patients also show changes in the frontal lobes, 22% in deep brain structures called the basal ganglia, and smaller percentages in the cerebellum and brainstem.
The swelling primarily affects white matter (the brain’s wiring), though it can spill into the cortex (the outer layer) as well. In children, atypical patterns are even more common, with swelling extending well beyond the classic posterior regions. This variability means radiologists sometimes catch the diagnosis before other physicians do.
Treatment and Recovery
The core of treatment is addressing whatever triggered the episode. If high blood pressure is the cause, it needs to come down, but gradually. Dropping blood pressure too fast risks cutting off blood flow to the brain, kidneys, or heart. The typical goal is a 20% to 25% reduction within the first few hours. If a medication triggered the episode, stopping or switching that drug is essential. In one study, the median time from onset to getting the underlying cause under control was about 30 hours.
For most people, PRES lives up to the “reversible” in its name. Brain imaging abnormalities resolved in 88% of patients in one study, with complete resolution in 45% and partial resolution in 43%. But recovery isn’t guaranteed, especially in severe cases. In a study of patients with severe PRES requiring intensive care, 56% had a good recovery by day 90. The remaining survivors (44%) had significant functional impairments, and 16% of the overall group died. Bleeding or stroke complications occurred in about 14% of cases.
PRES in Children
Children’s brains differ from adult brains in important ways that affect how PRES plays out. Their blood vessels are more vulnerable to toxic substances, and their ability to regulate blood flow is still developing. Childhood PRES tends to show a wider range of symptoms and more atypical brain imaging patterns than the adult version.
The most common pediatric triggers are kidney disease, cancer treatment (especially combinations of chemotherapy drugs), organ or bone marrow transplantation, and autoimmune conditions like lupus. Because the presentation can look unusual in children, PRES is often initially missed by frontline physicians. Awareness of the condition in pediatric settings has improved, but it remains underdiagnosed.
PRES vs. Similar Conditions
PRES can look like several other neurological emergencies, which complicates diagnosis. Reversible cerebral vasoconstriction syndrome (RCVS) is the closest mimic. Both cause severe headaches and can lead to stroke, but RCVS involves spasms of the brain’s arteries rather than fluid leaking through vessel walls. The headache in RCVS tends to be sudden and thunderclap-like, while PRES more commonly presents with seizures and visual changes as the leading symptoms. MRI patterns also differ: PRES shows brain swelling, while RCVS shows narrowed arteries. The two conditions occasionally overlap, making imaging critical for sorting them out.
Stroke, meningitis, and certain types of brain inflammation can also mimic PRES. The symmetrical pattern of swelling on MRI, concentrated in the back of the brain, is the most reliable way to distinguish PRES from these other conditions.