Posterior Reversible Encephalopathy Syndrome (PRES): Brain Swelling That Usually Reverses
Last updated September 4, 2026.
Posterior reversible encephalopathy syndrome, PRES, is a sudden swelling of the back regions of the brain, triggered by a surge in blood pressure, by eclampsia in pregnancy, by kidney failure, or by certain medicines, especially immune-suppressing and chemotherapy drugs. It announces itself dramatically: seizures, severe headache, confusion, and loss of vision over hours. The name carries its prognosis: in most people, once the trigger is removed and the pressure controlled, the swelling and the symptoms reverse over days to weeks.
What is happening in the brain
The brain's blood vessels normally tighten to protect it when blood pressure rises. When pressure surges past what that protection can handle, or when a drug weakens the vessel lining, fluid leaks into the brain tissue. The back of the brain, which handles vision, is the most vulnerable region, which is why visual symptoms dominate. The scan picture is striking and, in typical cases, largely disappears on the follow-up scan.
PRES is brain swelling with its prognosis in its name: reversible for most, fastest when the trigger is treated in hours. Headache, seizure, and vision change on high-risk drugs or after delivery means the ER now.
Start a free AI doctor consult →The triggers to know
The big three are a blood pressure emergency, eclampsia of pregnancy, and medicines: transplant anti-rejection drugs, several chemotherapy agents, and some autoimmune treatments. Kidney failure and autoimmune flares sit behind many cases. In anyone on those medicines, or in pregnancy with rising pressure, the symptom trio of headache, seizures, and visual change is a same-second emergency, because hours of high pressure deepen the injury.
How it is treated and what recovery looks like
The treatment is the trigger: blood pressure brought down smoothly, the offending drug stopped, the eclampsia managed with magnesium and delivery. Seizures are controlled in the usual ways. Most people improve markedly within days, and the scan changes fade over one to two weeks, though some people are left with lingering headaches, vision quirks, or a tendency to seizures that needs longer medication. A minority, mostly those treated late or with bleeding into the brain, keep lasting injury, which is why the emergency response is not a wait-and-see response. Recurrence is possible if the trigger returns, so afterward the blood pressure or the drug choice becomes a permanent part of the medical history, and future prescribers need to know it happened.
- Headache, seizure, vision change: act in hours, not days. In pregnancy, on transplant or chemotherapy drugs, or with kidney failure, that trio means the emergency department immediately.
- The word reversible is earned by speed. Most people recover well, and the difference between full and partial recovery is usually how fast the pressure came down and the trigger stopped.
- Tell every future prescriber. If a drug caused your PRES, that drug family is on your permanent avoid list. Your history of PRES belongs in every medication review.
If you are weighing the risks and benefits of any medicine mentioned here, our overview of how medicines are tested and monitored for safety explains what those conversations are built on.
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Common questions
Is PRES permanent brain damage?
Usually not. In most people the swelling and symptoms reverse over days to weeks once the trigger is treated, and the follow-up scan clears. A minority, mostly those treated late or with bleeding, keep lasting effects, which is why the emergency response matters.
What causes it?
A surge in blood pressure the brain's protection cannot handle, eclampsia in or after pregnancy, kidney failure, and certain medicines, especially transplant anti-rejection drugs, some chemotherapy, and some autoimmune treatments.
Why did it affect my wife's vision most?
The swelling favors the back of the brain, which is where vision is processed. Headache, seizures, and confusion come with it, but visual loss, blurring, or blind patches are often the loudest symptoms, and often the last to clear.
How long does recovery take?
Improvement usually starts within days of the pressure being controlled and the trigger stopped. Vision is typically the last thing to return, and the scan changes take one to two weeks to fade. Some people need seizure medication for a stretch afterward.
Can it come back?
It can if the trigger returns: uncontrolled blood pressure, or the same drug being restarted. That is why a history of PRES belongs in every future medication review, and blood pressure control afterward is not optional.
Can eclampsia happen after the baby is born?
Yes. Postpartum eclampsia and postpartum PRES are recognized, mostly in the first days to week or two after delivery. A severe headache, visual change, or a seizure after delivery is an emergency even when the pregnancy itself was smooth.